Base class virtual method is called, instead of derived method
What is object slicing?
What is the method for converting radians to degrees? I run into this occasionally and always forget how to do it.  One of those things that pop up ever so often.  Also, what's the formula to convert angles expressed in radians to degrees and back again? Is there a UNIX command to list all recently removed files from a system Accidentally a rm -rf command was launched to my root directory instead of current directory. I stopped file removing by Ctrl+C but some files has already been removed. Is there a LINUX command to list all recently removed files from the system to get the affected applications ?  Operating System: CentOS 6.3 What is "function*" in JavaScript? How to rename objects with python? I want to rename the number 1->picture (32) with python not the number 2->picture with the (3745), can someone help me with that ? A weak converse of $AB=BA\implies e^Ae^B=e^Be^A$ from "Topics in Matrix Analysis" for matrices of algebraic numbers. It is a well known fact that if $A,B\in M_{n\times n}(\mathbb C)$ and $AB=BA$, then $e^Ae^B=e^Be^A.$  The converse does not hold. Horn and Johnson give the following example in their Topics in Matrix Analysis (page 435). Let $$A=\begin{pmatrix}0&amp;0\\0&amp;2\pi i\end{pmatrix},\qquad B=\begin{pmatrix}0&amp;1\\0&amp;2\pi i\end{pmatrix}.$$ Then $$AB=\begin{pmatrix}0&amp;0\\0&amp;-4\pi^2\end{pmatrix}\neq\begin{pmatrix}0&amp;2\pi i\\0&amp;-4\pi^2\end{pmatrix}=BA.$$ We have $$e^A=\sum_{k=0}^{\infty}\frac 1{k!}\begin{pmatrix}0&amp;0\\0&amp;2\pi i\end{pmatrix}^k=\sum_{k=0}^{\infty}\frac 1{k!}\begin{pmatrix}0^k&amp;0\\0&amp;(2\pi i)^k\end{pmatrix}=\begin{pmatrix}e^0&amp;0\\0&amp;e^{2\pi i}\end{pmatrix}=\begin{pmatrix}1&amp;0\\0&amp;1\end{pmatrix}.$$   For $S=\begin{pmatrix}1&amp;-\frac i{2\pi}\\0&amp;1 \end{pmatrix},$ we have $$e^B=e^{SAS^{-1}}=Se^AS^{-1}=S\begin{pmatrix}1&amp;0\\0&amp;1\end{pmatrix}S^{-1}=\begin{pmatrix}1&amp;0\\0&amp;1\end{pmatrix}.$$   Therefore, $A,B$ are such non-commuting matrices that $e^Ae^B=\begin{pmatrix}1&amp;0\\0&amp;1\end{pmatrix}=e^Be^A.$  It is clear that $\pi$ is important in this particular example. In fact, the authors say what follows.      It is known that if all entries of $A,B\in M_n$ are algebraic numbers and $n\geq 2,$ then $e^A\cdot e^B=e^B\cdot e^A$ if and only if $AB=BA.$   No proof is given. How does one go about proving that? When an account is deleted, the username in the user's posts and comments is changed to a generic user&lt;userID&gt;. But the username stays the same on close and delete notifications on posts the user had voted to close / delete1. I think it shouldn't, especially for users who used their real name as their username, if they chose to distance themselves from the site and remove their accounts, it makes sense that they wouldn't really want their name plastered on close and delete notifications.   A perhaps easy way to avoid the actual username remaining visible would be to change it to the generic user&lt;userID&gt; (or anything generic enough, like "anonymous") prior to deletion, and wait a bit for the generic username to propagate all over the site. If I'm not horribly misreading , this was part of the process in the old days.   This could be automated or added as a suggestion to the .  Glaring example can be seen , where the deleted user also posted a comment where their name is properly anonymized:        1 I've seen it on close notifications and self deleted answers. I'm not sure it happens on deleted questions, or deleted answers that aren't self deletions, and I don't have a way to verify it - other than stumbling on them accidentally Why does pressing a transform hotkey not display the axes on the selected object? I open Blender 2.80 (official release, not a beta or RC) and get the new scene with the usual 3 objects present (camera, light and cube). I select the cube, press 't' for the tools menu and click on the Move tool. The usual 3 axis glyph appears at the cube's origin as expected. But if I use the hotkey 'g' to activate the move transform instead of selecting the tool from the menu with the mouse this glyph does not appear. The exact same problem exists if I use the a hotkey for rotate or scale as well. Why? Is there some clickable checkbox setting hidden somewhere that could have disabled this? From all the hard drives I have bought, they never seem to be as large as the advertised size; from 320 GB down to 290 GB, from 500 GB down to 450 GB, etc. Is there a technical reason for this? I have damaged the screen on my phone, so much so, it will not allow me to get the data to transfer onto my laptop. On opening Samsung Kies, it is saying that the connected device is locked. Please enter password on the connected device. I can only assume its the pattern lock they are referring to as I have managed to unlock the sim.  As I am unable to do this due to the screen being cracked, I wondered whether there is any other way of doing this, before sending the same onto my insurance company, as they are saying that I will lose all the data! Cant see why seeing as its just the hardware that is damaged and not the software. Apparently $1+2+3+4+\ldots+n = \dfrac{n\times(n+1)}2$.  How? What's the proof? Or maybe it is self apparent just looking at the above?   PS: This problem is known as "The sum of the first $n$ positive integers". Increment Record based on field What does "Meta" mean? I am fairly new to Stack Overflow and just stumbled across Meta Stack Overflow.  I can't seem to figure out what the purpose of the "Meta" site is. Can someone please explain it to me? Is there a built-in that removes duplicates from list in Python, whilst preserving order? I know that I can use a set to remove duplicates, but that destroys the original order. I also know that I can roll my own like this:  def uniq(input):   output = []   for x in input:     if x not in output:       output.append(x)   return output   (Thanks to  for that .)  But I'd like to avail myself of a built-in or a more Pythonic idiom if possible.  Related question: Is there a word for happiness made possible by a tragic situation? Is it possible to reintegrate a Horcrux? As anyone who is familiar with Harry Potter knows, a horcrux is made when someone commits murder and stores a piece of their soul in something. Would it be possible for this someone to later recover and reintegrate their soul piece(s), should they want to? I think I have heard that the following is true before, but I don't know how to prove it:     Let $A$ be a matrix with real entries. Then the minimal polynomial of $A$ over $\mathbb{C}$ is the same as the minimal polynomial of $A$ over $\mathbb{R}$.   Is this true? Would anyone be willing to provide a proof?    Attempt at a proof:  Let $M(t)$ be the minimal polynomial over the reals, and $P(t)$ over the complex numbers. We can look at $M$ as a polynomial over $\Bbb C$, in which case it will fulfil $M(A)=0$, and therefore $P(t)$ divides it. In addition, we can look at $P(t)$ as the sum of two polynomials: $R(t)+iK(t)$. Plugging $A$ we get that $R(A)+iK(A)=P(A)=0$, but this forces both $R(A)=0$ and $K(A)=0$. Looking at both $K$ and $R$ as real polynomials, we get that $M(t)$ divides them both, and therefore divides $R+iK=P$.   Now $M$ and $P$ are monic polynomials, and they divide each other, therefore $M=P$.  Does this look to be correct?    More generally, one might prove the following     Let $A$ be any square matrix with entries in a field$~K$, and let $F$ be an extension field of$~K$. Then the minimal polynomial of$~A$ over$~F$ is the same as the minimal polynomial of $A$ over$~K$. How do I compare 2 rows from the same table (SQL Server)? I need to create a background job that processes a table looking for rows matching on a particular id with different statuses. It will store the row data in a string to compare the data against a row with a matching id. I know the syntax to get the row data, but I have never tried comparing 2 rows from the same table before. How is it done? Would I need to use variables to store the data from each? Or some other way? (Using SQL Server 2008) What is lock escalation? On per-site metas, users are given a rank based on meta participation, and this ranking is seen on the default tab of the users page on each per-site meta. How is this participation numerically calculated to give a ranking? Is it by votes? Something else? Are community wiki posts included in this? Differential equation: autonomous system This isn't homework. I have no idea what theorems I should be looking at to solve this. Guidance, partial and total solutions are all welcomed.     Let $f$ be a locally lipschitz function in an open set $G\subseteq \Bbb R^n$. Consider the autonomous system $y'=f(y)$.      Let $y(x,\xi)$ be the value at point $x$ of the maximal solution that satisfies the initial condition $y(0)=\xi$.         Prove that the domain of $y(\cdot, y(s, \xi))$ is $I-s$, where $I$ is the domain of $y(\cdot ,\xi)$.   Prove that for all $s, t$ such that $y(s, \xi)$ and $y(t+s, \xi)$ exist, then $y(t,y(s,\xi))$ also exists and $y(t,y(s,\xi))=y(t+s, \xi)$.   If $y$ is a maximal solution and there exists $T&gt;0$ such that $y(0)=y(T)$ and $f(y(0))\neq 0$, then $y$ is a periodic solution and not constant.   If $y$ is a solution whose domain is $(a,+\infty)$, if $\eta:=\lim _{x\to +\infty}y(x)$ and $\eta \in G$, then $f(\eta)=0$.      EDIT  I found an alternative solution for 3. Please check my proof and give feedback in comments:  let $u$ be the restriction of $y$ to $[0,T]$, now let $\overline u$ be the periodic extension of $u$ to $\mathbb R$. It is easy to see that $\overline u$ is a solution to the given differential equation. But since $f$ is locally lipschitz, $\overline u$ must coincide with $y$ wherever they are both defined. Since $y$ is a maximal solution, it must be $\overline u$, so $y$ is defined on $\mathbb R$.