title list | subreddit list | post_id list | score list | link_flair_text list | is_self list | over_18 list | upvote_ratio list | post_content stringlengths 0 20.9k ⌀ | C1 stringlengths 0 9.86k | C2 stringlengths 0 10k | C3 stringlengths 0 8.74k | C4 stringlengths 0 9.31k | C5 stringlengths 0 9.71k |
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[
"Can someone explain to me what Galois representations are?"
] | [
"math"
] | [
"g5n83"
] | [
9
] | [
""
] | [
true
] | [
false
] | [
0.73
] | Hello, . I'm planning to delcare my math major soon and am only in first year math classes. I'm taking Discrete Math now and we did some elementary number theory. Number Theory is definitely a big interest of mine and my math instructor told me Galois representations are important to it, especially cryptography, since ... | Okay. Well, I can give you a brief rundown of what these things are, although I'm not quite sure if it will help. It typically takes a year of algebra before you can start studying things like representations of Galois groups, and probably even longer before you start to learn about group cohomology. So a is a set with... | I'm not sure it will be too easy to explain without knowing a decent amount of algebra. Do you know what any of the following terms are: group, ring, field, Galois group, module, vector space or field extension? I can try to do some explaining if you don't, but it would make a huge difference if you knew what a field e... | that is, that it satisfies all the field axioms which I never mentioned.. You sir must be a math textbook author | If you just read through the book Fearless Symmetry you will have a good impression of what they are. | Excellent post! Very informative |
[
"Teaching math using historical techniques"
] | [
"math"
] | [
"g5rur"
] | [
3
] | [
""
] | [
true
] | [
false
] | [
0.57
] | [deleted] | These are the kinds of things we did in my History of Mathematics class. Just google history of mathematics and you'll find a lot of materials. Crest of the Peacock is a great book for some math history, as is Brief History of Mathematics. | Also see the book A Journey Through Genius, though this might be a little too advanced. Depends on the class. | Also see the book A Journey Through Genius, though this might be a little too advanced. Depends on the class. | There is a lot of research from the constructivist perspective wherein they developed instructional sequences based on the idea to let students construct mathematical knowledge about a concept similarly as the historical development of that concept. | If you want to be really authentic you need to make them wear on of these if they get anything wrong. |
[
"Not sure what to do with this very old textbook"
] | [
"math"
] | [
"g5tmk"
] | [
4
] | [
""
] | [
true
] | [
false
] | [
0.59
] | Several years ago, a student gave me a copy of Elias Loomis' 1882 textbook "The Elements of Analytic Geometry." The book is in very rough shape (the front cover is missing and the spine is mostly gone), but I really like it. I don't expect it is worth much money, nor am I interested in trying to get any money out of it... | Restore it. Keep it. Have an awesome desk piece. | My all means keep it and restore it. Use it or show it to those who can. Old textbooks are usually better than newer ones. Newer ones often have many pages of silly glossy pictures. The old books are well written and to the point. A colleague of mine has xeroxed 30 pages or so from a 1910 trigonometry book and passe... | I believe I'll do just that. Thanks. | I don't know if that's the same book that's on archive.org . Does it mention calculus in the title? I agree with rhlewis that the old math books were very well written and are usually superior to their modern equivalents. I have a trig book from 1878 that develops the material better than any book I've seen. | Any academic library rebinds and re-covers books. I know that mine will do this as a service for a minimal fee (about $20). They also do this for PhD dissertations. |
[
"Is there a strategy you can use in Deal or No Deal?"
] | [
"math"
] | [
"g6llz"
] | [
3
] | [
""
] | [
true
] | [
false
] | [
0.58
] | I was watching Deal or No Deal the other night, and I had a revelation. A few weeks ago I saw where 100 prisoners have 100 boxes with each box containing a different prisoner's name. Each prisoner gets to open 50 boxes, and if they open the box with their name in it they get to go free, and the boxes are reset. If they... | No you're code is fucked beyond comprehension. 1) You have a bug in the do while loop. assume $a[24] contains case 25....... you'll enter an infinite loop. 2) you never remove a case from $a. This has 2 problems - one, like your bug mentioned in 1, shows you can hit the same case twice. 2 - you never remove a case init... | This doesn't affect the monty hall problem. Yes it does. In fact, that's the for the unintuitive probability switch in the Monty Hall problem. In the Monty Hall problem, if the host just opened a random door and didn't make sure to not open the door with the prize, then 1/3 of the time he will reveal the prize, and 2/3... | If the cases are randomized, I don't see how this would improve your chances. The interesting part of the first problem, is that there are 100 boxes and 100 prisoners. The boxes aren't re-arranged after after each prisoner looks, so the collective has the opportunity to open 5000 boxes. If you know the algorithm by whi... | I don't think so... but I can't quite figure out how'd you'd even accurately apply the logic of one problem to another. For one, it's a 31% chance that they all won't die (which is to say, there's a 31% chance that there will not be loops greater than size 50 in a random permutation of 100 elements). With DoND you don'... | I always thought the best way to do it would be to take the sum of the available cash, divided by the number of cases left (to get expected payout), and then keep going with random selection until you get an offer that exceeds expected payout. |
[
"On the Googol: An Investigation, by a friend of mine"
] | [
"math"
] | [
"g5nj7"
] | [
55
] | [
""
] | [
true
] | [
false
] | [
0.85
] | [deleted] | Just reading this post is making my allergies flare up. | the largest prime number has over 6 million digits. FTFY ;) | the largest prime number has over 6 million digits. FTFY ;) | Check out Grahams Number. | I do not understand the fascination behind these numbers. We routinely use 600-digit numbers for RSA in Internet communications. The largest prime we know of, M20996011, has over 6 million digits. |
[
"What is a good Mac-compatible freeware graph-drawing/making program for math, economics, etc.?"
] | [
"math"
] | [
"g5v8m"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | Is there such a thing? I'm starting to do my homework and projects in LaTeX. | xfig | Perfect- thank you! | Dia is pretty good for freeware, but the UI is subtly irritating and you have to deal with the ugliness that comes with apps ported over from linux. Your mileage may vary, but personally I'd rather just pay for something good like Omnigraffle (which is only $100, and well worth it). If you are looking to make graphs (d... | Check out R, the programming language, and sage math . Both are sort of deep ends for what you're probably heading into, but the initial pain of learning a powerful tool is well worth the long term benefit. http://en.wikipedia.org/wiki/R_\(programming_language\) http://www.sagemath.org/ | Have you considered R? The New York Times uses it to produce many of their graphs . Available on Mac, Linux, windows http://www.r-project.org/ http://cran.r-project.org/ The base graphs are pretty decent, but there are two very good graphics packages (free, easily downloaded and installed on the fly) that do some great... |
[
"O'Reilly is selling a 58 page book for 30 USD"
] | [
"math"
] | [
"g54k2"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.25
] | I know that it's not the quantity of the pages but the quality that creates the value but this book is an excerpt from another book ( ) that has 436 pages and is being sold for 40 USD. | So just pay $10 more and get the bigger book. It's not that this is a ripoff, it's that the other book is an incredible deal. In all seriousness though, it's probably because there's some initial investment cost in making a book. It's probably something like $x for binding, making the cover, printing, publisher's fees ... | I just think the following ratio does not make much financial sense (given that the 30 USD book is an excerpt of a 40 USD book): 58 pages @ 30 USD, 436 pages @ 40 USD But maybe I'm paying more per page for the excerpt to avoid reading the additional 378 pages. ;) | The question is how much money you are making or might make my programming in R. If knowing R well would get you a $10,000 contract for a week or a few days worth of work or a good six figure job then the book might appear to be under priced. Looking at pages is like comparing libraries by square footage. Value is w... | Apparently, those were the 58 pages. | Shit, my copy of "The C Programming Language" was $50 like 20 years ago, and that was an and dense book even at ~270 pages. That better be some quality documentation on what is essentially a GNU project. |
[
"What's really inside a Poisson Bracket?"
] | [
"math"
] | [
"g57kh"
] | [
15
] | [
""
] | [
true
] | [
false
] | [
0.67
] | Hi, good people of ! Ordinarily I would have posted this in , since that’s my (ug/b.s.) major, but I’m afraid a question like this would be swept away in the ‘tsunami’ of nuclear-power stories. (ouch, too soon?) My question concerns a comment my professor made to me about and their use in calculating physics quantit... | For a non-interacting ensemble of particles, knowing an individual q_1 vs. p_1 is equivalent to knowing the whole 6N** dimensional phase space distribution, because the phase space density is separable (this is easy to understand because no interactions --> all particles behave independently, and to get the full phase ... | but not the other way around in general That is true, but I think about it like this: From a nondegenerate Poisson bracket, you can get a symplectic form. A Poisson manifold with a degenerate Poisson bracket foliates by integral manifolds for the generalized tangent distribution (generalized in the sense that the dime... | omg, lulz. edit: whoever downvoted, I completely agree. "Fish" is not the note I was hoping this discussion would start out on. | I am more of a symplectic guy myself, but what I will say holds true for poisson brackets (even though they are more general than symplectic forms. Given a symplectic form, you can create a poisson bracket (but not the other way around in general) The solution to the differential equation you wrote will be tangent to ... | Before answering your question, let me first give a brief summary of the role of the Poisson bracket in Hamiltonian mechanics. In terms of the Poisson bracket, Hamilton's equations can also be written as dF/dt = {F,H} , where H is the Hamiltonian and F is any function on phase space. If the Hamiltonian is autonomous ... |
[
"Need help with a riddle!"
] | [
"math"
] | [
"g5c5t"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.47
] | 1 11 21 1211 111221 312211 What is the next number in the sequence? | There's actually quite a bit mathematically interesting about it. It's known as Conway's look and say sequence. One interesting fact is that the ratio of consecutive terms approaches a constant, which is the only real root of a 71st degree polynomial. | Thanks for the link! I stand corrected, but I still don't like "guess-the-next-number-in-this-sequence" puzzles. | Let me google that for you: http://lmgtfy.com/?q=1+11+21+1211+111221+312211 | 13112221 I hate hate hate this riddle, because there's nothing mathematically interesting about it - it's just some dumb trick. (S_k+1 is just an encoding of S_k - if S_1 is 1, then S_2 is 11, read as "one one", S_3 is 21, read as "two ones", etc.) | It's just like the "Why are manholes round?" interview questions: the right way to find the solution is to know it beforehand. |
[
"I am seriously considering switching majors from Nuclear Engineering to Math but I have a few questions."
] | [
"math"
] | [
"g50na"
] | [
1
] | [
""
] | [
true
] | [
false
] | [
0.57
] | Let me first say that this has to do with the mess in Japan with their reactors; that is not why I want to switch majors. I am considering switching because I began to realize last semester that 1) I really like math and 2) sticking with nuclear engineering would not allow me to take any more math courses. Also I got s... | "Mathematicians are also mostly even less concerned with why something works." Huh? Are you joking? The "why" is the whole point of mathematics. | Firstly, you type like you're on uppers. Secondly, if math is what you want then go for it. Especially if you enjoy it. You don't want to be in a career and wish you were doing something else. | If you want to major in math then major in math. Do yourself a favor though and double major in CS too. Some people might say that being a double major is unnecessary because you can get work in programming without it. This is true but it's just that much harder. Not everyone appreciates what it means to have a math... | So you've never taken a math class outside of introduction to differential equation for scientists I'm guessing? | you're on uppers You mean upper division work? Then yeah and I'm a junior. |
[
"Quick Survey, what is your level of mathematical education?"
] | [
"math"
] | [
"g6pbt"
] | [
20
] | [
""
] | [
true
] | [
false
] | [
0.75
] | [deleted] | High-School + MIT OpenCourseWare 18.01 Single-Variable Calculus MIT OpenCourseWare 18.02 Multi-Variable Calculus MIT OpenCourseWare 18.03 Differential Equations Currently, going through MIT OpenCourseWare 18.06 Linear Algebra | Ph.D. | Fuck yeah. You rule. | Third year math major at UC Berkeley | First year undergraduate, reading maths (UK) |
[
"How far into your undergrad were you when you published your first paper?"
] | [
"math"
] | [
"g61sd"
] | [
3
] | [
""
] | [
true
] | [
false
] | [
0.54
] | I'm halfway through my second year of a math undergrad, and am really starting to think about doing research. I've talked to a couple professors and I'm fairly certain they'd be willing to take me on, but I feel like I haven't learned nearly enough to contribute anything meaningful to the world of mathematics. Is it n... | Unless you are a particular prodigy, publishing as a sophomore isn't going to happen. It's very, very rare to be published as an undergraduate at all. Legitimate research isn't easy - that's why people get PhD's. Concentrate on finishing your undergraduate work and get into grad school. There will be plenty of time to ... | As a British person - what? I didn't publish anything until the end of my first year as a PHD, I'm pretty sure most of the other people on my course hadn't published anything either, maybe something as part of their master's degree. Is it expected that you publish as an undergrad in America? I'm not sure I would reco... | It's normal in math to not publish till well into your PhD. Publishing definitely gives you a boost but it's not expected in math, even for the top tier schools. | I don't think it's particularly common for people to publish papers (outside of publications that are aimed directly at undergraduates, anyway) during their undergraduate program. My first publication was submitted early on in my Master's, and in my experience you're not expected to publish any earlier than that. Your ... | I agree, in fact I think this is exactly what REU's are for. I just wouldn't expect what they've done to be at a level where you can publish. |
[
"Is it possible to map a globe from the perspective of a toroid (or circuit)?"
] | [
"math"
] | [
"g585m"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | [deleted] | You probably want to consider the three-dimensional problem, which doesn't have intersections. Your question sounds like this: Given a divergence-free vector field, can we construct a metric (with isolated singularities) in which its curvature vanishes? | I understand completely. But seriously, thanks for at least answering the question. One of the things that the other commenter mentioned made me realize was that (1) the way I'm imagining this definitely involves forking paths so, (2) the way I imagine this will result in multiple transpositions of a single point, (3) ... | First things first, your question is not about topoi. Your question is not about topoi. That is a word you should forget for quite a while, until you know how to use it properly. (There is nothing wrong with forgetting words; it is one of the best ways to not sound like a fool.) Second, what you describe is (probabl... | Jeeze. Sorry I made you cranky. | I feel like that is a bit over-reacting. I'm just trying to point out that there are several things that you could change and/or clarify in order to make your question more conducive to an answer. Mentioning topoi will not help - it's a stab in the wrong direction, which is more likely to confuse people than to help t... |
[
"Bayesian Approaches to Uncertainty: The Case of Reddit Comments"
] | [
"math"
] | [
"g5vsp"
] | [
129
] | [
""
] | [
true
] | [
false
] | [
0.95
] | Currently Reddit comments are sorted by "best" by default. What this means is that they are sorted in order by the lower-bound of the 95% confidence interval over the percent of votes that are upvotes (I will explain what that means in plain English in a moment). You can read details . This is basically a way of dealin... | That was actually the original plan for reddit. It was supposed to learn what you liked and then recommend things to you. | That was actually the original plan for reddit. It was supposed to learn what you liked and then recommend things to you. | And C) it adds per-user (and thus, essentially un-cacheable) computation to page display, and reddit has a of users and a lot of page hits :) | curious what you do for a living? My company has built a very sophisticated Bayesian Network Reconstruction platform. We've been working in biotech for 10 years and started branching out to other verticals (finance, business intelligence, payer/provider, etc.). http://www.viascience.com looking for a job? :) | But this assumes that there are only two possibilities - an upvote and a downvote. But of course there is a third important possibility, no vote at all. I don't think you can ignore this. I suppose one approach would be to break it down into two events. There could be the upvote event, and then there could be a down... |
[
"I have another puzzle for you"
] | [
"math"
] | [
"g5cgk"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.44
] | The following multiplication problem uses each number 0-9 only once. What are the missing numbers? 2?? X ?4 = ??0?? | 297 * 54 = 16038 | how did you go about it? | thank you! | Fun problem, took me about 3 minutes while drunk. | I'm not vadim-1971, but as a programmer, I'd have written a script. As a smart programmer I'd have first eliminated the variants that are known to be impossible (e.g. even number * even number = odd number). As an armchair mathematician I'd have then realized that I may then as well just do it on paper since I've alr... |
[
"What's the term I'm thinking of, r/math?"
] | [
"math"
] | [
"g42ka"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | You know sometimes you'll see the term "A (open circle) B"? What is that open circle? I keep thinking it's the dot product, but I'm not sure. It's been a long time since last I saw it. | Function composition? What's the context? | I'm basically dealing with an integral equation. See, for a class assignment I needed to read a journal article and write a 2-page summary about it, plus give an oral presentation in class. I understand it reasonably enough that I believe I'll be fine, but I'm just not sure what the open circle represents. The two term... | It's probably function composition. | Yes, that's it! That's what I was looking for, it's been ages since last I heard that. Thanks! EDIT: Also thanks to breetai for hitting the nail on the head though I didn't realize it until now. | Yes, but lol |
[
"How many norms are there?"
] | [
"math"
] | [
"g5ibd"
] | [
5
] | [
""
] | [
true
] | [
false
] | [
0.77
] | Forgive me if the question seems a little naive or vague. I'm aware that there are at least a countably infinite number of norms - I suppose I should clarify here that I just mean norms on a vector space, mapping a size to each vector in the space. Anyways, I'm aware that you have the p-norms, and if you allow p to be ... | The -norms are countably infinite, not countably infinite, because the reals are uncountable. A complete classification is possible in terms of convex sets. | Ah, yeah, my bad. That was more of a typo than a logical error. And thank you! | Well, norms are functions with certain constraints, so really, you could look at the classification of functions. | Pardon me if I'm wrong, but I feel like the second paragraph of my comment went unnoticed. According to Wikipedia, all seminorms on a vector space can be classified in terms of absolutely convex absorbing sets in . There's more detail in the link. Hope that helps. | Anyways, I'm aware that you have the p-norms, and if you allow p to be real (and I can't see why you couldn't?) you have a countably infinite number of norms there. I think you mean uncountably infinite...? As for your real question, I don't know--but it might help to clarify if you have criteria for norms to be equiva... |
[
"So where do you ask for math help?"
] | [
"math"
] | [
"g449j"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.44
] | Hello, I've been trying to ask redditors for math help, but so far I've had limited success. Is this the correct venue? Am I doing something wrong? Is the way I am asking not very accessible? I am not complaining and I am grateful for any help I can get. Cheers, Tony | /r/learnmath and /r/cheatatmathhomework are good places to ask for help. Edit: I see you've posted in /r/learnmath before. Your questions are about representation theory, which is getting to the limit of what /r/learnmath and /r/cheatatmathhomework will be able to help you with. They're are a lot of people there who ca... | In addition to math.stackexchange, I also find physicsforums.com useful. | If they can't answer your question at stackexchange, ask it at mathoverflow. if they can't answer it there, figure it out yourself, type it up and submit it to Bull. AMS | #math on irc.freenode.net | I would like to point out that in addition to mathexchange, the XKCD forum's math section have some well-versed mathematicians there. |
[
"Complex Analysis Research topic"
] | [
"math"
] | [
"g4n86"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.44
] | I have to come up with one for undergrad complex analysis, and I spent the last week trying to come up with one, but I really can't. I'm not a math enough person to come up with one, so I would really like some help here. | Look at Residue Theory. It's a cool application of complex analysis to solve one dimensional trig integrals. It would be just at the undergrad level and I'm sure you know something about Laurent series. | Thanks! I'll have a look. | Um, what are the guidelines/requirements for your research project... Surely you aren't expected to do original research for an undergrad class project. So are you supposed to just learn about something and write a report about it? | Analytic continuation, conformal mapping, and harmonic conjugates are pretty neat topics at an undergrad level. Analytic continuation is where given a function that is analytic on a certain domain, you find a function that intersects with that domain and has the same values as the function on the intersection, but is d... | Class requirement. |
[
"What am I doing wrong here?"
] | [
"math"
] | [
"g4jor"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.22
] | The triangle and values were given. The math is my work. Why don't the values match? Edit: Sorry if this isn't the best section. The triangle was a question on the quiz we took today. I spent a good 15+ minutes trying to figure out what I was doing wrong. | What am I doing wrong here? Not posting to r/cheatatmathhomework . | Slashes go the other way. \frac not /frac. | Who gave you this picture? Was it part of an assignment? Were there instructions like "explain what is wrong here"? Because something is wrong (and I'm not talking about your algebra). | The triangle is not valid. | [; \frac{5}{6} \neq \frac{6}{x} ;] What you can do to get matching values is replace the left equality... consider the large triangle (the one made up by the two smaller ones sitting side by side) and the Pythagorean thm. Edit: TeX edit thank you root |
[
"Does the fact that a constant of such significance as pi exists represent a fallacy in our entire number system?"
] | [
"math"
] | [
"g48xc"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.22
] | [deleted] | just sitting at about a [3.14} I think you missed this part in the OP's post. | I don't understand the question. Are you saying irrational numbers reveal a flaw in mathematics? That makes no sense. | Oh. Right. Highness level. | I hate to blow your mind like this, but just a fun little fact: "Most" real numbers are irrational. The "density" of rationals in the reals is 0, and thus are very very rare and uncommon. As such, it shouldn't be too surprising that many mathematical constants such as the golden ratio, e, pi,... are all irrational. N... | I hate to blow your mind like this, but just a fun little fact: "Most" real numbers are irrational. The "density" of rationals in the reals is 0, and thus are very very rare and uncommon. As such, it shouldn't be too surprising that many mathematical constants such as the golden ratio, e, pi,... are all irrational. N... |
[
"What is this general problem called?"
] | [
"math"
] | [
"g4mrh"
] | [
2
] | [
""
] | [
true
] | [
false
] | [
0.56
] | For my research, I've implemented a simulation environment that models smartphones moving around a geographical area. For starters, I am also simulating a cellular network topology spanning across the geographical area. As smartphones objects move around, they take measurements of the cellular signal strength they perc... | What exactly are the comparisons you're trying to make? If I understand what you're doing correctly, it sounds like all you need is statistics. The "perceived cellular network" is just a set of samples that you want to compare with a particular expectation, the "real cellular network." | This is true on a grid-square by grid-square basis, I am comparing the desired result with the samples I have. It's working fine, I just don't know if that's acceptable. The real-world model is naturally continuous, so I am already introducing error by representing it as a discrete grid, and therefore I don't know if m... | It sounds to me like you might want to look into the area of "differential equations". You have a collection of data points that could possibly be interpolated to give "boundary conditions" for a differential equation. This equation will be based on the physics of how cellular signals behave (which I know nothing abou... | perhaps you can use topological network theory, this is the guy: rob ghrist | Hm - at first I was like network topology, how would that help? However, there do seem to be some relevant papers here, thanks for the link! |
[
"I am looking for an algorithm to address the traveling salesman problem. However, this one is a variant."
] | [
"math"
] | [
"g4i9u"
] | [
7
] | [
""
] | [
true
] | [
false
] | [
0.64
] | I have two salesmen, not one. And the constraint is that if any one of the salesman visits any city, the other guy cannot go there. can anyone point me to any literature? Thanks. (I wanted to submit this to but they do not have a text based submission option) | Dammit...I'm a lurker and you made made me post. A TSP with more than one salesmen is actually a Vehicle Routing problem. You will find a lot of literature for the standard VRP. As I am studying this stuff I can tell you that the Variable Neighborhood Search works very well for this problem. The VNS has three component... | I think /r/compsci is your best bet. | Well 30 stops really isn't that bad, If you want me to give you any information that you couldn't find with a google search for Traveling salesman (information that relates to your variant) I will need more details, specifically everything palordrolap asked for.. | OK, I will discuss the problem in its entirety. I have a dual arm robot. I have a set of boxes that I want it to move. There are the following modes in which the boxes can be moved: While thinking about what would be an optimal way to address the sequence (and the associated arm) I thought it might help if I cast the p... | Maybe look into simulated annealing, I think it would work well because it is a very simple algorithm and it could easily be applied to your problem specifically. The algorithm is quite simple and abstract enough to be applied to a range of problems. Basically you have a whole bunch of possible states (S) where each s ... |
[
"A<B<C<D are positive integers, the reciprocals of which sum up to 1. What is the largest possible value of D?"
] | [
"math"
] | [
"g3eul"
] | [
22
] | [
""
] | [
true
] | [
false
] | [
0.89
] | A<B<C<D are positive integers, the reciprocals of which sum up to 1. What is the largest possible value of D? This neat little problem appeared in . I determined the solution in the same way as the puzzle's author, but "our" solution relies on the process of elimination. How would I go about finding a general solution,... | Suppose A>=4. Then 1/B, 1/C, 1/D < 1/4, and so 1/A+1/B+1/C+1/D < 4*(1/4)=1. So A<4. Suppose A=1. Then you're fucked obviously. So 1<A<4, ie, A=2 or A=3. It's clear that taking the least value for these smaller terms gives larger upper bounds for greater terms, so: Suppose A=2. Then 1/B+1/C+1/D=1/2, so it can't be ... | Well, I think the solution for 4 is: 2, 3, 7, 42. This suggests to me a conjecture, that the sequence always starts with 2, and each next term is the product of the previous terms, plus one (except on the end). So: Is that right? | The answer you're looking for is (almost certainly) Sylvester's sequence with all terms decremented by one. I am trying to think of a nice proof but all of my arguments have been defeated by the fact that there are a lot of stupid irrelevant integers that can screw up nice things. | Seems right. | It's clear that taking the least value for these smaller terms gives larger upper bounds for greater terms. While I think this is probably true, it is not obvious to me. All that is obvious to me is that: It's clear that taking the least value for the second-greatest term gives a larger upper bound for the greatest ter... |
[
"How can I become more comfortable with math?"
] | [
"math"
] | [
"g3hjt"
] | [
14
] | [
""
] | [
true
] | [
false
] | [
0.81
] | Hey , I'm a Computer Science student who is struggling a lot with Calculus, and really just mathematics in general. I understand the theorems and I understand what I need to do to get the solutions, however when I actually sit down and do tests, assignments, and even practice homework, it all falls apart. Now, I've bee... | I know this doesn't answer your question in a practical sense, but you might find this quotation from John Norstad enlightening: Despite the fact that I did not become a mathematician, and I never use any of the math I learned in school in my computer work, I am convinced that I owe nearly all of what ability I possess... | [deleted] | Wow, I was just about to reply with the exact same thing and then I refreshed the page. A word to the OP: don't get discouraged by your struggles. Lower division math courses mainly just test your ability to memorize and apply formulas, which isn't too much fun and not what I think math should be about. If you like g... | Thank you, I really like that quote. | This is utterly fantastic, I've read a couple pages before bed and plan to read the rest tomorrow. |
[
"I need a list of all primes that fit in a 75 digit long base10 format."
] | [
"math"
] | [
"gbgq3"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | [deleted] | There are about 5.10 prime numbers that have exactly 75 digits. On a 2 TB hard disk, you can store about 2.10 such primes. So no, you can't download the "list of all primes that fit in a 75 digit long base10 format." | First sentence is correct; the second is not. It can't be done. There are approximately 10 / 2 such numbers. (Since most numbers between 0 and 10 have 75 digits, the contribution of numbers with 74 or fewer digits to this count can be disregarded, and we can just look at the number of odd numbers between 0 and 10 : alm... | This sounds like a professor gave you a troll task and you asked the internet without doing any research. You might as well be asking for a list of odd numbers with 75 digits; it can be done, but why? | Psh, I could build a simple DFSM around which an enumerator could be built that would print out all odd numbers with 75 digits. That's at least proof that it's doable. Such an action is proved impractical, however, by your excellent calculations. I suppose we just have different definitions of 'can be done.' Still, I t... | That DFSM would take a long, long time to run, and you couldn't store the results. But yeah, I think we agree. Btw: why do it in hardware? i=1 while i < 10**75: print i i += 2 |
[
"Linear Algebra: Projecting onto a vector space"
] | [
"math"
] | [
"ga6e8"
] | [
2
] | [
""
] | [
true
] | [
false
] | [
0.63
] | I just wrote a midterm for my LA class, and there was one question that I am confused about. I think it might have been formulated wrong. So the question was as follows: The inner product on the vector space P2 of all polynomials up to (and including) degree 2, over the reals, is defined as the integral from -1 to 1 o... | x lives in P3. P2 is a subspace of P3. | Also, the inner product over P3 (or P_N in general) is defined the same way as for P2. If the question didn't make this clear, it probably should have. | This question seems analogous to asking what is the projection of (0,0,1) onto R2 = span{(1,0),(0,1)}. As yesmanapple said, P2 is a subspace of P3. Similarly, you can think of R2 as a subspace of R3, and when you do that the question is analogous to asking for the projection of (0,0,1) onto R2 = span{(1,0,0),(0,1,0)}. | Although in that case it's less obvious that the natural extension from R to R would be to attach a zero-valued component on the right, unlike what happens when considering polynomials: there's an order on the coefficients and it wouldn't make sense to add, for example, x or x . Particularly if one thinks about the abs... | Yes, that's where most of my confusion stemmed from. Usually we're given an inner product and told it's defined on P_N, but here it said only P_2. But okay, so would the projection onto P_2 be the zero polynomial? |
[
"No cheating! How far can you go? 3.1415926535897931"
] | [
"math"
] | [
"g3jxi"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | Ready?? Go! | 3.14 Close enough for practical purposes. | I don't think that anyone has ever claimed that they memorized the digits of pi because of a need for accuracy. | I don't think that anyone has ever claimed that they memorized the digits of pi because of a need for accuracy. | engineer? | 32 decimal places, thanks to this poem (in spanish): 3,14159265358979323846264338327950 "Soy π lema y razón ingeniosa de nombre sabio que serie preciosa valorando enunció magistral, Por su ley singular bien medido el grande orbe por fin reducido fue al sistema ordinario usual." The lenght of every word corresponds to a... |
[
"Mathit: Please contribute your recommendations for people that are looking for jobs related to math."
] | [
"math"
] | [
"ga6sx"
] | [
16
] | [
""
] | [
true
] | [
false
] | [
0.8
] | Hi Mathit, I have a friend looking for a math related job. I figured I would kill two birds with one stone by helping my friend and perhaps those that run into this situation too. I figured I could create this post as a resource for the community for those looking for jobs related to mathematics. I want this post to ... | There are jobs, right? Ha! good point. We need to show: Let us assume an 'open' and non-empty set of math related jobs is in the Borel Sigma Algebra...... | As someone who is about to have a Bachelors in Mathematics, thank you. | Please do. It will be a huge disappointment if the list stays at "make your resume". There are jobs, right? | One point I often hear is "maths jobs don't necessarily have 'maths' in the title". A potential job is much more often called "analyst" than "mathematician". University departments often give some form of guidance on potential jobs at some points (eg. occasionally we have speakers from various places look for candidate... | Thanks! EDIT 1: would you mind giving a detailed list of mathematical society websites' career pages? I only put up American and Canadian Math Society Career links. |
[
"What's the most efficient way of learning math?"
] | [
"math"
] | [
"ga863"
] | [
1
] | [
""
] | [
true
] | [
false
] | [
0.54
] | Hey guys, I really would like to know the most efficient way of learning math. I am going to take a test next year and I really want to make sure that I ace it on my first attempt. I can understand the theory and I actually enjoy it. However, when it comes to practice everything just goes downhill. I can solve basic pr... | Get a textbook. Read it. Do all of the problems. All of them. | As a former math student and former math teacher, I would say the best way of learning math is to engage yourself with the text before you as if you had to present it to a classroom. Instead of just passing your eyes over the material, or memorizing it, write out what you understand as if you were going to use it as a... | Then get another textbook... | If you don't know if you did it right then you don't understand the material. Read it again and/or find other sources. | If you don't know if you did it right then you don't understand the material. Read it again and/or find other sources. |
[
"What's up with the antiderivative of exp( x^2 )?"
] | [
"math"
] | [
"ga9ds"
] | [
4
] | [
""
] | [
true
] | [
false
] | [
0.69
] | What is so special about the antiderivative of e ? Why doesn't it have a solution in trivial functions, and what is this error function thing that comes up? ( As background, I'm just getting through Calc II now, and have enough knowledge about integrals I can do things like the substitution rule and integration by part... | The antiderivative of the gaussian cannot be expressed by a combination of elementary functions - I can't give a proof of a rigorous version of this statement, someone else might help you there. The error function is to be its antiderivative (up to some constant factor) - if an integral comes up a lot in applications, ... | There is an algorithm called the Risch algorithm , which is a method for deciding if a function has an elementary function as an indefinite integral; and also, if it does, determining it. The theoretical basis of the Risch algorithm is Liouville's theorem . Edit: By the way, I bet you mean the Error function , exp(-x2)... | You might want to check your formatting. | Just put spaces after the exponents. | zelmerszoetrop is massively simplifying the discussion by only considering functions that are analytic (i.e. can be written as a power series). There are functions that are infinitely differentiable, but not analytic. Thisdoes not mean that his main point, that the elementary functions are named as such mostly due to f... |
[
"Hello, /r/math. Can you help save world's only \"Math Village\"?"
] | [
"math"
] | [
"gaff8"
] | [
128
] | [
""
] | [
true
] | [
false
] | [
0.92
] | The was built by volunteering math students and professors in a beautiful countryside a few years ago. It doesn't give any official certifications or college credits, yet hundreds of people all the way from high school students to professors gather during summer months to enjoy tinkering with mathematics there. The vil... | Sounds like a noble effort, and a sad reason for lack of funding...you have my support! And some hilarious redditor's axe, no doubt. | And my a...ffffffffffffffffffuuuuuuuuuuuuuuuu BTW, who knew that Denver, Colorado was in the BATMAN province. | You might want to crosspost this to r/atheism , they love it when they get to fight anti-evolutionists. | AND MY AXE!!! By the way: sent! | looks legit, I'll sign. |
[
"What percent of the surface area of a sphere can be seen by looking directly at the sphere?"
] | [
"math"
] | [
"gaar9"
] | [
7
] | [
""
] | [
true
] | [
false
] | [
0.71
] | I seem to have thought up this question a few days ago and can't get it off of my mind. I have at least determined that as the observer's distance from the sphere approaches infinity, the percent of the sphere seen approaches 50%. Can anybody help me solve this? Also, are there any conditions in which the entire surfac... | The earth is approximately spherical, can you see 50% of its surface right now? | The earth is approximately spherical, can you see 50% of its surface right now? | I model it as a circle in R and tangent straight lines from the circle hitting some point in the real line (i.e. a photon being shot from the edge and hitting an observer's eye). If you draw the trigonometric circle, then for some distance x, arctan x = θ will tell you an θ that is the angle of the circle at which your... | I like both flebron and ISS's ideas, and if you actually work it out, it's much nicer than expected: Top half of the unit circle can be represented by the equation y=sqrt(1-x ) and the slope of the tangent line at some point x=a is the derivative: -a/sqrt(1-a ) and using the point-slope equation (y-y0)/(x-x0)=slope for... | I seem to have thought up this question a few days ago and can't get it off of my mind. I have at least determined that as the observer's distance from the sphere approaches infinity, the percent of the sphere seen approaches 50%. Can anybody help me solve this? You only read the title. |
[
"Cubic Pattern"
] | [
"math"
] | [
"gan0r"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | [deleted] | The only cubes in the integers modulo 9 are 1, 0, and -1. (This is awfully cryptic, but I'm sure someone else can explain better than I would be able to.) | Oh you mean Well the thing where you keep summing the digits gives the remainder when dividing by 9. (This should be proved somewhere else). so the numbers are of the form 3n+1, 3n+2, 3n+3 and their cubes are 9*something+1, 9*something+8 and 9*something+0. So that proves the pattern you found. | Depends on the reader, I'm sure. :) | Depends on the reader, I'm sure. :) | http://en.wikipedia.org/wiki/Digital_root#Some_properties_of_digital_roots |
[
"Since its Friday and I survived the week at school, can we get a math joke thread going?"
] | [
"math"
] | [
"gbggo"
] | [
95
] | [
""
] | [
true
] | [
false
] | [
0.84
] | Here's one I thought of yesterday, What did the finer topology say to the coarser topology? All your base are belong to us. | Wow, I'm going to be busy, aren't I? The original poster is alluding to the game , a 1989 arcade game that was translated poorly from the original Japanese. Specifically, the Japanese phrase "君達の基地は、全てCATSがいただいた" was erroneously translated as "All your base are belong to us", when it actually means "With the help of Fe... | The commenter is alluding to a common joke theme, where the joker asks what the result is when two items are "crossed", or combined. For example: Q: What do you get if you cross a parrot and a centipede? A: A walkie talkie. In this example, a parrot, known for being one of a few animals which can speak, is combined wit... | The commenter is alluding to a common joke theme, where the joker asks what the result is when two items are "crossed", or combined. For example: Q: What do you get if you cross a parrot and a centipede? A: A walkie talkie. In this example, a parrot, known for being one of a few animals which can speak, is combined wit... | The math joke in the OP depends on both math jokes and internet memes. A full explanation of the joke must therefore touch upon each topic. | The math joke in the OP depends on both math jokes and internet memes. A full explanation of the joke must therefore touch upon each topic. |
[
"Given the forum...I'm very intimidated to ask, but....."
] | [
"math"
] | [
"gamm3"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.4
] | [deleted] | Don't be intimidated. We don't bite. What level of mathematics did you reach in high school? Are you familiar with calculus? | Speak for yourself. I haven't bitten a tasty college freshman in weeks! Geometry and trigonometry, huh... yes, I'll second the man apple. Are you familiar with calculus? Physics comes to mind, if you're familiar with calculus. I also wonder if Engineering courses might be a good idea considering you enjoyed geo and tri... | That is such a reasonable question to ask - there's really no need to preface with groveling. Maybe you could look into a discrete math class at your college? I found studying basic logic, sets, graphs, and proofs to be very approachable and rewarding. | I think one of the most interesting branches of geometry is differential geometry. You use some tools from calculus and linear algebra to study the curvature and smoothness of space, mappings between different geometric surfaces, geometry on curved surfaces (non-Euclidean geometry), etc. It has many applications throug... | I think one of the most interesting branches of geometry is differential geometry. You use some tools from calculus and linear algebra to study the curvature and smoothness of space, mappings between different geometric surfaces, geometry on curved surfaces (non-Euclidean geometry), etc. It has many applications throug... |
[
"Multiples of nine add to nine"
] | [
"math"
] | [
"gad2t"
] | [
19
] | [
""
] | [
true
] | [
false
] | [
0.74
] | I noticed that any number whose digits add to 9 is a multiple of nine. For example 27 2+7=9 or 5463097281 5+4+6+3+9+7+2+8+1=45 4+5=9 (5463097281/9=607010809). I am fairly certain that this is simply because of its position in base ten number system and that the same would hold true for, say, 4 in base 5. Is there a w... | There's a thing called modular arithmetic that solves this. Modular arithmetic is a type of division that only cares about remainders. For example, 9/9 = 1 R0, where R is the remainder after division or in modular arithmetic, replace the division signs with "mod", throw out the quotient, and only worry about what the r... | Slightly differently written - intuitive way is to see that if we have number ABCD which can be represented as: A 100 + C (999+1) + B (9+1) + D. 999, 99, 9 are obviously divisable by 9, so if we divide whole number by 9, remainder is actually remainder of (A+B+C+D). Works for any amount of digits, of course. It's not ... | Nice post. You have a future in the lucrative field of textbook authoring if your day job doesn't work out. | it's a pretty well known result from basic number theory using modular arithmetic . In base ten we write numbers like 261=2*10 +6*10 +1*10 this is relevant to 9 because 10 is equivalent to 1 modulo 9, which means that 261==2*1 +6*1 +1*1 ==0 (mod 9) which is another way of saying that 261 is divisible by 9. There are... | lucrative field of textbook authoring BWAHAHAHAHAA classic! |
[
"Trig or Stats? Opinions Wanted"
] | [
"math"
] | [
"gautm"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | I have to decide what Math courses I want to take for my 'I put this off till the end of school' situation. I am deciding between a 240 level Statistics class or a 122 level Trigonometry class. It may be apples and oranges, but I was wondering what everyone thought about which class is better for someone with very li... | Considering you've been avoiding math I say go with stats. Having an understanding of stats can be helpful in many situations in work and life and it's easier than trig. Basic trig is pretty easy but many people find trig identities and trig equations extremely difficult. Trig is more for if you desire to go into hig... | Trig would probably be nothing but tests. Statistics generally includes a lot of homework/projects/assignments. I like trig better, but I used it a lot in my engineering and upper level math classes. Stats would probably be easier, but more work.... | Depends on what you want to be able to do later. | I am looking for the easiest class possible. I need it to fulfill some bullshit loophole I got caught in at my school. This is a moment of 'get me the hell out of here and I don't care about learning anymore' | Then please don't do stats |
[
"Trying to develop an algorithm to find a mapping between scores and probabilities"
] | [
"math"
] | [
"gavgv"
] | [
1
] | [
""
] | [
true
] | [
false
] | [
0.67
] | [deleted] | It is possible to construct a conditional probability function as follows: P( buy | score ) = P( buy , score ) / P( score ) You have all these quantities. You know: P( score = s ) = (people with score s) / (total people) P( buy , score = s ) = (people with score s that bought) / (total people) Since your algorithm prod... | Just from a practical point of view, what is wrong with histograms? (also, this should probably be in /r/statistics ) | Aw, I saw the title and came here all ready to recommend David Temperley's . But you don't mean that kind of score. | Well, scores are a floating point number, so chances are that only one person will have any given score. I guess it seems like there should be a way to do this without "bucketing" the scores, similar to how the approach described in the top answer to this question does what it does without any arbitrary bucketing. | Just from a practical point of view, what is wrong with histograms Arbitrary bucketing. (also, this should probably be in /r/statistics ) Why, isn't it math? |
[
"DAE hate when people use = as a shorthand for is?"
] | [
"math"
] | [
"gat7b"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.31
] | Like "math = good" or something, it seems like enough people are doing this regularly that there's no going back. It really hurts my brain seeing this because I immediately think "well then good = math, and everything else that "= good" also "= math"" none of which makes any sense or was intended.. | I don't know why you're getting downvoted so much, but I'm with you on this one. It definitely bothers me. It would be one thing if it was used as a shorthand in texting (like using ur instead of you're) or some similar situation. But it pops up all the damn time. Honestly, I think people just do it sometimes because t... | It's more widespread. Pics subreddit Books subreddit IAmA subreddit | It's more widespread. Pics subreddit Books subreddit IAmA subreddit | It's more widespread. Pics subreddit Books subreddit IAmA subreddit | I think people just do it sometimes because they think it makes them seem smarter- like look, I'm using equations in my writing. that's a good point! |
[
"How do we feel about an IRC chat channel?"
] | [
"math"
] | [
"g9bpq"
] | [
11
] | [
""
] | [
true
] | [
false
] | [
0.75
] | I could do most of the legwork on making one, lemme know what y'all think. | Last time I was in a reddit IRC channel, it was 90% stupid memes and nonsense. | Well.. Im not sure if the guys at Freenode would appreciate an increasing traffic from reddit if we advertise their channel on our sidebar, I am not sure if they are used to some "certain" level like mathoverflow. I guess somebody could ask one of the @'s there if they'd be ok with it.. | I dont know, what would be the difference with #math at Freenode? They're doing a pretty good job.. | The leg work? Such as joining the channel to create it? | All of them aren't that way, just so you know. |
[
"What are some interesting topics in Cryptography?"
] | [
"math"
] | [
"g9gif"
] | [
9
] | [
""
] | [
true
] | [
false
] | [
0.77
] | I will be writing an undergraduate-level research paper on some area of Cryptography, and I am not sure what to do it on. I'm aware that this is a pretty broad question but since there are just so many topics under this umbrella I thought it might help to see if you guys had any suggestions. EDIT: Thanks a ton guys, th... | Elliptic curve cryptography. | Authentication, Web of Trust vs Hierarchical Certificates Practical security: How does your mom know, her banking is secure? What should the bank do, to make this easy for her? What do banks really do? Show that Quantum Key Distribution is useless (or the opposite). How comes most of your classmates, friends, professor... | you might want to crosspost this to /r/crypto | Just slinging ideas here: | A practical fully homomorphic encryption system would blow my mind if it could be developed. This would allow computation to happen on ciphertext. E.g., you could upload your data, encrypted, to a compute server or cloud computing service or something like that and perform computations on it without ever having to decr... |
[
"Looking for some math book recommendations for my reading pleasure."
] | [
"math"
] | [
"g9h60"
] | [
15
] | [
""
] | [
true
] | [
false
] | [
0.86
] | As a first year undergraduate in mathematics and statistics, I was wondering if any of the redditors here could recommend me some good books on math and statistics that would expand my horizons for math and stats. EDIT: I have just ordered and , Thanks for all of the recommendations! | Get yourself a copy of the edited by Tim Gowers. This is a panoramic overview of most of pure mathematics today, written in an encyclopedia style by some of the best mathematicians and mathematical expositors currently living. Most of the book is likely to be beyond you right now, but it's the kind of thing you can s... | Gödel, Escher, Bach. | How to Prove It: A Structured Approach by Velleman | I'm a connoisseur of math book popularizations... Probably my favorite, and I think an excellent choice for a first year undergrad, is "Mathematics: The New Golden Age" by Keith Devlin. It provides an overview of most of the major discoveries in mathematics since 1960, across all subdisciplines, and isn't afraid to t... | Absolutely. Be warned that it is heavy reading: both physically and mentally. |
[
"Linear Algebra - understanding vector spaces?"
] | [
"math"
] | [
"g9jd6"
] | [
23
] | [
""
] | [
true
] | [
false
] | [
0.87
] | Does anyone know of good resources on understanding vector spaces? I'm having trouble wrapping my mind around how to prove something is a vector space using the 10 axioms. For instance, i know that a 3rd degree polynomial isn't a vector space because the first axiom fails, but I don't understand why. | Not closed under addition, bitch. | Whereas polynomials of degree at most 3 are! | The axioms for a vector space require that there be some element "0" which has the property that 0 + v = v + 0 = v for all vectors v in your space. It's not obvious that there isn't some third degree polynomial which has this property. Clearly 0 (the zero polynomial) has the property, but perhaps in this wacky space th... | The axioms for a vector space require that there be some element "0" which has the property that 0 + v = v + 0 = v for all vectors v in your space. It's not obvious that there isn't some third degree polynomial which has this property. Clearly 0 (the zero polynomial) has the property, but perhaps in this wacky space th... | A vector space is a set (space) of things (vectors) where: It then becomes important to study functions on these sets that obey familiar-looking properties involving those addition and multiplication operations. |
[
"Does anyone know the answer to this math riddle/puzzle question? It involves four digits."
] | [
"math"
] | [
"g9d57"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | My chemistry teacher told the class to solve it, anyone who does gets bonus marks and etc. This is the question. "Write a 4 digit number whose value is equal to the first digit to the power of the second digit multiplied by the 3rd digit to the power of the forth digit." Sorta like this: abxy = ( a )( x ) | It is simple. The minute I heard the problem, I knew that the answer was a continued fraction. Which continued fraction, I asked myself. Then the answer came to my mind. | 2592 | thank you!!! | But how did you find it? Brute force search? | http://www.wolframalpha.com/input/?i=a*1000+%2B+b*100+%2B+c*10+%2B+d+%3D+%28a^b%29%28c^d%29%2C++1+%3C%3D+a+%3C%3D+10%2C+1+%3C%3D+b+%3C%3D+10%2C+1+%3C%3D+c+%3C%3D+10%2C+1+%3C%3D+d+%3C%3D+10 |
[
"Any competition(sports or otherwise) will have some underdogs and as a rule of thumb there will always be an upset. Does it make sense to bet on an underdog in the hopes of a big payout?"
] | [
"math"
] | [
"g9zc7"
] | [
1
] | [
""
] | [
true
] | [
false
] | [
0.6
] | Also, does my betting on both winner and loser ensure my winning, suppose I bet the same amount on both? | If p is the probability that the player you bet on will win, W is the amount you'll win if the player you bet on wins, and C is the cost of playing, then you should bet if pW > C. | It all depends on the probability and payout of the various outcomes. | Of course, but what would be the minimum odds to always make money.. Someone should have thought of it by now.. | If you're serious about this, then you need to know that oddsmakers adjust payouts such that the probability of winning times the winnings amount is less than the amount wagered, typically 95% of that amount. This leaves the house with 5% regardless of the outcome. If you bet on both sides, you'll just give the house e... | Take a look at something I wrote on UK football (soccer) odds: http://ibbly.com/Betting-on-football.html |
[
"So today I proved that zero is equal to one"
] | [
"math"
] | [
"ga2ck"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.15
] | [deleted] | While its alright to define ∞ to have the properties you listed, 0(∞) is meaningless. Also, 1(∞)=∞=2(∞) certainly does not imply that 1=2. What you've written is far from a 'proof'. | "∞", this sideways 8 is not a number | We just had a thread about this. | black holes are where God divided by zero | You can't say that a/0 = ∞ for any real a. a has to be greater than zero, because 0/0 can't be defined satisfyingly. Certainly not as ∞, anyway. |
[
"How do CASs calculate symbolic integrals?"
] | [
"math"
] | [
"g9x6r"
] | [
7
] | [
""
] | [
true
] | [
false
] | [
0.83
] | Doing integration by hand, there are things you just have to "see" and different algorithms (substitution, parts, trig subs, etc.) that you have to choose from. How do CASs (like Mathematica or Maxima) determine which algorithm to use? Is there some meta-algorithm, or is it a trial-and-error heuristic process? | I always assumed it was through craploads of special-casing. | I believe that in the real world, it is a largely heuristic process, but the Risch Algorithm exists. | You can find how WMathematica does it on this reference page . In general, for integrating elementary functions, there's the Risch algorithm , altough it's worth noting that "no software (as of February 2011) is known to implement the full Risch algorithm".. | Symbolic Integration I: Transcendental Function by Manuel Bronstein details a couple of methods. | Risch Algorithm, as linked to above, really is the best way to go. |
[
"How to avoid careless mathematical errors?"
] | [
"math"
] | [
"g9t5d"
] | [
3
] | [
""
] | [
true
] | [
false
] | [
0.57
] | Hi //math. I am a high school student who happens to be VERY good at math, but who consistently fails to get As on tests due to careless errors. Most of the time, they come from forgetting a 0 after a decimal place, multiplying instead of dividing, putting a decimal point in the wrong place, or just factoring wrong. ... | Here are some tips. First of all, makes careless mistakes. All the time. Heck, a famous theorem in the field of partial differential equations had a simple that nobody found for ten years! (The theorem turned out to be true anyways, thankfully.) Hate to break it to you, but handwriting is a major cause of mental mis... | For the handwriting: develop an appreciation of how a page covered in formulae . At some point I started thinking of my pages as works of textual art, like Japanese calligraphy or hieroglyphics- because I wanted them to look interesting I began to be more conscious of how I formed the letters. Amazingly, I think this a... | Get used to your common mistakes. That way, you can think "In this situation, I usually do that mistake, so I'd better be extra careful on that point." Re-read your demonstrations in reverse order. If you factorized something, expand it back and check it's the same as the original formula. If you have variables, assign... | Get your head straight. No, you are not good at math. You be good at math, but it will take effort. There is a clue in the wording you use. To stop making careless mistakes, start caring what you write. Check stuff for sense. To go further with any of the interesting math-based stuff you need to really develop that fee... | Hand writing is such a big one. Having tutor lots of HS and college students, this seems to give lots of people trouble, they cannot even read the work they just did. |
[
"question about the Lorentz Group and topology"
] | [
"math"
] | [
"ga0vl"
] | [
1
] | [
""
] | [
true
] | [
false
] | [
0.6
] | So I've read that the Lorentz group is not "connected". "Connected" is a topological property in this context (I think), so there must be some way to assign a topology to a group, which I is part of Lie Group theory, but I don't really know. I know a bit about topology. My guess is that if you represent the Lorentz gro... | We need to make a few definitions. A group is a set G together with a pair of functions: composition GxG -> G and inverse G -> G, satisfying certain properties, as I'm sure you know. A topological group is a group G which is also a topological space and such that the composition and inverse functions are continuous. I... | You can take the underlying set of a group and put a topology on it, or take a topological space and give it a binary operation that makes it into a group. It turns out that this is only useful if the topology and the group operation are compatible in the sense that multiplication in the group is continuous under the g... | Thanks for your reply, it was very helpful. but I didn't quite understand what you meant by "preimage of R+ and R- under the determinant". I guess the determinant is a map from matrices to R (or in this case +-1) but I can't see why that preimage being disconnected tells you that the sets in R are disconnected. oh, I g... | By R+ I mean {x in R | x > 0} . This set is open. And yes, since det is continuous, so is its preimage. Let R>=0 denote the nonnegative reals. It is closed. Since the matrices in the Lorentz group are invertible, the preimages of R+ and R>=0 are the same. Thus, it is open and closed -- a connected component. Sim... | okay I think that is clear now. one more thing for clarification: are you using R+ and R- for convenience only? the same argument would work if we took the preimage under the determinant of say (1/2,3/2) and [1/2,3/2] (and something similar around -1) right? |
[
"(possibly stupid) Question about infinite sets, cardinality, and linearity."
] | [
"math"
] | [
"g9r0e"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.43
] | So I was telling a friend about the continuum hypothesis, at least my limited understanding of it, and he asked me, if you have two parallel linear functions, and you treat the domain and range of each as a set, would the set of the domain of one function and the set of the domain of the other function have the same ca... | I think you're confusing yourself. When dealing with infinite sets there isnt such a thing as "twice the cardinality". I mean, you are getting shorter lines in the image of your functions, yes, but the number of points in any of those lines is exactly the same. | Yup | 2 * W = W for any infinite cardinal W. | Take any infinite subset of R. It's either countable, and thus having the same cardinality as N, or not countable, and having the same cardinality as R. You need the continuum hypothesis to say this. | Yeah, thanks for pointing that out. Maybe I'm trying too hard to think about it intuitively. So let me see if I have this straight. If we take, for example, the set of real numbers between 1 and 2, inclusive, and the set of real numbers between 1 and 3, inclusive, those two sets have the same cardinality? |
[
"A calculus pickup line..."
] | [
"math"
] | [
"g8plq"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.29
] | Hey babe, how about we go back to my place and you let me find the area bounded by your curves... | Don't you mean 10,000,000? It's 10 not the 7!. Either way, you may need to factor in area codes. There are 295 area codes in the US and Canada combined. 2,950,000,000 unique sequences is a hell of a lot to brute force, as you'll probably repeat sequences very often the more you've seen. Assuming pi is completely random... | Don't you mean 10,000,000? It's 10 not the 7!. Either way, you may need to factor in area codes. There are 295 area codes in the US and Canada combined. 2,950,000,000 unique sequences is a hell of a lot to brute force, as you'll probably repeat sequences very often the more you've seen. Assuming pi is completely random... | I would like it if you were my problem set because then you would be really hard and I would do you on my desk. | How can I know so many hundreds of digits of pi and not the 7 digits of your phone number? | They're in there, you just have to figure out where they are! |
[
"I have one week to relearn High School Algebra"
] | [
"math"
] | [
"g8ne6"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.25
] | I'm 25, haven't taken a math course since high school, and next week I am taking the placement test to get into college algebra(the only math course I need for grad school). I only need to get 10/25 questions right and the test covers: " * order of operation * rules of exponents * simplifying expressions in... | These are quite easy when you think about them in terms of multiplication. What I mean by that is e.g. x = x x x x x x x. So to prove something like x x = x just view it like x..m of them..x x...n of them...x = x...m + n of them...x. Another useful identity is ( x ) = x you can view that one like a rectangle e.g. ( x )... | download khanacademy videos (via the torrent). Use the [ and ] keys in VLC to alter the speed... that's how I cover lots of ground fast for revision. | I know it's been beaten to death, but I recommend you use Khan Academy and go through the videos on algebra. A week is more than enough time. In general, please post this kind of stuff on /r/learnmath . | Very. It's obviously important to do some problems and past papers after watching. | I was so going to PM you my email address in case you had any question or you needed extra studying or something. Then I read your username ... not cool .. |
[
"How is this \"troll math\" any different from integration?"
] | [
"math"
] | [
"g8rhl"
] | [
18
] | [
""
] | [
true
] | [
false
] | [
0.7
] | [deleted] | First of all, the troll math sequence of shapes certainly does converge pointwise to the circle. Think about it: For any arbitrarily small precision, you could take a sufficiently fine step size such that the troll curve was within the circle plus the precision. The idea is that the of the approximation approaches the... | Fwiw, it doesn't matter that it's non-differentiable by slope. You could easily make the squares out of lines with slopes of -1 and 1. That's just a 90° rotation. You'd still have to deal with the fact that at any corner the limits are different from each side... Right angles result in a discontinuous derivative functi... | If you pick reasonable parametrizations of the troll sequence functions, they converge to a parametrization of the circle. Which is, of course, differentiable everywhere. And the troll sequence functions are differentiable almost everywhere, which is why we can compute their length. In fact, the set of points on whi... | Just to clarify, though, it does approach a circle pointwise. | gotcha. 45 degrees though |
[
"Am I just mathematically retarded?"
] | [
"math"
] | [
"g8sjz"
] | [
3
] | [
""
] | [
true
] | [
false
] | [
0.67
] | Hey guys, I bet you guys get this a lot and I'm sorry if it doesn't belong here but perhaps there's someone here who's similar to me. Anyway, when I was young I used to be pretty okay at mathematics...but I had several bad teachers especially in Jr. High and now I have a TERRIBLE foundation. Slowly I became worse and w... | Have you tried reteaching yourself math from the beginning? Working through arithmetic and algebra step-by-step? You can't learn higher math until you've mastered basic pattern recognition, and that isn't a skill you'll be taught in a college class. Work through of problems in basic math, especially the problems at the... | You can google the topic or go to the library and check out another book. | Do you know why the practice problems are much harder than the examples? The training wheels have to come off at some point. if you want pick out the easy problems first, the ones that are easy as example problems, but do them all. Don't give up because they're hard, keep working on them! Also whatever you don't unders... | Have you tried reteaching yourself math from the beginning? Working through arithmetic and algebra step-by-step? You can't learn higher math until you've mastered basic pattern recognition, and that isn't a skill you'll be taught in a college class. How would I do that? Sounds good. I think that no matter how much I tr... | What math class are you taking now? What math classes did you take before this one? What grade did you get in that class? My advice is to do more practice problems. If that seems to hard or you just feel lost then maybe you should not be in that class and need to take the one below it. I have a bias being an engineeri... |
[
"Does a physicist need real analysis?"
] | [
"math"
] | [
"g8y2f"
] | [
2
] | [
""
] | [
true
] | [
false
] | [
0.6
] | I need to choose which courses math courses to take in addition to the mandatory ones. Any extra math courses I take are in addition to the standard courseload which is already quite heavy, so I can't take anything and everything. The question is whether taking Real Analysis would be useful for a physicist. At first gl... | You don't need real analysis for anything except pure maths. However, the techniques you learn in analysis, and the way it forces you to think from axioms rather than intuition, are both extremely useful even if you replace the epsilons with something that has real-world meaning. | Typically, an undergraduate real analysis course is an overview of the basics: metric spaces, limits and different forms of convergence and continuity, and some integration theory. Maybe the topics themselves aren't useful for physics, but the tools and the mathematical maturity you earn are very useful. If you hope to... | I would argue that, so long as OP is okay with learning topology without a clear motivation, it's better to go topology and then real analysis rather than the other way around. A lot of things make far more sense in that order, especially when you start branching into analysis in C or R (as opposed to R | I think you need real analysis for topology, do you not? | Only Calculus, Linear Algebra and basic Complex Analysis are listed as prerequisites for General Topology at my university. |
[
"Jobs for Theoretical Mathematicians"
] | [
"math"
] | [
"g93nv"
] | [
14
] | [
""
] | [
true
] | [
false
] | [
0.86
] | So, here I am, with a M.S. in theoretical mathematics, and no idea what to do with it. There seems to be a definite push for me to go into finance, but I have very little background in financial math, statistics, probability, etc. I do have a fairly thorough understanding of computers science and programming, but I'm n... | hint: username | hint: username | You could probably land a teaching/lecturing post at a community college. I had an offer from one when I was at that stage in my life (I currently live on the second floor of the Ivory Tower and love it). | The book 101 Careers in Mathematics might be of assistance in helping you think more broadly about possibilities. In this thread you'll find my answer of how I went from degrees in mathematics to managing the design, development, and test of spacecraft mechanical systems. | I would highly suggest CS. Programming and learning languages are mechanics and techniques. To me, math powers a large part of the quality and performance of your implementation. Also, it allows you to create something profound from your understanding of the numbers. |
[
"derivative of a sphere's surface area?"
] | [
"math"
] | [
"g8alp"
] | [
3
] | [
""
] | [
true
] | [
false
] | [
0.58
] | [deleted] | The derivative of the surface area is probably useful if you want to calculate the force that resists changing the radius of a spherical balloon due to elasticity and/or surface tension. The second derivative probably tells you something about the stability of this force, and how fast a stable configuration would reson... | The derivative of the surface area would be the amount by which the surface area changes for a given infinitesmal change in radius dr. One could think of it as the sum of the perimeter changes for a stack of circles making up the surface 2-sphere. | Interesting question! I liked Melchoir's and youcanteatbullets' answers (esp. the latter's). Which brings to mind: is there such a thing as an intuitive calculus text? Could someone recommend such a thing? I haven't studied calculus since engineering school, and I kinda miss playing around with stuff like this. | Intuitively, the dV element (infinitesimal change in volume) of a sphere can be thought of as (surface area) x (dr), so this is perhaps how to think of dV/dr = surface area. Now, if we take a sphere of radius r (and thus surface area 4πr ), and turn it into a circle of the same area, we can think of the dS element as (... | Yes. Taking a derivative is like taking a boundary operation. The same principle holds in higher dimensions and this is one way to interpret the fundamental theorem of calculus. |
[
"suggestions for visualization of complex functions?"
] | [
"math"
] | [
"g7zbv"
] | [
6
] | [
""
] | [
true
] | [
false
] | [
0.8
] | I'm trying to get an idea of how things move around on the complex plane under different maps. Any suggestions of easy-to-use apps or things I can prod Mathematica into doing (I suck at code) that give reasonably understandable pictures back? EDIT: my task isn't so much to build intuition on what these maps do--I've al... | In case you haven't seen this before . I also have a book called Visual Complex Analysis which is kind of neat. | This applet is great to build an intuition. Yesmanapple has sound words of advice, but you'll see that the task is a bit harder than it seems, even in simple cases. Good luck and have fun, complex analysis is awesome ! | Needham's is probably the best math textbook I've ever read (Munkres is also very good, but not quite at that level). | No need for Mathematica. Just draw two planes; one for the domain and one for the image. Play around with the image of vertical/horizontal lines, circles, rays, etc. | Also, wolfram|alpha will do this for you. |
[
"Is there an infinite number of proofs for every theorem?"
] | [
"math"
] | [
"g7xfk"
] | [
2
] | [
""
] | [
true
] | [
false
] | [
0.57
] | Can you point me to some resources on this topic? I have been googling for a bit and haven't found much. | Yes! Only trivially though, since we can always add extra (and superfluous) steps to the end of the derivation. We can also add extra premises to the beginning of the argument, or extra, unnecessary and non-invasive conditions. | Exactly. As per Occam's razor, I think we can skip the step where we add and then subtract an elephant. | This reminds me of a job interview I had at Apple... INTERVIEWER: Well, you've come up with two algorithms for solving this problem. Can you think of any more? ME: I can think of arbitrarily more by adding useless steps. | I think this question only makes sense with respect to a formal system. Eg. Consider a system with only one axiom and no inference rules. Then a theorem in this system and has exactly one proof. Still, with a given system this could be an interesting question. Does a theorem in say Peano arithmetic have infinitely many... | Practically there are only one or two proofs that are useful. However, you can add useless things to any proof, much as you can solve equations by adding and subtracting one many times. |
[
"On Formally Undecidable Stanzas of Limericks and Related Poems"
] | [
"math"
] | [
"g99bo"
] | [
5
] | [
""
] | [
true
] | [
false
] | [
0.78
] | My author is really a nerd. A Gödelian limerick? Absurd! I cannot exist; He just hurt his wrist. From writing me he was deterred. | I'm not sure of your intention in posting this, but this is as good a time as any to share some math-inspired poetry. Firstly, you have the poem Love and Tensor Algebra by Stanislaw Lem. Unfortunately for us, it was written in Polish, and adapted by Michael Kandel into English. In all honesty, the poetry and spirit of ... | So the set (0, 1) is open but bounded? | My intention was to be silly and slightly clever, so thank you for those. This is an excellent place for them. | Technically, a closed set contains its limit points (think of these as end points). Hence (0,1) is open, but [0,1] is closed. A bounded set is one that has an lower and upper bound. Hence [0,5] is bounded, as it has 0 as a lower bound, and 5 as an upper bound. The real number line, however, isn't bounded (although it i... | That's correct. |
[
"Does it ever seem like mathematics is taught backwards?"
] | [
"math"
] | [
"g8u8y"
] | [
250
] | [
""
] | [
true
] | [
false
] | [
0.91
] | I thought of this question after coming across , and it really resonated with me. For a little background, I am a third-year college student currently enrolled in an undergraduate Real Analysis class in the US. So often, I feel that I am learning mathematics backwards. A professor will start a lecture (or a series of l... | It's funny: I teach using constructivist math series and there are more than a few lessons whose goal is to have students discover the algorithm rather than just giving them the algorithm and a bunch of examples to practice it on. Almost invariably when we arrive at the algorithm someone asks why I didn't just tell the... | A professor will start a lecture (or a series of lectures) with a complex definition; and then he will go on to prove results about this seemingly arbitrary definition that materialized out of nowhere. Soon, theorems are stated and proven and often this sheds light on the reason for the definition, but this is not alwa... | The more positive approach would be, as I say to my own students: if you 'discover' it on your own, there is a higher probability that you'll remember it. | Counterpoint: Think about the way Statistics is taught to non-mathematicans. Every engineer, business student, nurse, biologist, and prettymuch anyone else learns some basic statistics during their undergraduate degree, and every single one of them absolutely despise it. The statistics they learn really is of a high le... | Do you smack them around with "If I just told you the algorithm, you'd copy it down and forget it!"? Then you fail that kid for back-talking, and no one questions you again. |
[
"How do I reconstruct an image using a Fourier Transform's magnitude and phase?"
] | [
"math"
] | [
"g8ef6"
] | [
1
] | [
""
] | [
true
] | [
false
] | [
0.56
] | [deleted] | Inverse fourier transform gets you back to the original image. In matlab it's the ifft function. For a 2D image you have to take the ifft along both the rows and the columns. There may be a function that does that (ifft2, I think). | A pretty big vector | I know it is a trivial case, but a JPEG is a fourier transform. I found a Mathematica notebook a couple of years ago that showed how to do exactly this with a photograph. I will look and see if I can find it again; will post if I still have it. | What is the input for the ifft function? | Thanks! |
[
"A question involving absolute value inside of absolute value expression."
] | [
"math"
] | [
"g8fl4"
] | [
1
] | [
""
] | [
true
] | [
false
] | [
0.6
] | I know how to solve absolute value equations and inequations well enough, but I just recently stumbled upon something like this |2x-5-|5x+9||=-x I have no idea how to begin solving that. I thought about figuring out when is 5x+9 positive, and then trying to solve for thr whole equation, but that just didn't seem to to ... | |2x-5-|5x+9||=-x Perhaps I'm misreading something, but... I don't think that has a solution. The LHS is an absolute value (nonnegative) and the RHS is the negation of a square (nonpositive), so you could only have equality where both sides are zero - but that isn't possible either. edit: hm, I suppose I'm only consider... | It's not nearly so simple when using complex numbers, however. | To solve these problems of multiple absolute values, use the following algorithm. Working from the inside out, every time you hit an absolute value, branch into two possibilities. In the first case, assume the interior is positive, and replace |f(x)| = f(x). In the second case, assume the interior is negative, and repl... | Could you replace every x with a+bi, and every |x| with sqrt(a Not sure how you'd handle |5x+9|, but am I on the right track? | With my method, you'd need to split your problem into an infinite number of cases, as the absolute value sends all the values on a circles of radius r (centered at the origin) to the same value. That does seem rather difficult. |
[
"I can't find any online video lectures (e.g. iTunes U) for undergraduate level Probability and Statistics."
] | [
"math"
] | [
"g98tn"
] | [
5
] | [
""
] | [
true
] | [
false
] | [
0.78
] | My instructor seems to be in a world of his own and now I'm beginning to flounder in my course. As for my text book - A First Course in Probability - learning is coming painfully slow. Help is much appreciated. | http://www.khanacademy.org/ | Academic Earth has a good video lecture series on Probability here . | Try MIT OpenCourseWare. This seems likely to serve your needs. Also, I feel your pain. Ross is terrible. | Well then, screw all three of you! :-P Those were going to be all three of my suggestions. I'll just go back to my thesis. /pout | Looks promising. Thanks! |
[
"Rate my Undergraduate Math Program!"
] | [
"math"
] | [
"g7g9j"
] | [
1
] | [
""
] | [
true
] | [
false
] | [
0.55
] | [deleted] | I'm not an older mathematician by any stretch of the imagination, but that program (especially with the Math and Grad Prep concentrations) appears very, very strong; definitely with more available variety than my undergrad program has had. Not to mention the fact that UIUC is a very well respected school for mathematic... | At UF math majors take Calc 1,2,3, DiffEqu, Sets and Logic, Linear Algebra, Advance Calc 1&2, and Abstract Algebra. Then add 4 math electives to that and you got a BS in math (Well there is other stuff like foreign language and humanity courses but I don't think that's what you care about) | Good idea :). Here in Mexico the requirements go as follow: The major lasts 4 years divided in 3 blocks, the first block is 2 years and is directed to physicists, people doing actuarial sciences, computer science and math majors. We take, the first semester, an introductory algebra course which consists in intro to mat... | Pretty good. There are far worse programs. However, I'd have to say, the minimum requirements to graduate are fairly low. If you want to have a strong major, you should take more than that. | The grad program, especially the algebra program, at Urbana-Champaign is excellent, and I wouldn't expect the undergrad to be lacking either. |
[
"What are your all-time favorite math books?"
] | [
"math"
] | [
"g8bjd"
] | [
14
] | [
""
] | [
true
] | [
false
] | [
0.73
] | Books that inspired you, clarified complex ideas, gave you a fresh perspective on old ideas you you thoroughly understood, etc. Textbooks or otherwise. | Abstract Algebra by Dummit and Foote. | Hartshorne: Algebraic Geometry Not that I've even really understood half of it, but it is so well written and concise, with interesting exercises to keep you occupied for as long as you want. | I'll try to link to where there's a preview available. Check Amazon for reviews. Halmos, Naive Set Theory (ignore the incorrect cover) - I read this in the bathroom. I like to describe it as a haiku on the basic principles of set theory. A classic, and my overall favorite math book. Hirsch, Smale, and Devaney, Diffe... | that's easy: Basic Notions of Algebra by Shafarevich. Don't be mislead by the title. | "Mathematical Methods in the Physical Sciences." Mary L. Boas. It covers everything from basic stats and calculus up through some pretty high level stuff (Green's Functions, Residue Theory, Legendre Polynomials, etc). Clearly and concisely presented. I use it to figure out what the hell other math textbooks are tal... |
[
"Need help getting math-literate."
] | [
"math"
] | [
"g7jl8"
] | [
2
] | [
""
] | [
true
] | [
false
] | [
0.6
] | Hola. Just finished reading Malcolm Gladwell's "Outliers", confirming my long standing suspicion that my math-illiteracy is due to laziness and / or poor education. I've got higher degrees in social science, but I really think it's embarrassing for an educated man to suck at math. Equations in research articles fill me... | Obligatory link to Khan Academy. | What sort of level are you at? When you say "I can do math in my head easily enough" this indicates that you think of math as arithmetic, adding and subtracting etc, which I wouldn't really class as math. On the other hand, you talk about looking at research papers. If you mean math research papers, it is to think you ... | What sort of level are you at? When you say "I can do math in my head easily enough" this indicates that you think of math as arithmetic, adding and subtracting etc, which I wouldn't really class as math. Hehehe... exactly. Picture anything above what you class as "not math" as being out of my comfort zone. Politics an... | Surprised I haven't come across this earlier. Thanks, mate. | I went through the same thing back in 2003. Fresh out of the military and I barely knew how to count. As I was pursuing my degree I started off by taking the lowest of all math classes. Although it was simple it helped me set up a good foundation for math. Several years later I ended up taking cal 1,2, and 3. Personall... |
[
"Why isn't analysis taught to undergraduate engineers?"
] | [
"math"
] | [
"g8hjp"
] | [
9
] | [
""
] | [
true
] | [
false
] | [
0.72
] | I did engineering as an undergrad. Required math courses were Calc I & II, multivar, differential equations (strictly ODEs), and a course called "advanced engineering math" which was a grab bag of remaining topics including some linear algebra and PDEs. One thing I was always aware of was that the math teachers, who we... | Because proving Bolzano-Weierstrass doesn't help engineers in the least. Analysis isn't important for engineers. Engineering is an applied science. Engineers want a kit full of tools that will help them solve their problems. The inability to prove the tools function has no bearing on their ability to function. Example:... | It may depend on the university you are attending. In some places, people just want to finish their undergrad and get to work, and presumably knowing analysis isn't essential. Having spoken with many engineering majors, I get the impression that many of them have a "the less math the better" attitude. On top of that, a... | Right, it's not important to the development of your average working engineer. It important to the development of Engineering as a discipline, and if you were to go to grad school and eventually do research in say, Control theory, or signal processing, it'd probably be a good idea to have a good education in these subj... | To be fair, the quick derivation tricks for polynomials, trig functions, etc. leave you cold when it's time to understand numerical analysis. It's an issue of conceptual primitives (PPT): if derivatives-as-limits are already a conceptual primitive for you, then the Euler method is trivial and can be mentioned en passan... | Control Theory, for example, relies heavily on the theory of martingales and other stochastic processes, which in turn rely on measure theory and probability. Also, filtering and signal processing are all just Fourier transforms. |
[
"Is a noisy sinusoid a non-stationary process?"
] | [
"math"
] | [
"g7o36"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | Assuming the noise is zero mean and AWGN, then doesn't that imply that the mean of the process is a function of time and hence it is non-stationary? | I don't think you've defined the process unambiguously. Have you fixed a sinusoid and then added random noise to it, or is the phase of the sinusoid random too? | I'm thinking of just a fixed sinusoid, with a linear phase and constant amplitude. I know the random phase case works out to be stationary. | Even without the noise, a fixed sinusoid is not a stationary process. | It's wide-sense stationary. | It's wide-sense stationary. How can it be if the mean is a function of time? |
[
"Could someone help me with this projective geometry question?"
] | [
"math"
] | [
"g7sjq"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | An automorphism f of A is a permutation of A sending collinear points into collinear points. The book then goes on to say that the fact that given a line l, f denotes a one-to-one correspondence between l and f(l) = l'. My question is, why couldn't there be a line m != l such that f(m) = l'? I don't see how it follows ... | Be that as it may, /r/math tries to filter some of the homework-style questions to the other subreddit, so as to preserve the frontpage for other discussions. Anyway, there are some good people over at that sub that can help you. | I'm sure someone here would be willing to answer your question. | It's not math homework, there was no "The proof of this is left to the reader as an exercise." | The automorphism f is a permutation, so it is a bijection (it has an inverse). | But it's a bijection of points, and there are as many points in a line as there are in two. |
[
"The most famous edit in Rock and Roll History (Strawberry Fields Forever) has been solved... by the same guy who figured out the opening chord to A Hard Day's Night"
] | [
"math"
] | [
"fvdde"
] | [
18
] | [
""
] | [
true
] | [
false
] | [
0.77
] | null | The way author talks about formulas and equations in vague generalities as if they are some sort of magic cracks me up. | Direct link to the relevant pages in : http://jasonibrown.com/pdfs/Notesv43n1-2.pdf | I love this out of place paragraph: Strawberry Field was the name of an orphanage in Liverpool which was located near John Lennon's childhood home. He apparently always liked the name. It has basically no relevance to the preceding or succeeding paragraphs (which are topically connected). | I don't understand why this is news. I already knew about the splice from reading the Wikipedia article , where it has been for a long time, with citations to sources from 2005 and 1988. | You don't end your proofs with "TA-DA!"? |
[
"Autodidacts: Where are you now and where are you heading?"
] | [
"math"
] | [
"g7lm5"
] | [
27
] | [
""
] | [
true
] | [
false
] | [
0.78
] | Question those teaching themselves mathematics, Where have you got so far with your study and where aer you heading toward? | I just use books. I really don't like Khan Academy. | High school student, currently self-learning from Spivak's Calculus. Heading towards anything math throws in my way. :) I'm interested in learning as much math as I can pre-university (and of course, as much as I can while I'm at the university). | While this might be a troll I nonetheless have encountered this attitude in real life and so I'm more responding to this sort of sentiment rather than the poster since I cannot ascertain their intentions. I think it's a strange attitude to have because it suggests that one should only do things that have a high likely ... | Did all the calculus courses. Learned set theory and vector calculus, then topology. Studied a little Manifolding and Tensor Analysis (Only the applied side though). Studied a little Probability Theory. Right now I am learning Statistical Mechanics and Conformal Field Theory. | I'm teaching myself mathematics in the hopes that one day I can get a career doing something involving maths. I'm also doing it to pass the free-time I have between now and getting into college (a story for another post). Needless to say I made mistakes, I was lazy, and I am now getting a second chance at college. I lo... |
[
"The sum of 1+2+3+4...to infinity = WTF??"
] | [
"math"
] | [
"gf9a0"
] | [
3
] | [
""
] | [
true
] | [
false
] | [
0.54
] | I'm no math major, and this is the first I've heard of this. I was just listening to a debate and one guy mentioned that the sum of the series 1+2+3+4 to infinity is equal to -1/12. I checked the web because I thought I surely hadn't heard correctly, but Wikipedia indicates he's right! How is it possible to sum a serie... | If you actually read the Wikipedia article, it says that the sum of that series is -1/12. That doesn't mean that the actual sum of the series is -1/12. In fact, this series diverges (it goes to infinity). The Ramanujan sum is just a way of assigning a useful number to a divergent series which captures certain propertie... | I'll try to help you understand how these non-intuitive sums can come up just by doing (relatively) ordinary things. To keep things simply, let's consider 1+2+4+8+16+... , which diverges, however, let's pretend for a moment that it does equal some value, i.e. s=1+2+4+8+16+... Now, notice that 2*s=2+4+8+16+32+..., so 1+... | Nice explanation! Another way to look at it is to work backwards from what theworstnoveltyacct explained. Start with something simple, s = -1, and express s in a more complicated, but equivalent way: s = -1; 2s = -1 + s; 2s + 1 = s Now is the tricky part. Let's suppose we can write s as a series of numbers. Since s... | 2's complement arithmetic is a kind of approximation of 2-adic arithmetic, where numbers are represented by strings of 0s and 1s that extend infinitely far to the left. As a 2-adic number, -1 is represented by an infinite string of 1s: ...111. Anyway, my point is that 2's complement arithmetic is perfectly content to d... | That is absolutely not true. 1+2+3+4+... is a divergent series. The sum is undefined. The Ramanujan summation , an entirely different thing with some similar properties, is -1/12. |
[
"Path Independence Day!"
] | [
"math"
] | [
"gfng7"
] | [
2
] | [
""
] | [
true
] | [
false
] | [
0.6
] | Let's make a day where we celebrate the achievements in Math! Let's do it by taking a day off and going to explore Nature! Pick a spot to go to (Mountain top, Creek, etc.) and pick the longest most non-sensical route to get there. For the return trip, take the shortest route. Get home! | I'd have to disagree. My favorite branches of mathematics have precious little to do with real life. | Why don't we celebrate the achievements of math by doing more math? | We do that every day already. | Fibonacci really doesn't apply to nature. | I think it would be a good idea to remember that Math isn't for just numbers on paper, it's the application to real life that's important. I think that most of mathematicians would disagree. |
[
"Is there a system of n equations that can be solved uniquely for n+1 unknowns?"
] | [
"math"
] | [
"gf8b2"
] | [
16
] | [
""
] | [
true
] | [
false
] | [
0.83
] | I've always figured that if you've got n equations, then you can solve for at most n unknowns uniquely -- linear or not. Try as I might, I can't come up with a system of n equations in n+1 unknowns from which all n+1 unknowns can be uniquely obtained. So... Any counterexamples? Is this a well-known result that my un... | This of course very nicely generalizes to a single equation that uniquely determines as many unknowns as you like: a² + b² + c² + ⋯ = 0 | x^2 = -y^2 (over the reals) | If you restrict your question to polynomials over an algebraically closed field, the answer is yes. In fact I claim that if X is a variety (possibly nonreduced) of Krull dimension n+1, then any system of n equations on X has a solution set of Krull dimension at least 1. Let n be the smallest number such that the clai... | Well, I can shift the answer by whatever I want. For example, (x-2) + (y-3) = 0 has the unique solution (x, y) = (2, 3). Maybe a more visual example would be: x = 1 x^2 + y^2 + z^2 = 1 This is the intersection of a plane and a sphere, but I have rigged it so that they intersect at only one point, namely (x, y, z) = (1... | Regarding your original concern: Is this a well-known result that my undergrad math courses somehow never addressed? and regarding: How broadly applicable is the concept behind this answer? The trick is to shift your perspective and think of "solving an equation" to "getting a zero". You seem to think zeroes are "dege... |
[
"Which should I take first: differential equations, or linear algebra?"
] | [
"math"
] | [
"gfoxp"
] | [
4
] | [
""
] | [
true
] | [
false
] | [
0.7
] | I'm a computer science major looking to also do a math minor, and my advisor is giving me a choice between taking differential equations or linear algebra in the fall. I need to take both, but I'm just wondering if there is anything in one course that will make me appreciate the other course more. | Take linear algebra first. You'll need alot of it for differential equations. I'm surprised Linear Algebra wouldnt be a prereq for DE's | Linear algebra, without questions. It's really fundamental, used basically everywhere (since is linear at a first order approximation), much more important than DE. And of course, solving linear DEs (the simplest class) is reduced to linear algebra. | This is not obvious. On the one hand LA is better first because it can be very helpful when dealing with the systems of DEs which usually turn up in a DE course. On the other hand LA is often a more abstract course which some students find more challenging whereas DE is very often cookbook-like, meaning you just semi... | It's usually not, but most people who take DEs (physicists, mathematicians, engineers and the like) have to take linear algebra in first year anyway. | I agree with this. My college doesn't have the usual Diff Eq course as part of the calculus sequence (only an upper level theory course on ODEs), so I learned DEs in physics. I thought the fact that the general solution to the homogeneous equation plus any particular solution gives you the full solution set was pretty ... |
[
"Stupid question: Why is the expected value usually written with square brackets?"
] | [
"math"
] | [
"gfpwg"
] | [
4
] | [
""
] | [
true
] | [
false
] | [
0.75
] | Why do people usually write E[X] instead of E(X), but always Var(X)? I've just always wondered about that. | In physics it's <angled brackets> | I use parantheses -shrug- | There are many books that use neither brackets nor parentheses; they just write EX. For example, Hoel, Port & Stone , and occasionally Grimmett & Stirzaker use that notation. Expectation, by the way, is not always a number (e.g. the expected value of a random vector is a vector). | I am just guessing here, maybe because it's a functional? In the sense that a random variable is a function from a probability space into the real numbers and the expected value assigns a number to this function? Functionals are often written with square brackets in some disciplines. Then again, of course also 'Var' is... | I thought it might have something to do with linearity. Note that E[X] is a linear functional, but Var(X) is not. But in any case, there are plenty of things that are linear but aren't written with square brackets. |
[
"So say you have a group of cities..."
] | [
"math"
] | [
"gft4k"
] | [
2
] | [
""
] | [
true
] | [
false
] | [
0.75
] | A friend and I were doing a thought problem and can't seem to come up with a solution. Maybe R/Math can help... Say you have a group of cities of arbitrary count. Each city has exactly one or more roads that lead to other cities, but no city has roads that lead to every other city. It is assumed that a path between 2 r... | a) Use Dijkstra's algorithm b) Every permutation of the cities = n! | Dijkstra's algorithm That will find the shortest path. You can stop the algorithm as soon as any path is found if you want. | But this is breadth-first-search with a priority queue, so it will be less efficient than a simple BFS for identifying the components. Or am I missing something? | You just want to find some path? I think given no additional information, you can't be much more efficient than a simple breadth-first search - successively visiting all neighboring cities you have not visited yet. This determines the "connected components". Concerning your bonus question, if you're interested in disjo... | If you like this stuff, you should look into learning more about computer science! |
[
"Need help with some ring proofs."
] | [
"math"
] | [
"gefd6"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | [deleted] | /r/cheatatmathhomework and /r/learnmath are good places to post questions like this. Also, your professor defines a PID in the ? That's a pretty fundamental concept to not get any class time. | hmm, #10 looks iffy to me, I thought Z[sqrt(2)] mod (2 + sqrt(2)) was isomorphic to the field with two elements. In particular, it's not hard to show that (2 + sqrt(2)) is the ideal (sqrt(2)), and it's pretty easy to see that if you mod out by that, you get Z/(2). | Thanks, I wasn't even sure I was in the right subreddit. I'll post some things in those too. He's been a pretty good professor in my opinion, but often neglects to explain important concepts in class. It's frustrating. Cheers! | On #7, I think he meant to say F has characteristic not 2. Otherwise Z/(2) is a counterexample; I'm not sure off the top of my head what happens in larger char 2 finite fields. For characteristic not 2, every nonzero element is distinct from its negative. Pair them off and they sum to zero. Regarding #4, have you cover... | Just by looking at your homework you can tell he likes algebraic geometry. Where exactly are you having troubles? |
[
"finding all the possibilities of a bingo game"
] | [
"math"
] | [
"gelfn"
] | [
2
] | [
""
] | [
true
] | [
false
] | [
0.6
] | Quick explanation: I was recently trying to find all the different ways to achieve a bingo in a specific bingo game, namely three triple dots. This means getting a sequence of three dots in a row either vertically or horizontally (no diagonal) three times on one 5x5 bingo card without using the free space (middle). ex... | So the dots can overlap and the 3 blocks of 3 can be in different directions? That changes things! By the way, 512 * 2 = 1024 != 924. | So the dots can overlap and the 3 blocks of 3 can be in different directions? That changes things! By the way, 512 * 2 = 1024 != 924. | Also curious for a more precise explanation of the problem. Why no middle spot? Maybe OP can redo the formating? | I think you accidentally some formatting. Anyway, let's look at the case where the 3 dots are horizontal. They must be on rows 1,2,4,5 (if I'm reading the question right, see below) and for each of the three rows they're on there are 3 possibilities for the first filled cell (1,2 or 3). So for horizontal orientation th... | I'm not exactly a bingo connaisseur, so I was trying to interpret the question as well as I could. I might just have to head over to bingooverflow to get the experts' opinion on this one. |
[
"Can direction be determined from 3 dimensional accelerations?"
] | [
"math"
] | [
"geqj8"
] | [
11
] | [
""
] | [
true
] | [
false
] | [
0.87
] | I was going back and forth on whether or not to post this in /math, or /physics and couldn't make up my mind, so I'm going with /math :) I enjoy measuring things. A lot, probably too much. If I can measure something in real time, and put it in excel, I'll do it. If I were a less frugal person, I would gave spent hun... | Specifically for the question in the title, no. Think of it this way, if I'm standing in an airplane that's not accelerating (but still could be flying in some direction) and I get pushed (accelerated), can I tell which direction the airplane is flying? There's not enough information. You would need to know something... | No. You need the accelerations in all six degrees of freedom ; three-dimensional acceleration is not enough. That said, apparently the iPad 2 has both an accelerometer and a gyro, so perhaps you can do it on the newer hardware. | Good point, we should focus on the problem at hand. I can see that working for a car on a flat surface. For normal driving conditions, though, even without skidding, I think you still have four degrees of freedom: Plus, when you consider the operation of the shocks, it seems like significant energy might leak into the ... | Good point, we should focus on the problem at hand. I can see that working for a car on a flat surface. For normal driving conditions, though, even without skidding, I think you still have four degrees of freedom: Plus, when you consider the operation of the shocks, it seems like significant energy might leak into the ... | Correct, there would be too much error from estimating the unknowns that would only worsen as time goes on. You'll need a gyroscope to keep a constant "heading" data set. |
[
"C++ code for quickly finding eigenvectors"
] | [
"math"
] | [
"gf1i4"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.45
] | Hi, I'm working in Matlab and the eigenvectors calculations are getting bogged down for the giant matrices that I'm working with. I'm looking at exporting the job to a c++ mex routine and was wondering if anyone had suggestions on different libraries to look at. edit: The matrices that I'm dealing with are very sparse,... | Matlab should be pretty efficient calculating eigenvectors. Otherwise, there are many different methods for calculating eigenvectors. It would probably be useful if you told us more about your problem. | Sure can, sorry for the lack of details. I'm looking to compute the primary eigenvector of a large (20,000 x 20,000 at least) very sparse, symmetric matrix. Matlab starts getting bogged down right around this size and I'm hoping to find a new method that will let me computer eigenvectors for matrices on the upwards siz... | Thanks for the response! Sorry I didn't include these details in the original post. 1) Yes, the matrix is very sparse 2) Yes, it is symmetric 3) The smallest it will be is about 20,000 x 20,000 Thanks! | Thanks for the response! Sorry I didn't include these details in the original post. 1) Yes, the matrix is very sparse 2) Yes, it is symmetric 3) The smallest it will be is about 20,000 x 20,000 Thanks! | Thank you very much for the great response! Did not think I was going to get this helpful of a reply, much appreciated! |
[
"Help me learn advanced math?"
] | [
"math"
] | [
"gf0rd"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.29
] | [deleted] | This isn't all that advanced, just vector calculus and physics. I'm sure there are some Khan Academy videos on the subjects. | Not to sound condescending, but if you don't know where to start, I doubt you'd be committed to learning. | Okay. | By their convention of writing vectors in boldface, shouldn't the "Tau" be written in boldface. | Pick up Stewart's Calculus . Read the whole thing. Do every problem. Pick up Fundamentals of Physics by Halliday, Resnick, and Walker. Read the whole thing. Do every problem. Don't think I'm joking. |
[
"Operations Research?"
] | [
"math"
] | [
"gezq3"
] | [
4
] | [
""
] | [
true
] | [
false
] | [
0.7
] | I'm a Math/CS major, and I need a math course to take next semester. I'm already taking the course that's basically an introduction to Analysis, which should be fun. I was also going to take either Topology, Algebra or Complex Variables (basically an introduction to Complex Analysis). However, all three of these appare... | I'm in an OR course this semester, and you're pretty much correct in that it is a lot of calculation. In terms of theory, it definitely is not on par with high level theoretical math. If you're looking for proofs and beauty, look elsewhere. That said, it is a fascinating subject in its own right, but for the practica... | I have a friend that is in an operation research course. At my university it is taught by the Industrial & Systems Engineering department not the math department. He showed me what they work on and most of the work is done with excel and visual basic macros. He said the most advanced math they use is adding/subtracting... | I'm doing my Ph.D. in OR, so maybe I can shed some light on the subject. OR contains many sub-fields such as supply chain management, data mining, optimization, simulation, stochastic modeling, financial engineering, and others. In short, it uses math to describe how complex random systems work. The theory behind many... | Yours was the comment that forced me to make up my mind. I will probably just take Algebra or the Complex variables course (I wonder if it is sane to take an intro to Real Analysis and an intro to Complex Analysis in the same semester). I really wanted to take Topology, but the teacher has apparently gone insane... Any... | Hmm. I can tolerate calculating stuff up to an extent, but the last class I took that sounded anything like your description was a Physics lab, which about made me hate college altogether. So, maybe it's better if I don't take this class... |
[
"Subspace question"
] | [
"math"
] | [
"gdjp9"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | I know this solution may seem simple but bear with me: M consists of all all functions f in C[0,1] such that f(x) is rational for all x ∈[0,1] Verify that M is a subspace or show that it fails to satisfy one of the defining properties of a subspace. So in this problem I tried showing that letting aP ∈ M when P∈M and a=... | By C[0, 1], you mean the set of continuous functions from the interval to the real numbers R, as a vector space over R by pointwise addition and multiplication of functions? Then yes, your solution seems correct. 1 is rational for all x in the interval, but pi*1 is rational for no x. | Why doesn't p=0 work? I tried that he just told me no. I don't really see the reason because 0 is a rational number and certainly, as you said, contained in the interval. | To nitpick, if you just pick any P in M, it isn't necessarily true: what if P is 0? Then pi 0 = 0 is still in. Or what if M is empty? If you show there is an P in M with P(x) nonzero for some x, that sound be enough. The thing is, the only continuous functions from the interval to Q are the constant functions (by, s... | Because pi*0 = 0 is in M. It is a function on the interval that takes values in the rationals. You are looking for a counterexample. | facepalm* |
[
"Can't seem to get my way around this integral."
] | [
"math"
] | [
"gdjgp"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | Firstly this is for the first year of my Mphys course, but this particular question does not contribute towards my grade at all. Can provide proof if there are any suspicions. It's the double integral of (xe )/y under the domain bound by {0<=x<=1} and {x <=y<=x}. Everything I've tried gives me the integral of something... | Switch the order of integration: [;\int\limits_0^1{\int\limits_{x^2}^x{\frac{xe^y}{y}\,dy}dx}=\int\limits_0^1{\int\limits_y^{\sqrt{y}}{\frac{xe^y}{y}\,dx}dy} ;] After some reduction you should get down to [;\frac{1}{2}\int\limits_0^1{(e^y - ye^y)\,dy} ;] The first term in the integrand is easy; use integration by parts... | I haven't worked through it fully, but it would seem to me that you can avoid that nasty power of e by integrating through x first. Draw the domain. It's the same as {0 < y < 1}, {y < x < y }. I didn't do it out fully, but I think you just do that, then you have a bit of integration by parts or something (or good knowl... | First step: reverse the order of integration. I can't type the accompanying sketch in this box, but the new integral is over the region 0 < y < 1, y < x < sqrt(y). Now the inner integral is easy, and the outer one, while not pretty, can be integrated by by parts. | I just flipped the range of integration and it's something nice... [; \int {x=y} x e / y dx dy ;] | I'm an engineer, so no math is too trivial for me! Mathematica returns a value of (1/2)(e-2), or a numeric value ~=0.359. The exact input for mathematica is: Integrate[(x*E )/y, {x, 0, 1}, {y, x , x}] It may look like the order of integration is reversed, but that's just another quirk of the syntax in mathematica. If y... |
[
"A question about categories: Morphisms should be maps, right?"
] | [
"math"
] | [
"gejpi"
] | [
23
] | [
""
] | [
true
] | [
false
] | [
0.85
] | I was doing a bit of reading about the language of category theory (or "senseless abstraction" or "just gimme the arrows" or what have you), and I noticed that the definition written here makes no mention of the fact that morphisms are functions. The defintiion on shares this feature. However, all basic categories tha... | Let G be a directed graph. Let FG have vertices of G as its objects, and (possibly empty) paths in G as its morphisms. FG is a category, called the "free category on G" or "path category of G". Let Hask have {types in the programming language Haskell} as its objects, and Haskell functions as its morphisms. This is a ca... | I'm sure people will have more to say about this eventually, but one thing you may be interested in is Mitchell's Embedding Theorem , which says that you can think of any abelian category as having modules for objects and functions between modules as morphisms. I don't know if there's something in the same spirit for ... | every poset X can be made into a category, with objects being the elements of X, and a morphism from a to b if and only if a<b. likewise every group is a category of one object *, with an invertible morphism from * to * for each group element. the point is, even though categories are useful for studying objects and map... | Other posters have covered key examples/counterexamples, but here's more food for thought: in many categories, morphisms are families of functions, or functions together with additional data. Examples: Consider a topological space [;T;] and the category of sheaves of abelian groups on [;T;] . Then a morphism of sheave... | Is there a basic example of a category where the morphisms are not ACTUALLY functions? Sure, the category whose objects are natural numbers and there is an arrow from n to m is n <= m. |
[
"Does anyone in /r/Math have just a B.S./B.A. in mathematics or statistics? What have you done with your degree so far?"
] | [
"math"
] | [
"gdmvl"
] | [
9
] | [
""
] | [
true
] | [
false
] | [
0.74
] | I'm graduating this semester with a B.A in mathematics and as a certified statistician (minor and certificate in statistics). I'm not even sure where I could work besides a high school (which is something I don't want to do). Also, more school isn't an option, right now, because I just lost my father so I'm supporting ... | I have a BSc in Maths and I am currently doing an MSc in Maths. | I'm sorry to hear about your dad passing away. Normally, I'd tell you to shoot higher and that being a DBA is a waste of your degree, but this is a special circumstance. Instead, I'll point to some videos you can use to get started. $29/month is cheap for an all-you-can-eat education. (Do it for a month). A good di... | I'm sorry to hear about your dad passing away. Normally, I'd tell you to shoot higher and that being a DBA is a waste of your degree, but this is a special circumstance. Instead, I'll point to some videos you can use to get started. $29/month is cheap for an all-you-can-eat education. (Do it for a month). A good di... | sgoguen is absolutely right, being a DBA is a waste of much of one's math degree. Data Warehousing and BI definitely begin to move one closer to using something from your degree. Your introduction to finance will position to be really successful in that arena. Shameless plug: I have blog that plays around with Mathemat... | sgoguen is absolutely right, being a DBA is a waste of much of one's math degree. Data Warehousing and BI definitely begin to move one closer to using something from your degree. Your introduction to finance will position to be really successful in that arena. Shameless plug: I have blog that plays around with Mathemat... |
[
"Help find a proof"
] | [
"math"
] | [
"gdul7"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | I thought of the following question/theorem: We have a 2D figure A with an area S that can pass through a whole with the same contours as figure A. For example: Now the question is: Intuitively for me such figure should not exist, but how to prove it? | Let A be a set in R and let S be a set in R such that S contains A. Then m(S) >= m(A). Assuming m(S) = m(A) we have S = A union D where D has measure zero. Thus, aside from D, S is just A. | m(A) is shorthand for "the area of the set A" (technically it's "the measure of A") TheBB is trying to characterize all possible shapes of B, but messed up the variables and used S instead of B. Here is a more informal version of what he's saying: If B fits through an A-shaped hole, then B must be contained in A. Then ... | Certainly, but you're not going to like the answer. Let A be {0,1}, B is {1}. Each is closed and of measure zero. | Such a figure can exist. The main idea is that you can remove certain so-called measure zero sets from sets and the area is unchanged. For instance if you have a square and you remove a vertical line from that square, the area is unchanged. So you could remove any set that has measure zero. | I have no idea what are you saying. Did you try to prove or disprove the existence of B? |
[
"Question about a Powerball ticket I have."
] | [
"math"
] | [
"ge4ft"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.27
] | [deleted] | There are (59-4)+1 ways of selecting 4 sequential numbers between 1 and 59. The last number can be any of the remaining 55 untouched numbers (note that this will also allow for 5 consecutive integers... if you don't want this to be an option you can just pick from any of the 53 valid choices and take edge case behavior... | My calculation works exactly for answering your question, but what you stated might not be exactly what you meant. For example, 1-2-3-4-5 would be a selection of 5 numbers in which 4 of the integers are consecutive, but (obviously) it also has 5 consecutive integers. My nested parentheses were just there to discuss how... | My calculation works exactly for answering your question, but what you stated might not be exactly what you meant. For example, 1-2-3-4-5 would be a selection of 5 numbers in which 4 of the integers are consecutive, but (obviously) it also has 5 consecutive integers. My nested parentheses were just there to discuss how... | I think you have some error.. both WolframAlpha and Google agree with me. (example: http://www.wolframalpha.com/input/?i=59+choose+5 ) Did you calculate 59 pick 5 instead? | And this is why I should watch what I type into my TI-83. I'll be fixing my post ... Thanks .. HAHA! I forgot to divide by 5!. Life goes on. |
[
"How quickly/possible can one learn...."
] | [
"math"
] | [
"gdzia"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.4
] | [deleted] | Math is not hard. Understand it conceptually, not just the steps to complete problems one after another. http://www.khanacademy.org/ | One problem with Khan Academy is that he goes slowly that a smart but uneducated person would easily be bored. | Learning anything is about motivation and self-discipline. Just put in hard-work and anything feasible is possible. | I see, I think if you manage to do it consistently 3-4 hours a day, that you're going to succeed in your goal. By the way, if I may ask, why do you want to learn that specific subjects? Only because it is taught in HS, or do you want to learn even more mathematics, but think that is prerequisite? Or for some other reas... | Again I can't give an answer from personal experience. However, from poking around the homeschooling community I picked up the vibe that the Kumon books are reasonably well respected, as are the books used in the Singaporean high schools. The unifying theme seems to be a mastery oriented approach to the material. Your ... |
[
"Not smart enough! How can I do this?"
] | [
"math"
] | [
"gcxax"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.5
] | Hello! I am trying to create an equation which would match the following list of values. The input value would be a number from 0 to 100 (101 possible values), with a range of 0.12 to 8.00, with 1.00 being the halfway point (50). I've tried as much as I know, which isn't a whole lot in the world of math beyond basic al... | I suggest a very cludgy piecewise function. Though seriously, maybe think about what the graph of this would look like? Something like exponential/logarithmic/hyperbolic? If you're feeling independent, go put two columns of data into excel and have it do a linear regression. | This table comes from an old game written by two math professors. Everything in the game is definable with some math logic, either simple or uberadvanced. This is one of the items they never shared the formula to. Most have been figured out by fans, but to my knowledge nobody has figured out this one. I was hoping to a... | So, just for public eyes I plotted the data in excel, and I think it should be obvious that this is not a simple function. You can clearly see a sharp turn at 1. Beyond 1, it looks (to me) like a linear function, so that's good news. Before 1, though, it's not exactly straight. Is this sample data, such that there is s... | This can be done with an interpolating polynomial. The one that's easiest for me to understand is the Lagrange interpolating polynomial . However this will be a gigantic polynomial so I'm not sure how helpful it'll be. You say that you're looking for some sort of pattern; I'm sure this won't reveal it to you. Here's... | For future visualization for everyone too lazy for excel: [0, 25], [26, 50], [51, 75], [76, 100] (ignore the trendline in the first interval, I gave it a 6th order polynomial for shits and giggles and didn't remove it before uploading) |
[
"Help me optimize a combinatoric problem"
] | [
"math"
] | [
"gd3m9"
] | [
4
] | [
""
] | [
true
] | [
false
] | [
0.7
] | Hi Reddit I have a problem I hope some of you can help me with, thus far I have tried just about everything**. I have a combinatoric problem I need some help with for my master thesis in physics (well parallel programming atm...) Assume we have n set of numbers (wavefunctions) distributed on n nodes in a cluster. I wis... | Two questions: At each round, each node can send one piece of information to at most one other node. Correct? Is there a limitation on the amount of information that each node sends to another one in a given round? If you answer the above questions with a yes and a no respectively, then for every c>0, your task can be ... | 1 is a definite yes 2 is strictly speaking a no, but each communication round will take as long the longest transmission, and if you send more than one data set from 1 node to another, these two nodes will now share at least 2 elements, which might not be optimal. (sometimes it will be necessary). But n communication r... | Oh, sorry. I meant n communication rounds (for every c>0). So, I can describe a protocol which, for instance, has the following parameters: the number of rounds is O( n ); the longest transmission at each round has size O( n ); and each node performs n-1 computations in total. Let me know if that's interesting enough f... | I would very much like to see the protocol behind this! | Here's the protocol. First thing, fix a graph over your n nodes, a graph with the following two properties: (i) every two nodes are connected by a path of length 3, and (ii) the number of neighbors of each node is O( n ) (where for simplicity, this notation will suppress logarithmic factors). Such a graph exists and is... |
[
"Divisibility by 3"
] | [
"math"
] | [
"gd09y"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.43
] | [deleted] | I see it as an if/else thing. If I am too lazy to divide the number by 3 then: I just keep on adding the digits until I end up with a single digit. | You're complicating this. Just keep summing your new numbers again and again until you reach a manageable number =P | Interesting, I remember it being taught specifically with the extra steps. It really annoyed me because the teacher examples included the "Now, is 15 divisible by three? Let's add the digits..." and I kinda spaced out watching them add one and five :\ | whereas your method would make them go cross eyed. :) But it teaches them what's actually going on. If a number ends in 0,2,...,8 it is not prime. Okay. But why? If the square root results in an integer it is composite. Okay. But why? And so on. | Amongst the many rules, if a number is divisible by 3 then it's a composite number. Eh? If a number is divisible by (greater than 1), then it's composite. |
[
"Question about primes"
] | [
"math"
] | [
"gda4u"
] | [
4
] | [
""
] | [
true
] | [
false
] | [
0.67
] | So I've heard that the distribution of prime numbers approximates ln(x). Would this be the same for say numbers with 2 total prime factors, or 3? I'm just wondering because I realized that the highest amount of prime factors you can have in a given domain is n when the domain is < 2 . Not sure what that means but it se... | This is known as the Prime Number Theorem . It states that the number of primes less than or equal to a given number x behaves like x/ln(x) as x gets bigger. Looking at the graph of the functions on that wiki page will show you that this doesn't necessarily mean they are the same or that one is a good approximation o... | With some algebraic manipulation, you can work out that the upper bound on the number of prime numbers is sum of 1/k, k=1 to n Then you can use integration to achieve a lower bound of ln(n). Terrance Tao proved a ground breaking theorem about the distribution of primes. I don't know much about it, because it's beyond m... | It was Tao and Green. I saw Green give a talk and I have a vague recollection of it being quite elegant but I might be thinking of something else. He listed the longest sequence they've found which is only 24 numbers. | However this book only just states the Prime Number Theorem because its proof is quite complex. I see you | Tao and Vu showed that there are arbitrary long arithmetic sequences in the prime numbers. Which just means you can find sets of primes of the form p,p+k,p+2k,p+3k,p+4k as long as you want in the prime numbers. It's an easy thing to state, a very hard to thing to prove. |
[
"I tried to convince my fiance to wait until 3/14/15 to get married"
] | [
"math"
] | [
"gdfpb"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.44
] | [deleted] | That just means he should get married in the evening of 3/14/15. ;) | The infinite expansion of pi is conjectured to contain any given finite sequence of digits as consecutive digits. Your fiancée should be satisfied with any date given you dig through that pi thoroughly | =/ | I now have a new life goal. | Well, to five significant digits, pi is more like 3/14/16, but your fiancé might be even less happy about that. |
[
"Are fractions more precise/accurate than decimals?"
] | [
"math"
] | [
"gdhlp"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.25
] | [deleted] | They are the same. Please see any of the numerous threads on /r/math about why .999... = 1. | You can't "make 0.99... as arbitrarily close to 1 as you like"; 0.99... is a fixed constant, equal to 1. | You can't "make 0.99... as arbitrarily close to 1 as you like"; 0.99... is a fixed constant, equal to 1. | http://en.wikipedia.org/wiki/0.999 ... | Here and here for example. Also, /r/learnmath is a good place for questions like this. |
[
"My favorite integers."
] | [
"math"
] | [
"gdgb1"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.13
] | (Correct me if any of this is incorrect. Not a math major.) 0, because it is the only integer that is neither positive nor negative. 1, because it is the only integer that is neither a composite nor a prime. 2, because it is the only even prime. | Negative numbers can certainly be prime. -2 generates a prime ideal in the integers which qualifies it as a prime element. | Negative numbers can certainly be prime. -2 generates a prime ideal in the integers which qualifies it as a prime element. | -1 is also neither composite nor prime and -2 is also an even prime. | -2 is listed in the examples. | -2 is listed in the examples. |
[
"I need help with a math problem involving combinations"
] | [
"math"
] | [
"gc9o0"
] | [
0
] | [
""
] | [
true
] | [
false
] | [
0.47
] | [deleted] | Try http://www.reddit.com/r/learnmath/ or http://math.stackexchange.com/ | Hello Please Thanks Bye? What is even the question? | Pointless comment is pointless. | fix a length, x say for condition 2), just see that there are x choices to put one of 3 symbols. for condition 3), do similar (two cases here, either 2 or 3 digits). fill the rest in with the other characters (26+26) (includes upper and lower case). something like 3x 10+(x-2) 52 + 3x 10+(x-2) 10}/3!}*52 sum over x=6,7... | There are several things to note here: also order is important so you will be using permutations. eg the password 1234 is different than 4321 |
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