What is it called when a pawn takes a pawn by being passed by another pawn?
How useful is that rule and how many times we can use that in one game?  Under what conditions can the en passant rule be used?  How often does it come up and is it a good idea to use it?
What is the official name for the "special" ASP.NET tags like this:  &lt;%# %&gt; &lt;%= %&gt; &lt;%@ %&gt; &lt;%$ %&gt;   I can't seem to figure out the conceptual or well known name for these, so I'm having trouble searching for more info.  As a bonus, can anyone give me a quick rundown of all of the possible "special tags" and what each one of them does (or point me to a resource)? Finding out NSArray/NSMutableArray changes' indices Performance of try-catch in php What kind of performance implications are there to consider when using try-catch statements in php 5?   I've read some old and seemingly conflicting information on this subject on the web before. A lot of the framework I currently have to work with was created on php 4 and lacks many of the niceties of php 5. So, I don't have much experience myself in using try-catchs with php. Multiple servers acting like a single one with all the hardware? by now I have 10 servers for hpc, power computing oriented. My users need to launch several processes using qmake. The users are used to work with ubuntu 9.10, and the software from the repositories is switable for them.  I've deployed ubuntu 9.10 to all 10 servers (pxe rocks).  By now we work with parallel-ssh and cluster-ssh, which allows as to launch the same process to all servers. With this tools this tools the servers remain as independent but with the same software and the same launched command.  Now we would like to go to next step and see all the servers as a single one with all the resources from the other 9 as if was its resources.   The difference would be substantial in time to process and also time to design the command to launch.  Any advice on wich software to use will be very useful?  Thanks In a tic-tac-toe implementation I guess that the challenging part is to determine the best move to be played by the machine.  What are the algorithms that can pursued? I'm looking into implementations from simple to complex. How would I go about tackling this part of the problem? So I was reading this:  and while the answers for the first question are good, nobody gave much attention to the second one. In fact, people only said that it can be proved without giving any proof or any.  So, if I have a Lagrangian and ADD an arbitrary function of $\dot{q}$, $q$ and $t$ in such a way that the equations of motion are the same, does this extra function MUST be a total time derivative?   EDIT Ok, I changed my question a little bit:  Question: If I have a function that obeys the Euler-Lagrange equation off-shell, this implies that my function is a time derivative? (This was used in Qmechanic's answer of this other question: , equation 14.)  Also, why people only talk about things that change the Lagrangian only by a total derivative? If this is not always the case that keeps the equation of motion the same, so why is it so important? And why in the two questions I posted about the same statement on Landau&amp;Lifshitz's mechanics book only consider this kind of change in the Lagrangian? Suppose that $(s_n)$ converges to s. Prove that $(s_n^2)$ converges to $s^2$ I am really struggling with my proofs class, I don't really understand how to prove a statement like this, or what the epsilon is standing for..  Suppose that $(s_n)$ converges to s.  Prove that $(s_n^2)$ converges to $s^2$ directly without using the fact that $lim(s_nt_n)=st$  Suppose that $(s_n)$ converges to s. Then, since $(s_n)$ is convergent, there exists an $M_1$ such that $|S_n|&lt;M_1$, for all $n\in \!\,\mathbb{N} \!\,$. Let $M=M_1+|S|$ (I don't completely understand this step...). Then given $ε&gt;0$, there exists N such that n>N implies that $|s_n-s|&lt;ε/M$. Thus for n>N, we have $|s_n^2-s^2|=|s_n-s|*|s_n+s|&lt;(ε/M)(M)=ε$. Hence, $s_n^2$ converges to $s^2$. How to diagnose computer lockups and freezes? Why does a Ball bounce back if Forces are Equal and Opposite? When a ball is thrown onto a wall, the ball exerts a force onto the wall. According to Newton's Third Law, the wall will exert an equal and opposite force to the ball. Thus, how would the ball be able to bounce back? Shouldn't it just slide down the wall? Is there always an equivalent metric which is not complete? My background and gameobjects are 2d sprites not UI images ,I want to know how to make my background scale with screen size and positions of 2d sprits on it don't change after building game (webGl) like scale canvas with screen size and anchor points in UI elements .  Before building the game   After building Sometime in the 1970s (I think) I saw a really awful film set in a small town by a lake. The film opened with some people camping out in the woods. One of them was zipped up in a sleeping bag. Something (as yet unidentified) moved in between the sleeping camper and the camera, and we heard a "crunch." When the creature moved off, we saw that it had bitten the head off the camper, causing a fountain of blood to spout of of the neck. Far from being shocking or gory, it was so badly done as to be laughable.  The main story was that these huge and nasty mutated creatures were coming out of the lake and eating people. A local industrial company was under suspicion for poisoning the lake, but repeated water tests showed it to be clean.  In the end, someone had the idea of testing the water at the bottom of the lake, which revealed it to be heavily poisoned with mercury. As mercury is much heavier than water, it had sunk, so the previous tests (done from a small row boat) had missed it as they only sampled the water at the surface.  They got it all sorted out eventually, and the bad guys ended up in prison.  After the credits had rolled, and you thought it was all over, another monster reared up in front of the camera and roared. I think we were supposed to go "Oh no, it's not all over!" However, the few people stupid enough not to have left by now laughed at the ridiculous sight and left, shaking their heads wondering why they had bothered!  I have a morbid fascination to see it again. Anyone have any idea what it was called? Is there anything we can do to locate companions in the world easier? Keeping track of where everyone is is hard.  I could be out in the wasteland while Dogmeat will let me know he found something. That's great, but then it's a chore trying to find him a lot of times. Sometimes, he'll even run ahead and attack enemies and I'll lose sight of him. Only if I leave an area sufficiently far enough, he'll come back and meet with me which isn't always possible. I know I can listen out for him but visual indicators would be better. But none of this works if I sent him to a settlement but needed to find him and he hasn't returned yet.  Is there anything we can do to make locating companions in the world easier? \centering doesn't seem to center my text I am trying to center this page but it will not work.  All is get is for the first line to be indented about one "tab" space to the right, but the second line will not shift.  However, the first line's indent does not appear to be centered either.  Is it possible that the binding offset or the indentfirst package is interacting with this negatively?  All of the other pages seem to work just fine. Any help would be appreciated.  \documentclass[12pt, a4paper, twoside]{article} \usepackage[margin=1in,bindingoffset=15.5mm,heightrounded]{geometry} \usepackage[T1]{fontenc} \usepackage{indentfirst} \begin{document} \pagestyle{empty} \vspace*{36 pt} {\centering \textbf{\emph{\Huge{Since I Saw You Last,\\There's a Change Upon You}}} } \end{document} jQuery serialize does not register checkboxes Most of the time, I use good and well interchangeably. However, on many occasions I would find well or good a misfit. Please suggest the proper usage. How do I get attention for one of my own questions without a good answer? I asked a question almost as soon as I got my account. I got a few decent answers, but none of them helped solve my problem. The question has long since become buried by newer questions, and there's still no accepted answer. Unfortunately, because there are quite a few answers with votes, to a casual observer it probably looks like the question was answered and I just neglected to mark an answer as accepted, and the system does not consider it "unanswered".  Or, I asked a question that was a bit more difficult to answer. After waiting for some time, I received no answers, little or no comments, and only a few views. The question does show up in the "unanswered" list, but no one has answered my question.  In either case, what's the protocol for me to try to get this question answered?  I see several options:   Post the question a second time, possibly linking to the original, to get attention for the original question. This is encouraged on sites like Reddit.  However, it's probably not appropriate here, since we're encouraged to check for duplicates and not submit a question that's already been asked by someone else, so this probably falls under that heading. Wait for some kind of wiki-like talk page to be implemented, then post a plea on the talk page for input and hope that activity on the talk page bumps up the question. Edit the question, but do nothing further on the Stack Exchange site. If I edit my post to say that I haven't accepted any of the current answers but am looking for more, then the question might get answered eventually by people browsing through old questions to find something they can answer. Post the question on other sites, but link to my original question on Stack Exchange. People will either answer here, or they'll answer on the other site and I can post the accepted answer here myself.  This might be considered spamming, so it might be better to do this without the link.      For more information, see the "" page in the . Digitally selectable filter I have asked a  but I did not get an answer, as it was too specific. So I will build on it but make it a bit more broad spectrum.  I would like to make a digitally selectable BPF using transistors to select a component in the filter; resulting in the center frequency being changed.  I have used FilterPro to generate quick second order filters and get a rough filter response.  For all the designs, a Multiple-feedback was selected:  In the first picture, a center frequency at 108KHz with a bandwidth @ -3dB of 103K to 113KHz is given.    For the second, a center frequency at 117.5KHz with a bandwidth @ -3dB of 112.8K to 122.2KHz is given.    The only difference between these two circuits is R3.  If I were to implement a circuit as shown below, would it work and what transistor would be recommended? I have selected the  as the Opamp in the circuit design as that is what was used for the .    For the transistors, I was thinking of using the MOSFETs (2N7002) used in the ST7590 design as well. I want to implement the EM algorithm manually and then compare it to the results of the normalmixEM of mixtools package. Of course, I would be happy if they both lead to the same results. The main reference is Geoffrey McLachlan (2000), .  I have a mixture density of two Gaussians, in general form, the log-likelihood is given by (McLachlan page 48):      $$ \log L_c(\Psi) = \sum_{i=1}^g \sum_{j=1}^n z_{ij}\{\log \pi_i + \log f_i(y_i;\theta_i)\}. $$ The $z_{ij}$ are $1$, if the observation was from the $i$th component density, otherwise $0$. The $f_i$ is the density of the normal distribution. The $\pi$ is the mixture proportion, so $\pi_1$ is the probability, that an observation is from the first Gaussian distribution and $\pi_2$ is the probability, that an observation is from the second Gaussian distribution.   The E step is now, calculation of the conditional expectation:      $$ Q(\Psi;\Psi^{(0)}) = E_{\Psi(0)}\{\log L_c(|\Psi)|y\}. $$ which leads, after a few derivations to the result (page 49):      \begin{align} \tau_i(y_j;\Psi^{(k)}) &amp;= \frac{\pi_i^{(k)}f_i(y_j;\theta_i^{(k)}}{f(y_j;\Psi^{(k)}}  \\[8pt]                        &amp;= \frac{\pi_i^{(k)}f_i(y_j;\theta_i^{(k)}}{\sum_{h=1}^g \pi_h^{(k)}f_h(y_j;\theta_h^{(k)})} \end{align} in the case of two Gaussians (page 82):      $$ \tau_i(y_j;\Psi) = \frac{\pi_i \phi(y_j;\mu_i,\Sigma_i)}{\sum_{h=1}^g \pi_h\phi(y_j; \mu_h,\Sigma_h)} $$ The M step is now the maximization of Q (page 49):      $$ Q(\Psi;\Psi^{(k)}) = \sum_{i=1}^g\sum_{j=1}^n\tau_i(y_j;\Psi^{(k)})\{\log \pi_i + \log f_i(y_j;\theta_i)\}. $$ This leads to (in the case of two Gaussians) (page 82):      \begin{align} \mu_i^{(k+1)} &amp;= \frac{\sum_{j=1}^n \tau_{ij}^{(k)}y_j}{\sum_{j=1}^n \tau_{ij}^{(k)}}  \\[8pt] \Sigma_i^{(k+1)} &amp;= \frac{\sum_{j=1}^n \tau_{ij}^{(k)}(y_j - \mu_i^{(k+1)})(y_j - \mu_i^{(k+1)})^T}{\sum_{j=1}^n \tau_{ij}^{(k)}} \end{align} and we know that (p. 50)      $$ \pi_i^{(k+1)} = \frac{\sum_{j=1}^n \tau_i(y_j;\Psi^{(k)})}{n}\qquad (i = 1, \ldots, g). $$ We repeat the E, M steps until $L(\Psi^{(k+1)})-L(\Psi^{(k)})$ is small.        I tried to write a R code (data can be found ).    # EM algorithm manually # dat is the data  # initial values pi1       &lt;-  0.5 pi2       &lt;-  0.5 mu1       &lt;- -0.01 mu2       &lt;-  0.01 sigma1    &lt;-  0.01 sigma2    &lt;-  0.02 loglik[1] &lt;-  0 loglik[2] &lt;- sum(pi1*(log(pi1) + log(dnorm(dat,mu1,sigma1)))) +               sum(pi2*(log(pi2) + log(dnorm(dat,mu2,sigma2))))  tau1 &lt;- 0 tau2 &lt;- 0 k    &lt;- 1  # loop while(abs(loglik[k+1]-loglik[k]) &gt;= 0.00001) {    # E step   tau1 &lt;- pi1*dnorm(dat,mean=mu1,sd=sigma1)/(pi1*dnorm(x,mean=mu1,sd=sigma1) +            pi2*dnorm(dat,mean=mu2,sd=sigma2))   tau2 &lt;- pi2*dnorm(dat,mean=mu2,sd=sigma2)/(pi1*dnorm(x,mean=mu1,sd=sigma1) +            pi2*dnorm(dat,mean=mu2,sd=sigma2))    # M step   pi1 &lt;- sum(tau1)/length(dat)   pi2 &lt;- sum(tau2)/length(dat)    mu1 &lt;- sum(tau1*x)/sum(tau1)   mu2 &lt;- sum(tau2*x)/sum(tau2)    sigma1 &lt;- sum(tau1*(x-mu1)^2)/sum(tau1)   sigma2 &lt;- sum(tau2*(x-mu2)^2)/sum(tau2)    loglik[k] &lt;- sum(tau1*(log(pi1) + log(dnorm(x,mu1,sigma1)))) +                 sum(tau2*(log(pi2) + log(dnorm(x,mu2,sigma2))))   k         &lt;- k+1 }   # compare library(mixtools) gm &lt;- normalmixEM(x, k=2, lambda=c(0.5,0.5), mu=c(-0.01,0.01), sigma=c(0.01,0.02)) gm$lambda gm$mu gm$sigma  gm$loglik   The algorithm is not working, since some observations have the likelihood of zero and the log of this is -Inf. Where is my mistake? Check existence of input argument in a Bash shell script