How to make apex datatable header fixed
How do I support scrolling and lock/freeze the header row of a pageBlockTable?
Do we need inertial frames in Lagrangian mechanics? Relationship between gamma and chi-squared distribution If $$Y=\sum_{i=1}^{N}X_i^2$$ where $X_i \sim \mathcal{N}(0,\sigma^2)$, i.e. all $X_i$ are i.i.d. normal random variables of zero mean with same variances, then $$Y \sim \Gamma\left(\frac{N}{2},2\sigma^2\right).$$  I know the chi-squared distribution is a special case of the gamma distribution, but could not derive the chi-squared distribution for random variable $Y$. Any help, please? Comma before which I'm not sure which of the following sentences is correct. Is the comma mandatory, optional or unnecessary? I've googled a bit about this topic, but I got confused.     Our mapping contains 2000 words, which map to more than one lemma.   or     Our mapping contains 2000 words which map to more than one lemma.   Context: In total, there are more than 2000 words.  I've read  . If I understand the answers correctly, my "which map to more than one lemma" is a defining clause and no comma is required. But is it wrong to add one? Does the review queue page show only reviews requiring your action? Does it differ, and when does it? This confusion came up in comments .  On the site I use most actively (RPG.SE), I've noticed that the counts for each review queue appear to only indicate the reviews available to me requiring my action. Just to be clear, I'm talking about this number here:        Since I'm a 10k user, that's pretty easy to tell: even after doing all my reviews, and the review page saying there's 0 items in each queue, I might still have that 10k notice in my top bar saying there's [5] reviews pending, or some other number. So they must still be there, just waiting on other users to finish them, and it just doesn't show them to me. This is fine, I like this behaviour.  However, on Meta SE about an hour ago, there was 1 item in the close vote review queue. I reviewed that item. The count stayed at 1 on the review page. When I clicked to re-enter the queue in case there were new items, I was presented with this:        Another user in that meta question I linked claims this is normal behaviour for them on their own site (Christianity.SE I think?).  What's going on here? Are the review queues supposed to be customised just to what I personally can actually review at the time? Is there a bug, are sites customised differently, or is there just some kind of caching thing leading to a time delay on the review count getting updated? (As they say, it is always caching, but is caching really the culprit here too?) Why didn't Gandalf or Frodo Fly to Mount Doom? Why didn't Gandalf use his eagles to fly over Mount Doom and drop the ring? I know he feared what he would do if the ring overpowered him, so why not just give Frodo an eagle? And, if there would be too much risk in flying the ring to Mordor, couldn't the eagles fly them part of the way?  Why risk it with such a long walk; far less risky to fly over most of the journey. Advantages of using different metric signatures in relativity and QFT I am studying General Relativity and some basic QFTs. It bothers me a lot that different books use different metric signatures, i.e. $(-+++)$ and $(+---).$ Can anyone tell me the advantages of using both of them, or why some people prefer the former while some prefer the latter? I would like to know which one should I while tackling different problems. sir, problem about a host file sir, over department created a host file to run over office program in windows, but they give us dell system having operating system ubuntu 16.4 now my question is that how this add file in ubuntu to run the program. the windows command is given below  TO ACCESS FIORI - Please Follow the Instructions in this Video  Path:- C:\Windows\System32\drivers\etc  Copy attached Hosts File in the above path.  Fiori Link to access SAP in Google Chrome: How to quickly move one layer to a different group in large Photoshop files, without dragging? Why, with Springer's  svmono template, do the letters written with the \mathcal font change? It seems that \mathcal becomes \mathscr.  Edit: Look at this image:    With the svmono template \mathcal returns the first alphabet and not the (classical) latter.  Here the packages I use in my document:  \documentclass[envcountsame,envcountchap]{svmono}  \usepackage{subfiles} \usepackage[utf8]{inputenc}  \usepackage{mathptmx} \usepackage[bottom]{footmisc} \usepackage{microtype} \usepackage{stmaryrd}    \usepackage{amsmath} \usepackage{courier} \usepackage{mathrsfs}  \usepackage{amssymb}  \usepackage[all,cmtip]{xy} \usepackage{faktor} \usepackage{graphicx} \usepackage{mathdots} \usepackage[colorlinks={true},linkcolor={blue},citecolor={blue}]{hyperref} \usepackage[frame,width=15truecm,height=23.5truecm,center]{crop}   With this settings I have the above strange behavior of \mathcal. Recursivly Deleted Root Directory I recursively deleted the contents of my root directory with sudo privileges. My display reset, and windowing stopped working. I could no longer run non-buitin commands. Most of my directories (including the home directory disappeared).  What I meant to run:  sudo rm ./* -rf   What I believe I ran:  sudo rm /* -rf   I understand how this command works (see ).  I'm trying to get a better sense of how much (and what parts) of the original files and directory-structure physically remains on the hard-drive.  How much of these "remains" are recoverable? E.g is it possible to use data recovery software like TestDisk/PhotoRec to recover the full home dir itself? What about config files? How do I get the coordinates of a mouse click on a canvas element? What's the simplest way to add a click event handler to a canvas element that will return the x and y coordinates of the click (relative to the canvas element)?  No legacy browser compatibility required, Safari, Opera and Firefox will do. ant deploy error - Maximum size of request reached I used to deploy metadata using ant migration tool successfully but from last night I am getting the below error:  John@John:~/mm_workspace/TEST_Project/deploy$ ant deployUnpackaged  Buildfile: /home/john/mm_workspace/TEST_Project/deploy/build.xml  deployUnpackaged:  BUILD FAILED /home/john/mm_workspace/TEST_Project/deploy/build.xml:72: Failed to submit request to https://cs19.salesforce.com/services/Soap/m/35.0/00D293456000Qaf for user john@test.com.dev. Error: {http://schemas.xmlsoap.org/soap/envelope/}Client - Maximum size of request reached. Maximum size of request is 52428800 bytes.  Total time: 2 minutes 10 seconds   I think this is because of too much metadata that I am trying to deploy. For now, I am deploying classes and then VF pages and so on but I am looking for an option to deploy everything in one go without running into the above error.  I am sure that people are working on more complex projects than mine with lots of metadata and I am wondering how are they deploying with out hitting this error?  Thanks Why is "union" an exception to the "a/an" rule? Can I travel to UK with my Italian national daughter and husband with my permesso di soggiorno? I have an Italian permesso di soggiorno and I want to join my husband in the UK. My baby and my husband are Italian nationals. Can I travel with them with only the permesso di soggiorno? Can I buy PSN games and DLC without giving Sony my credit card info? Conky Widgets are Opening in their Own Windows I just upgraded to 16.04 and I'm getting all my customization set up again, but it seems that most Conky widgets are opening in their own window, instead of just appearing on the Desktop; although some are working correctly.  For example:  LSD (working properly):    Seamod (not working, opening in own window):    Since it's not affecting every single widget, I assume it could be an issue with the conkyrc with the widgets that aren't working, but this also never happened in 14.04 so I wasn't sure if maybe there was some compatibility issue in 16.04. My Google-fu has failed me in finding a solution.  If anyone can point me in the right direction, it would be much appreciated! :) Why are PCA eigenvectors orthogonal and what is the relation to the PCA scores being uncorrelated? I'm reading up on PCA, and I'm understanding most of what's going on in terms of the derivation apart from the assumption that eigenvectors need to be orthogonal and how it relates to the projections (PCA scores) being uncorrelated? I have two explanations provided below which use a link between orthogonality and correlation but fail to really explain it: , .  In the second picture it says that the condition $a_{2}^{T}a_{1}=0$  is imposed to ensure that the projection $y_{2}=Xa_2$ will be uncorrelated with $y_{1}=Xa_1$. Can someone provide an example to show why orthogonal vectors ensure uncorrelated variables?  What would happen in PCA if I chose vectors which are not orthogonal; is this even possible? I have read elsewhere that orthogonality is just a by-product of the covariance matrix being symmetric which would suggest that it's not possible to have non pairwise orthogonal eigenvectors. However in the first picture in search of the most 'suitable' matrix it almost seems as we are choosing $p_{1},\ldots,p_{m}$ to be orthogonal to give us a more convenient matrix $\textbf{P}$ one which has nice properties.  I've read other posts on this topic but have been unsatisfied with incorporation of the intuition with uncorrelated variables. I really appreciate any help in understanding this confusion!! Is there a guideline about when to end expressions with semicolons? Toggle Switch to swap the connections of two buttons I am trying to mod my arcade stick so I can switch two commonly swapped buttons on the controller.  Essentially they are simple 2 terminal momentary switches connected directly to the controller PCB. I would like to switch their responsibilities, so in my case the Back button and the LB button on the XBox pcb I would like to swap so the Back actuates the LB button on the PCB and the LB actuates the Back button.  My assumption is that I would need a switch with 8 terminals, 4 in 4 out.  What type of switch am I looking for? What is a "Nested Quantifier" and why is it causing my regex to fail? I have this regex I built and tested in regex buddy.  "_ [ 0-9]{10}+ {1}+[ 0-9]{10}+ {2}+[ 0-9]{6}+ {2}[ 0-9]{2}"   When I use this in .Net C#   I receive the exception  "parsing \"_ [ 0-9]{10}+ +[ 0-9]{10}+  +[ 0-9]{6}+  [ 0-9]{2}\" - Nested quantifier +."   What does this error mean? Apparently .net doesn't like the expression.  Here is the regex buddy so u can understand my intention with the regex...  _ [ 0-9]{10}+ {1}+[ 0-9]{10}+ {2}+[ 0-9]{6}+ {2}[ 0-9]{2}  Match the characters "_ " literally «_ » Match a single character present in the list below «[ 0-9]{10}+»    Exactly 10 times «{10}+»    The character " " « »    A character in the range between "0" and "9" «0-9» Match the character " " literally « {1}+»    Exactly 1 times «{1}+» Match a single character present in the list below «[ 0-9]{10}+»    Exactly 10 times «{10}+»    The character " " « »    A character in the range between "0" and "9" «0-9» Match the character " " literally « {2}+»    Exactly 2 times «{2}+» Match a single character present in the list below «[ 0-9]{6}+»    Exactly 6 times «{6}+»    The character " " « »    A character in the range between "0" and "9" «0-9» Match the character " " literally « {2}»    Exactly 2 times «{2}» Match a single character present in the list below «[ 0-9]{2}»    Exactly 2 times «{2}»    The character " " « »    A character in the range between "0" and "9" «0-9»   In short...  What is a Nested quantifier?