this is my first time using Ubuntu 14.04 version.  I'm not sure what I've done, but I can't shut down my laptop. But if I log in as the guest, then it will shut down if I press the button and I'm not getting used to terminal. How can I solve the problem?
I recently upgraded from Ubuntu 11.10 to 12.04. If it makes any difference, my system is a Dell Inspiron 1520.   I encounter a problem whenever I shutdown or restart; it kills all running processes (as far as I can tell), but once I get past the shutdown text screen and the screen goes black,  my computer doesn't power off. The fans still run and the screen is still on, etc. I have to hold down the power button in order to complety shut down.   Does anyone know how to resolve this problem?
Given that $W$ is a subspace of $V$, prove: $\dim W=\dim V \implies W=V$ Suppose $W$ is a subspace of the finite-dimensional vector space $V$ and $\dim W = \dim V=n$  Let $\{\overrightarrow w_1,\ldots,\overrightarrow w_n\}$ be a basis for $W$ and $\{\overrightarrow v_1,\ldots,\overrightarrow v_n\}$ be a basis for $V$.  The set $\{\overrightarrow w_1,\ldots,\overrightarrow w_n,\overrightarrow v_1,\ldots,\overrightarrow v_n\}$ still spans $W$. Since $W$ is a subspace of $V$, $W\subset V$ and all the $w_i$'s can be written in terms of $\{ \overrightarrow v_{1},\ldots,\overrightarrow v_n\}$.  $\therefore$ We can remove one by one all the $w_i$'s from the set $\{\overrightarrow w_{1},\ldots,\overrightarrow w_n,\overrightarrow v_1,\ldots,\overrightarrow v_n\}$ while still having it span $W$, which leaves us with the set $\{\overrightarrow v_1,\ldots,\overrightarrow v_n\}$. We know it to be linearly independent since it is a basis for $V$. Therefore the basis of $V$ is also a basis of $W$. From there on, it is trivial to prove double inclusion $W\subset V$ and $V\subset W$ which gives us $W=V$.  Is my approach correct? Post apocalyptic journey in search of knowledge from fallen society (ours) I'm racking my memory for a post-apocalyptic novel that I borrowed from a library maybe 15 years ago, but I'm sure it was published a few years before that though (maybe early 90s?).  I remember a party of people travelling across the flooded USA after some kind of apocalypse (climate change/flooding?). Towards the end of the book the group makes their way to New York(?) and finds a partially flooded library, discovering a set of books that gives hope for the return/rebuilding of society. Is 'that is' optional? When I write something like this:     I am a man that is doing these things.   Is it correct to shorten it like this?     I am a man doing these things.   And does it require commas? Is it possible to use multiple desktop environments on same system? I am using Ubuntu 12.04. I want to try out KDE and other desktop environments.   But I'm not sure if I'll like them enough to switch permanently. I want to be safe and make a transition in a piecemeal fashion.  Is it possible to install KDE on Ubuntu and yet not do away with the default Unity shell?  Could I install multiple desktop environments and switch between them by tweaking some startup configuration and then rebooting? Was Kylo Ren's Blaster Bolt Freezing Really Force Telekinesis? In this questions answer its stated that Kylo Ren freezes the blaster bolt in midair with telekinesis:       Because he is extremely skilled in Force telekinesis, Kylo Ren is able   to freeze not just objects but even blaster bolts in midair.   But as a commenter already pointed out, this seems nonsense (even in star wars force physics). The blaster bolt is, as far as I know, a cloud of plasma. If it is stopped by telekinesis, why should it continue its old path with its old speed after it is released? Wasn't it more a completely new force ablility like "time freeze"? While I admit in a case of time freeze the bolt should not have flickered all the time. Also the plasma should have expanded and vanished or simply cooled down releasing its energy to the surrounding air.  So when it was force telekinesis Kylo must have done the following:   Stop every atom in the plasma cloud Keep the cloud compressed and in form and shape. Isolate it to prevent the heat flow or keep it on temperature (is this still telekinesis?) Not just releasing it but accelerate it again exactly on its old path and speed.   This would be indeed a greate never seen mastery of telekinesis. And very ineffective. And if he wanted to be cool, wouldn't it be even cooler to change the path after the "release" so that it hits one of his enemies?  So what was going on there? Pure telekinesis or something else? Did the writers intend this? Or did they just not thinking it to the end? Is there a better way to do optional function parameters in JavaScript? I've always handled optional parameters in JavaScript like this:  function myFunc(requiredArg, optionalArg){   optionalArg = optionalArg || 'defaultValue';    // Do stuff }   Is there a better way to do it?  Are there any cases where using || like that is going to fail? Creating the Nabla operator (also known as Del operator) as an operator Posts flagged for attention but there are none The comment with the Flagged Posts that seems to be new as of today states there are posts with flags awaiting my attention but the counter shows zero and when I go into flagged posts there is nothing waiting for me. How do I find the common ratio of a geometric sequence? A geometric sequence has its first term equal to $12$ and its fourth term equal to $-96$.   How do I find the common ratio? And find the sum of the first $14$ terms I've been making a map for 1.10 and it's going great, but 1.11 shows great mobs to use for it. However, most things have channged in command syntax. For example, /kill @e[type=ArmorStand,r=6] is now /kill @e[type=Armor_Stand,r=6]  What about /testfor? I can't find a way to testfor a player to stand on a block and give them an effect.   What's is going on in this image is that a redstone clock is running into this command /testfor @a[1117,20,507,r=1] (if I was to stand on them cords the comparator would turn on and power that command block), but it only works in 1.10... from 1.11 snapshots, I've seen some errors of it, like it now needs to have {} at the beginning and end of it. (e.g. /testfor @a{[1117,20,507,r=1]})   It's still not working, though, so does anyone know how to get it to work? Need help to interpret output of free command I would appreciate help in interpreting the output of 'free -m' below.    -bash-4.2$ free -m               total        used        free      shared  buff/cache   available Mem:          15793        7112          88        7840        8591         611 Swap:         16891        5289       11602    If I have nearly 11GB free then why am I seeing swap usage.  Shouldn't that be 0?   Also, the 'shared' value is 7840.  Is this memory available for a new application? Is only 'cache' memory available for new applications?  In other words, 'shared' and 'buffer' memory are not available for new applications? How should I interpret the 'available' column with a value of 611?  How is this value arrived at? Received W-2 but was never paid I just now received a W-2 from a company that I worked for 3 days as a contractor. I had to leave country for 2 months due to a family emergency. Since the employment duration was very short, I was not paid. I was told that they don't want to charge the client because 3 days is not enough contribution.  Since I had to leave country the same day, I did not argue with them and told it's okay if they feel right.  Now I have a W-2 from them saying they have paid me about $1500. I contacted them but I have not received any reply yet.  I just want to be prepared. What can I do here? How to check if a number is a power of 2 Today I needed a simple algorithm for checking if a number is a power of 2.  The algorithm needs to be:   Simple Correct for any ulong value.   I came up with this simple algorithm:  private bool IsPowerOfTwo(ulong number) {     if (number == 0)         return false;      for (ulong power = 1; power &gt; 0; power = power &lt;&lt; 1)     {         // This for loop used shifting for powers of 2, meaning         // that the value will become 0 after the last shift         // (from binary 1000...0000 to 0000...0000) then, the 'for'         // loop will break out.          if (power == number)             return true;         if (power &gt; number)             return false;     }     return false; }   But then I thought, how about checking if log2 x is an exactly round number? But when I checked for 2^63+1, Math.Log returned exactly 63 because of rounding. So I checked if 2 to the power 63 is equal to the original number - and it is, because the calculation is done in doubles and not in exact numbers:  private bool IsPowerOfTwo_2(ulong number) {     double log = Math.Log(number, 2);     double pow = Math.Pow(2, Math.Round(log));     return pow == number; }   This returned true for the given wrong value: 9223372036854775809.  Is there a better algorithm? Best practices for catching and re-throwing .NET exceptions When voting to migrate an off-topic question, why is the list of sites limited? Is there a standard delay for consumer ratings of apps on the App Store? I have an app that's been out for a couple of weeks. Its not exactly selling like hot cakes yet, but I'm pretty sure I've gotten a rating or a review by now. But nothing shows when viewing either in iTunes or directly on the AppStore on the iPhone.  Is there a standard delay as to when ratings/reviews show up, that Apple imposes, especially for new apps? Or do you think there is some problem with Apple's system? If I've got a file (or files) selected in Windows Explorer, the only way I've found to "unselect" them is click with the mouse on some empty space.  I thought Esc would do this, but it doesn't. Also changing focus with Tab or Shift + Tab doesn't work; the file(s) are still selected even if focus goes to the address bar for instance.  Does anyone know of a keyboard shortcut to do this? I am not able to sum all the opportunities under the account ?  How will I do that?  What I have to use in this to run the trigger? Is it possible to create because opp. is child and account is parent ?  trigger sumAllopptyAmtAccount on Account(before insert) {     Set &lt; ID &gt; AccID = New Set &lt; ID &gt; ();     if (Trigger.isInsert)         for (Account oppAc: trigger.New) {             AccID.add(oppAc.AccountID);         }     List &lt; Account &gt; acc = [select id, SumAll_Opprty__c from Account where id in: a.AccID];     List &lt; Opportunity &gt; opp = [selece id from Opportunity where AccountID in: a.AccID];     for (Account a: acc) {         a.SumAll_Opprty__c = con.size();     } } I just saw now that a new build had rolled out in which the comment upvote and flag options are always visible. Previously, one had to mouse over the area in order to see them.  Why was this just changed? Is it to support touch screens? I'll admit, it was difficult to find the flag button using my touchscreen laptop running Microsoft Edge.  Cross-site duplicate on MSO: How should I act if I discover a user plagiarizing fellow users' posts? What if I find someone plagiarizing external resources without attribution?  See also: