in my attempt to review, i discover that the thing that seems to occur most often is that new users with 0/1 reputation are answering questions that have accepted answers and are years old, and the answers say almost exactly what previous answers said, and there is no activity on the question for a long time.  often, one of the answers has 10+/50+ upvotes, and still the new user is attempting to add an answer.  it would seem helpful if there were a "duplicate answer to old accepted answer" in the following dialog, because the situation is not that it is not an answer, and not that it is "poorly formatted" (though i suppose it sometimes could be considered a "content problem").  it is really merely that it is adding nothing to the discussion except noise for a question that has an accepted answer and isn't really going to get upvotes since it's really identical to an existing answer.
While the etiquette of dealing with duplicate answers , there hasn't been a great way to deal with these, "Uh, yeah, I said this, too" types of behavior than the almighty downvote.   It would be nice to have a "Duplicate Answer" option on the flag menu. Five flags auto-deletes the answer, as with any other flag. In order to prevent abuse, the flagged answer would have to have the last owner edit (including original post) be younger than the original answer's original posting by at least 2 minutes.  Also, this ability should be a 5,000+ rep privilege, since we currently have no fanfare of rep from 3,001 to 9,999, and a power like this has a bit more umph than closing a question.  Thoughts?
Is "from where" grammatically equivalent to "from which"? What part of speech are non-human "interjections" like "oink" and "bang"? As a spin-off from :  If a human exclaims something like "ouch!", I believe it's considered an interjection.  But if a pig exclaims "oink!", what is the part of speech?  And if a bell goes "bong!", what is the part of speech?  You could speak of "an oink" and "a bong" as nouns, but I mean in a context like      The man went "ouch!", the pig went "oink!" and the bell went "bong!"   Are interjections only for humans? I'm using the Webform module for Drupal 8. The module confirmation settings for a form are the following:   Page (redirects to new page and displays the confirmation message) Inline (reloads the current page and replaces the webform with the confirmation message.) Message (reloads the current page/form and displays the confirmation message at the top of the page.) URL (redirects to a custom path or URL) URL with message (redirects to a custom path or URL and displays the confirmation message at the top of the page.)   But how am I able to submit a form via AJAX so that the page doesn't reload on submit, but a confirmation message still replaces the form? What did I do wrong?    EDIT:  Here is the solution which works:  First you have to hook the form alter function and set an AJAX callback (as in ):  use \Drupal\Core\Form\FormStateInterface;  function MYTHEME_form_alter(&amp;$form, FormStateInterface $form_state, $form_id) {   if ( isset($form['#webform_id']) &amp;&amp; $form['#webform_id'] == 'MYWEBFORM' )   {     // add an AJAX callback to the form submission     $form['actions']['submit']['#ajax'] = array(       'callback' =&gt; '\Drupal\MYMODULE\Controller\DefaultController::processFormSubmission',       'event' =&gt; 'click',     );   } }   Then in the processFormSubmission function you can process the form (put use \Drupal\Core\Form\FormStateInterface; at the top of your file) like:  // Instantiate an AjaxResponse Object to return. $ajax_response = new \Drupal\Core\Ajax\AjaxResponse();  /* do sth */  // in the DOM: replace the form with the text 'form submitted' $ajax_response-&gt;addCommand(new \Drupal\Core\Ajax\HtmlCommand('#MYFORM', 'form submitted'));  return $ajax_response; I have a large set of data points of the form (mean, stdev). I wish to reduce this to a single (better) mean, and a (hopefully) smaller standard deviation.  Clearly I could simply compute $\frac{\sum data_{mean}}{N}$, however this does not take in to account the fact that some of the data points are significantly more accurate than others.  To put it simply, I wish to preform a weighted average of these data points, but do not know what the weighting function should be in terms of the standard deviation. Character Limit in HTML How do you impose a character limit on a text input in HTML? How to derive $[x_i, F(\vec p)] = i \hbar \frac {\partial F(\vec p)}{\partial p_i}$ indicates that the following relation is &quot;easily shown&quot;: $[x_i, F(\vec p)] = i \hbar \frac {\partial F(\vec p)}{\partial p_i}$, however I'm having some trouble showing it.  I think I'm just messing up the multivariable Taylor expansion (of $F(\vec p)$).  Can one of you walk me through it or link me to site that will?  Thanks.  Edit: Here's what I get (without using $x=i\hbar \frac \partial {\partial p}$ which I haven't proven yet): $$F(\vec p) = F(\vec 0) + \sum^3_{j=1} \frac {\partial F(\vec 0)}{\partial p_j}p_j + \frac 12 \sum^3_{k=1} \sum^3_{j=1} \frac {\partial^2 F(\vec 0)}{\partial p_k \partial p_j} p_j p_k + \dots$$ so $$(x_iF(\vec p) - F(\vec p)x_i)\psi$$ $$= x_i[F(\vec 0)\psi -i\hbar \sum^3_{j=1} \frac {\partial F(\vec 0)}{\partial p_j}(\nabla \psi)_j + \hbar^2\frac 12 \sum^3_{k=1} \sum^3_{j=1} \frac {\partial^2 F(\vec 0)}{\partial p_k \partial p_j} (\nabla \psi)_j (\nabla \psi)_k + \dots]$$ $$- [F(\vec 0)x_i\psi -i\hbar \sum^3_{j=1} \frac {\partial F(\vec 0)}{\partial p_j}(\nabla x_i\psi)_j + \hbar^2\frac 12 \sum^3_{k=1} \sum^3_{j=1} \frac {\partial^2 F(\vec 0)}{\partial p_k \partial p_j} (\nabla x_i\psi)_j (\nabla x_i\psi)_k + \dots]$$ where $$(\nabla x_i\psi)_j=\frac {\partial x_i}{\partial x_j}\psi + x_i\frac {\partial \psi}{\partial x_j} = \delta_{ij}\psi + x_i\frac {\partial \psi}{\partial x_j}$$ and $$(\nabla x_i\psi)_j(\nabla x_i\psi)_k=(\delta_{ij}\psi + x_i\frac {\partial \psi}{\partial x_j})(\delta_{ik}\psi + x_i\frac {\partial \psi}{\partial x_k}) = \delta_{jk}\psi^2 + x_j \psi \frac {\partial \psi}{\partial x_k} + x_k \frac {\partial \psi}{\partial x_j} \psi + x_i^2 \frac {\partial^2 \psi}{\partial x_j \partial x_k}$$ Thus: $$(x_iF(\vec p) - F(\vec p)x_i)\psi$$ $$=  x_i[F(\vec 0)\psi -i\hbar \sum^3_{j=1} \frac {\partial F(\vec 0)}{\partial p_j}\frac {\partial \psi}{\partial x_j} + \hbar^2\frac 12 \sum^3_{k=1} \sum^3_{j=1} \frac {\partial^2 F(\vec 0)}{\partial p_k \partial p_j} \frac {\partial \psi}{\partial x_j} \frac {\partial \psi}{\partial x_k} + \dots]$$ $$- [F(\vec 0)x_i\psi -i\hbar \sum^3_{j=1} \frac {\partial F(\vec 0)}{\partial p_j}(\delta_{ij}\psi + x_i\frac {\partial \psi}{\partial x_j}) + \hbar^2\frac 12 \sum^3_{k=1} \sum^3_{j=1} \frac {\partial^2 F(\vec 0)}{\partial p_k \partial p_j} (\delta_{jk}\psi^2 + x_j \psi \frac {\partial \psi}{\partial x_k} + x_k \frac {\partial \psi}{\partial x_j} \psi + x_i^2 \frac {\partial^2 \psi}{\partial x_j \partial x_k}) + \dots]$$ From here it doesn't look like those higher order terms are all going to cancel out. How to promote algebraic expressions to operators in quantum mechanics? Okay, I know that in quantum mechanics the quantum observable is obtained from the classical observable by the prescription   $$ X \rightarrow x,\quad P \rightarrow -i\hbar\frac{\partial}{\partial x} $$   in the position basis. Now my questions are:    What if $x$ or $p$ appears in the denominator in a classical expression?  How to promote this to a quantum expression? What would be the meaning of division by an operator?   My expression likely contains a mixture of $x$ and $p$. For e.g., it could contain terms like $$\frac{p}{x^2}$$ or $$\frac{xp}{(x^2 + a^2)^{3/2}}.$$    How to resolve products of non-commuting operators like $x$, $p$ in a satisfactory way? Every time I go to install a new app, I get the message "Insufficient storage", and an unable to install anything!  I am using Samsung GT19060 my internal memory is 8GB. I have not downloaded anything but anytime I try to download something it will tell me low memory space. Prove $\sqrt{2}$ is between $\dfrac{a}{b}$ and $\dfrac{a+2b}{a+b}$ Let $a$ and $b$ be positive integers. Show that $\sqrt{2}$ always lies between $\dfrac{a}{b}$ and $\dfrac{a+2b}{a+b}$.  Please give the easy solution as possible. I'm trying to wrap my head around this very Hello World-y problem in game development. I've created a TicTacToe game in XNA so I guess the next step would be a  clone.  Keep in mind that I have no knowledge on game programming or even what maths I should apply to where. That's why I'm asking this question.    To the question: How can I determine where the ball should bounce when it hits the paddle at the bottom of the screen?  I'd imagine it would be something like:   Capture speed and angle from incoming ball. Detect where it touched the bar (far left, far right, center) and according to that give it a higher speed if it touched the outer areas. This is where I'm stuck. Hehe.   Any insights? I realize this is not a straightforward answer type question, but I'm sure it's one everyone faces at some point.  I'm reading the book Linear Algebra that was recommended on this website, but I still have no idea if I should apply it here. What's a word like "disregard" or "bypass" that means "hides"? Why are my photos not crisp? I use a Canon EOS Rebel T3i (600D) with the kit lens. I have experimented a lot with different settings and modes, but I feel like I have wasted many good shots that could have looked amazing, if only they were a little bit sharper.  I use auto-focus on most of my pictures and make sure to choose the right focus point, but all of my photos are still a little bit out of focus. When I zoom in, I can see that the pixels are not very crisp or well-aligned.  I am not sure if this issue is caused by my equipment or skills. What command should I use to rotate wood to S,N,W,E,D and U?  I read the entire world edit guide and tried some things but all the results are not satisfactory. A regular function can contain a call to itself in its definition, no problem.  I can't figure out how to do it with a lambda function though for the simple reason that the lambda function has no name to refer back to.  Is there a way to do it?  How? Can I determine if an argument is string literal? 99% of the time, I'm clear on when I should use "a" versus "an." There's one case, though, where people &amp; references I respect disagree.  Which of the following would you precede with "a" or "an," and why?   FAQ FUBAR SCUBA   [Note: I've read the questions  and , but the rules given there don't necessarily apply here.]    [Edited to add]  Here's a shorter (and hopefully clearer) version of the question…  In written English, which is correct (and why): "a FAQ" or "an FAQ"?  Some references with differing opinions:   an: the  and  a: the Microsoft Manual of Style for Tech Publications, 3e either: the  and Does a photon in vacuum have a rest frame? induction proof: $\sum_{k=1}^nk^2 = \frac{n(n+1)(2n+1)}{6}$ I encountered the following induction proof on a practice exam for calculus:  $$\sum_{k=1}^nk^2 = \frac{n(n+1)(2n+1)}{6}$$  I have to prove this statement with induction.  Can anyone please help me with this proof? Every Function in a Finite Field is a Polynomial Function From a bank of past master's exams I am going through:     Let $F$ be a finite field. Show that any function from $F$ to $F$ is a polynomial function.   I know that finite fields are fields of $p$ elements for $p$ prime [EDIT: It's actually $p^n$ for $p$ prime; see comment below]. Since I have $p$ choices for the $p$ elements to map to, then I have $p^p$ distinct functions. I think every function can be written in the form $f(x) = a_{p-1}x^{p-1} + \dots + a_0x^0$. For then given the values $f(0), f(1), \ldots f(p-1)$, I can solve for the coefficents by the linear system of equations  $$ a_0 + \sum_{i=1}^{p-1} n^i a_i = f(n).$$  This then gives me a $p-1 \times p-1$ square matrix over the field $\mathbb{F}_p$:  $$\left( \begin{array}{ccccc} 1&amp; 0 &amp; 0 &amp; \ldots &amp; 0 \\ 1&amp; 1 &amp; 1 &amp; \dots &amp; 1 \\ 1&amp; 2 &amp; 4 &amp; \dots &amp; 2^{p-1} \\ \vdots &amp; \vdots &amp; \vdots &amp; &amp; \vdots \\ 1 &amp; p-1 &amp; (p-1)^2 &amp; \dots &amp; (p-1)^{p-1} \end{array} \right) \left( \begin{array}{c} a_0 \\ a_1 \\ a_2 \\ \vdots \\ a_{p-1} \end{array}\right)  = \left( \begin{array}{c} f(0) \\ f(1) \\ f(2) \\ \vdots \\ f(p-1) \end{array} \right)$$  If I can show this matrix is invertible, then I can always find the $a_i$. But I am a bit stumped on how to show this (partially because I don't think I've ever done linear algebra in a vector space over a finite field). It does not seem easy to show linear independence, or nonzero determinant, or full row rank.    Alternatively (I just thought of this), can I show this is true by arguing that the map between the two sets (the set of polynomials of degree $p-1$; and the set of functions $F \to F$) is injective, and that it must be a bijection because the sets have the same cardinality $p^p$? How can I monitor the memory usage? I have used top to see the memory usage at the moment. But I would like to monitor the memory usage over a period of time. E.g start monitoring and then execute a few commands, and final stop the monitoring and see how much memory that have been used during the period.  How can I do this on Ubuntu Server?  I guess I could start a cronjob every 5th second or so, and invoke a command that log the current memory usage in a textfile. But what command should I use to get the current memory usage in a format that is easy to log to a text file?