Matrices which commute with all the matrices commuting with a given matrix
Matrices $B$ that commute with every matrix commuting with $A$
Access: Making a Pivot Table with Multiple, Same Values as Columns I need rules to drop some malicious Apache connections Obligatory: This is not a duplicate of , which is concerning the much older duplicate closure process.  Have a gander at . Notice anything weird?  The Community♦ user was invoked by the question asker to self-close as a duplicate (presumably of the comment below, which links to ), but the list of duplicates is entirely empty. So it would seem the question asker was able to close their own question as a duplicate of... nothing?  Screenshot, in case the post is altered later:    Any idea what happened here? How can I remove Amazon search results from the dash or disable the feature? How can I disable Amazon search results in the Dash? Deciphering the RSA encrypted message from three different public keys I have three different 1024-bit public keys with common exponent $e$ but different moduli. A message $m$ is encrypted (without padding) using the three keys, which results in three different encrypted messages.  Given the three pairs of public keys $(N_i,e)$ and the encrypted messages $c_i=m^e\bmod N_i$ , how do I decipher the original message $m$ ? Why are one-way plane tickets more expensive than return tickets? I need to install a new TeX/LaTeX/ConTeXt package on my computer.  I'm running Ubuntu/Fedora/Slackware/Some-Version-Of Linux.  What are the possible ways to do this?    Note:&nbsp;&nbsp; We get a number of questions that essentially reduce to this one; it was felt a good idea to have one question-and-answer that can cover all the standard methods.  See  for the discussion.  The question-and-answer are CW so that more information can be easily added.  If you have information to add, please do so.  If you are unsure, leave a comment here or (preferably) in .  Comments on the question and answer will be periodically removed to ensure that the information is clear. Find when three numbers have the same remainder when divided by the same number If three numbers 112, 232, and 400 are each divided by the number D, each of their quotients will have the same remainder R. Find R where R>1  How should I approach this? Prove $(a^2+b^2)(c^2+d^2)\ge (ac+bd)^2$ for all $a,b,c,d\in\mathbb{R}$. Deploy a project using Git push Is it possible to deploy a website using git push? I have a hunch it has something to do with using  to perform a git reset --hard on the server side, but how would I go about accomplishing this? Is it possible to convert a Physical Ubuntu Install (Intel based PC with Ubuntu 10.10) to a virtual box disk, so that I can use that same environment on a separate pc or can keep it virtual for testing?  Something similar to "Disk2VHD" which converts a physical Windows 2K3 and above box into a VHD or VMware image.  Will be grateful for your assistance ! Kind Regards How do I develop black and white negatives at home? Can you eradicate a disease without finding a Cure first? If you eradicate a disease in Pandemic without finding a cure first (ie remove all of one colour from the board) does it remain eradicated or can it still come back unless it has also been cured?  The rules are a bit unclear on this point ... Or I missed the rule that explicitly states this. It's so annoying to drag it over and over again. How to change default position of a console? When is JavaScript's eval() not evil? I'm writing some JavaScript code to parse user-entered functions (for spreadsheet-like functionality). Having parsed the formula I could convert it into JavaScript and run eval() on it to yield the result.  However, I've always shied away from using eval() if I can avoid it because it's evil (and, rightly or wrongly, I've always thought it is even more evil in JavaScript, because the code to be evaluated might be changed by the user).  So, when it is OK to use it? $a\equiv\bar a\!\pmod{\!kn}\Rightarrow a\equiv\bar a\!\pmod{\! n};\ $ $(a\bmod kn)\bmod n=a\bmod n.\ $ Congruences persist mod factors of the modulus I noticed relation between modulo operation and number which is power of two  Example I have to calculate $ 3431242341 \mod 2^5 $, which is $ 5 $ but it is equivalent to  $ ( 3431242341 \mod 2^9 ) \mod 2^5 $   I tried many examples and it seems to be true in general, and I am not sure if it is a coincidence or true in general that I can use first modulo operation ( greater number) and the result will be the same. Array initialization syntax when not in a declaration Calculating the expected values of the min/max of 2 random variables Cookie path and its accessibility to subfolder pages Compute Galois group of $\mathbb F_q/\mathbb F_p$ I have to compute Galois group of $\mathbb F_q/\mathbb F_p$ where $q=p^n$. I know already that $\mathbb F_q/\mathbb F_p$ is galois, so I don't need to prove it. Moreover, I know that \begin{align*}\sigma :\mathbb F_q&amp;\longrightarrow \mathbb F_q\\ x&amp;\longmapsto x^p\end{align*} is an automorphism that fix elements of $\mathbb F_p$ and thus $\sigma \in Gal(\mathbb F_q/\mathbb F_p)$.  Now, I know that if $k&lt;p^n$ then $\sigma ^k(x)=(x^{p})^k=x^{pk}\neq 1$ and thus $\sigma $ is of order $p^n$. Now if I can prove that $|Gal(\mathbb F_q/\mathbb F_p)|=p^n$, then $Gal(\mathbb F_q/\mathbb F_p)=\left&lt;\sigma \right&gt;$ and it would be finish, but I can't prove it since even $X^q-X$ split over $\mathbb F_q$, theis polynomial is not irreducible, and thus, I can't conclude. So how can I find an irreducible polynomial of degree $q$ that split over $\mathbb F_q$ ?