text stringlengths 336 41.1k | meta dict |
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Q:
Is the domination number of a combinatorial design determined by the design parameters?
Let $D$ be a $(v,k,\lambda)$-design. By the domination number of $D$ I mean the domination number $\gamma(L(D))$ of the bipartite incidence graph of $D$.
Is $\gamma(L(D))$ determined only by $v,k$, and $\lambda$,
irrespectiv... | {
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} |
Q:
constructing a Data Frame in Rcpp
I want to construct a data frame in an Rcpp function, but when I get it, it doesn't really look like a data frame. I've tried pushing vectors etc. but it leads to the same thing. Consider:
RcppExport SEXP makeDataFrame(SEXP in) {
Rcpp::DataFrame dfin(in);
Rcpp::DataFrame d... | {
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} |
Q:
List Manipulation and Removing Cases
I've imported a large data set, manually removing headers in the .rtf file where it originates. However, when I import this data, I receive this output:
data = Import["//pathtofile//data.rtf"]
Notebook[{Cell["1 3.32 10 10 10 670 600 1
2 2.26 6 8 5 ... | {
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} |
Q:
NA replacement using median value
I have the following dataset:
5 3 3 5 10 10 3 8 2 12 8 6 2 5 6 5 10 4 3 5 4 3 3 5 8 3 5 6 6 1 10 3 6 6 5 8 3 4 3 4 4 3 2.5 1 4 2 2 3 5 10 4 4 6 3 2 3 8 3 4 4 3 3 4 ... | {
"pile_set_name": "StackExchange"
} |
Q:
Why are there so many errors (missing \right or extra \right)?
I've counted and checked but can't seem to find the problem.
\begin{flalign*}
u_0(x,\ t)\ =&\ x\left[t\ +\ \frac{t^3}{3}\right],\\
u_1(x,\ t)\ =&\ x\left[t\ -\ \frac{2t^5}{15}\ -\ \frac{t^7}{63}\ -\ \frac{t^{2-\alpha}}{\Gamma(3\ -\ \alpha)}\ -\ \frac{2... | {
"pile_set_name": "StackExchange"
} |
Q:
Inequality for moments of sums
Suppose the random variables $X_i$ are independent and satisfy $E[X_i] = 0$. Then the following inequality holds:
$$E\left[\left(\sum \limits_{i = 1}^n X_i\right)^4\right] = \sum \limits_{i = 1}^n E[X_i^4] + 3\sum \limits_{i \ne j} E[X_i^2X_j^2] \le 3\left(\sum \limits_{i = 1}^n E[X_... | {
"pile_set_name": "StackExchange"
} |
Q:
Derivative of a function of matrix
I am trying to derive the gradient of the function $f(X) = AXZ + XZX^TXZ$ where $A,X,Z \in R^{n \times n}$ with respect to $X$ matrix. I read a post Matrix-by-matrix derivative formula about matrix derivate, but I am not able to follow it. In my case $\frac{\partial f(X)}{\partia... | {
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} |
Q:
Magic Square Mixups [Challenge]
This kind of puzzle is different than your normal magic square puzzles. Here are 3, in increasing difficulty. Some numbers have been switched, and you have to find them and swap them around to make the magic square valid again.
The zeros are for formatting placeholders.
The numbers... | {
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} |
Q:
Problem proving a trigonometric result.
Question: If $\frac{\tan(\theta-\phi)}{\tan\theta}+\frac{\sin^2\alpha}{\sin^2\theta}=1$, show that $\tan\theta\tan\phi=\tan^2\alpha$.
My attempt:
$\frac{\tan(\theta-\phi)}{\tan\theta}+\frac{\sin^2\alpha}{\sin^2\theta}=1$
$\implies\frac{\frac{\sin(\theta-\phi)}{\cos(\theta-... | {
"pile_set_name": "StackExchange"
} |
Q:
Definite integral evaluation, how to solve it?
Hi guys I'm trying to solve the following integral that I've found in a paper:
$\int_{-l}^{l}$$\frac{\delta x}{((\frac{a-x}{r})^{2}+1)^{0.5}}$
The authors report the following result:
$sinh^{-1}(\frac{l-a}{r})+sinh^{-1}(\frac{l+a}{r})$
Any idea on how the steps requir... | {
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} |
Q:
How to place braces in multiple equations
I have the following expression:
\begin{equation}
\begin{aligned}
%C1
\sum_{i = 1}^{m}{y^{C_1}_i} &= m\beta_0^{C_1} + \beta_1^{C_1}\sum_{i = 1}^{m}{x_{i1}^{C_1}} + \cdots + \beta_q^{C_1}\sum_{i = 1}^{m}{x_{iq}^{C_1}}\\
\sum_{i = 1}^{m}{y^{C_1}_ix_{i1}^{C_1}} &= \beta_0^{C_... | {
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} |
Q:
Delete, drop, kill ALL factor levels from Dataframe
Lets take mtcars as example and create a new variable:
mtcars$name <- rownames(mtcars)
mtcars[,] <- lapply(mtcars, factor)
mtcars[,] <- lapply(mtcars, as.numeric)
Now the names are converted into numerics which i definitely dont want
> mtcars
... | {
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} |
Q:
Why doesn't my d3.js line chart work?
I'm currently learning d3.js, and as a task I am trying to build a line chart using a custom data source. For some reason, I can't get the line generator to work, and it seems like it can't create the d attribute for the path element. I don't seem to get any error messages eit... | {
"pile_set_name": "StackExchange"
} |
Q:
How many divisors of N ended by 5
I must know how to find how many divisor of N ended by 5 ? In my exercise, I have $\ N=63'000 = 2^3*3^2*5^3*7 $ and I can found the number of divisors of N using $\ (3+1)*(2+1)*(3+1)*(1+1)=96$
Among these 96 divisors, how many ended by 5 ? How can calculate this ?
Thank you so mu... | {
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} |
Q:
Detect â in a string
I'm trying to detect the character â in a string in Objective C and can't seem to get it to work. It's displaying a bullet point when it's finally displayed on screen, so maybe that's why I can't detect it?
In iOS 10 these bullet points display larger than they should, so I need to find the ra... | {
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} |
Q:
Merging CSVs based on common column using bash on Mac
The bash code below is used for hierarchical merge of 16 CSV file (one per year, each is about 5 GB). It is based on an answer on this forum "Joining 2 CSV files based on common field name" However, it is quite slow. Any idea for improvement? Multiprocessing or... | {
"pile_set_name": "StackExchange"
} |
Q:
Multilinear generalization of Cauchy-Schwarz inequality
Let $V$ be a real vector space, and let $(\cdot,\cdot;\cdot,\cdot) : V^4 \to \mathbb{R}$ be a multilinear form with the following properties:
$(x,y;z,w) = (y,x;z,w) = (x,y;w,z)$ (symmetry in the first and second pairs)
$(x,x;z,z) \ge 0$ (positive semidefinit... | {
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} |
Q:
Conserved quantities in supersymmetric theory
Given the following supersymmetric action
$$
\mathcal{S}=-\frac{T}{2}\int{d^2x\;\eta^{\alpha\beta}\eta_{\mu\nu}\left(\partial_\alpha X_\mu\partial_\beta X^\nu-i\bar{\psi}^\mu\rho_\alpha\partial_\beta\psi^\nu\right)}
$$
I want to show that the following quantity is cons... | {
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} |
Q:
Show implicit function satisfies the following propety
Assume the equation $f(\frac{x}{z}, \frac{y}{z})=0$ defines an implicit function $z=g(x,y)$, and that all functions are differentiable. Show that
$$x\frac{\partial z}{\partial x}+y\frac{\partial z}{\partial y}=z$$
My attempt: Define $u(x,y)=\frac{x}{z}, v(x... | {
"pile_set_name": "StackExchange"
} |
Q:
Sliding windows along last axis of a 2D array to give a 3D array using NumPy strides
I am trying to use the function as_strided from numpy.lib.stride_tricks to extract sub series from a larger 2D array, but I struggled to find the right thing to write for the strides argument.
Let's say I have a matrix m which con... | {
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} |
Q:
analysis complex
I need to show that the function $z^n$ with $n \in \mathbb{Z}$, is entire, using the conditions of Cauchy-Riemann. My problem is to calculate the partial derivatives of this function.
Can someone help me?
Thank you.
A:
Entire function.
if $f(z) = u + iv$ then $\frac {\partial u}{\partial x} = \... | {
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} |
Q:
Switching the order of differential operators
A function $f(x,y)$ is transformed to variables $(u,v)$ with $x=uv$ and $y=\dfrac{u}{v}$ so the first partial derivative with respect to $u$ is $$\frac{\partial f}{\partial u}=v\frac{\partial f}{\partial x}+\frac1v\frac{\partial f}{\partial y}\tag{1}$$ Show that the se... | {
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} |
Q:
Derivatives from the value to the power of $1/\rho$
I know from check information in the task that $$\frac 1 \rho\cdot {\frac{\partial}{\partial \phi}}(\cos^2\phi\cdot \tanh z) - \frac \partial {\partial z} \left( \sin2\phi \cdot \ln \sqrt[{\Large\,\rho\,}] \frac{\cosh\rho}{\cosh z} \right)=0$$
After calculation... | {
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} |
Q:
parse a subset of HTTP header to identify host web address
The HTTP protocol is all contained in the data portion of TCP packets.
As an assignment I need to parse HTTP headerfields (for purposes of this question lets only consider host web address) only using string parsing functions, I cannot use any existing lib... | {
"pile_set_name": "StackExchange"
} |
Q:
Cannot convert #{ad.userid} of type class java.lang.String to class javax.faces.component.UIComponent
I am getting home page, but when going to a JSP page which has a h:inputText I am getting the following error:
root cause
javax.servlet.ServletException: javax.servlet.jsp.JspException: org.apache.jasper.el.JspE... | {
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} |
Q:
Limit of $\mu(\theta)=\frac{e^{\theta}(\theta-1)+1}{(e^{\theta}-1)\theta}$ when $\theta \to \pm \infty$ & $\theta \to 0$
Let $\mu(\theta)$ be defined as:
$$\mu(\theta)=\frac{e^{\theta}(\theta-1)+1}{(e^{\theta}-1)\theta}.$$
I would like to show limit when $\theta \to \pm \infty$, I know that it is $0$ and $1$, but ... | {
"pile_set_name": "StackExchange"
} |
Q:
how to decrypt xxtea?
I am trying to se if I can use XXTEA in my application.
The code that I found on Wikipedia code is only for encryption and there is no code for decryption.
How can I decrypt with XXTEA?
I am developing c++ in windows (visual studio 2012)
A:
The code snippet in the article apparently uses ... | {
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} |
Q:
Find $2^{n-1}\prod_{k = 1}^{n-1}{\left(\cos\theta - \cos\left( \frac{k\pi}{n} \right)\right)}$
Evaluate:
$$2^{n-1} \left(\cos\theta - \cos\left( \frac{\pi}{n} \right)\right)\left(\cos\theta - \cos\left( \frac{\pi}{n} \right)\right)...\left(\cos\theta - \cos\left( \frac{(n-1)\pi}{n} \right)\right)$$
The answer is
... | {
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} |
Q:
Home directory messed up
Recently, I installed Ubuntu 12.04. For some reason, i backed-up my home directory contents to another directory(say bkp dir). Precisely, I moved Documents, Pictures, Downloads, etc.. to bkp directory. Now, Deleted all my original home directory contents. I restored all the bkp directory c... | {
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} |
Q:
How to concatenate string of numbers in VBA
[Updated] Thank you all for your guidance.
I have modified the code as below.
But the macro did not run, nor generated any errors.
I did not want to double quote each item in the variable "columns" either.
Thank you very much for any helps.
Thanks!
My code is as below:
I... | {
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} |
Q:
Find the closest month-day to a date, no matter the year
I have the following vector of dates (length = 51863)
dates_sim <- seq(from=as.Date("1871-01-01", format = "%Y%m%d"), to=as.Date("2012-12-31", format = "%Y%m%d"), by="days")
And a data frame of dates, with 125 rows and 51863 columns. For each date of my vec... | {
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} |
Q:
Equation formatting (alignment)
According the question I have written the file but I got something wrong. Can you please check?
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
&\begin{aligned}
& \ddot\phi_3&+\phi_3+2g_2p_1 \cos(\tau+\alpha)[p_2\cos(\tau + \alpha) + q_2\sin(\tau + \alp... | {
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} |
Q:
Downvotes com comentários linkados
Ao notar tantas reclamações e sugestões e mesmo que digam que é o crescimento da comunidade parece estar um tanto evidente que os votos não são bem usados por uma parte dos usuários e aqueles que sabem votar ficam com medo de comentar (justificar) votos negativos com medo de reta... | {
"pile_set_name": "StackExchange"
} |
Q:
Issue with Json file for Highstock
I'm actually be doing a project in my studies and i will take json data from webservice for set it in highstock.
My webservice (file in php language) return actually this json format
[{"jour":"22","mois":"1","an":"10","heure":"10","minute":"0","p_ac":"143"},{"jour":"22","mois":"... | {
"pile_set_name": "StackExchange"
} |
Q:
can we a prove ⊢ (α → α) → (α → α)
The system L0 is defined as follows:
Axioms:
A1 (α → (β → α))
A2 2. (α → (β → γ) → ((α → β) → (α → γ))
A3 ((¬β → ¬α) → ((¬β → α) → β))
In one of my problem sheets, I am told that I am allowed to use the following theorem:
if
⊢ (α → α)
⊢ (α → α) → (α → α)
My attempt to solve/pr... | {
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} |
Q:
HQL with parameters NoSuchMethodError
I am sure I am overlooking something obvious
the following static query works fine
hqlQuery = "select user from User as user where user.id = 'userid' ";
but when I parametrize the query
hqlQuery = "select user from User as user where user.id = :me ";
Query query = session.cre... | {
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} |
Q:
Normalize and transpose data efficiently
I am trying to normalize and transpose stock market data according to each symbol and I have created this method, but I see the loop inside the function so slow. Is there any way to make it faster or do it in better way?
The function is:
normalize <- function(data, col){
... | {
"pile_set_name": "StackExchange"
} |
Q:
$xf(y)+yf(x)\leq 1$ for all $x,y\in[0,1]$ implies $\int_0^1 f(x) \,dx\leq\frac{\pi}{4}$
I want to show that if $f\colon [0,1]\to\mathbb{R}$ is continuous and
$xf(y)+yf(x)\leq 1$ for all $x,y\in[0,1]$
then we have the following inequality:
$$\int_0^1 f(x) \, dx\leq\frac{\pi}{4}.$$
The $\pi$ on the right hand side ... | {
"pile_set_name": "StackExchange"
} |
Q:
General unit tested solution to Project Euler Problem 8: Largest product in a series
Project Euler Problem 8
The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.
73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851... | {
"pile_set_name": "StackExchange"
} |
Q:
How to read the MPEG2VideoDescriptor in an MXF file?
Here follows the hex dump of the MPEG2VideoDescriptor:
06 0e 2b 34 02 53 01 01 0d 01 01 01 01 01 51 00
83 00 00 f3 3c 0a 00 10 a3 be 51 b2 00 05 e7 11
bf 82 21 97 f7 a0 14 ed 30 06 00 04 00 00 00 02
30 01 00 08 00 00 ea 60 00 00 03 e9 80 00 00 04
01 c9 c3 80 30... | {
"pile_set_name": "StackExchange"
} |
Q:
How to find $\partial\chi^2/\partial a$ where $\chi^2=\sum_{i=1}^N\frac{D(x_i)-a-b(x_i)^2}{\sigma_i^2}$?
How to find $\partial\chi^2/\partial a$ where $\chi^2=\sum_{i=1}^N\dfrac{D(x_i)-a-b(x_i)^2}{\sigma_i^2}$?
My attempt:
\begin{align}
\dfrac{\partial}{\partial a}\sum_{i=1}^N\dfrac{D(x_i)-a-b(x_i)^2}{\sigma_i^2} ... | {
"pile_set_name": "StackExchange"
} |
Q:
How can I set the parity bits when using screen to access a serial port
I typically use screen(1) to open a serial port with the command:
sudo screen /dev/ttyUSB2 115200
I've tried setting parenb (and a number of other things) using the following command:
sudo screen /dev/ttyUSB2 115200,cs8,parenb,-parodd,-cstopb... | {
"pile_set_name": "StackExchange"
} |
Q:
Reverse triangle inequality?
I have to prove the following inequality.
Let $\nu$ be a function on $[0,1]$ with one discontinuity point $x^{*}$. Furthermore, we set $\Delta\nu_{x}:=\nu_{x}-\underset{t\uparrow x}{\text{lim }}\nu_{t}$. We do the following assumptions. For $w_{x}:=\nu_{x}-\Delta\nu_{x^{*}}\mathbb{I... | {
"pile_set_name": "StackExchange"
} |
Q:
Vanishing integral for spacelike separated points
The integral I have is this:
$$
K(x,y) = \int_{\mathbb{R}} \sin(p(\theta) \cdot (x-y)) \ d\theta\
$$
where
$$
p(\theta) = m\begin{pmatrix} \cosh(\theta) \\ \sinh(\theta) \end{pmatrix} \quad (m>0),
$$
and $x$ and $y$ are points in Minkowski space.
For simplicity h... | {
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} |
Q:
Catmull-Rom blending functions
I have a non-uniform Catmull-Rom spline (so the $t_i$ parameter values are not uniformly distributed). Is there a simple way to calculate the blending functions of the control points? So the spline can be expressed as $f(t)=\sum_{i=0}^nw_i(t)p_i$ (where $p_i$ is the control point its... | {
"pile_set_name": "StackExchange"
} |
Q:
connected to Centos openvpn but no outside internet access
I am using Windows 7 to connect to a VPS server running CentOS 6.4
First off, I have read every single post and just cant find the solution to my problem
I configured my VPN server with openvpn, and finally got it working after on and off trying for 4 mont... | {
"pile_set_name": "StackExchange"
} |
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