Is Changing the Accepted Answer Frowned Upon? Sometimes I get a good answer and accept it, but the someone else posts a brilliant answer. I of course upvote it, but I avoid changing my accepted answer in most situations, since I feel it might be a bit frowned upon, so to speak.  Is it "bad practice" (for lack of a better term) to accept a different answer after you've already accepted an answer?
Is it poor form to switch accepted answers? I had a question of the form "does something like X exist?" Someone wrote a response to say that, No, X does not exist, but I could write it if I liked. I had suspected as much, so I marked his answer as the accepted answer. Today someone actually posted the code to do X for me, and I feel that the new poster deserves the "Accepted Answer" checkmark.  Is it poor form for me to pick a new Accepted answer? Does the original answerer get penalized in terms of reputation?  While the original responder's answer was accepted at the time, I feel this new answer is really more helpful.  Edit: Which of these responses should I accept? What does the notion of a single accepted answer mean with a question that is subjective that could have multiple "right" answers?
How can edge rings be selected in a predictable way? When trying to select multiple edge-rings Shift-Alt-RMB sometimes loops get selected in the one (green) way or the other (red) way.  I couldn't derive a general rule.   How can two or more face-rings following one direction be selected ?  (Easy to reproduce with a default torus mesh.) What is the meaning of ./ before a given path? How does a phonon cause two electrons to attract each other and form a cooper pair? We know that like charges repel each other. But my professor claimed that two electrons can attract each other as well. What he said was that due to screening an electron travelling at some speed won't repel another electron, but that they will, in some cases, attract each other due to weak phonon exchange. What does that mean? What is phonon exchange? Do two electrons really attract each other? Product rule intuition Can anyone think of an intuitive explanation of the product rule? I'm not asking for a derivation. To me it seems like quite an un-untuitive result, as apposed to the chain-rule (which is ironically harder to derive). I always stumble when using abbreviations in a sentence, as they inherently contain a period in them. How do I use a comma or a semicolon after an abbreviation? How about a period?  E.g. (This is an example of my quandary) Consider a particle in a potential well. Let’s assume it’s a simple harmonic oscillator potential and the particle is in its ground state with energy E0 = (1/2) &#8463;&omega;0. We measure its position (measurement-1) with a high degree of accuracy which localises the particle, corresponding to a superposition of momentum (and therefore energy) states.  Now we measure the particle’s energy (measurement-2) and happen to find that it’s E10 = (21/2) &#8463;&omega;0. Where did the extra energy come from?  In the textbooks it’s claimed that the extra energy comes from the act of observation but I wonder how that could work. Measurement-1 which probed the position of the particle can’t have delivered to it a precise amount of energy, while measurement-2 might just have been passive. No doubt there is entanglement here between the particle state and the measuring device but where, and which measurement? Correlation coefficient between a (non-dichotomous) nominal variable and a numeric (interval) or an ordinal variable I've already read all the pages in this site trying to find the answer to my problem but no one seems to be the right one form me...  First I explain you the kind of data I'm working with...  Let's say that I have an array vector with several names of city, one for each of 300 users. I also have another array vector with scores response to a survey of each user or a continuous value for each user.  I would like to know if exist a correlation coefficient that compute the correlation between these two variables so, between a nominal and a numeric/continuous or ordinal variables.  I've searched on the Internet and in some pages they suggest to use the contingency coefficient or Cramer's V or Lambda coefficient or Eta . For each of this measure the just say that they could be applied for such data in which we have a nominal variable and interval or numerical variable. The thing is that searching and searching, trying to understand every one of them, sometime is written or watching the examples that they are reasonable to use them if you have dichotomous nominal variable, except for Cramer's V, other time is not written any requirement for the type of data. A lot of other pages say that is right to apply regression instead, that is right, but I would just simply like to know if there is a coefficient like pearson/spearman for this kind of data.  I also think that is no so properly to use Spearman Correlation coeff since the cities are not sortable.  I have also built the function of Cramer'sV and Eta by myself (I'm working with Matlab) but for Eta they don't talk about any p-value to see if the coefficient is statistically significant...  In the matlabWorks site there is also a nice toolbox that says to compute eta^2 but the kind of input it needs is not understandable.  Is here someone that have done a test like mine? If you need more detail to understand the kind of data I'm using just ask me and I'll try to explain you better. I remember that the main character is trying to find the group that destroyed his home planet while he was on a mission. His planet was very difficult to live on and the people became expert in martial arts and were the best soldiers in the galaxy. They were mercenaries and often helped against tyrants. There was a very memorable section in at least one book about an initiation task that the main character had to do in that he had to survive in their wilderness for days. He was at some point surrounded in a old building by thousands of poisonous worm/snake creatures that he managed to survive until rescued by the leaders. I have read the Rules of a competition. The text of the Rules include a sentence as follows:     As per stated in the Rules the entrants will be notified by May 30th 2010.   Does the sentence above mean that May 30th is included in the term of notification or not? Force update from unsigned repository I'm using an unsigned repo in Ubuntu 16.04 from Debian multimedia:  deb http://www.deb-multimedia.org jessie main   To install deb-multimedia-keyring, I'm running:  apt-get update &amp;&amp; apt-get install deb-multimedia-keyring -y   This gives an error:  W: GPG error: http://www.deb-multimedia.org jessie InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5C808C2B65558117 E: The repository 'http://www.deb-multimedia.org jessie InRelease' is not signed. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details. Are Living Beings Turned Into Horcruxes Suceptible to Age, Disease, or Injury? From the HP books I know that Horcruxes grant a form of immortality. So, it is not possible for someone who created a Horcrux to die from old age or succumb to diseases. I guess the same is true for living beings turned into a Horcrux. But do living Horcruxes age normally? Is it possible to cripple them or sever their limbs, head or something like that, or do they instantly "repair" themselves like inanimate Horcruxes? I've seen plots of test/training error suddenly dropping at certain epoch(s) a few times during the neural network training, and I wonder what causes these performance jumps:    This image is taken from Kaiming He's Github, but similar plots show up in many papers. Arbitrary precision spline interpolation Player A taps  targeting Player B; its "deals 1 damage to target player" ability is placed on the stack.  Player B gets priority and responds with , targeting Goblin Fireslinger.  Both players pass priority. Snap resolves, and Goblin Fireslinger is returned to its owner's hand.  Does Player B still take 1 damage from Goblin Fireslinger's activated ability?  I know that if the creature had been killed/sent to the graveyard, the ability would still resolve, but I was told recently that because a player's hand is a private zone it couldn't. If anyone could confirm or deny this for me, it would be most appreciated. Jeffrey Wooldridge in his Econometric Analysis of Cross Section and Panel Data (page 357) says that the empirical Hessian "is not guaranteed to be positive definite, or even positive semidefinite, for the particular sample we are working with.".  This seems wrong to me as (numerical problems apart) the Hessian must be positive semidefinite as a result of the definition of the M-estimator as the value of the parameter which minimizes the objective function for the given sample and the well-known fact that at a (local) minimum the Hessian is positive semidefinite.  Is my argument right?  [EDIT: The statement has been removed in the 2nd ed. of the book. See comment.]  BACKGROUND Suppose that $\widehat \theta_N$ is an estimator obtained by minimizing $${1 \over N}\sum_{i=1}^N q(w_i,\theta),$$ where $w_i$ denotes the $i$-th observation.  Let's denote the Hessian of $q$ by $H$, $$H(q,\theta)_{ij}=\frac{\partial^2 q}{\partial \theta_i \partial \theta_j}$$  The asymptotic covariance of $\widehat \theta_n$ involves $E[H(q,\theta_0)]$ where $\theta_0$ is the true parameter value. One way to estimate it is to use the empirical Hesssian  $$\widehat H=\frac{1}{N}\sum_{i=1}^N H(w_i,\widehat \theta_n)$$  It is the definiteness of $\widehat H$ which is in question. Can non basic lands be tapped for colorless mana? For example,  has a mana fixing ability, but it doesn't say you can tap it for mana. Other non-basic lands have a mana ability listed on the card. Should I assume that Evolving Winds cannot be tapped for mana?  Basic lands don't have mana tapping abilities listed, but are assumed you can tap them for mana of the color they represent. In US hotels, what happens if you skip checkout and just leave the hotel? Every time I check out of a hotel, they ask me if my stay went fine, let me review my incidental charges and ask if they should charge the credit card used to check in.   But what if I simply walk out of the hotel without formally "checking out"? They have my credit card on file and these days you don't even have to return your room key if you want to keep a souvenir. Would it be rude and create more work for hotel employees?  The question arose after spending 15 minutes in the check out queue at a major US hotel. I'd like to estimate the correlation between:  An ordinal variable: subjects are asked to rate their preference for 6 types of fruit on a 1-5 scale (ranging from very disgusting to very tasty) On average subjects use only 3 points of the scale.  A continuous variable: the same subjects are asked to quickly identify these fruits, which results in an mean accuracy for the 6 fruits.   Is Spearman rho the best method to analyze these data and/or are there other good methods I could consider? Modified files in a git branch are spilling over into another branch I am working on a git repository with a master branch and another topic branch. I have switched to topic branch and modified a file. Now, if I switched to master branch that same file is shown as modified.   For example:  git status in git-build branch:  # On branch git-build # Changes to be committed: #   (use "git reset HEAD &lt;file&gt;..." to unstage) # #       modified:   cvsup_current #   Switch to master branch  [root@redbull builder_scripts (git-build)]# git co master M       builder_scripts/cvsup_current Switched to branch "master"   git status in master branch  [root@redbull builder_scripts (master)]# git status # On branch master # Changes to be committed: #   (use "git reset HEAD &lt;file&gt;..." to unstage) # #       modified:   cvsup_current #   Why is that the file is shown as modified in master branch even though it was modified in git-build branch?   My understanding was that the branches are independent of each other and when I change from one branch to another the changes do not "spill over" from one branch to another. So I am obviously missing some thing here.   Anyone got a clue stick? \numcases with \tag I would like to label some cases with specific tags, and was hoping for something like  \begin{numcases}{A = } \frac{r}{a} &amp; r &gt; a \tag{G} \\ \frac{a}{r} &amp; r &lt; a \tag{H} \end{numcases}   utilizing the numcasesenvironment from the cases package, and \tag from amsmath. However, the two don't seem to be compatible:     ! Package amsmath Error: \tag not allowed here.   Is there any alternatives that would do what I hope to accomplish?