Sorry I was unable to find any keyword to search for this problem. My code is below  #include <iostream> using namespace std; class Name {     public:         Name() {             cout << "Asif";         } };  int main() {     Name obj(); // why Constructor not calling here?      return 0; }   If it's not calling the constructor then what process is running in this code?

Is there any good reason that an empty set of round brackets (parentheses) isn't valid for calling the default constructor in C++?  MyObject  object;  // ok - default ctor MyObject  object(blah); // ok  MyObject  object();  // error   I seem to type "()" automatically everytime. Is there a good reason this isn't allowed?


Unlike any other site, Area 51's main site is unencrypted, its login forms are partially or wholly insecure and its login forms completely break under the browser extension HTTPS Everywhere. That doesn't happen on any other sites. This is madness Sparta.  Mere months ago Mark Henderson : Let's encrypt all the things. But:   When I use the HTTPSEverywhere extension on Firefox 50.0.2, the login form appears secure until you try to log in, at which point it barfs  Unable to log in with your OpenID provider: <Big Wall of Red Text>   and I can't login. And when I disable the extension I get either an unsecured or only partially secured form, leaving it unclear to me if my PW is being sent in clear text over the intertubes.  Then when I'm logged in the site isn't secure at all.   In case that matters I'm running Linux and it's fully up-to-date with security patches.  Can Area 51 get area defenses (cryptography) actually worthy of the name?

I recentely tried to log-in / sign-up for  using my SE account (which works on ,  and sign-up here) but it showed me an OpenID related error. (See below)  I could reproduce this error across multiple days and browser refreshes and using my other OpenID provider.  Error message (shown in red, obfuscated my e-mail address):  Unable to log in with your OpenID provider:  The openid.return_to parameter (http://area51.stackexchange.com/users/authenticate/?s=bd394805-cf55-4e8e-ad73-21485a09a989&dnoa.userSuppliedIdentifier=https%3A%2F%2Fopenid.stackexchange.com%2Fuser%2F642b1038-5c91-40d4-83ab-eb92db46c3d1) does not match the actual URL (https://area51.stackexchange.com/users/authenticate/?s=bd394805-cf55-4e8e-ad73-21485a09a989&dnoa.userSuppliedIdentifier=https%3A%2F%2Fopenid.stackexchange.com%2Fuser%2F642b1038-5c91-40d4-83ab-eb92db46c3d1&openid.claimed_id=https%3A%2F%2Fopenid.stackexchange.com%2Fuser%2F642b1038-5c91-40d4-83ab-eb92db46c3d1&openid.identity=https%3A%2F%2Fopenid.stackexchange.com%2Fuser%2F642b1038-5c91-40d4-83ab-eb92db46c3d1&openid.sig=4emyzuA31ChHU0LabPGJXldbN8GeKN%2FFBJXJy69yD10%3D&openid.signed=claimed_id%2Cidentity%2Cassoc_handle%2Cop_endpoint%2Creturn_to%2Cresponse_nonce%2Cns.alias3%2Calias3.mode%2Calias3.type.alias1%2Calias3.value.alias1%2Calias3.type.alias2%2Calias3.value.alias2&openid.assoc_handle=hrQL%21IAAAAGzBtFeNGBLU2o04XSWr7ISRAbO-B2tZCK3L61IzAsuQQQAAAAEdoTN6rf9fqaP1oekJGXGXJeB8fNSVuByptp5yx1VpQbAzQwF6HJzh6a0DwedydNJ-wwpJQoN5dOLEFmndZt-L&openid.op_endpoint=https%3A%2F%2Fopenid.stackexchange.com%2Fopenid%2Fprovider&openid.return_to=http%3A%2F%2Farea51.stackexchange.com%2Fusers%2Fauthenticate%2F%3Fs%3Dbd394805-cf55-4e8e-ad73-21485a09a989%26dnoa.userSuppliedIdentifier%3Dhttps%253A%252F%252Fopenid.stackexchange.com%252Fuser%252F642b1038-5c91-40d4-83ab-eb92db46c3d1&openid.response_nonce=2015-06-12T12%3A30%3A42Z7tADDeYZ&openid.mode=id_res&openid.ns=http%3A%2F%2Fspecs.openid.net%2Fauth%2F2.0&openid.ns.alias3=http%3A%2F%2Fopenid.net%2Fsrv%2Fax%2F1.0&openid.alias3.mode=fetch_response&openid.alias3.type.alias1=http%3A%2F%2Faxschema.org%2Fcontact%2Femail&openid.alias3.value.alias1=mycorrectaddress%40web.de&openid.alias3.type.alias2=http%3A%2F%2Faxschema.org%2FnamePerson&openid.alias3.value.alias2=SOJPM) the request was made with.    As noted in the comments I'm not the only one, so I'd guess it may be not something I can fix. So will this be fixed?  Repro steps (using SE OpenID):   Get an Stackexchange OpenID account (like I have) (optional?) Add other OpenID providers and check they're working (StartSSL in my case) Please note: "You" don't have an "account" for the Area 51 subpage yet and still need to do the initial sign-in. Go to the Area 51 SE page Hit "Log-in" in the top-bar Hit the "log-in using stackexchange" button Enter your e-mail and password and submit Get the above error   Repro steps (using other OpenID)   Perform as above (until step 4), but this time step 2 is mandatory Hit "more OpenID options" Provide your OpenID link XXX.provider.com (works on crypto, server fault, ...) Authenticate against your provider Receive a variation of the above error (can be included if needed)


I was watching . At minute 23:20 he does some "magic" with unpacking that I am having hard time understanding.  The "magic line" is   fail = [ { **row, 'DBA Name': row['DBA Name'].replace("'",'').upper() } for row in fail ]   I have searched for similar examples but I couldn't find any. Can you explain what is going on in this code? Can you point me to some similar examples?

In the following method definitions, what does the * and ** do for param2?  def foo(param1, *param2): def bar(param1, **param2):


If I want to turn a local git repository into a regular (non versioned) folder what do I have to do?   I've had an SVN project before and in that case I had to delete an SVN folder from every directory. I've read git has one project folder but after some searching it sounds like there is more to it.   PS I do not want to export a repository because not all the contents are checked in.

I've been wondering whether there is a good "git export" solution that creates a copy of a tree without the .git repository directory. There are at least three methods I know of:   git clone followed by removing the .git repository directory.  alludes to this functionality but starts with "Just read the desired tree into the index..." which I'm not entirely sure how to do.  is a third party script that essentially does a git clone into a temporary location followed by rsync --exclude='.git' into the final destination.   None of these solutions really strike me as being satisfactory. The closest one to svn export might be option 1, because both those require the target directory to be empty first. But option 2 seems even better, assuming I can figure out what it means to read a tree into the index.


I currently have a document (), where I define the paper size and one sided design as class options. I use the KOMA-Script class scrbook.   in A4 format for printing on usual printers at university and watching at the screen in A5 format for professional printing (well, it was not printed so far, but I would like to try this)   At the moment, I have a TODO list what to change when I switch from A4 toA5:  * In `GeoTopo.tex`...   * ... replace `a4paper` by `a5paper`,   * ... replace `oneside` by `twoside` and   * ... replace `\usepackage[...]{hyperref}` by `\usepackage{nohyperref}` * In `titlepage.tex`: replace `10cm` by `4cm`   Is there any (La)TeX solution so that I would only have one thing to get these different configurations?  I think it might look like this:  \newcommand{\CompileConfiguration}{A4} ... \if\CompileConfiguration==A4     \usepackage[...]{hyperref} \else     \usepackage{nohyperref} \fi   My thirst thought was to make it dependent on the paper size. But I have no idea how the condition would look like in this case.   An even better solution would define a variable even before \documentclass. But I have never seen anything before \documentclass except nag, so I doubt this is possible. Especially, even for the example above, I don't know the details. Is it == for comparison or =?   I have seen  \ifundefined \ifnum \ifodd \ifdim \iftrue \iffalse \ifx   so maybe there is no string comparison. But I don't know what other type \CompileConfiguration has (or how I could define it e.g. as a boolean)

I would like to be able to set a flag at the beginning of the main flag (say output) that tells if I want to produce a paper document or an electronic document.   Then I should check this flag to define or not empty pages, hypperref, oneside or twosides, etc.  How could I do that ?


This may be a really basic question with the simplest of answers, but as much sense as it makes to think that black holes are not, in fact, black but invisible - because light would be gravitationally lensed from all directions around the black hole, 'covering' the hole - I am yet to find an artist's impression portraying the black hole as anything other than, well, a 'black hole' in space. Even the movie 'Interstellar', which is meant to have unimaginably realistic graphics and has undergone a gigantic amount of physical simulations to achieve such, portrays the black hole in that stereotypical manner. Or, perhaps, my intuitive speculations are unjustified?

Are black holes in a sense transparent? Meaning, they don't 'hide' any stars that happen to be 'behind' them?  A regular object obviously blocks a point source of light emanating from 'behind' it. Meaning it creates an area of space photons cannot get to us from. But a massive object curves space, and so via gravitational lensing we can sometimes see distant stars that are 'behind' other stars (by behind I mean that if the star in the middle would suddenly vanish, the trajectory of photons traveling from the distant star to Earth would have passed through the volume now occupied by the middle star).  My thinking, is that black holes curve space so much, that from ANY source of light outside it, light has a trajectory to reach us on Earth (assuming of course no other object blocks it on its way).  The reasoning for this is: Suppose we draw the straight line between us and the light source (as if the black hole wasn't there at all). Photons from our light source crossing the event horizon would obviously 'fall' inside. A photon in theory traveling exactly tangent to the event horizon would in a sense go 'into orbit' around the black hole (obviously there is no such thing, because the black hole isn't perfectly spherical, and there are quantum effects and so forth. But I'm focusing on the geometry), crossing our straight line exactly at the intersection of our line and the event horizon. Any photon passing near the event horizon, but a bit farther, would follow a curve that intersects our line a little farther from the event horizon. Continuing this, there would be at last be a photon that would exactly curve our way.


Previously Google was unable to find events on the site I'm working on because it was restricted to logged in users. We specifically added a small feature to view upcoming and past events by popularity. Each page contains X number of structured data 'event' objects (each with schema.org object properties etc.), and my goal has been to get Google to index this data.  My site has ~65k total events, 21k in the future and 44k in the past. Overall, Google only recognizes 5,293 total indexed items (as per Google Webmaster tools, adding up all the www/non-www and http:/ versus https:// and combinations etc.), and on the Structured Data tab of the same tool it shows only 1,413 items (I assume of all the indexed content, these are the only ones it is labeling as events?).  I requested a "fetch as Google and render", with a deep-index to fetch pages linked to the requested page (only 10 of these to use per month), for urls for the base /upcoming-events and /past-events, as well as upcoming & past-events?page=3, but so far I've only seen 1500 pages indexed.  Should I just wait more time?  Could the paging setup (it's not fully implemented yet) be missed by Google?  Here is the  if anyone wants to examine the content (for relevance only).

I have a new website with 140k pages, according to my sitemaps.  After submission of my sitemap index to Google, the Googlebot has started crawling the site a couple of hours ago, and at a steady pace, but it's doing so too slowly: roughly one request per minute.  At such rate, it'll take 100 days for the site to be indexed!  Is there a way to increase the rate?  Why does all Google documentation suggest that they don't recommend changing the crawl rate, and that changing the crawl rate will only make the crawling slower?


I have a live streaming API call(Twitter Stream via Datasift) which I have to consume and show it in my application. When I tried to consume it in the browser, the call never ended. It just kept on pushing the data as it happened. And that is the point of the Live streaming actually. When I tried to consume it using HTTP Web Request Get Method, the Response Stream never ended and so I wasn't able to read the stream.  I understand this is not the way to do it. Can some one suggest me how to do it in c#.  Edited: (Extra Information) The API returns the data continuously as and when some one has tweeted with the keyword we sent as a parameter in the API call. So the response never actually ends. When I tried doing it asynchronously, it hit the call back method only once and I wasn't able to read the stream either. Where as when I tried the same API call from a browser, it kept on giving the results as and when some one has tweeted with the keyword. SO it is just not about asynchronous consuming of web request.

How can I use HttpWebRequest (.NET, C#) asynchronously?


If I have a list, say a=[1,2,3,4]  I want to specify a length, let's say 3, then I can find all the subsets: [[1,2,3], [1,2,4], [2,3,4]]  Does Python has a function so that I can do this quickly?

I have a list with 15 numbers in, and I need to write some code that produces all 32,768 combinations of those numbers.   I've found  (by Googling) that apparently does what I'm looking for, but I found the code fairly opaque and am wary of using it. Plus I have a feeling there must be a more elegant solution.  The only thing that occurs to me would be to just loop through the decimal integers 1–32768 and convert those to binary, and use the binary representation as a filter to pick out the appropriate numbers.   Does anyone know of a better way? Using map(), maybe?


Is there any reason for doing something like:  a="abc"   or  a='abc'   The quotes seem completely superfluous, but then there might be some hideous corner case... I'm interested in Bash and Sh in particular, but answer about the other ones as well if you can and will.

The old advice used to be to double-quote any expression involving a $VARIABLE, at least if one wanted it to be interpreted by the shell as one single item, otherwise, any spaces in the content of $VARIABLE would throw off the shell.  I understand, however, that in more recent versions of shells, double-quoting is no longer always needed (at least for the purpose described above).  For instance, in bash:  % FOO='bar baz' % [ $FOO = 'bar baz' ] && echo OK bash: [: too many arguments % [[ $FOO = 'bar baz' ]] && echo OK OK % touch 'bar baz' % ls $FOO ls: cannot access bar: No such file or directory ls: cannot access baz: No such file or directory   In zsh, on the other hand, the same three commands succeed.  Therefore, based on this experiment, it seems that, in bash, one can omit the double quotes inside [[ ... ]], but not inside [ ... ] nor in command-line arguments, whereas, in zsh, the double quotes may be omitted in all these cases.  But inferring general rules from anecdotal examples like the above is a chancy proposition.  It would be nice to see a summary of when double-quoting is necessary.  I'm primarily interested in zsh, bash, and /bin/sh.


I'm taking care of the company's website for a while. The guy who was doing so before me was fired because reasons. So for the past 3 months I've been keeping it up to date and adding/deleting stuff. Not a big deal, I know a bit of PHP so it is not a problem.  However, the problem is not there.   The manager told me as soon as I took the charge that there was "magic" going on behind the server. Every night, there are a few scripts written in PHP that update our website and the database. Well, I know which scripts are being executed, and where they are; but I can't find why they are being executed.  The scripts are located in the controllers/tasks folder inside our server, but there's nothing in the task scheduler.  How can I find out how are these tasks being programmed, and if I can change their frequency? Thanks before hand.  DATA Windows Server 2003 running WAMP 2.1, which includes   Apache 2.2.11 MySQL 5.1 PHP 5.3   PS. Excuse my poor english.

This is a  about  the use of a *AMPP's stack.    I recently had a talk with some experienced people and they suggested to me not to use a WAMP stack, and instead install apache, mysql and php separately.  I don't understand why they have suggested this, though, so can anyone tell me?  Is there a particular disadvantage of WAMP, or a particular advantage to installing all of them separately?  Since a WAMP stack itself is composed of apache, mysql and php, then what's the difference between using the WAMP stack and installing them all separately?


Notifications that inform you of a received badge show an image of the badge.  This image always appears in the style of the badges from the site you are currently viewing, not the site the badge came from.  This seems incorrect.

It's so cool that the notification reminds you of the colour of badge you've earned. But I am a little puzzled by the symbols:      Is it feasible to use the symbol from the earned site? At the moment it uses the symbol from the site I happen to be on (as you can see by looking to the left of the dropdown in each case.)


I downloaded clash of clans on my sisters apple account. I then made my own apple account. When I try purchasing gems I can't because it says something about the app not being downloaded from this apple account.  Is there a way I can't delete clash of clans and then re download it without losing any progress?!! Please help!! I also have a gamecenter account.

I downloaded Clash of Clans using my sisters Apple ID and her Game Center, on my iPhone. I backed up my phone. Then when I got my new phone and I created a new Apple ID and new Game Center for me.  I had kept all my progress from my earlier phone. However, now when I try to buy gems, it pops up with this message:     This item is for an app that has been purchased by a different Apple ID. To buy this item with this Apple ID you must first purchase the app.   I am guessing this means I have to delete the app and re-download it, but I am afraid I will lose all my progress.  Is there an easy solution for the Apple ID confusion?


Criteria criteria = session.createCriteria(Student.class); criteria.add(Restrictions.eq(STD_ID, stdId)); criteria.add(Restrictions.le(START_DATE, dateOfService)); criteria.add(Restrictions.ge(END_DATE, dateOfService)); results = criteria.list();   Is it possible to convert the criteria object to SQL query or while debugging in Eclipse is it possible to see the generated SQL query?

Is there a way to get the (to-be-generated) SQL from a Hibernate Criteria?  Ideally, I would have something like:  Criteria criteria = session.createCriteria(Operator.class);  ... build up the criteria ... ... and then do something like ...  String sql = criteria.toSql()  (But this of course does not exist)   The idea would then be to use the SQL as part of a huge 'MINUS' query (I need to find the differences between 2 identical schemas - identical in structure, not in data - and the MINUS is not supported by Hibernate)  (BTW I know I can check the SQL from the log files)


I've read conflicting information regarding the meaning of the idiomatic phrase "take the cake".  I am quite confused, because based on one source it means something is exceedingly good and according to another - exceedingly bad.   Could someone shed some light on which of the two is the actual/prevalent meaning of the phrase?  For example which of the two uses sounds more natural? "He drank all the milk and left the empty bottle in the fridge! That really takes the cake!" or "Thanks for all the help! You really take the cake!"

So, I'm reading up on a  and I see two that bear a striking similarity.   "Take the biscuit (UK): To be particularly bad, objectionable, or egregious.     "Take the cake (US)": To be especially good or outstanding.   Now I can understand why cake is "good" and "outstanding". In the USA we're rational, and that makes sense to me. However, why are biscuits "bad", "objectionable" or "egregious"? It would seem to me that if the country thought so poorly of biscuits they'd naturally go away. Personally, I like biscuits too; and, I especially like biscuits with gravy.  Why do people in the UK hate biscuits, and how did the saying "take the biscuit" come to be?  You can hear an example of


Compute $\lim_{n\rightarrow\infty} H_n-H_{\frac{n}{2}}$ where $H_n=\sum_{i=1}^n\frac{1}{i}$.   Alternatively, we can rewrite $H_n-H_{\frac{n}{2}}$ as $\sum_{i=\frac{n}{2}+1}^n\frac{1}{i}$ if this form is easier to manipulate.  I really have no idea where to begin with this problem. Any help/hints would be greatly appreciated!

What is the sum of the 'second half' of the harmonic series?  $$\lim_{k\to\infty}\sum\limits_{n=k+1}^{2k}{\frac{1}{n}} =~ ?$$  More precisely, what is the limit of the above sequence of partial sums?


i'm flying from Frankfurt to Seattle(condor airlines - Boeing 767-300 economy class) in few weeks for the first time, and the seat width in the plane is 17 inches,while my width is around 19 inches, will there be any problems ?

As I said in another question, I'm bringing my parents to visit me here in Sweden next year.  My mother is around 280-300 pounds and 5'6" (130-135kg, 1.67m). I am concerned that she might be asked at the airport to buy a second seat. If it's likely I would rather just buy the second seat in advance, because I don't want her to be embarassed/humiliated by some random employee. As well, I won't be there, they will be travelling alone and aren't used to dealing with airports and they won't know what their rights are.  In terms of how it will affect other passengers, it's not important, she will get a window seat and my dad will sit in the middle seat, so I don't see it affecting anybody.   She insists it's fine, "the last time I flew I fit easily!" but that was 20 years ago when she was half the size.   They will be flying BA or SAS, definitely not Ryanair.  So - where is the cutoff? Is a 300 pound 5'6" woman going to be too big to fit in a single airline seat? Or am I worrying about nothing?


I want to measure time of getting elements of ArrayList. I know that using ArrayList we can get any element in constant time. I tried to check this writing code, but it returns wrong result for first element.  My code:  private long getGetTime(int position) {     long elapsedTime = 0;     long start = System.nanoTime();       list.get(position);      long end = System.nanoTime();     elapsedTime = end - start;      return elapsedTime; } preapareStructure(); System.out.println("read 0, time: " + getGetTime(0)); System.out.println("read size/2, time: " + getGetTime(list.size()/2)); System.out.println("read size-1, time: " + getGetTime(list.size()-1));   And this returns something like this:   read 0, time: 10243 read size/2, time: 843 read size-1, time: 843

How do you write (and run) a correct micro-benchmark in Java?  I'm looking for some code samples and comments illustrating various things to think about.  Example: Should the benchmark measure time/iteration or iterations/time, and why?  Related:


One of my project's title tag doesn't appear to be getting crawled by Google properly. The title tag of the home page reads:  <title>Grande Prairie Jobs | Job Board for Grande Prairie, Alberta and Area</title>   Google, on the other hand, indexes the title as gpjobs.ca.    Is there something I'm doing wrong here? Any insight would be really helpful.   One thing, the first  of the document is gpjobs. Could this be causing the  incorrect title? I guess I just don't understand why Google would index it with the <h1> rather than the <title>.  Edit: To clarify for whoever marked this question as a duplicate of , my site actually had a landing page where Google indexed it correctly. After launching the site and submitting a sitemap, Google has indexed the title as above. What I'm trying to establish and correct, is why the site has an indexed title of the first h1 on the page and not the title. I expected the title to be picked up.

I'm just wondering how it is possible that IGN.com has this in its title tag:      Video Games, Cheats, Walkthroughs, Game Trailers, Reviews, News, Previews & Videos at IGN   while on Google its title is simply "IGN".   How can one achieve such a thing? Does it use some special meta tag I can't see?


For my math internal assessment, I'm looking at the Collatz Conjecture and different ways to try and solve it.   I wanted to see if there were any possible partial solutions for it by which I mean if we take a specific type of number the conjecture would be true for all of those numbers.   For example, the collatz conjecture is true for all m where m=2^n since the powers of two will keep being even until it reaches one. However, I wanted a more complex proof for another type of numbers(Say, for all powers of 3 or for all prime numbers if it were possible) so I wanted to know if there are any such partial proofs you could think of

Obviously it is proven that all powers of 2 fall to one after applying the rules an arbitrarily large number of times. But are there some other subsets of natural numbers, for which the Collatz Conjecture has been proven? As some comments have pointed out there are some proofs by brute force for at least the natural numbers to 2^64. Are there other known subsets, not proved by brute forcing but because of a rigorous mathematical proof?


I currently have the ASUS ROG GL553VE. and while gaming, i usually open up ROG gaming center and Real temp. what i noticed is that my GPU usually gets 84C and my CPU's get about 75-89C. is that kinda normal? i am playing with a cooling pad too. i ask other people about this problem, and some said that its not normal since its too hot, and some said that it is normal since gaming laptop really does get hot when playing.

So I have a Compaq CQ50-215CA and my sister was using her laptop on her bed and I was just using it quickly to check my email. The surface of the laptop was really hot and I opened Speccy to see that the CPU and GPU temperature was 96 C. A couple months ago, my laptop was on the desk without a cooling pad and I was playing a game. Using GPU-Z back then, I had a reading of 104 C. Even with a cooling pad on a desk, running several processes/games keeps me around 88-90 C.  Is this normal for a laptop and what's the highest temperature the internals can handle? Besides a cooling pad, are there any other more effective ways of cooling a laptop?


I am in need of Skype but, when I upgraded my system to ubuntu, I found that the Skype is not available in Ubuntu Software Center. Even if I download the package from the Skype the Ubuntu Software Center does not allow to install it.  Its too bad that Ubuntu does not support very popular software Skype.

I want to install Skype, but I can't locate it in Software Center or by using Synaptic Package Manager. Can anyone help me?


When I check for updates on Windows 10, the system starts to install automatically all the updates found. Is there any way to choose before installing updates like in previous windows versions?

We've upgraded some machines to Windows 10 and realized there were some updates which updated as required. However, I realized there was no option available to stop the download similar to that on Windows 7 and 8.1. The only way I could stop the download was to stop the Windows Update service.  My question is does anyone know of a way to stop auto updates or is stopping the service is the only solution?


I'm currently reading through a textbook on Real Analysis, and the following is written:     "The great advantage of Leibnitz symbols is that, when they are properly   interpreted, we can treat the symbols d f, d y, dx, and so on, as if they represent members   of IR and carry out various algebraic operations, and the resulting formulas will have   meaning." - Patrick M Fitzgerald, Advanced Calculus, P114   In my physics courses, we very frequently say things like, "If you have a small amount of charge $dq$ in a small volume $dV$, we can define the charge density $\rho$ as $\frac{dq}{dV}$. However, I have been warned in the same classes that treatment of differentials in this manner is not mathematically rigorous and can lead to issues. What issues? I am not sure.  At the same time, in my Real Analysis course, we were told that $\frac{df(x)}{dx}$ should be treated as just notation, and not as a fraction.  And then I read the quoted text above, which appears to be merging the two concepts.  My question is this: How can differentials be treated? When is it rigorous to have a small amount of charge $dq$ be defined as $\rho dV$? My friends and I have grown skeptical of derivations of physics concepts when differentials were used, because we have been told to be skeptical. When is this warranted? When is it not? What do I watch for?

In the book Thomas's Calculus (11th edition) it is mentioned (Section 3.8 pg 225) that the derivative $dy/dx$ is not a ratio. Couldn't it be interpreted as a ratio, because according to the formula $dy = f'(x)dx$ we are able to plug in values for $dx$ and calculate a $dy$ (differential). Then if we rearrange we get $dy/dx$ which could be seen as a ratio.   I wonder if the author says this because $dx$ is an independent variable, and $dy$ is a dependent variable, for $dy/dx$ to be a ratio both variables need to be independent.. maybe?


I'm having some trouble with a simple NullPointerException when trying to construct my own iterator for a HashTable, and I was wondering if this is the proper way to do it. I seem to get errors at the allEntries.add part of the code. Any help would be really appreciated!!  public class HashIterator implements  Iterator<HashNode<K,V> > {     HashLinkedList<K,V>  allEntries;      /**      * Constructor:   make a linkedlist (HashLinkedList) 'allEntries' of all the entries in the hash table      */     public  HashIterator()     {          //  ADD YOUR CODE BELOW HERE           for (int i=0; i<numBuckets; i++) {             HashLinkedList<K,V> currentBucket = buckets.get(i);              HashNode<K,V> curNode = currentBucket.getHead();             while (curNode != null) {                  allEntries.add(curNode.getKey(), curNode.getValue());                 curNode = curNode.getNext();             }          }          //  ADD YOUR CODE ABOVE HERE      }

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?


The gravitational lensing formula is given by equation $a=4M/r$. Is there any experimental data for this equation. I am trying to plot a curve for this equation and the real experimental data and check for the accuracy. I would really appreciate a table of data for the angle of deflection at each $r$ and $M$ if possible. Thanks.

Can anyone provide me with (or point me to) real life gravitational lensing data that I can plug in to the first equation on this page (the standard lensing equation):   together with the luminous mass and distance to the galaxy(s).  I've looked for papers online and have not found any simple data that can be readily plugged in to the equation (I am not familiar with the details of how exactly the lensing is measured and have gotten lost in the mountains of data in the papers).  Thanks


According to  Wikipedia pages are among the links that will be oneboxed. I tried to onebox  but it did not work. The progress meter flashed for some seconds and then the link was shown like a truncated inline link. Then I tried with  and it neither worked. Thus, it seems that oneboxing does not work for . Is this a bug? Here is a screenshot showing what happened:  And here is .

While idly chatting over at  (boring room name, I know. Anyone have any better ideas?), we noticed that  articles (like ) don't onebox. There , while . After some more , it looks like the system only takes two-letter language codes. This should be expanded to accept any language or flavor of Wikipedia.


A similar question to mine was answered here on stackexchange:    However, I am unable to follow the formulas so perhaps someone could show the calculation and the way they arrived at it to answer this question.  My card game is very similar, except the counting of cards goes all the way from 1 (Ace) through to King and then restarts.  If you can make it through an entire deck of cards without hitting the same ranked card you win.  So, for example, if you call out Ace - 2 -3 - 4 - 5 - 6, etc. and hit "7" when you've just called out "7", you lose.  What is the chance of winning this card game?

I have a very simple problem.  Lets assume that I have a well shuffled deck of 52 cards. I start drawing the top card always and when the card matches its rank I lose. J=11 Q=12 K=13.  If there were only 13 cards I could easily use the $\ \frac{!n}{n!}$ for derangements in order to solve this. The problem is that there are 52 cards so when I pass 13 I start from 1 again so I don't know what is the probability to win. Example of the game     1st card: 4 - Continue   2nd Card: A - continue   3rd Card: K - Continue   4th Card: K - Continue   5th Card: 6 - Continue   6th Card: 9 - Continue   7th Card: 10 - Continue   8th Card: A - Continue   9th Card: J - Continue   10th Card: 3 - Continue   11th Card: 2 - Continue   12th Card: 8 - Continue   13th Card: A - Continue   1st card: 5 - Continue   2nd Card 2 LOSE   So actually I have to count from 1 to 13 4 times and if I draw all 52 cards then I win. What's the probability?


10GB of files: 516 files in 14 folders.  Why does it take a significant amount of time to list contents (10-25 seconds)  in the explorer?  This laptop is maxed out in terms of RAM and has a SSD drive.  No Antivirus is installed.

I don't know whether this is my laptop SSD hard drive issue or it is Windows 10 issue. A quick  of mine is here, showing an .   Though now, Oct 2015, I still have the problem every time I open File Explorer right after a reboot.  E.g. Opening drive D: will take me 20 seconds to have the file list loaded; the content displayed as "Working on it" when we wait. I expect it to be immediately available when opened; the same as previous Windows 7.  Do you have the same problem? How can we get around that?


With the PC build I am planning, I want to have a dedicated Hard drive for Steam. While I could just get the biggest Hard drive possible, I need to work out how much space I'll need at the very least for my current library (to see what my options are).  While I could just select every game in my library and download them all I already have some games installed currently which I keep installed for updates (ie. Terraria, Starbound) and to be honest I don't want to be uninstalling these only to have to re-download them (as my internet isn't all that fast)  I also have ~>300 games + DLC and while there is a System Requirement (Storage) on Games and DLC I believe that it only gives me the space requirement for the base game and not the DLC (ie. Megadimension Neptunia VII and one of it's DLC, the Weapons Pack, both say it takes 17 GB)  So is there a way to calculate how much Harddrive Space is needed for one's entire Steam Library (including DLC) without uninstalling it all?

I have a lot of games on Steam, far more than my puny hard drive can hold at once. However, in the future I may want to store all of them locally.   Is there any way to figure out about how much hard drive space I'll need to install all of my Steam games, including the ones that I don't currently have installed, without sitting down with a calculator and manually adding everything up?


I am looking for a way to toggle from the quad viewport (top,left,front,persp etc) to making one viewport larger Blender 2.8 is amazing but the hotkeys and viewport navigation is not intuitive. This is an example in Silo: Here I have a quad viewport and I moused over to perspective and hit spacebar and it went full display in quad layout. From there I can hit spacebar again and mouse over another view, hit spacebar again and can toggle back and forth. Does Blender have that ability or is it something I might have to script in Python?

I am new to blender. Pressing ⎈ Ctrl⎇ AltQ opens the quad view. How to maximize any one of the four views of the quad view?


(use , and didn't work's)  After reinstall my ubuntu from 16.04 to 14.04. My C program can't be executed. My username is the same.  I have used:    chmod +x ./hello  chmod -R 775 hello   I am still getting:  bash: ./hello: Permission denied   I use GUI, to tick execute or change permission group or kind, it suddenly back after few second. But I can read and write every file inside it, when I compile it again, then execute, it's always didn't works.    How can I solve it?  (read many other question, but still didn't works for me..)  $ ls -l total 160 -rw------- 1 reigin reigin  1323 Agu 31 07:14 bentuk.class -rw------- 1 reigin reigin  2438 Agu 31 07:14 bentuk.java -rw------- 1 reigin reigin  1290 Sep  1 04:16 bentukq.class -rw------- 1 reigin reigin  2183 Sep  1 04:16 bentukq.java -rw------- 1 reigin reigin   644 Agu 29 05:09 deret.class -rw------- 1 reigin reigin   841 Agu 29 05:09 deret.java -rw------- 1 reigin reigin  1471 Agu 27 04:30 Fkonversi.class -rw------- 1 reigin reigin  8519 Sep 20 14:44 hello -rw------- 1 reigin reigin   264 Sep 20 09:06 hello.c -rw------- 1 reigin reigin   262 Agu 25 23:52 hello.c~ -rw------- 1 reigin reigin   417 Agu 26 00:00 hello.class -rw------- 1 reigin reigin   281 Agu 26 00:00 hello.java -rw------- 1 reigin reigin   182 Sep  1 18:13 HelloWorld.java -rw------- 1 reigin reigin  8612 Agu 26 01:20 jumlah -rw------- 1 reigin reigin   484 Agu 26 01:20 jumlah.c -rw------- 1 reigin reigin   557 Agu 27 05:43 jumlah.class -rw------- 1 reigin reigin   645 Agu 26 00:22 jumlah.java drwx------ 1 reigin reigin  4096 Sep 17 12:46 lat2 drwx------ 1 reigin reigin  4096 Sep 17 12:46 lat3 -rw------- 1 reigin reigin  8517 Sep 20 09:23 new -rw------- 1 reigin reigin   250 Sep 20 09:23 new.c -rw------- 1 reigin reigin 25424 Agu 31 07:18 noted.txt drwx------ 1 reigin reigin  4096 Sep 20 11:42 ong -rw------- 1 reigin reigin  1006 Agu 31 06:16 suhu.class -rw------- 1 reigin reigin  1354 Agu 31 06:15 suhu.java drwx------ 1 reigin reigin     0 Sep 17 12:46 suhuu -rw------- 1 reigin reigin   645 Agu 26 10:17 terbesar.class -rw------- 1 reigin reigin   865 Agu 26 01:29 terbesar.java -rw------- 1 reigin reigin  8664 Sep  1 11:24 test -rw------- 1 reigin reigin   266 Sep  1 11:24 test.c -rw------- 1 reigin reigin  8758 Agu 29 03:36 tigainteger -rw------- 1 reigin reigin  2343 Agu 29 03:30 tigainteger_.c -rw------- 1 reigin reigin  2345 Agu 29 03:34 tigainteger.c -rw------- 1 reigin reigin  1184 Agu 27 13:46 tigainteger.class -rw------- 1 reigin reigin  2776 Agu 27 13:09 tigainteger.java   grep result :  # mount | grep 'on /media /dev/sda7 on /media/reigin/data type fuseblk (rw,nosuid,nodev,allow_other,default_permissions,blksize=4096)

I have a script that I need to execute on an NTFS partition. The script's permission is set to 600.  I attempted to modify the permissions by running chmod 755 script.sh, which doesn't report a failure or anything - but it also doesn't change the permissions on the file:  $ stat script.sh    File: `script.sh'   Size: 297070      Blocks: 584        IO Block: 4096   regular file Device: 811h/2065d  Inode: 35515       Links: 1 Access: (0600/-rw-------)  Uid: ( 1000/  xxxxxx)   Gid: ( 1000/  xxxxxx) Access: 2010-09-30 14:05:16.041621000 -0700 Modify: 2010-09-30 14:05:05.070157000 -0700 Change: 2010-09-30 14:05:05.070475000 -0700  $ chmod 755 script.sh $ stat script.sh    File: `script.sh'   Size: 297070      Blocks: 584        IO Block: 4096   regular file Device: 811h/2065d  Inode: 35515       Links: 1 Access: (0600/-rw-------)  Uid: ( 1000/  xxxxxx)   Gid: ( 1000/  xxxxxx) Access: 2010-09-30 14:05:16.041621000 -0700 Modify: 2010-09-30 14:05:05.070157000 -0700 Change: 2010-09-30 14:05:05.070475000 -0700   As you can see, it remains unchanged.


In order to compare two floats (float64) for equality in Go, my superficial understanding of IEEE 754 and binary representation of floats makes me think that this is a good solution:  func Equal(a, b float64) bool {     ba := math.Float64bits(a)     bb := math.Float64bits(b)     diff := ba - bb     if diff < 0 {         diff = -diff     }     // accept one bit difference     return diff < 2 }   The question is: Is this a more generic, more precise, and more efficient, way to compare two arbitrarily large or small floats for "almost equalness", than the old abs(diff) < epsilon hack? My reasoning being that if one allows only one bit difference in the binary representation, then the compared numbers certainly could not be any more equal, apart from strict equality, which obviously (as pointed out in the comments) can be checked with == for floats.  Note: I have edited the question to make it more clear.

Consider the following code:   0.1 + 0.2 == 0.3  ->  false   0.1 + 0.2         ->  0.30000000000000004   Why do these inaccuracies happen?


I am trying to register new users to my database using jsp. When i do i get this error java.lang.NullPointerException   From this page i enter the variable to the database  <%@page import="storage.data"%> <%             String ps="";             String v_name="";                v_name =request.getParameter("vname");              ps=request.getParameter("pass");               data dt=new data();                 out.println(v_name + ps);                 try{                      dt.st=dt.cn.createStatement();                     out.println("1");                     String insert="insert into voters values(myseq_voters.nextval,'"+v_name+"','"+ps+"',sysdate)";                     out.println("2");                     dt.st.executeUpdate(insert);                     out.println("3");                         //response.sendRedirect("adduser.jsp?usad="+1);                 }                 catch(Exception ex){                 out.println(ex);                 } %>   And this is my code to connect it to the database  package storage; import java.sql.*;   public class data {          public Connection cn;         public Statement st;         public ResultSet rs;          public data()         {             try{                  Class.forName("oracle.jdbc.OracleDriver");                 //cn=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:XE","mustafadb","111");                 //jdbc:oracle:thin:@localhost:1521:XE [system on Default schema]                 cn=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:XE","voter_db","111");             }             catch(Exception ex){}         } }

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 wonder if that´s normal. When I smooth my mesh it looks kinda odd. If it´s not supposed to do that...what am I doing wrong? How do I fix it?

While rendering a mesh with smooth shading on, I get a dark region/shadow on certain faces. The effect is more evident when smooth shading is applied to a mesh containing ngons, with the ngons turning black when rendered.   The blackening effect is visible in the viewport too.  How can I solve this problem?


I have installed the new Stack Exchange app on my android. Since I log into my SE accounts with my Yahoo OpenID on the desktop site, I tried logging into the SE app through Yahoo but it gives a security warning & doesn't allow me to log into SE.  Can I transfer my existing account from using Yahoo to the Stack Exchange OpenID? I obviously don't want to start fresh with a totally new account.

I no longer use the service that I originally used to register, and would like to change the service I use to log in, or at least add a second account.  Is this possible? How do I change my login provider or associate a backup method to log in?     For more information, see "" in the .


I know we need 1500 points to be able to create tags on Stack Overflow.  Now I wonder about the rules around removing or editing tags.   Would it need consensus of a certain number of people to approve the operation to be effective?

During the re-tagging of questions, tags sometimes become orphaned from existing questions.  Are these zombie tags ever removed from the ?  What if a tag is misspelled and needs to be removed? How do we get rid of it?


There have been quite a few plane crashes the past week and this question popped into my head of which I need a good explanation in science about the possibility of survival or not and why.   Assuming I am on a plane that is quickly losing altitude, just before the plane hits the ground I jump off the plane.   Is it even possible to jump? If I can jump, will the gravitational pull be different and thus make me survive? Would this be equal to jumping off the ground? (Assume that I am immune to the plane explosion)

Imagine you're trapped inside a free falling elevator. Would you decrease your impact impulse by jumping during the fall? When?


I have multiple images that need to float to the bottom right of each "entry" without overlapping the next "entry":    .body {   border-style: solid;   border-color: green;   border-width: 3px;   background-image: url(images/background.gif);   margin-right: 10%;   margin-left: 10%; }  #top {   border-style: solid;   border-color: red;   border-width: 2px;   background-color: white;   text-align: right; }  .good {   border-style: solid;   border-color: orange;   border-width: 2px; }  .entry {   border-style: solid;   border-color: blue;   border-width: 3px;   padding: 5px;   margin-top: 10px;   background-color: rgb(196, 226, 255); }  .date {   border-style: solid;   border-color: purple;   border-width: 2px; }  p {   border-style: solid;   border-color: black;   border-width: 2px; }  #footer {   border-style: solid;   border-color: yellow;   border-width: 3px;   background-color: white; }  .entry img {   overflow: hidden;   float: right;   clear: both; }

 Eating Journal

 Good things to eat and where to find them

09/06/201: Dosa

     Dosas are a favorite in India. They are made from a chickpea and rice batter that is fried on a griddle. In India these are very cheap . . unfortunately, they will cost you in Toronto.

     If you like Indian food, check out Karaikudi in Scarborough.

 08/24/2017: Pide

     If you haven't tried  Pide , also known as Turkish Pizza, your life is not complete.

     My current favorite Pide Restaurant, is Mr. Pide in Greektown, Toronto. Order the  Lahmacun !

 08/22/2017: Falafel

     One reason to wake up every morning -- Falafels!

 If you like falafels, check out Ali Baba's. They have two for the price of one falafel sandwiches on Tuesdays!

 07/10/2017: Spicy Pot

 Ma la xiang guo is a dish from the Sichuan/Chongqing region of China. You can select a number of different items that are cooked together. This dish uses a special numbing spice (ma) together with spicy chilli (la) cooked until fragrant (xiang) in a     big pot (guo).

 Unfortunately, I haven't found a good restaturant in Toronto that serves this. You can make it at home using with this recipe.

 (c) Author of the Eating Journal - Abdel Zhang

     This is how it looks now:    And this is how I want it to look:    Thank you to anyone the can help me!

I have floated images and inset boxes at the top of a container using float:right (or left) many times. Recently I hit a need to float a div at the bottom right corner of another div with the normal text wrap that you get with float (text wrapped above and to the left only).  I thought this must be relatively easy even though float has no bottom value but I haven't been able to do it using a number of techniques and searching the web hasn't come up with anything other than using absolute positioning but this doesn't give the correct word wrap behaviour.  I had thought this would be a very common design but apparently it isn't. If nobody has a suggestion I'll have to break my text up into separate boxes and align the div manually but that is rather precarious and I'd hate to have to do it on every page that needs it.  EDIT: Just a note for anyone who comes here. The question linked above as a duplicate is in fact not a duplicate. The requirement that text wrap around the inset element makes it completely different. In fact, the response to the top voted answer here makes it clear why the answer in the linked question is wrong as a response to this question. Anyway, there still doesn't appear to be a general solution to this problem but some of the solutions posted here and in the linked question may work for specific cases.


I know that when number of protons is high, the nucleus of atoms become unstable due to repulsive force and is radioactive. But why is that the nucleus also becomes unstable when there are too many neutrons?

In basic chemistry, we are taught that an atom has roughly the same number of neutrons and number of protons, this doesn't seems to hold for larger atoms, but it is always roughly proportional (i.e. you seldom find an atom with 100 protons but 1 neutron, that just does not happen). Why is that?


This may seem really trivial, but somehow it really annoys me.  I'm somewhat OCD, so I can't bear to have any unread notifications. Sometimes, when I'm reading a post, and I see a notification, I'll click it, see what it is, then quickly return. However, the notification icon is still there, and I have to refresh to get rid of it.  Also, if I write a comment, then click a link on the page, then click the back button, I have to refresh to see the comment I made.  Yup. I know, first world problem... but it really bothers me. Besides, it's all in the details.  Is this due to the way that the browser caches pages, or a bug in stackexchange?

Browser: Chrome  When the bar at the top of the page appears when you earn a badge, and you then navigate to another page (I clicked on the recent icon), then go back, the bar reappears each time.


I'm new to the community, I hope I'm not doing anything wrong. So, I'm trying to develop a Turing machine simulator. I want to exit a for construct after the if construct (which is inside the for) is executed ONCE. Is there an easy way to do it or I do have to redo all the coding?

I have a loop that is doing some error checking in my PHP code. Originally it looked something like this...  foreach($results as $result) {     if (!$condition) {         $halt = true;         ErrorHandler::addErrorToStack('Unexpected result.');     }      doSomething();  }  if (!$halt) {     // do what I want cos I know there was no error }   This works all well and good, but it is still looping through despite after one error it needn't. Is there a way to escape the loop?


I swim every day/Monday.   But could I say:     I swim each day/Monday.   PS: I know there are already questions like , but please, try to understand my question before marking it duplicate without asking me if the other one replies to my question. I already read the other page, but I ask here if I can use it IN THE PRECISE EXAMPLES I HAVE GIVEN.   (forced to emphasize a lot, because very often people here read only half of the question, and mark it as duplicate)

Practically every part of the banana tree is used by man.   I think this sentence is correct but my grammar book say there should be each instead of every. I know we can't use every as a pronoun but in above sentence every part used as a single unit.  Correct me if I am wrong.


I'm trying to make a walk cycle on a character, but there's a problem. When I loop the walkcycle, the steps kind of ease in and out, making the feet slide even when the character is moving at a constant speed.  Could somebody please point out how to fix this issue? Is there a process to create a walkcycle that ensures that the feet move at a constant speed while they're on the ground?  EDIT This is different from the "duplicate" question in that I am not looking for a general answer on how to make a movement be steady, but specifically how to work with a walk cycle.

When I make an animation, it always starts out slow, then speeds up, then slows down at the end.  I cannot figure out how to fix this.


I have a website which offers different services in different places. So I have a search page that filters services and places. I use wordpress CMS and Search filter pro plugin.  My urls are something like this: www.example.com/search/?_sft_category=ss&_sft_location=mm I wrote code to have different titles and meta description for each filter dynamically. I want these URLs to become indexed and rank in the first page of the Google search results.  The problem is that these pages didn't get indexed.  Even when I fetch these URLs using Google Search Console, it says they are excluded because of canonical tag to the search page.  How can I change it to allow Google to index the pages?

This is a general, community wiki  question and answer pair intended to address any questions   concerning the reasons a site or specific site contents do not appear   in search engine results.      If your question was closed as a duplicate of this question and you   feel that the information provided here does not provide a sufficient   answer, please open a discussion on .   My site (or specific pages on my site) is not appearing in search engine results.  Why isn't my content indexed and what can I do about it?


I am trying to find all units in $\mathbb Z[\sqrt{2}]$. Suppose $x=a+b\sqrt{2}$ is a unit. Then there is $y=c+d\sqrt{2}$ such that $$xy=(a+b\sqrt{2})(c+d\sqrt{2})=1$$ So $$ac+2bd+(ad+bc)\sqrt{2}=1$$  From here one deduces $$ad+bc=0,$$$$ac+2bd=1$$  I've tried to find $c$ and $d$ from here or to get restrictions for $x=a+b\sqrt{2}$ but I couldn't. I would appreciate some help.

How can I show that the units $u$ of $R=\mathbb Z[\sqrt{2}]$ with $u>1$ are $(1+ \sqrt{2})^{n}$ ?   I have proved that the right ones are units because their module is one, and it is said to me to do it by induction on $b$ and multiplication by $-1+\sqrt{2}$. I have already shown that the units of this ring has norm $1$ and all the numbers with norm $1$ are units, this may help.


iPhoto starts launching when iPhone is connected even though it never used to before Yosemite. Steps described in:  does not work in Yosemite. Yosemite seems to ignore the iPhoto settings.

How can I prevent iPhoto/Photos/Image Capture from launching everytime I plug in my iPad/iPhone?


I want to combine multiple mobile 4G internet(Jio) phone connection (Usb Tethering or hot spot) to get high speed internet on my Mac OS X. Solution that i checked are -  Use paid software . (costly) Use Hardware  (costly) First convert from usb to RJ45 (not sure how to do it without using multiple routers) then put Loadbalancer Install software like  (not sure how well will it perform)  If you know some very good/efficient way to do it, please mention it will help others as well ( because many people are working from remote location due to COVID-19)

I have 2 internet sources    3G based Huawei E3533 Dongle (usb) with unlimited bandwidth and speed (Remote NDIS based Internet Sharing Device )  4G Huawei router (Wi-Fi) with limited bandwith and speed but faster in browsing and better ping (online games and streaming)    I want to use first one with IDM and steam downloads and some specific applications , and the second one with steam games , firefox etc   i have tried speedify but the solution is not good for me it combines the 2 sources in one output using vpn .   there is a hardware solution using load balancer in some routers but i can't afford it .  any software solution ?


I render the html  in php ,and use jQuery   .they have such  html code :

   In some condition , it will remove this

, and become :

   I have to judge this two situations ,I try  different  way , but the result is strange .    var selectTr  = $('.selectClass') ;     if( selectTr ){       console.log("i am undefined") ;     }   it do not print anything .    var selectTr  = $('.selectClass') ;     if( typeof (selectTr) == "undefined"  ){       console.log("i am undefined") ;     }   it do not print "i am undefined " .  so i  try  it  console.log(typeof (selectTr))  , it is object  .  My problem is that :  how to judge a empty object and why it is object instead of null  or undefined?

How can I check the existence of an element in jQuery?  The current code that I have is this:  if ($(selector).length > 0) {     // Do something }   Is there a more elegant way to approach this? Perhaps a plugin or a function?


Sorry to bother, however, a friend and I have been sitting at this problem for a while and we seem to be quite stuck. We have to create a PriorityQueue class which interacts with an Elements class. The idea in the main method is to put elements according to a priority into the queue and then return those elements in the right order. Now, if we try to use this code, we get an java.lang.NullPointerException. Our getPriority looks like this:  public int getPriority() {  return priority; }   We really don't know where the Null Pointer Exception comes from...  public class PriorityQueue {  static final int SIZE = 32;  Element[] q = new Element[SIZE];  int len;  int head = 31;  int tail = 31;   // Insert an element into the queue according to its priority  boolean put(Element x) {   if (head == 0) { return false;}    else {    for (int g=31; g >= 0; g--) {     if (q[g].getPriority() == x.getPriority()||(q[g].getPriority() < x.getPriority() && q[g-1].getPriority() > x.getPriority())) {      for (int y=g; y >= head; y--) {       Element z = q[y];       q[y] = x;       q[y-1] = z;      }     }    }   } head--; return true; }  // Return the element with the highest priority from the queue Element get() { return q[head]; }  // Return the queue length int length() { return q.length; }  // Print the queue contents public String toString() {     return q.toString(); } }   Thank you very much 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?


2670.82+202.38   2873.2000000000003  Try it for yourself. I have no idea what's going on here. Is this a quark of Javascript? The Chrome Browser?

Consider the following code:   0.1 + 0.2 == 0.3  ->  false   0.1 + 0.2         ->  0.30000000000000004   Why do these inaccuracies happen?


We know that waves are of two types: transverse and longitudinal, and we have studied about de Broglie waves as well,    so which one of them is it? Or we have other means to classify them?

What does a  wave look like? Are de Broglie waves transverse or longitudinal?   Can they be polarized?    What about the de Broglie wave of a ground state neutral spin-zero Helium 4 atom?   What experimental evidence do we have that supports the detailed nature of a de Broglie wave?     I have always assumed that de Broglie waves were mathematically  identical to electromagnetic waves, but I just realized there is no basis for this assumption, and in fact it must be false, unless there is an analogue to both the magnetic and the electric components of the electromagnetic wave.  So what does a de Broglie wave "look like"?


Imagine a situation where there are 10 people 5 of which adamantly want to close a question, the other 5 adamantly want it to remain open.  So the first 5 people cast close votes and the question becomes closed.  Then the next 5 people case reopen votes and the question is reopened.  Now what happens?   Can the first 5 people vote to close again? or can only different users vote to close now?  What happens if the question keeps getting closed and reopened?

When the OP posted , the contents looked like "AAAA AAAA AAAAAAAAA". Obviously, no-one was going to understand this, so we downvoted and voted to close. After closure, I immediately voted to delete the question. A few seconds later, the OP updated the question. I voted to re-open, and a few minutes later, the question was re-opened.  I've just reviewed the Q&A, and it's garbage:   The question is unclear (the fiddle doesn't match the question's code). The only answer was was invalidated after the question was updated again (it pointed to a typo). The invalid answer was accepted with the  "My problem was somewhere else but I did learn that JSFiddle needs the tag table. thanks" (note: has nothing to do with the question).   For these reasons, I decided to cast a close vote, which summoned the following screen:   As you can see, there are no pending close votes, but the screen still shows that I have already cast a close vote. This looks like a bug (possibly caused by my previous delete vote?).


A question on  got me thinking, ignoring , "Do we weigh less in the morning?"  During the night, the sun is above us, and the earth below us. Conversely, at night, both the earth and the sun are "below" us. Our mass obviously stays the same, but would there be a greater gravitational pull on us since the added gravity from both the earth and the sun on the other side are acting on us?  Or do we not notice the gravitational pull from the sun, for the same reason astronauts aboard the ISS don't notice the gravitational pull from the earth?

Using $g = \frac{Gm}{r^2}$, the force on a point mass located at 1 AU from the Sun ($m = 2 \cdot 10^{30} \text{ kg}$) is about ~0.006 N/kg.  Does that mean that, e.g., a 70 kg person is ~42g lighter during the day, and ~42g heavier at night? That seems like it could make a big difference for things like measuring gold bars or other weight-sensitive items. (Gold arbitrage: buy your gold during the day and sell it during the night! Risk-free profit!)  This makes me suspect that I'm overlooking something obvious, because a ~0.05% weight difference seems like something everyone would have noticed long ago. So what am I missing?    Edit: A few answers below indicate that there shouldn't be any weight difference, because the Earth orbits the Sun in free-fall. But if that's the reason, does that mean that a 1:1 tidally-locked Earth-Sun system wouldn't experience differential gravity from the Sun on opposite sides? That doesn't seem right.


I have a list that looks like this: name_list=['ramon del rio,georgina genes,jorge lópez']  And I want to create a byte array. To do this I am running the following code, for i in name_list:     name_list_bytes.append(list(map(lambda x: str.encode(x, "UTF-8"), i.split(','))))  print(name_list_bytes)  [b'ramon del rio', b'georgina genes', b'jorge l\xf3pez']  As you can see the name "jorge lópez" is transformed "to "jorge l\xf3pez". How can I overpass this transformation and transform the name correctly? [EDIT] I found out that python encode function has a 2nd argument that controls the characters and what should python do when those characters are present in the string. for i in name_list:     name_list_bytes.append(list(map(lambda x: str.encode(x, "ascii", "ignore"), i.split(','))))  print(name_list_bytes)  [b'ramon del rio', b'georgina genes', b'jorge lpez'] #removes the unknown asscii character.  The "ignore" arguments removes the ascii characters, although I am looking for replacing them with the proper value. I guess that the best way although tedious is to identify those characters and replace them by hand.

I have a Unicode string in Python, and I would like to remove all the accents (diacritics). I found on the web an elegant way to do this (in Java):  convert the Unicode string to its long normalized form (with a separate character for letters and diacritics) remove all the characters whose Unicode type is "diacritic".  Do I need to install a library such as pyICU or is this possible with just the Python standard library?  And what about python 3? Important note: I would like to avoid code with an explicit mapping from accented characters to their non-accented counterpart.


I am trying to make a script which is supposed to open a new gnome-terminal and issue a command (launch a jetty server). If I try only : gnome-terminal, a new gnome-terminal is opened. If I try : gnome-terminal -e ls, I get a warning message :  Option “-e” is deprecated and might be removed in a later version of gnome-terminal. Use “-- ” to terminate the options and put the command line to execute after it.  Here, the new gnome-terminal is not always opened. If I try this command fast 10 times, maybe 2 terminal will open... Same if I try with the recommended syntax : gnome-terminal -- ls. What is the correct way to achieve this?

So I know if I type gnome-terminal or xterm, a new window will be popped out. Then I checked the man page for these two, nothing relevant found.  Then I noticed under Mac you can do it with the program open. But it seems under Linux it's not that trivial.  Does anyone have experience?


GR/Big Bang Model implies that there was a singularity about 13 billion years ago, in which all the matter and energy along with the observable universe (or perhaps, the entire universe) was contained. This small point yielded an infinite density, coupled with infinite temperature and infinite energy. Also that it was infinitely small. Would it be safe to presume that spacetime curved infinitely during the era of this bewildering singularity? And if spacetime curves, it gives rise to gravity as stated by GR. Since there was infinite spacetime curvature, would there have been infinite gravity?

TV documentaries invariably show the Big Bang as an exploding ball of fire expanding outwards. Did the Big Bang really explode outwards from a point like this? If not, what did happen?


Sometimes, there are questions on here about undergraduate students publishing research (see , , and ). The answers don't seem particularly surprised that this is happening or try to dissuade the asker, they treat it like a normal question.  In my entire life, I've never heard of undergraduates publishing results apart from a handful of examples from famous science prodigies.  Furthermore, my experience of undergraduate was not conducive at all to publishing. I graduated from a mediocre UK university, and there was no original research done at all. Undergraduate is for getting you up to speed on the foundations of a field, preparing you for postgraduate where you study one sub-field, then a PhD where you push the boundaries of a sub-sub-field.  The questions linked above give advice like, "Discuss it with your supervisor". But as far as I'm aware undergraduates don't have supervisors.  Is this really as common as it would seem from questions on here? Is it a regional thing? Something that happens only at top universities?

I’m currently in the first semester of MSc of psychology in a university in Germany and we got a lecturer from a university abroad who wanted to know what we had published. To his surprise, none of us had any publications. For us at least, not having any publications when entering the graduate program is normal.  I know of a couple of peers who were able to publish their bachelor’s thesis and one person who had several publications even before he started his masters, but at our university those are the exception, rather than the rule.  How is the situation in other countries and disciplines? Do undergraduates generally have any publications?


With Windows XP ending support next Tuesday, I was scrapped for time to find another replacement OS. I was told to install a Linux-based operating system as a replacement and I decided to try this version out. I didn't want to pay someone to install it for me, so I tried it on my own.  I downloaded "Ubuntu 12.04 LTS- 32-bit" () and waited about an hour for it to download the 730MB file. It was an image file (ISO file), so I used  "Free ISO Burner" to attempt to burn it. After three failed attempts to burn the file on a 4.7GB disk, I extracted the file with Winrar. I left the room and came back to find that the Ubuntu menu was up. The 730MB OS took up ALL of the disk space for the 4.7 GB DVD for some reason. Anyways, I clicked "Demo and Full Installation," then clicked on "Help Me Boot From a Live CD," since the computer didn't boot from the DVD after four attempts. It looked like it was working, but it stopped about the quarter of the way with the message:  An error has occurred: Permission denied. For more information please see the log file: c:\docume~1\hp\locals~1\temp\wubi-12.04.4-rev280.log   Link to Log ()  And that's my problem so far. Do I erase everything that was written on that disk and try to burn it over? Do I need an additional program to run it?   My specs:   HP (L2000) Windows XP Professional Edition (32-bit) Processor: AMD Turion(tm) 64 Mobile Technology ML-40 Hard drive: 93GB worth of space available (45GB used) RAM: 1024MB Display adapter: ATI Mobility Radeon Xpress 200 (Video RAM: 128MB)

I would like to see a full how-to guide on how to install Ubuntu.


Is there an effective tool to convert C# code to Java code?

I needed to convert a Java 1.5se app to C# 2.0.  Does anyone know of a tool (preferably free/open source) to do this?


My problem is that I can't ring or loop-cut a set of polygons that are co-planar.    This is the sort of thing that's happening, as you can see I can only affect 2 faces at a time. I've cleaned up the mesh, welded all vert's and made sure there aren't any holes in the mesh in the area that I was to cut a ring/loop.

Alright so I've seen some postings about loop cuts and done some research. I am very new to blender and modeling overall. I am trying to loop cut this concrete barrier. Now I'm following a tutorial and kind of did my own thing in some areas. I cleaned it up following some instructions in another answer here on stack exchange.  I can't for the life of me figure out why I can loop cut around the whole bottom:   ...but not the whole middle:   I see this marked as answered by another question. That question refers to ngons and inside faces. Now once again I'm totally new to this. I looked on the inside. I don't believe I have inside faces or any ngons by the terms I've read online in my research.  Here is a wireframe picture and the inside view:     Maybe I'm missing something the answers on other posts are saying. If so and you know what it is I'd be very appreciative of what it is.


So I want to replace PulseAudio 8 on my Ubuntu 16.04 with PulseAudio 11 (because the latter has better support for bluetooth headsets).  I've managed to compile PulseAudio 11 from source, and everything seems to work fine after I do sudo make install, however, every once in a while Ubuntu Software Updater upgrades PulseAudio and rolls me back to version 8.  I cannot just uninstall the standard PulseAudio package, because there's a ton of packages that depend on it, as well as a bunch of libraries that PulseAudio itself needs (and which Ubuntu's package manager wants to remove when their dependency disappears).  Is there a "proper" way of doing this, that plays nicely with packages?

I installed program (call it, for example,progA) by building it from source code, and then finally calling sudo make install and sudo ldconfig.   However, it seems apt-get hasn't gotten the memo, because when installing progB, which depends on progA, apt-get recommends I also install progA. Why is this, and what could I do?


All in the question. I'm not sure how to do it because I keep running into more problems. Please explain your steps.

In how many ways can $7$ girls and $3$ boys sit on a bench in such a way that every boy sits next to at least one girl  The answer is supposedly $1,693,440 + 423,360 = 2,116,800$


Starting with assuming $A[x]$ is a domain I only take the elements of $A$ and view them as polynomials of degree zero and use the hypothesis  My problem is going the other way:  Let $A[x]$ be a domain, we take two polynomials $\sum_{i=0}^n a_i x^i$ and $\sum_{j=0}^m b_j x^j$ with $a_i, b_j \in A$, $i \in \{1,...,n\}$ and $j \in \{1,...,m\}$ then:  $$\biggl(\sum_{i=0}^n a_i x^i\biggr)\biggl(\sum_{j=0}^mb_j x^j\biggr)=\sum_{k=0}^{m+n}\biggl(\sum_{i+j=k} a_i b_j \biggr)x^k =0$$  I believe that I have to prove the final sum is zero only if every $a_ib_j$ is zero but what if two elements cancel each other out without either being zero.  Any leads would be appreciated.

Theorem: If $R$ is an integral domain, then $R[x]$ is an integral domain as well.  Proof: Let $f(x)=a_0+a_1x+a_2x^2+\cdots+a_nx^n$ and $g(x)=b_0+b_1x+b_2x^2+\cdots+b_mx^m$ be two elements of $R[x]$. Let $0\leq i\leq n$ and $0\leq j\leq m$ such that $i$ & $j$ are the smalles numbers such that $a_i\ne 0$ & $b_j\ne 0$. $f(x)\cdot g(x)=\sum_{i=0}^{n+m}{c_ix^i}.$ $c_{i+j}=\overbrace{a_{i+j}b_0+a_{i+j-1}b_1+\cdots +a_{i+1}b_{j-1}}^{=0} +\overbrace{a_ib_j}^{\ne 0}+\overbrace{a_{i-1}b_{j+1}+\cdots+a_0b_{i+j}}^{=0}$ $=a_i+b_j\ne 0\Longrightarrow f(x)g(x)\ne 0$    I don't know why $a_{i+j}b_0+a_{i+j-1}b_1+\cdots +a_{i+1}b_{j-1}=0$ and $a_{i-1}b_{j+1}+\cdots+a_0b_{i+j}=0$.


I have a table where there are 2 columns: optionValues and optionNames . optionNames contains the text of a combobox and optionValues the value of each text , both are separated with ~. For example :  optionValues | optionNames    0~1       |   male~female   What I am trying is to create a function which will take as argument an optionValue and will return the optionName. Using the example above:  fn.GetOptionName(1) --will return `female`   How I can separate the values and get back the correct one?  This is what I started with but it wont work because it doesn't separate the values:  select @on = OptionNames from dbo.Table  where tablename = @tablename and fieldname = @fieldname and optionvalues = @fieldvalue   (I cannot change the db schema no matter if its good or bad)  EDIT  Found this function which returns a substring in a specific position:

Using SQL Server, how do I split a string so I can access item x?  Take a string "Hello John Smith". How can I split the string by space and access the item at index 1 which should return "John"?


so I have a problem, I need to put in a dot symbol between my equations in verbatim mode. For some reason it does not work in verbatim mode, but I surely need my equations in verbatim. So do you guys know how to solve it?  here is are the screenshots

I cannot insert mathematics symbols inside a verbatim mode in LaTeX. This how I do:  \usepackage{alltt}   \begin{verbatim}   1- Train triggers model \(  X_{i}  \)  -> Y_j (X_i: source phrase  composed of i words, Y_j : target phrase composed of j words   \end{verbatim}   Any ideas?


The following icon in the new profile:    feels like a refresh icon in a browser's address bar, not a "member for.." icon. It does not represent that, I suggest an icon similar to the "users" icon in some SE sites, something like:     but with one person in the icon. I know it is way too silly to be considered, but just saying it.

Update:  Thanks for all the feedback and bug reports! I am locking this thread so people don't keep answering it when we no longer monitor it.  If you see a bug or want to raise a feature request, please do so in the usual manner, as a new question.    Some of you may have noticed that  the  and  pages that we have been talking about for a while now on .  Most? Well, yes, the new design is dependent on a SE network-wide update (a new base css framework) that the design team have been working on. This is an ongoing effort and we will be launching the new pages as sites are moved to the new design.  You've all been hugely helpful already - much of what we love most in here came from  and  you gave us on Meta.     But it's possible that it's not quite perfect yet. If you find any bugs and have any feedback to give, please post these as answers to this post.  Just post one issue per answer - that would help us focus on specific items one at a time.


A lot of the time, it's handy to use outside resources to post information relevant to a question or answer, like  or .   On the one hand, link rot is a consideration, but would it be worthwhile to add a "useful links" page to the Help Center?

Create or allow for a community-wiki editable home page per tag. One where we could place essentially the tag-specific FAQ and other tag-specific links.


I’m a bit baffled about these two structures: going to and will. Here’s an example of where I get confused:   Liverpool’s players are known to be skilled. They ....... the match easily.  A) will win.    B) are going to win.  What is the right answer and why?

I know several questions were asked about the difference between "going to" and "will". Based on several answers (see, for instance, ,  and ), I understood that "will" is more spontaneous and "going to" is used with more planned actions.  So, it seems that everything is pretty fine. However, in , Kosmonaut has an answer in which he states: "Let's say that tomorrow you will walk your dog from 7 - 8 AM".  On the one hand, you probably planned to walk your dog long before and thus I should use "Let's say that tomorrow you're going to walk your dog from 7 - 8 am".   On the other hand, since I'm saying "let's say...", I'm deciding right now (thus, unplanned) that you will walk your dog. So, even though in this hypothetical situation you made a plan, I'm in a more spontaneous mood deciding right now that that's what you will do tomorrow, and, thus, I should use "will".  Which one (if any) of the above explanations is right?


I am new to Ubuntu and  I wonder if there's an application that i can install so  I can create mosaic out of my photos.  Any help is much appreciated.

I have a collection of images and an image that I want to generate from that collection.  What software is there available for Ubuntu for generating ? How to do it?


$a_k$ with $k \in \mathbb{N_0}$ is a sequence. Prove using the direct comparison test: $\sum^{\infty}_{k=0} a_k$  converges absolutely $\Rightarrow \sum^{\infty}_{k=0} a_k^2$ converges  $|a_k| \leq |a_k^2| \leq |c_k|$ I have to find a $|c_k| \geq |a_k^2|$, which absolutely converges. Then following the direct comparison test $a_k^2$ will also converge absolutely. Let $c_k := a_k^3$. Then: $|a_k| \leq |a_k^2| \leq |a_k^3|$ But if I do this then I wouldn't have the proper structure: $\sum^{\infty}_{k=0} a_k$  converges absolutely $\Rightarrow $ ........$\Rightarrow\sum^{\infty}_{k=0} a_k^2$ converges My try was: $\sum^{\infty}_{k=0} a_k$  converges absolutely $\Rightarrow a_k$ is a null sequence $\Rightarrow$ ... How do I get from a lesser sequence to a bigger sequence? One way I could think of was that, if $a_k$ is a fracture, where the denominator > numerator, then $a_k \geq a_k^2$ . This would fit with the direct domparison test. So I'm not sure how to go on.

Suppose that the series $\sum_{n=1}^{\infty}a_{n}$ converges while $\sum_{n=1}^{\infty}a_{n}^2$ diverges. Prove that $\sum_{n=1}^{\infty}a_{n}$ converges conditionally.


I have a player in one of the games I'm running that's a Goliath Paladin. He uses a greataxe and recently asked me if he could deal more damage like a "Large" monster could since he has a powerful build. The following is quoted from p.278 of the DMG:  Big monsters typically wield oversized weapons that deal extra dice of damage on a hit. Double the weapon dice if the creature is Large, triple the weapon dice if the creature is Huge, quadruple the weapon dice if it's Gargantuan...  So since he counts as one size larger than medium, I thought that this rule could apply to him. However, the powerful build mechanic only states:  You count as one size larger when determining your carrying capacity and the weight you can push, drag, or lift.  My players are usually good, and don't try to "break the game", but before I make a decision, I would like to know what a community of other players and GMs would think about this. Would he be able to deal extra damage?

With the new Elemental Evil Player's Companion released awhile ago, Goliaths were added to 5e. I'm unfamiliar with 3.5 and previous editions, but I know that they were included and wielding large weapons was a thing you could potentially do. Goliaths in 5e have the same trait as in 3.5e, it seems:  Powerful Build. You count as one size larger when determining your carrying capacity and the weight you can push, drag, or lift.  So, does this mean a Goliath can wield large-sized weapons? The pushing/dragging/lifting capacity for a strong Goliath (say 16 Str) would be nearly 1000 lbs (16 * 60) and the carrying capacity half of that. A heavy weapon weighs between 10-20 lbs, but this IS significant weight to be throwing around in battle, but I am unsure of the weight of a large weapon. My DM and I are unsure of the mechanics if a Goliath could. We talked about doing an extra die roll for damage, which is extremely strong, or treating the Goliath as if he were under the Enlarged Creature spell, which gives a +4 to damage, which seems more balanced in our opinions. Are there rules for wielding large weapons in 5e? Can a Goliath wield large weapons out of the box with no feats?


This is the curve I want to turn into a mesh:   This is what the outliner looks like:   Someone on this forum told me to select the BezierCircle, go to Object>Convert to>Mesh from curve  But if I do that, it looks like this:   I've messed around with this thing for literal hours, and I just can't figure it out. All I want is for Blender to turn that handle, into a mesh which I can edit like any other mesh.  This information may also be needed:

I followed a youtube tutorial to make the handle of this watering can. I had to make a path and a "bezier" circle, I don't really know what that means.    The outliner looks like this    I can't actually select the bezier thing or the curve by clicking on them, I have to select them in the Outliner. I'd like to do away with all of that stuff, it has the right shape now, I just want the mesh that you can see in the viewport, so I can reduce the polycount and export it. How do I do this? I tried pressing alt+C a couple of times with those things selected, as I found on the internet, but that didn't work.  Edit: Here's the file:


Prove that every planar graph is the union of at most $5$ acyclic   graphs.      Reminder: As union of two graphs $G_1(V_1, E_1)$ and $G_2(V_2, E_2)$ we consider the graph $G(V_1\cup V_2,E_1\cup E_2)$   I have tried induction on the number of vertices, but I seem to miss something

How can I prove that every planar graph can be expressed as a union of (maximum) five edge-disjoint forests?  Only thing I can think about is going somehow like the $5$ color theorem but I get stuck in the middle. Or with induction, but still something doesn't fit. Can you help?


I have a SOQL query on one of my org's custom metadata types that looks like: List<Metadata_Type__mdt> = [ SELECT String1__c, String2__c                                FROM Metadata_Type__mdt                               WHERE Number__c > 0                            ORDER BY Number__c asc ];  In this case String1__c and String2__c are both text fields and Number__c is a number field we use to sort the custom metadata records. When I look at the results of this query, though, they are ordered in such a fashion that the Number__c value for the records (in returned order) would look like 5, 7, 3, 4, 1, 6, 2. I also have something similar happen with another custom metadata type query that sorts using a text field. Is there something missing or incorrect with this query that could be causing a malformed ORDER BY result?

Cannot sort on a soql-request in a custom meta data type. When i perform SELECT .. FROM x__mdt WHERE ... ORDER BY x. Then field x cannot be numeric to get a correct order. Change it to a string-field ordering works ok. Playing with ASC/DESC makes no difference!


I do have a requirement like I need to calculate a person age with sysdate. Calculating the persons age should be exactly greater or lesser than 75years and 09 months with the sysdate. but at some scnearios its not working out. can any one of help with this issues.  IF TO_CHAR(bday,'mm/dd')='02/29' THEN age = ADD_MONTHS(bday-1,12*75); ELSE age = ADD_MONTHS(bday,12*75); END IF;   but this is not working at some conditions. could anyone help with this requirement

What would be the best way to calculate someone's age in years, months, and days in T-SQL (SQL Server 2000)?  The datediff function doesn't handle year boundaries well, plus getting the months and days separate will be a bear.  I know I can do it on the client side relatively easily, but I'd like to have it done in my .


Find all couples $(n,k)$ , $n \geq 2$ and  $0\leq $ k $ \leq n - 1$, such as : $\binom nk$ and $\binom {n}{k+1}$ are relatively prime. I first tried finding a link between the two using combinatorics, but it wasn't that easy, since they don't have a particular order, and any could be greater than the other. Then I recalled that if $n$ is prime, it's guaranteed that it divides both of them, I tried to apply this in a more general scenario, using a prime divisor of $n$, but it didn't succeed. Any ideas or tips?

Is the following conjecture true?     Given an $n>1$ and a $k$ such that $0<k<n$ then $\gcd\left(\binom{n}{k}, n\right)>1$   This was a question asked in my old Number Theory course that I recently remembered. It was posed after we learned that $p\mid\binom{p}{k}$ for $0<k<p$. We never resolved it either way. I expect it to be true and have an elegant answer, but I haven't been able to prove it.


I'm working on a project on LaTeX which includes heavy externalization of pgfplots figures, so I've hidden everything in a tex subfolder of the main one and work only there. Every time, though, I have to scan through all the files (they're like an hundred or more) to search my .tex source or my custom .sty files.  I've found the option output-directory and I'm using it, but it only moves the main .log and .aux files, and the .md5 from the externalized figures, however every other .pdf and .log relative to any single figure created with pgfplots is still in the main directory.  I usually compile straight from the shell and use vim to write the files. Can I do this?

The example bellow comes from the  (p610). It does not work my computer. Note that it works when I comment the option [prefix=figures/]. Any idea of what could go wrong here?  \documentclass{article} % main document, called main.tex \usepackage{tikz} \usetikzlibrary{external} \tikzexternalize[prefix=figures/] % activate  \begin{document} \tikzsetnextfilename{trees} \begin{tikzpicture} % will be written to ’figures/trees.pdf’ \node {root} child {node {left}} child {node {right} child {node {child}} child {node {child}} }; \end{tikzpicture} \tikzsetnextfilename{simple} A simple image is \tikz \fill (0,0) circle(5pt);. % will be written to ’figures/simple.pdf’ \begin{tikzpicture} % will be written to ’figures/main-figure0.pdf’ \draw[help lines] (0,0) grid (5,5); \end{tikzpicture} \end{document}


when i am selecting torus this(image attached) is what i am getting and there is no option of changing minor radius.

When you first add a cylinder, you have the option to change the number of vertices, etc, but once you do anything else in blender, it seems you no longer can edit those parameters.   Is there a setting anywhere or an add-on that allows these parameters to be edited later on? If not, how easy would such an addon/feature be to create for anyone reading this?


Consider following piece of code:  #include <iostream> using namespace std;  int main() {     double x = 1.77;     double y = 1.76;      double diff = x-y;     cout << "x-y = " << diff << endl;     if (diff <= 0.01)     {         cout << "x and y differ by less than 1.0/100 ..." << endl;     }     return 0; }   Following output I am getting:  x-y = 0.01   But I don't see the print x and y differ by less than 1.0/100... which is expected here because difference between x and y is 0.01.

Consider the following code:   0.1 + 0.2 == 0.3  ->  false   0.1 + 0.2         ->  0.30000000000000004   Why do these inaccuracies happen?


I am currently working on android stenography project, but at registration time the error was occur   "java.lang.NullPointerException: Attempt to invoke virtual method 'boolean com.example.devd.stangnograpyonimage.DBHelper.insertData(java.lang.String, java.lang.String, java.lang.String, java.lang.String)' on a null object reference"   DataBaseHelper.java  public static final String DATABASE_NAME = "STAGNODB"; public static final String TABLE_NAME = "Satgno_Table"; //public static final String COLUUMN_ID  = "ID"; public static final String COLUUMN_USERNAME  = "UserName"; public static final String COLUUMN_PASSWORD = "Password"; public static final String COLUUMN_NAME = "Name"; public static final String COLUUMN_EMAIL = "Email";   public DBHelper(Context context) {      super(context, DATABASE_NAME, null, 1); }  @Override public void onCreate(SQLiteDatabase db) {     try {         db.execSQL("CREATE TABLE " + TABLE_NAME + "(" + COLUUMN_USERNAME + " VARCHAR(50),"                 + COLUUMN_PASSWORD + " VARCHAR(50),"                 + COLUUMN_NAME + " VARCHAR(50),"                 + COLUUMN_EMAIL + " VARCHAR(50));", null);     }catch (Exception e){         Log.e("SQL Table Creation ", "Table Not Created");     } }  @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {     db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME); }  public  boolean insertData(String userName, String password, String name, String email){     SQLiteDatabase mydb = this.getWritableDatabase();     ContentValues cv = new ContentValues();     cv.put(COLUUMN_USERNAME, userName);     cv.put(COLUUMN_PASSWORD, password);     cv.put(COLUUMN_NAME, name);     cv.put(COLUUMN_EMAIL, email);     long result = mydb.insert(TABLE_NAME, null, cv);      if(result == -1){         return  false;     }     else {         return  true;     } }   MainActivity.java  public class MainActivity extends AppCompatActivity {     DBHelper myDB;     EditText etUserName, etPassword, etName, etEmail;     Button btnRegister, btnLogin;     @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         etUserName = (EditText) findViewById(R.id.etUserName);         etPassword = (EditText) findViewById(R.id.etPassword);         etName = (EditText) findViewById(R.id.etName);         etEmail = (EditText) findViewById(R.id.etEmail);         btnRegister = (Button) findViewById(R.id.btnRegister);         btnLogin = (Button) findViewById(R.id.btnLogin);         register();     }     public void register() {         btnRegister.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 boolean isInserted = myDB.insertData(etUserName.getText().toString(), etPassword.getText().toString(), etName.getText().toString(), etEmail.getText().toString());                 if(isInserted==true){                     Toast.makeText(MainActivity.this,"Data Inserted", Toast.LENGTH_LONG).show();                 }                 else {                     Toast.makeText(MainActivity.this,"Data not Inserted", Toast.LENGTH_LONG).show();                 }             }         });     } }

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 have the bootable dvd from the Aug 2015 copy of Linux Format Mag but cannot proceed past the login .. what is the default user / password?

When I boot Ubuntu 10.04.3 from a live CD, it asks me to enter a username and password. I have not booted before, and I haven't created an account.


$$0 = a(x^2 + \frac ba x) + c = a(x^2 + \frac ba x + \frac{b^2}{4a^2}) -\frac{b^2}{4a} + c$$ $$= a(x + \frac b{2a})^2 + c - \frac{b^2}{4a}$$ It is more than obvious that the above equation simplifies to the Quadratic Formula, yet I was curious as to why the method of simplifying is done as seen above from the original $ax^2 + bx + c = 0$ in that way, for instance how does it become $a(x^2 + \frac bax) + c$?

In algebra, all quadratic problems can be solved by using the quadratic formula. I read a couple of books, and they told me only HOW and WHEN to use this formula, but they don't tell me WHY I can use it. I have tried to figure it out by proving these two equations are equal, but I can't.  Why can I use $x = \dfrac{-b\pm \sqrt{b^{2} - 4 ac}}{2a}$ to solve all quadratic equations?


I would like to know if there is any way to change the login screen wallpaper, without changing the desktop wallpaper. In other words, how to independently change the login screen wallpaper. Thanks.

This has been bothering me very much. i have memory that Ubuntu 12.04 had this configuration? am i wrong? finally, is it possible for the login screen to have different wallpaper from the desktop? is this possible in Ubuntu 15.04? i would appreciate a stable understandable response. thanks :)  -ben


That'd save us some battery while being nice on the eyes at night. I love the black interface that reddit is fun app has and would love to see same on this app. Thanks.

Please provide a setting to select themes and an option for a white-text-over-dark-background (e.g. twilight, monokai) theme for the Android app.  This would make reading the posts much easier on the eyes.


I'm trying to loop through each files from current directory and subdirectories. But the problem is file names with blank-space are getting treated as separate files. How do I prevent that. I want to use for loop, here is my current code. for file in $(find . -type f -print) do     echo "$file"; done;

This question is inspired by    I see these constructs  for file in `find . -type f -name ...`; do smth with ${file}; done   and  for dir in $(find . -type d -name ...); do smth with ${dir}; done   being used here almost on a daily basis even if some people take the time to comment on those posts explaining why this kind of stuff should be avoided... Seeing the number of such posts (and the fact that sometimes those comments are simply ignored) I thought I might as well ask a question:  Why is looping over find's output bad practice and what's the proper way to run one or more commands for each file name/path returned by find ?


Why can't we have simple HTML in comments; or at least newlines and tabs?  I think it would be good if we had such functionality.

Hello  I would like to see changes in the comment section. Presently, we cannot start a new line. Everything gets posted in one line. Even the code looks horrible.   Also, to color the code in comments.


Does initialization statement can't be used in the case of switch statement ? Here is my code  #include <iostream> int nosenseFun(int choice){     switch(choice){         case 1:             int temp = 1;             return temp;         case 2:             break;         default:             return 0;     }     return 2; } int main(){     return 0; }   And when I compile it using g++, I got error message like that  testSwitch.cpp:14:14: error: jump to case label [-fpermissive] testSwitch.cpp:12:17: error:   crosses initialization of ‘int temp’   Does initialization statement can't be used in the case of switch statement ?

I've always wondered this - why can't you declare variables after a case label in a switch statement?  In C++ you can declare variables pretty much anywhere (and declaring them close to first use is obviously a good thing) but the following still won't work:  switch (val)   {   case VAL:     // This won't work   int newVal = 42;     break; case ANOTHER_VAL:     ...   break; }     The above gives me the following error (MSC):     initialization of 'newVal' is skipped by 'case' label   This seems to be a limitation in other languages too.  Why is this such a problem?


the sum of the series $\sum_{n=1}^\infty \frac{1}{2^{n}}$ is 1. It is easy to find since it is a g.p.  the series $\sum_{n=1}^\infty \frac{n}{2^{n}}$ is convergent by ratio test. How will find the infinite sum? I am  trying to rearrange the terms and to use the rearrangement theorem, but I can't complete


how to break automatically the lines in the following table? Thanks.  \documentclass[a4paper, 12pt]{report}     \usepackage[utf8]{inputenc} \usepackage[french]{babel} \usepackage{subcaption} \usepackage{verbatim} \usepackage{enumerate} \usepackage{makeidx} \usepackage{topcapt} \usepackage{setspace} \usepackage{rotfloat} \usepackage{makecell}  \begin{table}[H]     %\begin{center}     \topcaption{Comparaison des aspects généraux des méthodes d'analyse et de modélisation des connaissances.}     \noindent\makebox[\textwidth]     {         \begin{tabular}{|*{8}{c|}}         \hline         \diaghead{\theadfont Diag ColumnmnHead II}%         {Auteurs}{Attributs}&\thead{Caractéristiques}&\thead{Objectif}&\thead{Destinaires}&\thead{Type}&\multicolumn{2}{c|}{\thead{Etendue}}&\thead{Propriétés}\\         \hline         \footnotesize{} & \footnotesize{} & \footnotesize{} & \footnotesize{Ing pédagogique} & \footnotesize{Ing logicielle}& \footnotesize{}\\         \hline         \hline         \footnotesize{HNa XXXXXXXXXXXX} & \footnotesize{Basé sur l'analyse du comportement d’apprenants et l'analyse des traces d’usage (Usage Tracking Language)} & \footnotesize{Réingénierie d’un scénario pédagogique, Constitution d'une mémoire des indicateurs partagés} & \footnotesize{Enseignants} & \footnotesize{Patrons} & \footnotesize{x} & \footnotesize{-} & \footnotesize{}\\         \hline         \footnotesize{} & \footnotesize{} & \footnotesize{} & \footnotesize{} & \footnotesize{} & \footnotesize{} & \footnotesize{}\\         \hline         \footnotesize{} & \footnotesize{} & \footnotesize{} & \footnotesize{} & \footnotesize{} & \footnotesize{} & \footnotesize{}\\         \hline         \end{tabular}     }     %\end{center}     \label{tab: aspectsGeneraux} \end{table}

I am creating table in LaTeX and I need to get the text to perform line break automaticaly when it's too long. And if possible, I'd like to get the text alignment to the left. Is it possible to handle this situation?