Can someone show me the meaning of this symbol? I've googled but couldn't find it
Given $f(x) = \frac{1}{2}x^TAx + b^Tx + \alpha $   where A is an nxn symmetric matrix, b is an n-dimensional vector, and alpha a scalar. Show that  $\bigtriangledown _{x}f(x) = Ax + b$   and  $H = \bigtriangledown ^{2}_{x}f(x) = A$   Is this simply a matter of taking a derivative with respect to X, how would you attack this one?
How to search only unanswered questions with an open bounty ? My table doesn't fit; what are my options? Install CentOS 7 on HP dl120 gen9 server with b140i raid controller I'm trying to install CentOS 7 on a HP DL120 gen 9 server with a b140i controller. I have 4 1TB HDD setup in a raid 1+0 and the CentOS installer doesn't seem to recognize the logical drive created from the storage utility.  From my understanding i need some drivers for CentOS 7 to recognize the B140i controller. Also, the driver seems to be closed source by HP.  What is my approach here? Is there any other free linux OS that i can use on this server and that would recognize the raid controller?  Thank you. Find $\lim_{n \to \infty} \left[\frac{(n+1)^{n + 1}}{n^n} - \frac{n^{n}}{(n-1)^{n-1}} \right]$ (a question asked at trivia) What is this shell/Bash syntax: someVariable=someValue someCommand When scripting in bash or any other shell in *NIX, while running a command that will take more than a few seconds, a progress bar is needed.  For example, copying a big file, opening a big tar file.  What ways do you recommend to add progress bars to shell scripts? Install MySQLdb (for python) as non-compressed egg The install instructions are:  $ python setup.py build $ sudo python setup.py install # or su first   This gives me an .egg file. How do I tell the install to dump the files as a normal, uncompressed library?  Thanks! Proving that any permutation in $S_n$ can be written as a product of disjoint cycles I have attempted a proof of this, but upon looking at my notes, I feel it might be incorrect: it is noticeably simpler than the one in my notes.  Proposition: any permutation in $S_n$ can be written as a product of disjoint cycles.  Proof (attempt): $s\in S_n$. Let $\langle s\rangle$ act on $X=\{1,\cdots,n\}$. Define $x\sim x'\iff x'\in\text{Orb}(x)$ for $x,x'\in X:$ this is clearly an equivalent relation, hence the orbits partition $X$. Each orbit corresponds a cycle in $s$, so we are done.  Does this hold, or have I missed something vital? For you that have tested this, should we use Ubuntu and install different Desktop Environments (KDE/XFCE...) or we should install different distributions (Kubuntu/Xubuntu...). Are there any notable issues in performance / CPU consumption?  PS:  I know how to install them (already did), I wanted to know if anyone has any problems regarding the performance and what is better to install the desktop or to use the ditribution Continuous and bounded variation does not imply absolutely continuous What purpose does downvoting questions serve? Installing Guest Additions causing problems Every Christmas, Harry receives a mediocre gift from the Dursleys. In Harry Potter and the Chamber of Secrets he gets a toothpick.     At that moment, Hedwig swooped into the room, carrying a very small package in her beak.     “Hello,” said Harry happily as she landed on his bed. “Are you speaking to me again?”     She nibbled his ear in an affectionate sort of way, which was a far better present than the one that    she had brought him, which turned out to be from the Dursleys. They had sent Harry a toothpick    and a note telling him to find out whether he’d be able to stay at Hogwarts for the summer    vacation, too.    They hate owls, but obviously use them to contact Harry at school? Textbook clarification: $\log = \ln$ Textbook reads:     All logarithms are natural logarithms: $\log = \ln$.   Does this mean $n\log(n) = n\ln(n)$? "Notice: Undefined variable", "Notice: Undefined index", and "Notice: Undefined offset" using PHP Variance (different definitions) I'm new to statistics and reading stats books I found different definitions for Variance.  Definition1: $ s^2 = \frac{1}{n-1} \sum_{i=1}^n (x_i - \bar{x})^2 $  Definition2: $ s^2 = \frac{1}{n} \sum_{i=1}^n (x_i - \bar{x})^2 $  I would like to know why is used different definition for same thing? This is a  about IPv6 Subnetting.      Related:               I know a lot about , and as I prepare to (deploy|work on) an IPv6 network I need to know how much of this knowledge is transferable and what I still need to learn. IPv6 seems at first glance to be much more complex than IPv4. So I would like to know:   IPv6 is 128 bits, so why is /64 the smallest recommended subnet for hosts? Related to this:   Why is it recommended to use /127 for point to point links between routers, and why was it recommended against in the past? Should I change existing router links to use /127? Why would virtual machines be provisioned with less than a /64 worth of addresses? Are there other situations in which I would use a subnet smaller than /64?  Can I map directly from IPv4 subnets to IPv6 subnets? For instance, does an IPv4 /24 correspond directly to an IPv6 /56 or /120? My interfaces have several IPv6 addresses. Must the subnet be the same for all of them? Why do I sometimes see a % rather than a / in an IPv6 address and what does it mean? Am I wasting too many subnets? Aren't we just going to run out again? In what other major ways is IPv6 subnetting different from IPv4 subnetting? How to generate Bernoulli random variables with common correlation $\rho$? Where are the NetworkManager logs? A previous poster on the regular forums (  ) said /var/log/daemon.log, but I don't seem to have such a file. Do I need to enable logging? Help resizing posted images I often add pictures to my questions. Most of the time they come out the right size. Well, that used to be OK always, up until I started posting screenshots taken by my mobile. For example, this one:  This way, I'm sure you'll agree it is huge, decidedly too big, it takes up the whole body of the question, I mean. At present, the only way I have to resize it is the following code: &lt;sub&gt;(Click image to enlarge)&lt;/sub&gt;  [&lt;img src=&quot;http://i.stack.imgur.com/hKmRp.jpg&quot; width=&quot;210&quot; height=&quot;350&quot; alt=&quot;&quot;&gt;][1]  which I do not remember, and always have to recover from . Is there a simpler, less HTML-hacky (and, I'd expect, more Markdown-based) way of resizing it? PS The output of the above code is: (Click image to enlarge)