i'm trying to give the user the possibility to update the values of some fields concerning him by clicking on a container named #info-client Here I append the input areas after the click and once the #finish button is clicked the infos will then be updated. The problem i got is that the infos were updated yet they were showed more than once ( 2 times or even 3 .. )  $("#info-client").one('click', function() {   $("#info-client").children().hide();    // liste des champs   var c1 = $(' Nom : <input type="text id="identifiant">
');   var c2 = $(' Adresse : <input type="text" id="adresse">
');   var c3 = $(' Ville : <input type="text" id="ville">
');   var c4 = $(' Tel : <input type="text" id="tel">
');   var c5 = $(' Fax : <input type="text" id="fax">
')   var button = $('<input type="button" id="finish" value="Mettre à jour">');    $("#info-client").append(c1);   $("#info-client").append(c2);   $("#info-client").append(c3);   $("#info-client").append(c4);   $("#info-client").append(c5);   $("#info-client").append(button);    $("#finish").one('click', function() {     var identifiant = $('#identifiant').val();     var adresse = $('#adresse').val();     var ville = $('#ville').val();     var tel = $('#tel').val();     var fax = $('#fax').val();      c1.replaceWith("
" + identifiant + "
");     c2.replaceWith("
 Adresse : " + adresse + "
");     c3.replaceWith("
" + ville + "
");     c4.replaceWith("
Fax : " + tel + "
");     c5.replaceWith("
 Tel :" + fax + "
");    }); });

I have a bit of code where I am looping through all the select boxes on a page and binding a .hover event to them to do a bit of twiddling with their width on mouse on/off.  This happens on page ready and works just fine.  The problem I have is that any select boxes I add via Ajax or DOM after the initial loop won't have the event bound.  I have found this plugin (), but before I add another 5k to my pages with a plugin, I want to see if anyone knows a way to do this, either with jQuery directly or by another option.


Where any aliased command is stored? If I am aliasing "ls" as "l" then where will that aliased be stored? Does it affect .bashrc or .cshrc?

I have created an alias:  alias shh='sqlplus hfdora/hfdora@hfd1"     After creating this alias I was able to enter my database only by typing shh.  But after closing my shell, I wasn't able to find the alias next time. Even after typing only alias, shh was not showing in the list.  Is there any file to make an alias permanent so that it will not be erased?


When i click on my Windows system drive in the File Manager I get following error, Let me tell you that I checked all my drives with elivated cmd bu running chkdsk /x /r /f command.  Other Drives which also are exfat are being detected, i.e.  upto 150 GB drives. However this is the largest Drive around 750+ GB is not being detected & giving some page size don't match error.  Error mounting /dev/sda5 at /media/bhavik/Collections: Command-line `mount -t "exfat" -o "uhelper=udisks2,nodev,nosuid,uid=1000,gid=1000,iocharset=utf8,namecase=0,errors=remount-ro,umask=0077" "/dev/sda5" "/media/bhavik/Collections"' exited with non-zero exit status 1: stdout: `FUSE exfat 1.0.1 ' stderr: `ERROR: `pagefile.sys' real size does not equal to size (0 != 4294967296).

In Ubuntu 13.04 there was an option to use the PPA by Relan in order to get ExFat functionality. Seeing that in Ubuntu this functionality is now available from the repositories without the PPA I tried this but failed to make it work.  So my question is how do I enable exfat support?


Is it possible to get blender 2.79 UI into blender 2.8? Im not used to the new ui and i prefer the old one, so is there a way i can get the ui to be like the old one?

So today I decided to join the hype and check 2.8 out even though I am the kind of person who does not like to try betas, because I hate change. And anyways I was already shocked by the difference of the keyboard shortcuts. My question is: Is it a good idea to import the preferences from 2.79b or would you guys advice me from doing it and if it's OK to do that, which file should I import and where is it in the Blender Foundation old files? It would be nice if someone showed me the path.


I was taught that the 'spin' of an elementary particle was its inherent, unalterable magnetic moment due to its physical spin, or angular momentum, that may or may not actually exist. Therefore, if the quantum spin of a particle is not directly observable (because it probably doesn't exist, as such), but is measurable as its magnetic moment due to its seeming physical spin, how can its gyromagnetic ratio, or $g$-factor, be anything other than one? What am I missing here?

I am reading Schwartz's book on Quantum field theory. In the chapter anomalous magnetic moment (chapter 17) he mentions that Dirac equation naturally implies that the electron spin $g$-factor is 2. Can anyone please explain why does the Dirac equation implies that $g_s=2$?


How can I update Opera browser on Ubuntu 18? when I do sudo apt-get upgrade opera I face with this:  Reading package lists... Done Building dependency tree        Reading state information... Done Calculating upgrade... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation:  The following packages have unmet dependencies:  opera : Depends: libgstreamer-plugins-base0.10-0 (>= 0.10.16) but it is not installable          Depends: libgstreamer0.10-0 (>= 0.10.15) but it is not installable          Depends: gstreamer0.10-plugins-good but it is not installable  opera-stable : Conflicts: opera but 12.16.1860 is to be installed E: Broken packages   so how can I update it? I have Opera Version:56.0.3051.104.  Thanks in advance.

I am trying to install opera browser from the terminal.  I downloaded the 'debian' installer because it didn't show up in software center.  It completely destroyed my software center - it is frozen and I have no idea how to fix (I have a different thread for that though).  Can I use this thing called synaptic package manager to install Opera?  or am I stuck with Firefox?    How do I install Opera Browser?


There's a sentence: I think I must do it before he has finished / he will have finished his project.  What's correct?  Or maybe does it need another tense?

I've stumbled upon a sentence:     We can use it until better alternatives will have become available.   Although it sounds valid to me, I believe it conveys the same idea as      We can use it until better alternatives are available.   Am I missing something? Or is the former a more complicated way to express the latter?


Today's typical smartphone chargers are rated at 5 Volt & 1+ Ampere. The laptop USB can supply 500mA 100mA.    Why is it safe to charge the phone with 1/2 the rated current?  Is it like a slow charging mode where it's the phone's responsibility to recognize a computer USB port & lower down the current demand?  Does this mean I can potentially use a 5V/0.5A wall charger with my phone without any fear of damaging it?   Edit : It seems that the answers & comments are focused on 100mA vs 500mA that the laptop USB port can supply. I'm amending that in my question & rephrasing. The real question is, even 500mA is lesser than what the wall charger supplies i.e. typically 1+ Ampere.   Edit 2 : To those who marked this as duplicate : You are confusing this question with the one that's asking whether a laptop can supply more than 500mA. It does not specifically answers the 3 points above. I'm wondering if a laptop can charge a phone, then why can't a lower current rating charger be considered safe?

I heard that the current limit for a USB port is 100mA. However, I also heard that some devices can get up to 1.8A from a port. How do you get past the 100mA limit?


In British English, how do you write smartphone? Is it:   Smart phone Smart-phone Smartphone

Smart phone Smartphone Smart-phone   I am really looking for some help regarding hyphen (-) issue in text found in research article. Is there any standard method how to use it?


$$1 + \sum_{j=1}^{n} j!j$$  I want to find a formula for the above and then prove it by induction. The answer according to Wolfram is $(n+1)!-1$, however I have no idea how to get there. Any hints or ideas on how I should tackle this one?


My biology textbook says that a person with sickle cell anaemia is less prone to malaria. Why is that so?  I'm guessing that its because the malarial parasite needs human RBCs for completing its life cycle. So are the sickle-shaped RBCs inhospitable to the parasite? In what way exactly?

I am aware that there is such a thing called heterozygous advantage, which is due to the presence of a certain single allele, and that an example of this could be with "sickle-cell anemia".  I am quite curious as to how exactly this heterozygous advantage is created.   Could the increased resistance against malaria be due to natural resistance or natural selection?


This question has been asked between me and my friends for centuries. We were trying to make tiny novels of manga and produce an anime show for the art club we own. Seems as it is their culture and their talent. Can we really make only English anime/manga and dub it to Japanese?

Manga and anime famously originate from Japan, and the vast majority of the big names in manga and anime are Japanese; Hayao Miyazaki, Hideaki Anno, Hiromu Arakawa, and Masashi Kishimoto come to mind.  Outside of Japan, I can really only think of one creator who had their work become an anime/manga: The  was adapted into an anime and manga and was created by an Australian writer, Emily Rodda.  Aside from Rodda, however, are there any* international creators, particularly from the Western world, that have successfully published manga (or anime) in Japan, manhua in China, or manhwa in Korea? Have any Western studios created and produced** anime (or rather, anime-influenced) series?  * - An exhaustive list is not necessary; a few examples from various countries and maybe some stats versus Japan, if possible. ** - Not as a result of outsourcing.


I have a crash reported like:  Fatal Exception: java.lang.NullPointerException: Attempt to read from field 'android.view.View androidx.recyclerview.widget.RecyclerView$c0.a' on a null object reference at com.xx.xx.Fragment$23$1.run(TestFragment.java:4) at android.os.Handler.handleCallback(Handler.java:907) at android.os.Handler.dispatchMessage(Handler.java:105) at android.os.Looper.loop(Looper.java:216) at android.app.ActivityThread.main(ActivityThread.java:7625) at java.lang.reflect.Method.invoke(Method.java) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:524) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:987)   How to find the androidx.recyclerview.widget.RecyclerView$c0.a? Where is the crash happening?  Absolutely nothing to do with NullPointerExceptions. This question is about finding variables names in Crashlytics reports when classes are not symbolicated in the crashlog.

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


Is it possible to achieve something like this in LaTeX?    I want a curved arrrow pointing from 1st line to the other line and is coupled with an equation number which indicates the equation used. I want to be able to specify equation used manually like for example

I'd like to know if it is possible to create a equation like the one shown in the figure below. And if it is possible, how can I do it?  Desired characteristics:   Side comments aligned between equations Curved arrows pointing from one equation to another   Can someone help me?


Note: After asking this question, I found that the file browser Thunar, which comes with Xubuntu and is installable in any Ubuntu version, provides a bulk-renaming utility that works well for me.    I am trying to append timestamp hashes to files in directory or a userFileCode like a file password (for example all files of user have a prefix or suffix).   My problem is the mv command only works once so I cannot use wildcards like so  mv *.* *.*_dateHashsuffix   error says it's not a directory.   Seems like mv cannot handle multiple renames or do I have to use it like in cd /usr/bin && sudo mv test test_disabled && mv sudo sudo_disabled... in other words perhaps I have to pipe the ls > filelist.tst and then parse (do I use |grep here?) that separately in a .sh file script with executable permission run as so ./myscriptsname.sh or cant I use ls > directly in the script?  I see a use for this on my servers in the future to rename variables and files to prevent hacking. But a better idea altogether might be torrentDNS and zipSites in perhaps voxel based web browser with links to webpage content.

One of the ways I quickly rename files in Windows is   F2 > Rename > Tab (to next file) > Rename ...   But in Ubuntu/Nautilus, I can't tab to next file. But being on Linux, I think there must be a command line alternative.  However, sometimes, I may want more control over how to rename specific files. In that case, perhaps its better to be able to tab to the next file


I have found ~3 Pokémon out in the wild I have wanted to catch but when I try to tap them on the map but it doesn't do anything. They eventually run away/disappear after a certain period of time.   When I do manage to click on them to start the battle, I can throw the Pokéball just fine. It just sometimes won't load off the map and onto where I catch them I guess.  I do have my location on and have Wifi! I need help to Catch 'Em All!

After catching the first pokemon you are left to catch pokemon as you wish with no further explanation on how best to catch these pokemon.  After throwing around 10 balls and having them hit away/dodged and just rolling pathetically on the ground, I realised there must be a technique I missed.  How should you approach a wild pokemon encounter so as to maximise catching probability?


What are the general rules for knowing when command options are prefixed by -- as opposed to -?  Edit: An answer referencing a canonical source, such as steeldriver's is preferred. One suggested duplicate refers to Wikipedia which is okay but probably not as good as a GNU documentation link.  Second edit: I think the title is not my original so if it misleads, I'm sorry, it was not my edit. That probably explains why some comments direct me to the man page.

I often see a single dash - or double dash -- followed by linux commands or other installed linux programs.   What are the differences between single dash and double dashes?  Is it just about abbreviation?  For example, -v means --verbose most of the time.


I want to replace all occurrences of a particular, previously-determined (known) email address --- with another email address, inside a PHP file; no regex should be involved ; sed is the simplest way I know to do so. This worked (the email has been changed): sed -i 's/\$to = "example@example.com"/\$to = "example_1@example_1.com"/g' FILE  But I think it's generally wrong to do text processing with one liners especially if one finds them "too long", so I tried to break it to the following which doesn't work: sed -i \ ' \ -e s/ -e \$to = "example@example.com"/ -e \$to = "example_1@example_1.com"/ -e g ' \ FILE   sed: -e expression #1, char 8: unterminated address regex  How to break sed commands to nested parts when no regex and variable expansions are applied? (i.e. when no regex and variable expansions / special quoting rules are part of the operation)

sed 's/[long1][long2]/[long3][long4]/' file.txt   I would like to split this command onto multiple lines - f.x. something like this:  sed 's/     [long1]     [long2]   /     [long3]     [long4]   /' file.txt   Using \ or separating strings didn't work.


I am training a very simple 2D dataset with 2 features. Its tabular data and contains only numeric information. I tried using keras to train a neural network but the performance does not bulge. I wanted to let the network fully converge and overfit but it doesnt work.   overfitCallback = EarlyStopping(monitor='loss', min_delta=0, patience = 20) act= 'relu' last_act = 'softmax'  los = 'mse' ep = 100000 batch = 8 opt = keras.optimizers.Adam(learning_rate=0.001) # define the keras model model = Sequential() dense1= model.add(Dense(5, input_dim=2, activation=act,kernel_initializer='he_uniform')) dense2= model.add(Dense(2, activation=act)) dense3= model.add(Dense(1, activation=last_act)) model.compile(loss=los, optimizer=opt, metrics=['accuracy']) history = model.fit(data_train, target_train, epochs=ep, batch_size=batch,verbose=0,callbacks=[overfitCallback])

I'm training a neural network but the training loss doesn't decrease. How can I fix this?  I'm not asking about overfitting or regularization. I'm asking about how to solve the problem where my network's performance doesn't improve on the training set.    This question is intentionally general so that other questions about how to train a neural network can be closed as a duplicate of this one, with the attitude that "if you give a man a fish you feed him for a day, but if you teach a man to fish, you can feed him for the rest of his life." See this Meta thread for a discussion:   If your neural network does not generalize well, see:


$f(x) = \begin{cases} x^{\alpha }\left(1-cos\left(1-x\right)\right)^{\beta } & \text{if $\;\;\;0<x<1$} \\ \frac{1}{x^{\alpha }+x^{\beta }} & \text{if $\;\;\;1\ge x$} \end{cases}$  I split into two integrals:  $\int _0^1x^{\alpha }\left(1-cos\left(1-x\right)\right)^{\beta }dx\:+\:\int _1^{\infty }\left(\frac{1}{x^{\alpha }+x^{\beta }}\right)dx$  I want to use the comparison test. but I find it hard to choose $g(x)$ that will give me an answer for $\alpha$ and $\beta$

This question is realy hard for me and I'd like to get some advises:  $$f(x) =   \begin{cases}      x^{\alpha}(1-\cos(1-x))^{\beta} &  x\in (0,1)\\[6px]     \dfrac{1}{x^{\alpha}+x^{\beta}}  &   x\ge 1   \end{cases}$$  I need to find the values of $\alpha$ and $\beta$ that make $\int_{0}^{\infty}f(x)\,dx$ converge.  Now I think I need to split the integral to $\int_{0}^{1}f(x)\,dx$ and  $\int_{1}^{\infty}f(x)\,dx$ and check the converge for each integral. But I'm stuck here.


Would someone advise if there's any Expression or term which means 'to argue illogically only to argue'

Quite often, the phrase "x for x's sake" is used in English, and so one could describe someone as being "argumentative for argument's sake" to describe someone who is arguing for the sake of arguing.  However, is there an adjective that means the same thing?  For example, it could be used in the context:     I don't want to be [X], but [argument...]   ... indicating that your argument is necessary and not intended to irritate.


The following is a snippet from Gallian's Contemporary Abstract Algebra:  Chapter 10-Example 10:  We determine all homomorphisms from $\Bbb Z_{12}$ to $\Bbb Z_{30}$. By  $\phi(g^n) = (\phi(g))^n$ for all $n\in\Bbb Z$",  such a homomorphism is completely specified by the image of $1$. That is, if $1$ maps to $a$, then $x$ maps to $xa$.  By Lagrange’s Theorem and by " If $|g|$ is finite, then $|f(g)|$ divides $|g|$"  we require that $|a|$ divide both $12$ and $30.$ So, $|a|$ can be  $1, 2, 3$, or $6$. Thus, $a = 0, 15, 10, 20, 5,$ or $25.$ This gives us a list of candidates for the homomorphisms. That each of these six possibilities yields an operation-preserving, well defined function can now be verified by direct calculations. [Note that $\gcd(12, 30) = 6.$ This is not a coincidence!]  Can someone please explain why $\gcd(12,30)=6$ isn't a coincidence? I mean to ask why $\gcd(12,30)$ equals the number of homomorphisms from $\Bbb Z_{12}$ to $\Bbb Z_{30}$.

Although there are many attempts to the problem but I wasn't really able to understand those so I took some idea from examples and attempted it. Can someone just go through it please. My attempt: Let $\sigma:\mathbb{Z}_{m}\to \mathbb{Z}_{n}$. The kernel $\ker(\sigma)$ is a normal subgroup of $\mathbb{Z}_{m}$. So $\ker(\sigma)=\langle\frac{m}{d}\rangle$, where $d|m$. Now $\operatorname{im}(\sigma$) is a subgroup of $\mathbb{Z}_n$. So, now the order of the image should be $d$ so $d|n$. Now the number of homomorphisms when the kernel is of order $d$ will be $\sum_{d|m,d|n}\varphi(d)$. From here we can conclude that the no of homomorphisms should be $\gcd(m,n)$. Is this OK? Where am I making mistakes?


I have newly install edubuntu 14.04 LTS OS in my hp laptop. Now installing all the required software. But while playing mp3 files, it is informed that some plug in will be installed. But while try to install the same errors may occurs . I tried several times , but problem is same.   No mp3 file play with Rhythmbox. How is it minimized?

Yesterday I just installed the Ubuntu 12.04 for the first time, the problem is that I can't play and of the MP3 files that I have.    I get this error:       Required plugin could not be found Python (v2.7) requires to install plugins to play media files of the following type: MPEG-1 Layer 3 (MP3) decoder   Please help me so I can play the files. Thanks


Written with .   Let $f:[0,1] \to [0,\infty)$ be continuous. Suppose   $$ \int\limits_0^x f(t) dt \ge f(x), \text{ for all } x \in [0,1]$$   Then which of the following is true   A. No such function exists   B. There are infinitely many such functions   C. There is only one such function   D. There are exactly two such functions   See the end of the question for correct answer. I have been able to figure out that, perhaps $e^x$ is one such function so A is NOT the answer. Correct answer : - C Source - Tata Institute of Fundamental Research, Graduate School Admissions 2014

Let $$f\colon [0,1]\rightarrow [0, \infty )$$  be  continuous. Suppose that  $$\int_{0}^{x} f(t)\,\mathrm dt \ge {f(x)} \quad\text{for  all }x\in[0,1].$$  Then   $A.$ No  such  function  exists.  $B.$ There  are  infinitely  many  such  functions.  $C.$ There is  only  one  such  function  $D.$ There  are  exactly  two  functions.  Now  I  was  thinking,  since $\int_{0}^{x} f(t) dt$  is  the  area  under  the  graph  of  $f(t)$  from $0$  to  $x$ so it  can  be  easily  made  greater  than  the  value  of  $f(t)$  at  one  point, namely  $x$.  So  there   will  be  infinitely  many  such  functions  satisfying  this  condition.   Is  my  reasoning  correct or  not?  Thanks.


The minimize, maximize, and close buttons used to be in the upper left corner of windows, which I prefer because most of the content in the windows I use is on the left side, so it takes less mouse movement to get to the upper left corner.  Why was this changed? Is there a way to move those buttons to the upper left corner?

Is there a way to the switch gnome-shell window buttons to the left? I've gotten so used to them being on the left that them being on the right has thrown me way off.  (gnome shell has them defaulted to the right corner)


I haven't been able to infer whether latin characters are different from English alphabet or English alphabet are a subset of latin characters, as I came across several versions of latin.  Trying to find an answer as one of the driving rules of a foreign country says details on license should be in latin characters, so I am wondering whether my information printed in English qualifies for being in Latin?

I understand that the alphabet for the English language is not strictly English as languages such as French, Dutch and many more use the same alphabet, with few additions in other languages. Is Roman alphabet the common term to refer to this set of symbols for writing texts?


I tried to delete Ubuntu by doing what was found online:  Delete the partitions, then do an advanced startup into Command prompt to fix the MBR.  Oops, instead of the old GRUB Menu that comes up, allowing me to select Windows with the down arrow, it brings up GRUB command line. I am able to boot Windows by typing exit - this brings up the firmware settings allowing me to select Windows. But Ubuntu is still in the list, even though I deleted it.  What I want to do it get rid of GRUB so Windows can boot normally.  I have an Ubuntu installation disk but whenever I try to boot from it if brings up a unhelpful command prompt - initrampfs or something along those lines.  Also, I don't have a Windows Installation Disk.

I have absolutely no experience with Linux, and I desperately need to get my computer back up and running again with Windows.  How do I remove Ubuntu and reinstall Windows?    Editor's note: many of the answers are about removing Ubuntu from dual-boot but keeping Windows (which is a bit complicated), while other answers are about removing Ubuntu from single-boot (which is easy: basically just format the disk while installing Windows). The question as written is ambiguous between dual-boot or single-boot.


Background: To the best of my knowledge, most sexually-reproducing species of organism have two sexes, although there are also sexually-reproducing species of organism ( come to mind) which have only one sex. (Depending on one's definition of sex.)   are both sexually reproducing and apparently have more than two sexes. (Depending on one's definition of sex.)   with more than two biologically determined "gender morphs". It is even more debatable than in the case of fungi whether these morphs should be considered separate "sexes" or not, since their mating compatibility network is .  Question: Is there a theoretical maximum on the number of sexes a given species of organism can have?  Elaboration: There would also be a lot of different possibilities -- already with three sexes, one can imagine at least two different means by which sexual reproduction could occur -- any one of three combinations of two individuals from two distinct sexes (most likely in "rock-paper-scissors" fashion), or the combination of three individuals from all three distinct sexes.   How, for example, might either of these two scenarios be maladaptive compared to sexual reproduction of two individuals in species with two or fewer sexes?  I am asking about species with more than two sexes/mating types in general, not necessarily about situations where more than two sexes are involved in a single reproductive event. (Contrast with this .) I am also not restricting to animals, or even multi-cellular organisms, or even eukaryotes, since these restrictions might affect the answer. (Contrast with this .)  Note that  to the second related question implies that we should expect the mating compatibility network of  sexually reproducing organisms to be bipartite. But note that, as in the example of the side-blotched lizards, this doesn't necessarily preclude having more than two sexes, nor does it give a theoretical maximum to the number of possible sexes. And since I don't want to necessarily restrict to anisogamous sexually reproducing organisms (i.e. isogamous ones would also be fine), then that answer also does not provide a theoretical maximum for isogamous sexually reproducing organisms either.

Why, from the natural selection point of view, do only two sexes exist for animals?


I have installed VirtualBox 4.1.18 on Ubuntu 12.10 and I'm hosting Windows XP.  I want to share a folder between Ubuntu and Windows XP.  I have installed guest additions on the guest machine, but when I'm trying to access the shared folder, I can't find them anywhere.  So, where can I access those shared folders?

I have installed VirtualBox OSE on Ubuntu 11.04 and Windows XP pro as the virtual machine. Now I want to have a shared folder which can be accessed on both, my host Ubuntu machine, and my WinXP guest virtual machine.  How can I do that?


I'm trying to gasp the visual representation of $V/\ker f$ and in continuation the first isomorphism theorem in linear algebra.  My understanding is that, given the representation of a vector space $V,$ $V/\ker f$ is created by "erasing" all the dimensions $f$ maps to $0.$ That's where I get stuck. Any help would be appreciated  P.s The way I have linear algebra in mind is how it is presented in 3blue1brown's channel, if this is of any importance

I understand the concept of $\mathbb{Z}/n\mathbb{Z}$, but I am having a really hard time understanding how this concept of quotients applies to vector spaces. Suppose $V = \mathbb{F}[x]$ is a vector space and $U \le V$. What exactly does $V/U$ represent?


I want to post this problem in the suitable SE site. But, I don't know which is suitable.  My problem is:     In my office there is one iOS app which having 60 mb app size in   store. Now, am going to handle that project. Am believe that I can   reduce the size of the app by some optimizing. My question is, What   are the steps commonly followed by professional to optimize the   application by reduce the size?.   I only want help as for which Stack Exchange site I should post on.

There seems to be more than a few computer science/programming Stack Exchange networks (is that the correct term?). Stack Overflow, being the first, has by far the most users, questions, and answers.  What is the reasoning for creating the others, and are there clear guidelines for which kinds of questions should be posted? I can see a large amount of potential overflow, many cases of people not getting a good answer to their question, because the person who has the answer isn't browsing that particular network at the moment.  I understand that they were probably created for organizational purposes, but wouldn't it almost make more sense to just have them as categories under Stack Overflow, keep them separated but still connected, instead of making people have to create multiple 'account's, one for each network?  I am sure there was a very good reason to break them up, but as someone that is new to SE, it can be somewhat intimidating to decide which one to post in to ensure you get a good answer. For example, if I am a computer science student, my first instinct might to be to post in the computer science network, until I see that it literally has 1% of the users as the Stack Overflow network, which still seems to be for programming/computer science related questions.  So my second instinct would then to be to post it into the Stack Overflow site on the basis that I have a significantly higher chance of my question being seen and getting a good answer. Then I notice that there is also a 'programmers' network, and I don't even begin to know where that fits in. I, and I am assuming most people, will probably just post on Stack Overflow to be safe.  My question is, other than the short little description blurb of each one, is there a clear cut set of guidelines which what each network is intended for, what kinds of questions should go to each one, and is anything being done to encourage people to post in these newer, smaller (more specialized?) networks as opposed to just posting in big daddy Stack Overflow?  Now again, this is for computer science/programming/"why isn't this code doing what I want?" related questions, I am not saying that if I had a question about Linux or WordPress or something I would have the same confusion.


How can I uninstall steam from my ubuntu? I've tried the terminal step of sudo apt-get remove steam, but it tells me that it doesn't exist, and it does exist, I can see it, please help

Anyone know of a way to remove Steam from Ubuntu 12.04? Looked around the net but could not find an straight forward solution.    Thanks.


I don't know how to draw in Latex. Maybe someone has an idea how to make the diagram in the picture? Many thanks!  So here is my try:  \def\firstcircle{(0,0) circle (1.5cm)} \def\secondcircle{(0:2cm) circle (1.5cm)}  \begin{tikzpicture}     \draw[filled] \firstcircle node {$n_{ij}$}                   \secondcircle node {};     \node[anchor=south] at (current bounding box.north) {$t_i,  t_j $}; \end{tikzpicture}   Do someone know how to write $t_i$ on the left side and $t_j$ on the right side?

What I am up to is to write some exercises dealing with logical formulas for my students, like:     And the students should draw these formulas on . At the end of the lesson, I really would like to print the correct answer for them. I found a great resource on a forum thread at , which helped me a lot to make up some Venn diagrams with tikz, but have some problems with visualizing complements, like ~A.  A simple, modified version of the TeX file found on the forum linked above, can be seen below, which produces the following expression:    \documentclass{letter}   \usepackage{tikz}   \def\firstcircle{(90:1.75cm) circle (2.5cm)}   \def\secondcircle{(210:1.75cm) circle (2.5cm)}   \def\thirdcircle{(330:1.75cm) circle (2.5cm)}   \begin{document}     \begin{tikzpicture}       \begin{scope}     \clip \secondcircle;     \fill[cyan] \thirdcircle;       \end{scope}       \begin{scope}     \clip \firstcircle;     \fill[cyan] \thirdcircle;       \end{scope}       \draw \firstcircle node[text=black,above] {$A$};       \draw \secondcircle node [text=black,below left] {$B$};       \draw \thirdcircle node [text=black,below right] {$C$};     \end{tikzpicture}   \end{document}   Which looks like:    Could anyone please help me out plotting/defining some expressions dealing with complements? A nice example could be:    That should look like: (image from )    I do not insist on the red color :)  I would like to use the simplest possible solution, as I would like to mass generate the exercises with the help of . So any suggestion dealing with gnuplot, R or any other opensource packages is welcome. Thank you!    UPDATE (25/01/2011): added details based on answers.  Thank you @Leo Liu, you helped me a lot! I modified a bit the code you suggested to be able to color the area outside of the two circles also (in the H universe), but have no idea how to set a background to that polygon also. The code:  \begin{tikzpicture}[fill=gray] % left hand \scope \clip (-2,-2) rectangle (2,2)       (1,0) circle (1); \fill (0,0) circle (1); \endscope % right hand \scope \clip (-2,-2) rectangle (2,2)       (0,0) circle (1); \fill (1,0) circle (1); \endscope % outline \draw (0,0) circle (1) (0,1)  node [text=black,above] {$A$}       (1,0) circle (1) (1,1)  node [text=black,above] {$B$}       (-2,-2) rectangle (3,2) node [text=black,above] {$H$}; \end{tikzpicture}   And the image generated:    I will also look for even odd rule in the near future which does not make sense for me at the moment but looks really simple and promising!


I have a sensor at some arbitrary orientation (non-zero roll, yaw, pitch) given by quaternion $q_{0}$. I then pitch the sensor to orientation $q_{1}$. When I compute the relative rotation between the two as  $r = q_{1} q_{0}^{-1}$  Then I notice that the relative rotation has roll, pitch and yaw components. Why is this and how do I get a pure pitch from $r$?

Say I have a quaternion q which describes how to get from frame 0 to frame 1, and a quaternion r which describes how to get from frame 0 to frame 2. To get the "quaternion difference" between q and r, I do  $$ q_{d} = q^{-1} r $$ This is however in frame 1. How do I get the quaternion difference in frame 0?


We are using LS for reporting purpose. LS backup runs on primary every 15 minutes. On Secondary nightly restore via LS restore job is done daily at 10 PM.  While the nightly restore job is running, additional log backups are being taken and delivered.  Will the restore job restore the logs through the last one present when the job started? Or, will it keep restoring as long as there's another log to restore.  Let's say our log backups are taken at XX:05, XX:20, XX:35, and XX:50. Our restore job usually runs to, say, 6:00 AM. At that point, does it represent our primary database as it was at 9:50 PM (the last log taken before the restore job started), or as it was at 5:50 AM (because after it restored the 5:50 log, it didn't find another, so it quit)?  Naturally, our users want to know for their queries; whether the data reflects 10PM or 6AM can make a big difference.

I have set up log shipping between 2 SQL Servers (SQL Server 2008 and SQL Server 2012).  At first I took a full backup of the first one and restored it on the other one and then I set up the log shipping. The database's first backup-restore took a few hours and below are my questions that I need to understand :   How does the log shipping process know from when to start the logs it is shipping?  Does it start from when the last backup-restore process happened or from the moment the log shipping itself is set ? Can I be sure that no information was lost in these few hours ?


Android stores some application data in non-volatile memory that can be accessed without needing root privileges. Android stores other application data in non-volatile memory that can only be accessed with root privileges. What is the correct terminology to use to describe each of those storage areas, and what determines in which location an app stores its data?

Could you list all possible directories where Android apps may store data, providing description what kind of data are stored in each directory?


I am getting userId from database using HQL in my DAO class.But when itried to set it in session , it is giving null pointer exception . here is the code in DAO class.  @Repository("loginDAO") public class LoginDAOImpl implements LoginDAO{      @Resource(name="sessionFactory")     protected SessionFactory sessionFactory;     HttpServletRequest request;     public void setSessionFactory(SessionFactory sessionFactory) {         this.sessionFactory = sessionFactory;     } public Session getSession(){     return sessionFactory.openSession(); }     public boolean checkLogin(String userName, String userPassword) {          Session session=sessionFactory.openSession();         boolean userExist=false;         String sql_query="from Users as o where o.userName=? and o.userPassword=?" ;         Query query=session.createQuery(sql_query);         query.setParameter(0, userName);         query.setParameter(1, userPassword);         List list=query.list();          if((list.size()>0) && (list!=null)){             userExist=true;             //TO get the user id to insert into orders table              Users user=null;             user=(Users) query.list().get(0);             Long id=user.getId();             System.out.println("Id is "+ id);             **//This is giving Null Pointer             request.getSession().setAttribute("id", id);**               }         session.close();     if(userExist==false){System.out.println("user name or password wrong");}         return userExist;     }  }   i am sure that id has value. Thanks in advance.

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


Most of the time (but not always) when I post a comment it is only relevant for a short time - a day or two.  For example a comment might say "Please post some code." A reply might be "Thanks, I've added code to the question."  From this point on, both comments are nothing more than a distraction from the question itself, and from any more helpful comments which appear under the question.  If my comment received a few votes, it will appear in the short list of comments and possibly drown more valuable content.  If I'm diligent, I might come back and delete my comment, but then we have a hole in the conversation which can be even more of a distraction. Ultimately eventually the responder should come back and delete their response, but this is unlikely to happen if the responder is a passer-by and has no ongoing interest in the question.  The votes on answers to  indicate that the community preference is to delete your own comments when they become irrelevant, but in practice I don't think this happens often, and when it does, it can break comment continuity.  I'd love to see a mechanism whereby I could post a comment, and it would be deleted after a day or two. Users replying to the comment could use the same mechanism.

Meanwhile, in August 2009  as reason for comment flagging, and the comment flags show in the 10k tools. And  is on its way. Hence: I don't care for this request myself anymore. An explicit [status-declined] would be fine.    What about being able to set comments to auto-expire? Or, alternatively, set a comment to be removable by the author of the question or answer one comments on?  This way the communities would allow for some personal or funny comments (even like "Thanks") without those comments littering the sites forever. Or, when the original author is allowed to clean up, then comments that have been taken care of by editing the question or answer, could be removed.  Why?  As, , there's no way to send a personal message to other members, I find myself abusing the comments like some "poor man's private messaging system". I try to refrain from things like "Thank you", but sometimes I do want to point out something to someone. After a while (hours, days) I then  to remove them (hoping that no-one actually replied to them with another comment, like "Thanks, fixed it").  Like :    (I don't find this feature request very important (at all), I am quite impressed by what's been given us already, and I doubt there's a way to implement it without making things too confusing. Maybe I'm just trying too hard to keep things tidy and clean. Still, I wanted to share it, just in case someone comes up with something very clever...)


I have Ubuntu 16.04 and after enabling Secure Boot Nvidia drivers stops loading. Same is with VirtualBox kernel modules. When I try to force loading kernel  # modprobe nvidia_361 modprobe: ERROR: could not insert 'nvidia_361': Required key not available sign module   I read that from Ubuntu 16.04 version kernel prevents loading unsigned modules. Is there any way to turn on Secure Boot and use proprietary kernel modules, without compiling own kernel?

I have just updated my system from 15.10 to 16.04 via sudo do-release-upgrade. During this process, it displayed a screen with the following message:  Your system has UEFI Secure Boot enabled. UEFI Secure Boot is not compatible with the use of third-party drivers. (...) Ubuntu will still be able to boot on your system but these third-party drivers will not be available for your hardware. Disable UEFI Secure Boot? (yes | no)  Since the only third-party drivers that I am using are the NVIDIA graphics drivers, and since they have been working fine with Ubuntu 15.10 and Secure Boot enabled, I chose the "no" option here. I don't see why I should disable this for no good reason, and I assumed I can just reinstall the third-party driver via the system settings GUI after the update. Alas, no. Upon reboot, my login screen appeared in very low resolution. When trying to log in it immediately throws me back to the login screen. I have tried the following to fix the situation: sudo apt-get purge nvidia* sudo reboot  This leads to a purple screen and no reaction to Ctrl-Alt-F1. Logging in via SSH, I then did: sudo apt-get install nvidia-current sudo reboot  which again brings me the former scenario, with a very low-res login screen, and no way to log on. This is a pretty bad upgrade experience. Did anyone else have this, and what can I do to fix this? (while keeping UEFI Secure Boot enabled) Thanks.


I notice in  that one answerer used double parentheses where the other used square brackets:  if (( $(fileSize FILE1.txt) != $(fileSize FILE2.txt) )); then   ...  if [ $(fileSize FILE1.txt) != $(fileSize FILE2.txt) ]; then   I haven't seen double parentheses before - and googling doesn't help. Do they have exactly the same meaning? Any difference in portability? Reason to prefer one over the other?

I am a little bit confused on what do these operators do differently when used in bash (brackets, double brackets, parenthesis and double parenthesis).  [[ , [ , ( , ((   I have seen people use them on if statements like this :  if [[condition]]  if [condition]  if ((condition))  if (condition)


I'm taking a Elliptic Curves class as an undergraduate math major. We are using "Ellpitic Curves" by  Lawrence C. Washington.  I'm struggling and would like some other resources I could use to help supplement my study. I ordered "Rational Points on Elliptic Curves" by Silverman and Tate.  Ive done some searching but most of the recommendations ive found are more advanced and I think would be over my head. Is there anything else I could potentially get something out of? Many thanks

I just finished reading Silverman and Tate's Rational Points on Elliptic Curves and thought it was very interesting.   Could any of you point me to some more references (ex. books, articles) on elliptic curves? Someone suggested Silverman's Arithmetic of Elliptic Curves, but I don't have any background in algebraic geometry, so I'm not sure how well I would understand it (going to start studying commutative algebra - does that help?). Thank you!


I completely removed Windows 7 from my computer and installed a full version of Ubuntu on i.e no partition. I just got my Windows recovery disk and driver disk in the mail and I would like to remove Linux completely and re-install Windows.  Problem is the recovery disk will not boot automatically upon starting up.   Any suggestions?

I have absolutely no experience with Linux, and I desperately need to get my computer back up and running again with Windows.  How do I remove Ubuntu and reinstall Windows?    Editor's note: many of the answers are about removing Ubuntu from dual-boot but keeping Windows (which is a bit complicated), while other answers are about removing Ubuntu from single-boot (which is easy: basically just format the disk while installing Windows). The question as written is ambiguous between dual-boot or single-boot.


I am storing non-English characters in a MySQL data base for example: الجزائر  Unfortunately these characters get stored in my database and get displayed as questions marks like this:     ??????   I am using CodeIgniter active record as my Database abstraction layer and I have my database collation set as utf8_unicode_ci.  How can I store the characters properly using MySQL?

I'm setting up a new server and want to support UTF-8 fully in my web application. I have tried this in the past on existing servers and always seem to end up having to fall back to ISO-8859-1.  Where exactly do I need to set the encoding/charsets? I'm aware that I need to configure Apache, MySQL, and PHP to do this — is there some standard checklist I can follow, or perhaps troubleshoot where the mismatches occur?  This is for a new Linux server, running MySQL 5, PHP, 5 and Apache 2.


From what I've read I know that FHE requires "circuits" to construct functions and gates to operate on the FHE encrypted data. I've also read that these circuits are constructed from just addition, multiplication, and mixed multiplication. How does this work? How, only using those operations, can we construct a NAND gate for example?

I am actually trying to study homomorphic encryption (on lattices) but I'm facing a problem. Every paper that I have read so far talk about writing the function to evaluate on ciphertexts as a circuit, either boolean or arithmetic according to our scheme if I understood this part well. My problem is that I couldn't find explicit documentation on how to turn a function to a circuit.   Especially, in circuits, we can't have loops or conditions and I would have liked to apply my FHE scheme to the weights of a neural network, but I'm kinda stuck on how to represent the activation function (I think I would use the sigmoid, that can be represented with its Taylor expansion) and simple gradient descent.  Does anyone have a clue or a good paper to help me understand how to write such functions to circuits?


I tried a lot to take portrait pictures with blur background using my FujiFilm HS10 but haven't succeeded yet. I use f2.8 but still cannot get the effect. Can any of the experts give me any suggestion.

I have a compact digital camera, and in macro mode I can manage to achieve a blurred background, if the background is far enough away. Can this be done when taking non-macro pictures, and if not, is there a way to simulate it?  When I shoot portraits with my brother's DSLR, it is quite easy to fade out the background. But with my point and shoot camera, I haven't been able to take such photos.   I choose a large aperture for my camera but it still doesn't work. I know that standing further and zooming will result in a smaller depth of field, but it doesn't seem to be enough to get the really nice "bokeh" look. I've tried macro mode, and that will work if the subject is close enough and the background far enough away, but how can it be done with non-macro pictures?   Why are DSLR cameras are so much better in this area? What are the general recommendations to do this using a compact or super-zoom camera?


How to compute the following limit,   $\displaystyle \lim\limits_{n \to \infty} \int_0^1 \int_0^1 \ldots \int_0^1 \sin \bigg(\frac{x_1+x_2+\ldots+x_n}{n}\bigg)\,dx_1 \,dx_2 \ldots \,dx_n$ ?  I will greatly appreciate it if a solution only uses analysis. Thank you.

Let $f$ be a continuous function on the unit interval $[0,1]$. Show that $$\lim_{n\to\infty}\int_{0}^{1}\cdots\int_0^1\int_{0}^{1}f\left(\dfrac{x_{1}+x_{2}+\cdots+x_{n}}{n}\right)dx_{1}dx_{2}\cdots dx_{n}=f\left(\dfrac{1}{2}\right)$$  This problem is from Selected Problems in Real Analysis. But the author doesn't include a solution. Maybe there is a method for this sort of problem?  Maybe we can use this: $$\int_0^1\cdots\int_{0}^{1}\int_{0}^{1}\dfrac{x_{1}+x_{2}+\cdots+x_{n}}{n}dx_{1}dx_{2}\cdots dx_{n}=\dfrac{1}{2}?$$  I also found a similar problem in .


I am trying to evaluate $$\int_{-\infty}^{\infty} \frac{\sin(x)^2}{x^2} dx $$ Would a contour work? I have tried using a contour but had no success. Thanks.  Edit: About 5 minutes after posting this question I suddenly realised how to solve it. Therefore, sorry about that. But thanks for all the answers anyways.

I am looking for a short proof that $$\int_0^\infty \left(\frac{\sin x}{x}\right)^2 \mathrm dx=\frac{\pi}{2}.$$ What do you think?  It is kind of amazing that $$\int_0^\infty \frac{\sin x}{x} \mathrm dx$$ is also $\frac{\pi}{2}.$ Many proofs of this latter one are already in this .


Let $$ \frac{1}{1} +\frac{1}{2} +\frac{1}{3}+...+\frac{1}{p-1} =\frac{a}{b}$$ with $(a,b)=1$   and $p$ a prime number, (   $p>3$ ). Show that $ p^2 |a $.   I can't solve it.

Let $p\gt 3$, be a prime number and  $1+\frac{1}{2} +\frac{1}{3} +...+\frac{1}{p-1} =\frac{a}{b}$ when $a,b\in \mathbb N$ and $gcd(a,b)=1$.      prove that $p^2|a$.   I proved that $p|a$, but I cant prove $p^2|a$, and my idea is as follow:  By multiplying $(p-1)!$, we get:  $(p-1)!+\frac{(p-1)!}{2}+...+\frac{(p-1)!}{p-2}+\frac{(p-1)!}{p-1}=\frac{a(p-1)!}{b}$ $\,\,\,\,$ $(1)$  So, the number $\frac{a(p-1)!}{b}$ should be integer. consider the left hand of the sum of $(1)$ in the ring $Z_p$. Since in $Z_p$ the inverses are unique and what we have is indeed a rearrangement of all the congruence classes $mod\,p$. So:  $(p-1)!+\frac{(p-1)!}{2}+...+\frac{(p-1)!}{p-2}+\frac{(p-1)!}{p-1}\equiv 1+2+...+p-1\equiv \frac{p(p-1)}{2}\equiv 0$$\,\,\pmod p$. And from here, $p|\frac{a(p-1)!}{b}$, and that's mean: $p|a$.   I tried to prove the statement by considering the ring $Z_{p^2}$ but I get nothing.  Thanks in advance…


I am a beginner on calculating correlations and I would like to ask possibly a very simple question.  If I have two variables that I want to perform correlation on, and those variable are of unequal size, does this affect my correlation result?  Thanks

What is covariance in plain language and how is it linked to the terms dependence, correlation and variance-covariance structure with respect to repeated-measures designs?


I recently switched compilation of my tex document from pdflatex to xetex for reasons of typesetting occasional arabic text (the rest of document though is almost entirely in English).  However now I have the problem of ``misaligned'' equation parenthesis both next to the equation and in \eqrefs as visible here:   I switched to using fontspec, unicode-math and polyglossia packages to be able to compile with xetex.  I even tried redefining the format of the equation brackets, but nothing changed. Any Ideas what is happening here?  My document preamble looks like this:   PACKAGES \usepackage{hyperref} \usepackage[round]{natbib} \usepackage{setspace} \usepackage{latexsym} \usepackage{url} \usepackage{mathtools} \usepackage{unicode-math} \usepackage{booktabs} \usepackage{tikz} \usepackage{xcolor} \usepackage{graphicx} \usepackage[headheight=13.6pt]{geometry} \usepackage{multirow} \usepackage{verbatim}% \usepackage{subcaption} \usepackage{epigraph} \setlength\epigraphwidth{0.5\textwidth} \setlength\epigraphrule{0.5pt} \renewcommand{\epigraphsize}{\small\itshape} \renewcommand{\textflush}{flushepinormal} % flushright \usepackage{nomencl} \usepackage{color} \usepackage{algpseudocode} \usepackage{algorithm} \usepackage{algorithmicx} \usepackage{eso-pic} \usepackage{fancyhdr} \usepackage[norule]{footmisc} % no footnote rule [better if we use footrulewidth] \usepackage{gnuplot-lua-tikz}  \usepackage{polyglossia} \setdefaultlanguage[variant=american]{english} \setotherlanguage{german} \setotherlanguage{arabic} % FONT with xetex: \usepackage{fontspec} \fontspec{Helvetica Neue} \newfontfamily{\arabicfont}{Scheherazade}  \renewcommand{\headrulewidth}{0.2pt} \renewcommand{\footrulewidth}{0.2pt} \fancyhead{} \fancyhead[RO,LE]{\leftmark} \fancyfoot{} \fancyfoot[LE,RO]{\thepage} \pagestyle{fancy} \onehalfspacing  % SOME MATH (RE)NEWCOMMANDS [...]

I am compiling the following MWE using XeLatex within TeXnicCenter and get a garbled equation number:  \documentclass{article} \usepackage{amsmath} \usepackage{polyglossia} \setmainlanguage{hebrew} \newfontfamily{\hebrewfont}{Arial}  \begin{document} \begin{equation}\label{eq:1} 2+2=4. \end{equation} \end{document}      What is going on here?


We had an episode in combat tonight that I was not sure how to adjudicate. A player character (PC1) with a whip was 10 feet away from an enemy. In between PC1 and the enemy was another player character (PC2) that was prone. On the far side of the enemy was a third player character (PC3). Does PC1 have advantage due to flanking in attacking the enemy with the whip? Why or why not? If PC2 stands, can PC1 still attack the enemy using the whip, and would this affect advantage in any way?

The Variant: Flanking rules in the DMG (page 251) require adjacency, but is the intent that the Enemy has combatants on opposite sides and thus someone with Reach (and using the reach) could still flank even if not directly adjacent?  Looking for both RAW as well as Intent of the flanking rule.


My grandfather has been working on writing a book. All was going well until he called me to state that he has somehow messed up the file.  If you look at the image below, he has somehow added something to the right-hand side of all pages. Is it a table or something?    Does anyone know how to rectify this issue?  For anyone that would like to see the file itself, you can download it here:

I have a weird problem. I don’t know what I have done.  It have a blank page next to my page which like a extend but O cant insert any text. It look like a margin but it not. Just see my demo image, you will see the ruler in my office.     When you print it, it also have it too.   I try to copy and pasted it in new document by all of type paste. But it still have this.  It doesn’t have it when you have a new document or other file.  When I try to open this document from a zip file, it still occur.  Any idea?


When booting Ubuntu, I get this message:    Is it possible to change the text Ubuntu 12.04 to Loading, please wait. ?

With regards to Plymouth --  Are there alternative boot screens available?  What's the easiest way to change the boot screen?


I'm a recent graduate EE student and this is my attempt to gain experience and strengthen my resume so I'm eager to figure this out. I'm designing a dual channel floating output bench power supply that will supply 0-32V @ 5A with CC and CV operation modes. I intend on this being a long-term solution so I'm aiming for good power efficiency with a clean output signal. The safety and protection features I plan on including are a microcontroller based emergency thermal shutdown, reverse current protection, overvoltage protection, and of course a fuse. At first I intended on creating it using IC voltage regulators: switching pre-regulation + second stage linear regulation. My plan was that the switching output would match the linear output to minimize power loss in the linear regulator. The problems with this are wildly varying CC under load and difficulty finding regulators with the desired specifications. Having decided to check out the few schematics for commercial bench power supplies that I could find, I noticed that they don't seem to use IC voltage regulators at all! This leads me to wonder if it would be easier to create the linear regulator portion with discrete components instead of ICs. I've been having trouble finding resources which discuss the best methods of PSU design so I wanted to come here for a second opinion. Which method do you think is the best for me to create my desired product? Switching + linear, switching + discrete or something else?  The post here  poses the same question but it doesn't look like there was an answer to the actual question. I looked at it and it seems like they just discussed the safety of using a negative reference voltage.

After using the simple LM317 on breadboard variable power supply for a while, a need for a more rugged and reliable bench power supply has arose.    Short on money, i decided to build it as many other amateurs like me did. The thing is that, for my current needs i don't need a giant digitally controlled multi-channel 500 watt beast or something like that.  Instead what i really want is a low wattage positive and negative low voltage ouput -12v-0v-12v for example. However i really like that my power supply to be safe, reliable and fool-proof as far as possible. So after searching the web here and there, i found many designs that from my point of view fell in one of two divisions:-   Ones that use discrete op-amps and transistors. And ones that use integrated voltage regulators.   So -at least for me- i think that the ones with discrete op-amps and transistors are more prone to malfunctions and issues compared to the integrated ones with all of their internal over current and thermal protection circuits which would need to be discretely implemented in the bench power supplies that utilize discrete op-amps, however those designs have the advantage of ease of customization and more importantly that it is easier to have 0V output compared to 1.2V in integrated voltage regulator ones.    So i like advice to help me choose between circuits that utilize discrete op-amps like this circuit for example:-  Or ones that use integrated voltage regulators with their intrinsic robustness and low form factor.    Also as a side but related question i have seen many designs on the web that utilize negative voltage fed to the adjust or like pins to achieve 0V output from integrated voltage regulators like this single positive power supply:-     Or a positive and negative channels power supply that i really like its design because of simplicity (not because of laziness but to avoid the drawbacks that may come with complex designs especially when implemented by an amateur like me):- And the question is      Is it wrong or a system safety and reliability lowering act to feed negative voltage to adjust pin for LM317 for example?     I ask this question because the datasheet clearly states that the working output range is 1.2V-37V for LM317 for example, also no similar circuit is mentioned in the Typical Applications section except for the following one:- And even in that circuit, however the adjust pin is tied to the negative rail, it does't regulate during this interval instead it is shut until the next half wave at least that what i understand.    So at last to sum it up which alternative is best suited for my needs, its pros and cons and suggested circuits if possible.


Why was the Trade Federation so interested in Naboo? Why did they blocked Naboo especially since it's a small planet and apparently unimportant.

I don't understand why the Republic was so interested in the planet Naboo; it's a small planet in a big Galaxy. Queen Amidala didn't agree with the taxation of trade routes to outlying star systems, it's clear, but the Republic wants to have access to these planets uncontended. Why is Naboo so important to the development of the Republic?


I have an array object below. I want to remove secondItem and fourthItem. I tried doing this but no luck      var removed = item.splice(1)   How can I remove secondItem and fourthItem at the same time?      items:[]      0:       firstItem: "testing"       secondItem: "record"       thirdItem: 30       fourthItem: "40"     1:       firstItem: "testing2"       secondItem: "record2"       thirdItem: 33       fourthItem: 44   It should look like this after removal         0:           firstItem: "testing"           thirdItem: 30         1:           firstItem: "testing2"           thirdItem: 33

Say I create an object as follows: let myObject = {   "ircEvent": "PRIVMSG",   "method": "newURI",   "regex": "^http://.*" };  How should I remove the property regex to end up with new myObject as follows? let myObject = {   "ircEvent": "PRIVMSG",   "method": "newURI" };


This is my first question on stackoverflow and I hope my problem description is enough precise. I would like to add a class to some elements and then use those elements to trigger. But the following code (just an example) doesn't work. In the inspector I can see the class, but there is no reaction on click. Is there an easy solution?       $(".T").click(function(){     $(this).addClass("current"); });  $(".current").click(function(){     $("#Deko").hide(); });

I have a bit of code where I am looping through all the select boxes on a page and binding a .hover event to them to do a bit of twiddling with their width on mouse on/off.  This happens on page ready and works just fine.  The problem I have is that any select boxes I add via Ajax or DOM after the initial loop won't have the event bound.  I have found this plugin (), but before I add another 5k to my pages with a plugin, I want to see if anyone knows a way to do this, either with jQuery directly or by another option.


I filled out this survey to win a something. Then realized it was a scam. Felt really dumb. Anyhow, I gave my email, name, phone number and address. What can the do with the information I gave them?

Updated question because old one was embarassing: I saw a spam email from "PayPal" and I didn't realize that it was a phishing attempt. I gave the phishing site my name, telephone number, and email. What could he do with them?  Old question: Well, I saw a spam email, but I didn't realize that it's really a scam at first. I gave him my telephone number, address, and name. What would he do with them? Could he ruin ALL of my reputation with it?


Sometimes when I fry the potatoes for french fries, the potatoes stick to the pan which irritates me and I can't separate the potatoes because if I use the spoon a lot, it will cut the fries into pieces. Due to the scarcity of resources, I can't manage to buy a non-sticky pen. Kindly recommend me some solution.

I've tried frying potatoes (generally cubed small, like 1/4") in my cast iron pan but they frequently stick very badly. Badly enough so I've got to resort to scraping with a metal spatula. The pan is not like 50 years old and perfectly well-seasoned or anything, but I have no trouble with any other kind of food sticking.  They generally come out ok but just not very brown and crispy, as you would like fried potatoes to be.  Anyone have any advice? Temperature ranges to try to improve the results?


I have to iterate through property of one object base type that i get from database and i have to check if any property i snull. Here is some code:   req = "select * from Ga_Periodes_Absence";  var resultat = Session.CreateSQLQuery(req).List<object>();  foreach (var elem in resultat)  {      int i = 0;       i++;  }   resultat contains list of objects that I want to check if property of any of them is null. Any help please.

I have a class.  Public Class Foo     Private _Name As String     Public Property Name() As String         Get             Return _Name         End Get         Set(ByVal value As String)             _Name = value         End Set     End Property      Private _Age As String     Public Property Age() As String         Get             Return _Age         End Get         Set(ByVal value As String)             _Age = value         End Set     End Property      Private _ContactNumber As String     Public Property ContactNumber() As String         Get             Return _ContactNumber         End Get         Set(ByVal value As String)             _ContactNumber = value         End Set     End Property   End Class   I want to loop through the properties of the above class. eg;  Public Sub DisplayAll(ByVal Someobject As Foo)     For Each _Property As something In Someobject.Properties         Console.WriteLine(_Property.Name & "=" & _Property.value)     Next End Sub


I found this exercise in Matsumura, Commutative Ring Theory, (Exercise 7.2).     If $A\subset B$ are integral domains with the same field of fractions and $B$ is faithfully flat over $A$, then $A=B$.   Can anyone give me a proof for this statement or tell me where to find it?

Let $A \subseteq B$ be integral domains with the same field of fractions. Assume that $A \to B$ is faithfully flat. Why do we have $A=B$?  This is an exercise in Matsumura's book. Here is my idea: If $b \in B$, consider $I = \{a \in A : ab \in A\}$. This is an ideal of $A$. By asumption $I \neq 0$, and our goal is to show that $I=A$. It suffices to prove $IB=B$. But how can we achieve this?


This question was asked , but I think there will not be an answer, so let me recopy the question on Mathoverflow.  In the book of S. Kobayashi, hyperbolic complex spaces, there is the lemma (3.A.3) on the page 153, section Royden's extension lemma, whose statement is     Every exact sequence of holomorphic vector bundles $0\to E'\to E\to E''\to 0$ on a Stein manifold splits.   The author's argument is that the obstruction to a splitting lies in $H^1(X,\mathrm{Hom}(E'',E'))$ which is zero since $X$ is a Stein manifold.  Could someone explain what obstruction means and why it lies in this cohomology group? Thank you very much.


How can I unlock the screen lock in Android Lollipop without losing data?  I have forgotten the pattern.

I have an Android device which is running Android 4.0.3 (or something like that).  My little brother decided to try and guess my lock screen pattern the other day, and ended up locking me out.   I have since been unable to log back in to the tablet using my Google Account details. I provided the correct login details, however it says they are incorrect. Could this be connected to the fact I have no internet connection?  I have no internet connection as the device is WiFi only, and the WiFi is currently turned off. I cannot turn it on, as I am locked out.  How can I log back into my tablet without wiping the user data?


Memorex USB 8GB drive that shows 0 B available. I don't know if it's mechanically broken or something is wrong with it.  Even disk part shows it as (See Disk 2)    Any ideas?  EDIT: The bios shows it as 2231 PRAM...

I have a 32 GB USB stick. I was in Mac (VMWare) putting some stuff on. Then accidentally removed the drive. I put it back in, and wanted to format it. Using disk utility, I chose 1 partition, it automatically filled in 312 GB and I just clicked format or whatever. It didn't take long, then I could see the progress bar hanging at "Waiting for device to reconnect". Nothing happened for a while so I ejected it. Now comes the problem:  In Disk Utility (Mac): No sign of the USB drive.  In Paragon Partition Manager (Windows): No sign of the USB drive.  In Disk Manager (Windows): I can see that it's there. But it says: Disk 1 Removable (D:) No Media. When I right click it, I can only assign drive letters to it. No way to format.  In diskpart (Windows): diskpart list will show me the following: Disk 1, Status: No Media, Total Size: 0 B. When I eject the drive, the disk 1 will disappear. So I know that it's this drive. If I type clean, it will say that "There is no media in the device".  In HDD Low Level Format Tool 4.25 (Windows): Doesn't detect it at all.  In Device Manager (Windows): It is detected as USB Mass Storage Device.  In Gparted (Linux): Doesn't detect it.  In HP USB Disk Storage Format Tool 2.1.8 (Windows): It detects device as: "GENERIC USB Mass Storage 1.00 (0 MB) (D:)". When I press Start it gives me this error: "There is no media in the specified device"  In BIOS: Detected  In Spinrite (Live Boot): Doesn't detect it  Any help is appreciated.


Can I generate in C# auto-property with default value?  public class MyClass {      MyClass()      {          Reason = "my reason";      }       public string Reason{ get; set; } }

How do you give a C# auto-property an initial value?  I either use the constructor, or revert to the old syntax.    Using the Constructor:  class Person  {     public Person()     {         Name = "Initial Name";     }     public string Name { get; set; } }   Using normal property syntax  (with an initial value)  private string name = "Initial Name"; public string Name  {     get      {         return name;     }     set     {         name = value;     } }   Is there a better way?


I want to take photos of my son who will be dancing at a theatre. The lighting will be changing according to the scene. I need help with the setting in my camera. What settings should i use? I have a canon 70D with 18-135mm kit lens and external flash. Any help appreciated.

I am taking pictures of performers on stage.  Sometimes they have tungsten lighting, but then they can also have funky color lights of all sorts go off at them.  Here is a Flickr Album of the pictures I recently took:   I'm shooting with a Nikon D7000 on Auto, No flash, high speed multi shot, RAW mode.  I took about 1000 pictures, and about 15 of them were worth editing.  I figured that a monopod would be really helpful in keeping the camera steadier (most of my shots were blurry), and keeping me mobile to change angles.  I got a monopod, and I will use it at the next event.  I did see , but it is more about a point-and-shoot than a DSLR  What can I do to improve the quality of pictures that I take?


I have an old Ubuntu 14.04 computer and I want to give it away. I create a new administrator account and using this new account I deleted my old account and the entire content of this account. Is this a safe way to delete all the content of the computer ou Should I do an extra procedure?

I'm planning on selling a USB external hard drive that currently contains an old Ubuntu installation with stored passwords and banking information.  How can I securely erase the drive before selling it?


So I defrosted the sealed cooked unagi eel from the store like a week ago and left it in the refrigerator. It says I should keep it frozen. How long do you think it's safe to eat if I kept it in the refrigerator and it's not opened yet?

How do I know if a given food or ingredient I have is still good, or if I should discard it?  How can I best preserve a food or ingredient?     This broad question is intended as a "general reference" question to quickly answer many how long will food keep for? questions. Please feel free to edit this question to expand and clarify as needed.


I am learning appium and trying to call an object from one class to another and facing null pointer exception. Below is my code :  public class TestCommons {      public AndroidDriver driver;      public void setUp() {          DesiredCapabilities capabilities = new DesiredCapabilities();         capabilities.setCapability("deviceName", "MotoE");         File file = new File("D:/APK1/com.vector.guru99.apk");         capabilities.setCapability("app", file);          try {             driver = new AndroidDriver(new URL("http://127.0.0.1:4723/wd/hub"), capabilities);             driver.manage().timeouts().implicitlyWait(30, TimeUnit.SECONDS);          } catch (MalformedURLException e) {             e.printStackTrace();         }     }      public void tearDown() {          driver.closeApp();     } }   I wanted to use above class i.e "TestCommons" in other class. I want to use driver object.  Second class is below :  public class Day03 extends TestCommons {      TestCommons commons = new TestCommons();      @BeforeClass     public void beforeClass() {         commons.setUp();      }      @Test(enabled = true)     public void f() {          if (driver.findElement(By.id("com.vector.guru99:id/action_quiz")).isDisplayed()) {             System.out.println("Quiz is displayed");             driver.findElement(By.id("com.vector.guru99:id/action_quiz")).click();             System.out.println("quiz is click");          }     }      @AfterClass(enabled = true)     public void afterClass() {         commons.tearDown();     }  }   Getting null pointer in second program @:  if(driver.findElement(By.id("com.vector.guru99:id/action_quiz")).isDisplayed();   Can anyone clarify me please.

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


I'm trying to install the minimal Ubuntu installation on a USB drive (complete install, not a live boot).  After installation, however, when I try to boot from the USB, I get "Missing operating system". I think there might be a problem with grub, but I don't know how to fix it.  I've done an install to an USB before which messed up the main grub file, so I don't want to do that. This is the output of fdisk -l pertaining to the USB drive: Disk /dev/sdc: 4027 MB, 4027580416 bytes 124 heads, 62 sectors/track, 1023 cylinders, total 7866368 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x73a571aa  Device Boot      Start         End      Blocks   Id  System /dev/sdc1            2048     7616511     3807232   83  Linux /dev/sdc2         7618558     7864319      122881    5  Extended /dev/sdc5         7618560     7864319      122880   82  Linux swap / Solaris  Also, my boot partition may not be labeled as bootable, based on this output.  Please help! Update I followed Terrance's suggestion, so /dev/sdc1 is now labeled as a boot partition.  However, the drive still won't boot. I am not asking for how to install Ubuntu to a USB drive, I'm asking for help fixing a USB which I've already installed Ubuntu to. Update Terrance's updated answer solved it for me.  Just a note, to get it working on my USB I had to create a /boot/extlinux/syslinux.cfg file containing: PROMPT 0 TIMEOUT 50 DEFAULT arch  LABEL arch         LINUX ../vmlinuz-4.4.0-45-generic         APPEND root=UUID=[The USB UUID]         INITRD ../initrd.img-4.4.0-45-generic

If you are hurrying to reply, System → Administration → StartUp Disk Creator -- no, that's not what I'm talking about.   I want to try Ubuntu 11.04's Unity without touching my existing Ubuntu install.  To do this, I need to install the nVidia drivers first (sigh).  To do this, I need changes to persist a reboot.  To do this, I need to really install Ubuntu on a USB key.  How do you do that?    What I tried   I tried to make a USB key from , then boot from it, then choose "Install Ubuntu." The installer refused to install to the installation media itself. I tried, from my installed copy of Ubuntu:  sudo kvm /dev/sdb --cdrom .cache/testdrive/iso/ubuntu_natty-desktop-i386.iso   ...but the installer didn't detect the disk properly.


In this screenshot:    I see: 1. The current site I am on 2. My top 5 sites 3. A search bar to locate other sites.  All of this is really good - but I'm not sure I fully understand the impact of the "Stack Overflow" indented under Meta Stack Overflow.  Obviously, the relationship between a meta and main site is logical - but how is this intended to operate when looking at a non-meta site?  Will the order still exist and simply be reversed, will it be empty, or is there a set of business rules to define what will be there?

Well everything is in the title. Why is StackOverflow showing up with a indent and why don't I see my rep next to it like on the other websites.


I don't actually know what's up here, but I am writing server-client application and client sends a string to the server. I need to send the string "x" to the server, so it starts running code1, but when I do it, server runs code3. The funniest thing is System.out.println(x); prints "a" in the console.  Here is a fragment of server code(runs on win7, javac compiler):  sInput = new ObjectInputStream(socket.getInputStream()); sOutput = new ObjectOutputStream(socket.getOutputStream());  String x = (String) sInput.readObject(); System.out.println(x);  if (x == "a") {    /*      * code1     */ } else if (x == "b") {    /*      * code2     */ } else {    /*      * code3     */ }   And this is what client does(runs osx, javac compiler):  sInput = new ObjectInputStream(socket.getInputStream()); sOutput = new ObjectOutputStream(socket.getOutputStream());  String x = "a"; sOutput.writeObject(x);   How should I sort it out?  P.S. I know about exception declaration, they are removed to make the code shorter.

I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?


I know that the Schwarzschild radius is given by  $$r=\frac{2GM}{c^{2}}.$$  but I never seen a derivation for this equation.  1- Does anyone know how to derive this equation from general relativity?  2- If we had the metric $$ds^2=−A(r)dt^2+\frac{dr^2}{B(r)}+r^2(dθ^2+\sin^2{θ}dϕ^2)$$ , where $A(r)≠(1−\frac{2GM}{c^2r})$ and $B(r)≠(1−\frac{2GM}{c^{2}r})$, then what is the event horizon?

I know that the Schwarzschild radius is given by  $$r~=~\frac{2GM}{c^{2}}.\tag{1}$$  However, If we had the metric  $$ds^2~=~−A(r,t)dt^2+\frac{dr^2}{B(r,t)}+r^2(dθ^2+\sin^2{θ}dϕ^2),\tag{2}$$  where   $$A(r,t)~\neq~(1−\frac{2GM}{c^2r})\tag{3}$$   and   $$B(r,t)~\neq~(1−\frac{2GM}{c^{2}r}),\tag{4}$$   then what is the event horizon?


In this code, nextVal seem to be remembered by the function but i am unable to understand.  var gimmeSomething = (function(){         var nextVal;          return function(){             if (nextVal === undefined) {                 nextVal = 1;             }             else {                 nextVal = (3 * nextVal) + 6;             }              return nextVal;         };     })();      gimmeSomething();       // 1     gimmeSomething();       // 9     gimmeSomething();       // 33     gimmeSomething();       // 105

How would you explain JavaScript closures to someone with a knowledge of the concepts they consist of (for example functions, variables and the like), but does not understand closures themselves?  I have seen  given on Wikipedia, but unfortunately it did not help.


Find the limit, interpreting it as a limit of a summation of a suitably chosen function:  $$\lim_{n\to\infty} n \bigg( \frac{1}{n^{2} + 1^{2}} + \frac{1}{n^{2} + 2^{2}} + ... + \frac{1}{n^{2} + n^{2}} \bigg).$$

I'm asked to prove that $$\lim_{n \to \infty}\left(\frac{n}{n^2+1}+\frac{n}{n^2+4}+\frac{n}{n^2+9}+\cdots+\frac{n}{n^2+n^2}\right)=\frac{\pi}{4}$$ This looks like it can be solved with Riemann sums, so I proceed:  \begin{align*} \lim_{n \to \infty}\left(\frac{n}{n^2+1}+\frac{n}{n^2+4}+\frac{n}{n^2+9}+\cdots+\frac{n}{n^2+n^2}\right)&=\lim_{n \to \infty} \sum_{k=1}^{n}\frac{n}{n^2+k^2}\\ &=\lim_{n \to \infty} \sum_{k=1}^{n}(\frac{1}{n})(\frac{n^2}{n^2+k^2})\\ &=\lim_{n \to \infty} \sum_{k=1}^{n}(\frac{1}{n})(\frac{1}{1+(k/n)^2})\\ &=\lim_{n \to \infty} \sum_{k=1}^{n}f(\frac{k}{n})(\frac{k-(k-1)}{n})\\ &=\int_{0}^{1}\frac{1}{1+x^2}dx=\frac{\pi}{4} \end{align*}  where $f(x)=\frac{1}{1+x^2}$. Is this correct, are there any steps where I am not clear?


Hidden away in a storage room beneath Maz Kanata's Castle, Rey finds Luke's first / Anakin's second lightsaber      We last saw that weapon when Luke's hand was severed on cloud city, causing the hand and lightsaber to fall down the same chasm Luke later falls down.  How did it get from where we saw it last to eventually end up in Maz Kanata's Castle?

In The Force Awakens:      Maz Kanata tells Rey that the lightsaber she just picked up and had visions from belonged to Anakin and Luke and now it's hers.   The lightsaber that Luke got from Obi-Wan Kenobi in A New Hope was lost/destroyed when Luke fought Darth Vader in Star Wars: The Empire Strikes Back.  In Return of the Jedi Darth Vader compliments Luke on building a new lightsaber and tells Luke that his skills are now complete.   How could that possibly be the lightsaber that Anakin used originally, and that was then passed on to Luke, when that lightsaber no longer exists?  Writers notes, director's notes, interviews, cast interviews, etc. are welcome. Thanks.


Consider the Galois extension $K/\mathbb{Q}$ where $K=\mathbb{Q}(e^{2\pi i/11})$. I am asked to calculate the lattice of the intermediate groups of $G$.  I know that the minimal polynomial of $e^{2\pi i/11}$ over $\mathbb{Q}$ is $m(x)=x^{10}+x^9+ ... + 1$ and therefore $G$ has $10$ elements, and every element moves one root of $m(x)$ to another. The roots of $m(x)$ are the roots of unity $\xi,\xi^2,...\xi^{10}$ where $\xi^{11}=1$  How do I follow?

Let $F= \Bbb{Q}(\zeta_7)$ with $\zeta_7 = e^{2\pi/7}$. a) What is the Galois group of $F$ over $\Bbb{Q}$? b)Find all intermediate fields between $\Bbb{Q}$ and $F$. (Write each in the form $\Bbb{Q}(\alpha)$ for some specific $\alpha \in F$.) c) For each intermediate field $E$ above, give the Galois group of $E$ over $\Bbb{Q}$.  a) Since $\Bbb{Q}(\zeta_7)$ is the splitting field for the cyclotomic polynomial $x^6+x^5+...+1$, $Gal(\Bbb{Q}(\zeta_7)/\Bbb{Q}) \cong U_7 \cong \Bbb{Z}^{\times}_7 \cong \Bbb{Z}_6$. b) $Gal(\Bbb{Q}(\zeta_7)/\Bbb{Q}) \cong \Bbb{Z}_6$ So we have the following diagram for $\Bbb{Z}_6$,  And a corresponding diagram for $\Bbb{Q}(\zeta_7)$ for some $\alpha$ and $\beta$  Since $\Bbb{Q}(\zeta_7)$ has complex numbers, we can look at $\Bbb{Q}(i)$ to see if it has degree 2 or 3 over $\Bbb{Q}$. Since $x^2+1$ is its minimal polynomial, we see that $[\Bbb{Q(i)} : \Bbb{Q}]=2$ and so it must correspond to $\Bbb{Z}_3$, and $\beta=i$. Sending every number to its conjugate is one possible automorphism. Of course, it has order 2 and so is isomorphic to $\Bbb{Z}_2$. Since it fixes every real number, the corresponding intermediate field must be of the form $\Bbb{Q}(\alpha)$ for some real number $\alpha$, and must have degree 3 over $\Bbb{Q}$. If we look at $\zeta_7 + \zeta_7^6$, we see that $\cos(2\pi/7) + i\sin(2\pi/7) + cos(12\pi/7) + i\sin(12\pi/7)$ $= \cos(2\pi/7) + i\sin(2\pi/7) + \cos(-2\pi/7) + i\sin(-2\pi/7)$ $= 2\cos(2\pi/7)$ which is irrational. So $\Bbb{Q}(\zeta_7 + \zeta_7^6)$ is either a proper subfield of $\Bbb{Q}(\alpha)$ or is equal to it. But from the diagram, we know that there is only one other intermediate field, so $\Bbb{Q}(\zeta_7 + \zeta_7^6) = \Bbb{Q}(\alpha)$. c) The corresponding Galois group of $\Bbb{Q}(i)$ is isomorphic to $\Bbb{Z}_3$ and that of $\Bbb{Q}(\zeta_7 + \zeta_7^6)$ is isomorphic to $\Bbb{Z}_2$. Do you think this is correct? Thanks in advance


I'm planning an exhibition where I need to run an app which needs a keyboard, but no mouse. I want to lock the viewers into one fullscreen application. They should never be able to see anything except this one app. Nothing whatsoever.  So I'd set up a new user which will start the app (in fullscreen mode) as soon as the user logs in. The machine it's running on will be physically secured.  But they have access to the keyboard and could do unwanted things (even closing or switching applications is unwanted). Is there any way of preventing all keyboard based application switching, launching, shutting down, access to tty, login prompt... - such that the only way to leave the application (or simply see anything else) is using the power off button on the (secured) hardware?   The app is intended for Ubuntu 17.10.

I want to do a small computer just for internet browsing. I dont want to load a desktop environment to keep RAM, CPU and GPU ussage as low as possible. The computer is going to run on a ARM CPU. I dont care with Distro I use, I thought about good old plain Debian.


I am trying to shift the number 1 to the right. So originally, the bit mask should be: 1  Then, the bit mask should be: 01  Below is my code: int bitmask = 1; bitmask >>= 1; System.out.println(Integer.toBinaryString(bitmask));  The output however, is just: 0

I've been attempting to learn C in my spare time, and other languages (C#, Java, etc.) have the same concept (and often the same operators) ...   What I'm wondering is, at a core level, what does bit-shifting (<<, >>, >>>) do, what problems can it help solve, and what gotchas lurk around the bend? In other words, an absolute beginner's guide to bit shifting in all its goodness.


Who can edit "on hold" questions? My guess is users with more than 2K reputations and OP himself, is that correct?

Questions can be closed or marked as duplicates.  What does it mean for a question to be "closed"? What does it mean for a question to be marked as a "duplicate"? Who can close a question? What are the reasons for closing a question ? Is closure the end of the road for a question? When are closed questions eligible for deletion?   Related        For more information, see "" in the .


I have a Wordpress site and I am having issues displaying the uppercase O with the accent as seen below:  Ó   The lowercase o with accent as seen here  ó    displays fine along with a number of other characters.  The charset in the header is set to UTF8 and the DB column for each field is set to UTF8_general_ci.  Is there something special about the capital Ó?  When I print_r straight from the DB without sending to the browser, it prints out correctly, and it is stored in the table correctly as well.  It's just once it loads into the field the html that it displays incorrectly.

I'm setting up a new server and want to support UTF-8 fully in my web application. I have tried this in the past on existing servers and always seem to end up having to fall back to ISO-8859-1.  Where exactly do I need to set the encoding/charsets? I'm aware that I need to configure Apache, MySQL, and PHP to do this — is there some standard checklist I can follow, or perhaps troubleshoot where the mismatches occur?  This is for a new Linux server, running MySQL 5, PHP, 5 and Apache 2.


When talking about atomic mass in the periodic table of elements, is this number the mass of the element at rest?  If I understand correctly, the (relativistic) mass of an element will increase as the speed of that element increases, until the (relativistic) mass reaches infinity at the speed of light, right?

Some people say that mass increases with speed, some people say that the mass of an object is independent of its speed.  I understand how some (though not many) things in physics are a matter of interpretation based on one's definitions. But I can't get my head around how both can be 'true' is any sense of the word.  Either mass increases or it doesn't, right?  Can't we just measure it, and find out which 'interpretation' is right? e.g.: (in some sophisticated way) heat up some particles in a box and measure their weight?  ------------------------------  UPDATE  Right, so I've got two identical containers, each with identical amounts of water, each on identical weighing scales, and each in the same g field. If one container has hotter water, will the reading on its scale be larger than the other? If the answer is yes, and g is constant, does this mean that the m in w=mg has got bigger?


So you can take me seriously, let me first introduce myself: I am a PhD student about to finish my thesis and, thinking about future employment, I am considering to obtain an Oracle Java Certification, ammong other things.  The question I ask may sound odd, but I found this comic:   Apparently, having a PhD is considered as a downside when applying for a job in the software industry. I don't see how that may be funny, and the reason behind it.   Moreover, and actually what made me make this question here: having taken a course in a technology is considered much worse, for instance, than having grammar errors in the resume or mentioning your skills using MS Word. One guy even say "The point about certifications is dead-on". Other person comments "For most of the good Cisco certifications you HAVE to take the course, otherwise you will epic fail".   This make me wonder if the problem is to had taken the course to get the certification, not the certification itself. Maybe they mean that showing in your CV that you completed a 10 hours online course on "Starting with C language" is perhaps not a good idea. Otherwise I don't understand.   I hope someone can shed some light on this.

This question follow's JeffE's comment :     In most industries, a PhD has negative value.   I am curious about what potential negatives there may be with having a PhD, particularly in industries.  For example, my PhD has applications for image sensors, and the potential of working in that field is appealing—would having a PhD be a potential barrier? Would it be a case of how explicit the practicalities of the PhD can be made?  Would this make any difference?


Is this possible to get the cmd output as input in C using system()?. I want to read the output of the cmd as input.  For Ex. The command in system("echo %username%"); will result the current logged user name as output like Prasanthvel. I just want to read the output and store in a string to do some program.  Note : I don't want to save it into a text file, and this question is different from other questions in this forum or  the answers were not sufficient to do this.

I've got a utility that outputs a list of files required by a game.  How can I run that utility within a C program and grab its output so I can act on it within the same program? UPDATE: Good call on the lack of information.  The utility spits out a series of strings, and this is supposed to be portable across Mac/Windows/Linux.  Please note, I'm looking for a programmatic way to execute the utility and retain its output (which goes to stdout).


Show that the $\lim_{n\to \infty} \frac n{n+1} = 1$ using the limit definition. So far I have: Let $\varepsilon > 0$, there exists $N \ge 0$ such that, $|a_n-L|< \varepsilon$, for all $n \ge N$. $\left|\frac n{n+1} -1\right| < \varepsilon$. I have ended up with $\left|\frac 1{n+1} \right|  \le \frac n n = 1$ (which is $< \varepsilon$, for all $n$) I know there needs to be an n at the end, so for all $n >$ something $\varepsilon$. I am not sure what to do after $n/n$, or is that enough to show the limit of the sequence $= 1$. Thanks

I have to prove $ \lim_{n\to \infty}\frac{n}{n+1} = 1$ using Cauchy (epsilon) definition of a limit of a sequence.  How do I do that formally? It is clear to me that the limit is 1, after doing some manipulations with the fraction, but how do I show it formally using the Cauchy definition of a limit?  Thanks in advance!


This question explains better what this one tried:      In the history mathematics we always see how the numbers were created and for what purpose. Like ordering, calculation of areas and taxes. This is the most common approach on documentaries and so in the math books.  It's always easy to understand the basics: Add, subtract, multiply and divide. The reason it is easy is that it is intuitive. We can imagine those things happening in our minds through visual representations.  I'm digging these documentaries looking for the part where we jumped from these basic operations to the complex ones. At least to me, the complexity starts when we add negative numbers. For example, in this simple operation:   $1 + (-1) = 0$  It's easy to understand how to apply and use the provided logic of signs. But to me it is not easy to imagine what is really happening here. And when I say "happening", I mean that I can't create any object visualization of that operations, like the ones we learn on high school:  "Imagine that you have two breads. You have eat one. Now how many do you have?"  On that kind of visualization you can imagine the two objects and then you can take off one and see how it looks like. This can be done for all the basic four operations on small scales.  You could say that the operation above is the same as $1 - 1 = 0$ But that's not the case. Doing so you are omitting the signs part and using it just as predefined formula.  The main question is about when in the history and for what reason the man came out with the signs and that kind of operation. In other words: Which was the first step given after these basic and very intuitive operations? And which was the necessities that leverage these discoveries? Like the need to have a convention where plus and minus become minus.  It is easy to think of debts. In that case, can you provide a simple visualization like the mentioned above for the product of two negative numbers?

I'm currently a Calculus III student. I enjoy math a lot, but only when I understand its beauty and meaning. However, so many times I have no idea what it is I am learning about, althought I am still able to solve problems pertaining to those topics. I'm memorizing the sounds this language makes, but I dont understand them. I think a big reason why most children and teenagers really dread math over any other subject is because the only thing that is taught to them is equations and numbers, and to them is not being explained its significance. For if people really knew what it all meant, then they'd realize it's probably the most important think they should ever study. Even in college, at this relatively high level of math, they still do not preach its meaning, but rather scare you into cramming pages after pages of material so you can pass the next exam. When you have passed the exam, then it is safe for you to forget the material you just absorbed. This is the reason I often find myself bored of studying my current topics. For some things, I see the intuition behind it, and those are the things that keep me interested in calculus, but its often so hard to come up with a good meaning of what I'm learning all by myself.  It took mankind hundreds and thousands of years to come to where we are with math, so I dont expect to understand its true meaning in an hour, but I'd really like to. The school curriculum, here in America at least, doesnt teach meaning or utility. This is the reason so many youngsters always ask "when will we ever need to use this stuff?"-what a naive question this I learned to be. So I guess what I'm trying to say is that I've grown bored of this material, as we often cram 2 full sections of a topic in one day. Its impossible to keep up with its meaning, but if I am to survive this course along with more advanced courses to come, I must be able to understand its meaning. My textbook doesn't help me with this issue though- no math book can really teach intuition, but they dont even attempt to. They barely even go into the history of the current topic, and thats one of my favorite parts-I like to read about how a normal man came up with this theory that revolutionized the world. It makes math feel human to me, and that I too can understand it like men before me.   Most of the question answerers on this site are mathematicians, if not at least one in training. This means you have come to where you are by understanding what you have learned in the past. How have you done this? How have you been able to connect all the pieces? What are some good resources that will help in what I hope to do? How do I stop being a robot, and actually connect with what I'm learning?