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How should I deal with becoming discouraged as a graduate student? How to interleave the lines of two or more files? I have tried to get the 2 files output in a single file.  I have tried below command:  cat file1 file2   but here file2 data is appending to file1.  What I need is file1 1st line followed by file2 first line, and file1 second line followed by file2 second line etc.  Can anybody tell me how to do this in a simple way? I'm an Egyptian citizen, who holds Schengen visa and stay permit in Italy. Can I go to UK for some days with my stay permit and Schengen visa? String.split() *not* on regular expression? How did Walter White poison that character? I've seen Breaking Bad complete series 2-3 times, but I never found out how Walter White was able to poison Brock.  I mean did he himself directly feed the Valley of the Lilly berries to Brock or did he let Saul do the work? I can't figure it out. Drawing Day and Night on a Google Map I'm looking to plot day/night on a Google map, for an arbitrary point in time. I'm familiar with generating map tiles; I'm just looking for an algorithm to tell me whether a particular point on the globe is currently in daylight or darkness, or to otherwise plot the curve of the day/night interface onto the map.  I've done some searching, but it's possible I don't even know enough about the problem domain here to know what terms to search for!  Any ideas? Doesn't have to be perfect -- basically, I'm comparing Flickr geolocation data of sunrise and sunset photos (and their "date taken" timestamps) with reality, and this is to help me visualise it. Difference between a Structure and a Union Can I uninstall and reinstall Ubuntu Software Center? Floating point calculations in LaTeX? How can I search for special characters? Situation: It started out as me  for the literal string C-c in  but it ended up omitting the - sign and showing results which contained the strings C/C++ and C &amp; C++.  is an example of a post which contains that string of characters (yet fails to show up in the results).  Things I've tried:   post suggests that I can use the undocumented code: operator, but when I do that, it just wraps the whole term in double quotes like .  As @terdon in Unix &amp; Linux chat has , using this  does yield some relevant results, but it doesn't show me  that is supposed to be there. edit: It appears that the Symbolhound query no longer returns that result.  Finally,  says that you can search for literal characters, but as you can see:    Quoted phrases are exact matches except for case-sensitivity, for example, you can search  or .  The second example (symbols) leads to 0 results.  So by now I assume that the search engine has changed (but the old documentation still lingers on this site). Is there a method for me to search for strings that include special (or is it literal?) characters? Are the datum and the ellipsoid the same? What is a Datum?     The Earth is shaped like a flattened sphere. This shape is called an   ellipsoid. A datum is a model of the earth that is used in mapping.   The datum consists of a series of numbers that define the shape and   size of the ellipsoid and it's orientation in space. A datum is chosen   to give the best possible fit to the true shape of the Earth.  in this   article.... Let $F$ be a field, let $\omega$ be a primitive $n$th root of unity in an algebraic closure of $F$. If $a$ in $F$ is not an $m$th power in $F(\omega)$ for any $m\gt 1$ that divides $n$, how to show that $x^n -a$ is irreducible over $F$? The new GNU Octave 4.0.1 was released March 23, 2016.  I would like to find some standard way to install it in El Capitan (mine OS X 10.11.3) because it has significantly better support in some functions than Matlab, discussed in the thread .  I do brew search octave and get  homebrew/science/octave    Caskroom/cask/octave       Caskroom/cask/xoctave       where one of the first two should be a correct one. The project's homepage  for OS X is down  about installing Octave on OS X systems.  There is also ruby's way of installing Octave described in the thread  but for Yosemite.  I would like to find some standard way of getting Octave for OS X.   I do successfully brew update and brew upgrade before the commands. My Homebrew is 0.9.5 (git revision 80d1; last commit 2016-03-24).  . I run brew info octave but I get  Error: No available formula with the name "octave"     How can you install Octave in some standard way for El Capitan? Variance of the distribution of difference scores Let's say we are talking about the indigenous pukapuka who live in Pluto.  What is correct: "the pukapuka people" or "the pukapuka peoples"?  I've read somewhere the usage of "peoples" in this context, and it has surprised me. Logins with only HTTP - are they as insecure as I'm thinking? Recently I was thinking about how websites like gmail and amazon use HTTPS during the login process when accessing your account. This makes sense, obviously, since you're typing in your account username and password and you would want that to be secure. However, on Facebook, among countless other websites, their logins are done with simple HTTP. Doesn't that mean that my login name and password are completely unencrypted? Which, even worse, means that all those people who login to their facebooks (or similar sites) at a wifi hotspot in public are susceptible to anyone getting their credentials using a simple packet sniffer (or something similar)? Is it really that easy? Or am I misunderstanding internet security?  I'm a software engineer working on some web related stuff, and although at the current time I'm not too involved with the security aspect of our software, I knew I should probably know the answer to this question, since it's extremely fundamental to website security.  Thanks! Stop Edit/Rollback Wars: Limit Number Of Edits/Rollbacks Per User Per Post Per Day I came up with an idea for how to begin putting an end to the edit/rollback wars and then the ensuing comments battle...   What if you are only allowed to edit a post (not the author) once a day. What if you are also only allowed to rollback one edit to your post a day. There would not be a overall limit on the users ability to edit other posts other than the one edit per post per day. There would also not be a limit on the number of times a single post could be edited or rolledback (multiple users), but each edit/rollback would trigger the 24 hour wait... There is currently some threshold in place that allows a post to be edited after it is posted without calling it an edit.  This same threshold could apply to the edit in case a mistake is made (fat fingered, mis-tagged, etc.) which would allow the editor a window of time to correct a mistake before getting locked out.     If either the editor or rollerbacker feel that the current state of the post is not acceptable and they are out of mods for the day, then a moderator can get flagged through the current process. One of us is wrong, aren't we? I have just learned from what I consider a reliable source, that the following sentence is correct:     One of us is wrong, aren't we?   I would never in my life have written this, but I am assured that   As I realize comments don't live forever I will quote the relevant parts:     oerkelens : So you  would really write One of us is wrong, aren't we? I guess by analogy you would not bat an eyelid at One of these balls is blue, aren't they?   Matt Эллен : yes, "Then one of us is wrong, aren't we?" is exactly how it would be written. Same for the balls.   Could someone please enlighten me how it is possible that the number in a question tag supposedly has to be in discordance with the subject of the main clause?  I admit that I am not the youngest any more, and my school days are long gone, but back in the days, I was taught that  1. a verb and its subject concord in number 2. a question tag concords with the subject of the main clause  I was given examples like:     It is warm today, isn't it?   We will be on time, won't we?   Mary is pretty, isn't she?   John isn't the brightest, is he?   Some people may notice that the subject of the main clause seems to determine every time the subject of the question tag. When the main clause subject is singular, so are verb and subject in the question tag.  I was under the impression that a) this made sense and b) this would be a general rule.  I fully realize that grammar does not have to make sense, so a) is immaterial. As for b), today I learned I was wrong :)  So when (and possibly why?) do we form question tags that are different in number from their main clause?   To exemplify, also the other example sentence that I used and was corrected on:     One of these balls is blue, isn't it? (so this is wrong)   One of these balls is blue, aren't they? (and this is correct)   As an afterthought, does this strange grammatical number mix-up only appear in question-tags, or should I always refer to singular subjects in the plural if certain conditions are met? And what are those conditions?  Which versions are correct?     One of the cars is broken, aren't they? They (the car(s?) that is(are?) broken) should be fixed.   One of the cars is broken, aren't they? It (the car that is broken) should be fixed.   One of us must be wrong, mustn't we? We (the one(s?) that is (are?) wrong) should make amends.   One of us must be wrong, mustn't we? He (the one that is wrong) should make amends.   (In the last one, they could of course be used as the singular they, but that would avoid the issue...) How do I display 2 sections side-by-side? Is any UFD also a PID?