${var:=default} vs ${var:-default} - what is difference?
What is the difference between "var=${var:-word}" and "var=${var:=word}"?
Why didn't anybody Summon the Triwizard cup in the maze? We know that the Triwizard cup itself was Summonable. After all, Harry did Summon it in the graveyard.  So why didn't any of the contestants Summon it while in the maze?  Canonical answers, please. Difference between “with”, “at” and “for” with a business title and a company name The prepositions “with”, “at” and “for” are also used to associate a business title with a company's name. It seems that they are interchangeable, with no (significant) difference in meaning. The following examples taken from The New York Times website seem to confirm that:      Until now, said Justin Nielson, a senior analyst for the media   research firm SNL Kagan, “there really hasn't been any direct   competitor . . .      “The consumer is still deleveraging,” said Jason Goldberg, a senior   analyst with Barclays. “It's not a lack of supply; it's a lack of   demand.”      “There’s the party of fear and the party of despair,” Nikos Xydakis, a   political analyst and an editor at Kathimerini daily, said.   Are they really the same as for meaning? If it isn't so, what is the difference between them? Transforming Differential Equation to a Kummer's Equation I'm trying to transform an equation of the form $$ yw^{\prime\prime}(y) - [b - ay] w^\prime(y) - [d + ey]w(y) = 0 $$ into the form of a Kummer's or confluent hypergeometric differential equation: $$ y w^{\prime\prime}(y) + [f - y] w^\prime(y) + g w(y)  = 0 $$ I know it may have something to do with merging two of the singularities of the original equation, and maybe doing something with $y$, making it $\frac{y}{b}$ and taking b to infinity, but I don't know and can't find the details for this process, and for my equation specifically. There's not too much difference between the two but just enough so that I can't get it. Thanks in advance for any help! Why is my profile image different? When I first signed up on a Stack Exchange site and got a profile image, it was this one (see my current user card I'm actually not sure what I look like any more):     Later, I got  and SEDE profiles, and my user image there was a different identicon. Because . I would have a picture of it, but that's the problem. ... Thanks to , I have a picture:     On those two sites, it changed from that purple one to this new one recently:   I don't know when the change happened exactly, but I KNOW I didn't change it (I don't know how to change it, otherwise I would have changed it to my main pink one).  Why did this change? Can I get my other icon back or will I be stuck with this new one?   Also, are the gravatars at Area 51 and SEDE securely generated?    After looking in my profile settings, I really confused (I am seeing my wrong avatar in more and more places since I first posted this.):        Seriously.......    What...?    (I'm using this , but be warned that they will try to IP block you after a certain number of requests to force you to pay... May look for a better alternative later.) How to list files in a zip without extra information in command line In my bash command line, when I use unzip -l test.zip I get the output like this:  Archive:  test.zip   Length      Date    Time    Name ---------  ---------- -----   ----    810000  05-07-2014 15:09   file1.txt    810000  05-07-2014 15:09   file2.txt    810000  05-07-2014 15:09   file3.txt ---------                     -------   2430000                     3 files   But I am interested only by the lines containing the file details.  I tried to make filtering using grep like this:   unzip -l test.zip | grep -v Length | grep -v "\-\-\-\-" | g -v Archive | grep -v " files"  But it is long and prone to error (e.g a file name Archive in this list will be dropped)  Is there any other options with unzip -l (I checked the unzip man page and did not find any) or another tool to do so?  It is important to me to not really unzip the archive but just to look what files are inside. Which partition is mounted to where? I'm reading a lot of documentation on sed, and am still stumped on my particular use case.  I want to replace this line in a conf file with my own line:  Replace this line: #maxmemory &lt;bytes&gt; with: maxmemory 26gb  This is what I tried:  sed s/maxmemory.*bytes.*/maxmemory 26gb/ /etc/redis/redis.conf  I get the error: sed: -e expression #1, char 30: unterminated `s' command  Which stumps me because I don't know what that means. So my question is:  How can I accomplish what I want? What does that error mean? (so I can learn from it) Are there rules for using manacles in combat? I can't quite find in the PHB or DMG how to slap manacles onto someone during combat. PHB 152 describes how to break out of mundane manacles, while DMG 165 shows how Dimensional Shackles work (they are essentially magic manacles -- use 1 action to bind an Incapacitated target).  Is there an official rule on how to use manacles in combat, or do we have to use house rules? Are two (or N) resistors in series more precise than one big resistor? Let's say I have one 2 k&ohm; resistor with 5% tolerance. If I replace it with two 1 k&ohm; resistors with 5% tolerance, will resulting tolerance go up, down, or remain unchanged?  I'm bad with probabilities, and I'm not sure what exactly tolerance says about resistance and its distribution.  I am aware that in the 'worst case' it will be the same; I'm more interested in what will happen on average. Will the chance of getting a more precise value increase if I use a series of resistors (because deviations will cancel each other out)?  On 'intuitive level' I think that it will, but I have no idea how to do the math with probabilities and find out if I'm actually right. The search parameter isanswered ignores acceptances Customizing titlesec-etoc (further question) php function for collating external variables into a single object regardless of GET or POST I recall reviewing someone else's PHP code once and he had a function or class method that rolled all GET and POST variables into a single plain old object that could then be passed around. If the same name-value pair appeared in both GET and POST, POST would win.  Is there a well-coded PHP add-on out there of any sort that does exactly this? cardinality of all real sequences I was wondering what the cardinality of the set of all real sequences is. A random search through this site says that it is equal to the cardinality of the real numbers. This is very surprising to me, since the cardinality of all rational sequences is the same as the cardinality of reals, and it seemed fairly intuitive to me that if cardinality of a set $A$ is strictly greater than the cardinality of the set $B$, then cardinality of $A^{\mathbb{N}}$ should be strictly greater than cardinality of $B^{\mathbb{N}}$. It turns out to be false.  Some technical answers have appeared in this forum elsewhere but I do not understand them. As I am not an expert in this topic, could some one explain me in simple terms why this is happening?  Also is the cardinality of all functions from reals to reals also the same as the cardinality of reals? Remove the Yoast SEO Post Metabox Yoasts SEO plugin adds a metabox to the post edit screen. I'm trying to remove this for users who aren't editors or above.  I've tried putting a remove_meta_box call in on admin_init, trying to remove the action on $wpseo_metabox but to no avail.  How do I remove this metabox without requiring user intervention (the user should never know the metabox existed, so clicking on screen options is not an option ) Finding the index of an item in a list Which Stack Exchange website for machine learning and computational algorithms? I'm currently working on many machine learning and computational algorithms, such as Singular Value Decomposition, Support Vector Machines, and others.  I'd like to ask questions about these topics, but I don't know which Stack Exchange website to use to post my questions.   Should I use ? Should I use ? Should I use ? Should I use ?   How do I tell?  What criteria do I use? Recent reports claim that the gravitational waves detected by LIGO match up with the signal expected from two black holes merging as predicted by general relativity.  Additionally, the masses of both black holes were estimated. Questions:  How certain are we that the detected of gravitational waves are necessarily from two black holes merging?  Since supermassive black holes are typically at the center of a host galaxy, what happened to the galaxies that contained the two merging black holes?  For example, did their host galaxies merge?    Edit After reading the answers, I understand that the signals detected by LIGO are proof of the validity of gravitational wave generational artifacts as predicted by general relativity.  When additionally gravitational waves, caused by the merger of the supermassive black holes (those which ARE indeed located in the centers of the merging galaxies) will be detected, since mergers of galaxies could be observed by the methods independent of gravitational waves such as registering the fact of the quasar appearance (). Additional questions:  Could someone offer me the historical ASTRONOMY precedent when the second degree of inference (from the mathematical model, being associated with the theory of Physics) was accepted as the discovery of the astronomical object?  Could someone give a reference to trustable scientific publication, with the subject of study being discussion of requirements satisfying claim of astronomical discovery of an astronomical object?  Have independent scientific sources (outside of members of the LIGO team) analyzed methodology and results of the LIGO signal detection, and published their conclusions with regards of what was actually discovered? Ring Inside an Algebraic Field Extension Can anyone explain how we choose one sock from each of finitely many pairs without the axiom of choice?  I mean : To choose one sock from each of infinitely many pairs of socks requires the Axiom of Choice, but for shoes the Axiom is not needed.  The idea is that the two socks in a pair are identical in appearance, and so we must make an arbitrary choice if we wish to choose one of them. For shoes, we can use an explicit algorithm -- e.g., "always choose the left shoe." Why does Russell's statement mention infinitely many pairs? Well, if we only have finitely many pairs of socks, then AC is not needed -- we can choose one member of each pair using the definition of "nonempty," and we can repeat an operation finitely many times using the rules of formal logic (not discussed here). Do Wine Viruses only work while Wine is running? I heard Linux can get viruses through Wine,and I was curious if the viruses work only while Wine is running.  In other words, could I stop a virus from doing it's thing by just quitting Wine?