## In plain english, why does conversion from hexadecimal to binary work so cleanly?

Why does the trick of taking the binary representation of each digit and simply concatenating them work? e.g. 0x4E == 0100 concatenated with 1110, making 01001110

On some accounts I use my real name on-line(G+/fb/wiki/Personal blog), others(Q&A/Gaming) I use an alias. My question is: Security and privacy wise, what can people do with my real name? What are …

## Status of the $x^2 + 1$ problem

It is a long-standing conjecture (probably just as old as the twin prime conjecture, which has gotten a lot of attention as of late since Zhang and Maynard's breakthrough results this year) that ...

## Finding the limit of $\left(\frac{n}{n+1}\right)^n$

Find the limit of: $$\lim_{n\to\infty}\left(\frac{n}{n+1}\right)^n$$ I'm pretty sure it goes to zero since $(n+1)^n > n^n$ but when I input large numbers it goes to $0.36$. Also, when ...

## I worked for a company affiliated with a very publicly failed project. Should I take it off my resume?

I worked briefly for a company that had a recent highly publicized failed government project (I'm sure you can probably guess). While I did not work on that particular project, I think all the bad ...

## What's the function of a static constructor in a non static class?

I've noticed that a non-static class can have a static constructor: public class Thing { public Thing() { Console.WriteLine("non-static"); } static Thing() { ...

## Determining common divisors of two numbers

Is there a better algorithm for finding the common divisors of two numbers? Can this code be shortened? import java.util.*; public class Testing1 { public static void main (String args[]){ ...

## How prove this $1\times 3\times 5\times 7\cdots\times 2009+2\times4\times6\cdots 2010\equiv 0 (\mod2011)$

Question: show that $$1\times 3\times 5\times 7\cdots\times 2009+2\times4\times6\cdots 2010\equiv 0 (\mod2011)$$ my try: since \begin{align*}&1\times 3\times 5\times 7\cdots\times ...

## Does Slicing a (e.g. a[1:] == a[:-1]) create copies of the a?

A friend of mine showed me the following Python code: a[1:] == a[:-1] Which returns True iff all the items in a are identical. I argued the code is hard to understand from first sight, and ...

## How to change the font size of all theorem environments?

I have several theorem environments: \newtheorem{theorem}{Theorem} \newtheorem{definition}{Definition} \newtheorem{proposition}{Proposition} etc. and I want to change them so that they all use ...

## Wrapping function is continuous but why is its inverse function not continuous?

$f:[0,1) \to S$ where $f(t) = e^{2\pi t}$ is continuous. (Also it is called wrapping function.) Notice that the function is one to one and onto so $f^{-1}$ exists. Why is the Inverse (Unwrapping) ...

## different results of integration using Mathematica and MatLab

I have an integration, I get different results when I use Mathematica and Matlab. here is the integral: L=2; sn=1; a=10^(0.1*sn); b=10^(0.1*sn); c=0.01*a; result = 2*Sqrt[1/Pi]* Integrate[ ...

## Polynomial expression definition

I been reading wiki definition for Polynomial time, and it says: An algorithm is said to be of polynomial time if its running time is upper bounded by a polynomial expression in the size of the …

## Why does CSS work with fake tags?

In my class, I was playing around and found out that CSS works with made-up tags. Example: <style> imsocool { color:blue; } </style> <body> ...

## Integrating equations with units

I was looking through an old copy of Barron's AP Physics and found this problem relating to impulse which I was initially confused about how to integrate. Example 6.1 During a collision with a ...

## Thumb tension while playing bass guitar

I am doing "spider exercise" from JOHN PATITUCCI Bass Workshop 1 3 Left Hand Dexterity Builders chunk 1, After a couple of minutes I start feeling increasing left thumb tension, in 10 minutes it ...

## Is it worthwhile to give off-topic talks?

I am a graduate student. Occasionally for some reason I am asked to give a talk on my research at a conference whose stated purpose is almost completely unrelated to my research. To preserve my ...

## sign changes when going from int to float and back

Consider the following code, which is an SSCCE of my actual problem: #include <iostream> int roundtrip(int x) { return int(float(x)); } int main() { int a = 2147483583; int b = …

## DNS reverse query

When I do reverse DNS queries with IP address that I obtained from DNS query of one website, it shows many different domain names, why is it so? I thought if I do the reverse DNS query I will obtain …

## Reporting p-values $\le$ 2.22e-16

For some tests in R, there is a lower limit on the p-value calculations of 2.22e-16. I'm not sure why it's this number, if there is a good reason for it or if it's just arbitrary. A lot of other stats …

## Pde book suggestion.

I am studying PDE. And I want to know introduction to PDE book's names, which contain direclet problem, Sturm liouville problems, cauchy problems, euler, eigen functions and like this. But the ...

## Will metering from a DSLR apply to a film SLR?

I still like to shoot with film (I use a Nikon F3) but I like the immediate feedback of digital. I'm thinking of buying a used DSLR to help me get the framing and lighting right when I shoot static …

## Is a senior programmers advice about always using books a good idea?

I am a junior developer and have only been in the industry for 5 years. At my current company there is a senior let's call him Infestus. Occasionally I am being given opportunity to shine and do ...

## Equivalence of independent set and set packing

According to Wikipedia, the Independent Set problem is a special case of the Set Packing problem. But, it seems to me that these problems are equivalent. The Independent Set search problem is: given …

## Help needed in breaking a long equation which contains long sum

I have an equation which I want to split into two, but it always gives error when I use standard equation breaking techniques, like \split, \gather etc. The quation is given as ...

## Diagonalizable matrices A and B with $\mathrm{Tr}(A^k)=\mathrm{Tr}(B^k)$ have the same characteristic polynomial?

Let $A$ and $B$ be $n \times n$ matrices with entries in a field F. Suppose $A$ and $B$ are diagonalizable in some extension field E of F and that $\mathrm{Tr}(A^k)=\mathrm{Tr}(B^k)$ for all integers …

## How do I write a formula using a picklist and a date field?

I have a picklist field for "Interview Applicable" with the choices being "Yes" or "No". I also have a date field for "Scheduled Interview". I have a third field that is a text field. I'm trying to …

## A power series from $\frac{x}{9+x^2}$
I need to make power series from $\frac{x}{9+x^2}$, and I don't have any idea how. The only thing I know is how to make power series from $\frac{1}{1-q}$. Thank you!