I am biologist and just new to the field of quantum mechanics and trying to understand the subject by reading. It is said that virtual particles are created due to the uncertainty of energy when consider a time, energy conjugate pair. Which leads to violate the energy conservation principle temporarily. But how a huge uncertainty in energy creates virtual particles? How it could violate the energy conservation principle?

I've seen this claim made all over the Internet.  It's on Wikipedia.  It's in John Baez's FAQ on virtual particles, it's in many popular books. I've even seen it mentioned offhand in academic papers.  So I assume there must be some truth to it.  And yet, whenever I have looked at textbooks describing how the math of Feynman diagrams works, I just can't see how this could be true.  Am I missing something?  I've spent years searching the internet for an explanation of in what sense energy conservation is violated and yet, I've never seen anything other than vague statements like "because they exist for a short period of time, they can borrow energy from the vacuum".  The rules of Feynman diagrams, as I am familiar with them, guarantee that energy and momentum are conserved at every vertex in the diagram.  As I understand it, this is not just true for external vertices, but for all internal vertices as well, no matter how many loops deep inside you are.  It's true, you integrate the loops over all possible energies and momenta independently, but there is always a delta function in momentum space that forces the sum of the energies of the virtual particles in the loops to add up to exactly the total energy of the incoming or outgoing particles.  So for example, in a photon propagator at 1-loop, you have an electron and a positron in the loop, and both can have any energy, but the sum of their energies must add up to the energy of the photon.  Right??  Or am I missing something?  I have a couple guesses as to what people might mean when they say they think energy is not conserved by virtual particles...  My first guess is that they are ignoring the actual energy of the particle and instead calculating what effective energy it would have if you looked at the mass and momentum of the particle, and then imposed the classical equations of motion on it.  But this is not the energy it has, right?  Because the particle is off-shell!  It's mass is irrelevant, because there is no mass-conservation rule, only an energy-conservation rule.  My second guess is that perhaps they are talking only about vacuum energy diagrams, where you add together loops of virtual particles which have no incoming or outgoing particles at all.  Here there is no delta function that makes the total energy of the virtual particles match the total energy of any incoming or outgoing particles.  But then what do they mean by energy conservation if not "total energy in intermediate states matches total energy in incoming and outgoing states"?  My third guess is that maybe they're talking about configuration-space Feynman diagrams instead of momentum-space diagrams.  Because now the states we're talking about are not energy-eigenstates, you are effectively adding together a sum of diagrams each with a different total energy.  But first, the expected value of energy is conserved at all times.  As is guaranteed by quantum mechanics.  It's only because you're asking about the energy of part of the superposition instead of the whole thing that you get an impartial answer (that's not summed up yet).  And second... isn't the whole idea of a particle (whether real or virtual) a plane wave (or wave packet) that's an energy and momentum eigenstate?  So in what sense is this a sensible way to think about the question at all?  Because I've seen this claim repeated so many times, I am very curious if there is something real behind it, and I'm sure there must be.  But somehow, I have never seen an explanation of where this idea comes from.


"...isn't  the most powerfully magical number, wouldn't seven-?"   Well is it? The list link lacks...magic, most of the events being mundane or even coincidental.  Edit; because the question is fairly trivial without this change: Are there any examples of the number seven being magical in nature? In particular is there any actual magical advantage to having 7 horcruxes, or is it just sentiment?

While rereading the entire Harry Potter series I noticed that the number 7 occurs quite often, for instance:    Seven books Seven Horcruxes planned by Tom Riddle Seven Weasley kids Seven years at Hogwarts Seven Harry Potters Seven people in a Quidditch team   Did J.K. Rowling ever mention why 7 was so important in Harry Potter?


My friend let me start a character in Assassin's Creed Odyssey on his profile to see if I liked it. I did in fact like the game so I ordered it in the mail. Is there a way for me to transfer my progress to my account?

I'm trying to transfer my Final Fantasy XV game save data to my new user?


A person I know often drops the "to be" which would normally be before the verb in a sentence.  He'll say things like:   That needs fixed. It needs upgraded. They need looked at.   rather than    That needs to be fixed. It needs to be upgraded. They need to be looked at.   Is this just a personal quirk?  Is it colloquial or archaic?  It it grammatically correct?  Does it have a name?

I'm from Western Pennsylvania. Until I moved away, I never realized that when I omitted the to be from phrases like needs to be cleaned, my usage was different than what most English speakers are accustomed to. Is it wrong?


Let $f:\mathbb R$→$\mathbb R$ defined as   -  $f(x)=0$, if $x$ is irrational or $x=0$ and $f(x)=1/q$, if $x=p/q$, $p\in$$\mathbb Z$ ,$q\in$$\mathbb N$, $(p,q)=1$. What are the points of continuity of $f(x)$? I wanted to use simple left hand and right hand limits criteria but the uncertainity of $\epsilon>0$ (rational as well as rational) is restricting my thoughts to evaluate these.

In :  $$ \begin{align} t(x) = \begin{cases} 0 & \text{if $x$ is irrational}\\ \frac{1}{n} & \text{if $x = \frac{m}{n}$ where $\gcd(m,n) = 1$} \end{cases} \end{align} $$  I can prove the discontinuity at rational $b$ by taking a sequence of irrationals $x_n$ which converge to $b$.   But while going through an argument for continuity at irrationals.  I found this in a book.      On the other hand if $b$ is an irrational number and $\epsilon > 0$   then there is a     natural number $n_0$ such that $1/n_0 < \epsilon$.   There are only finite number of rationals with denominator less than   $n_0$ in the interval $(b-1,b+1)$. Hence we can find a $\delta > 0$   such that $\delta$ neighbourhood of $b$ contains no rational with   denominator less than $n_0$.   I understand the rest of the proof. But I am unable to prove the emphasized text. Although I find it intuitive.


Consider a regular polygon with n-sides  ith radius 1. I want to construct an equation in polar coordinates for this polygon.   On the internet, I found this:  (first part) Consider the equation of just one half of one side of the $n$-gon. It's the side of a right triangle opposite angle $A = π/n$. The hypotenuse of this triangle is $1$ (the radius of the $n$-gon), so the equation of this one side is $\cos(π/n)/\cos(θ)$, where $θ$ goes from $0$ to $π/n$. The other half of this side has the same equation, so we're already at the point where we know the equation of one side of the $n$-gon:  $r = \cos(π/n) / \cos(θ), -π/n ≤ θ ≤ π/n .$  (second part)Next, we will need to develop a function of θ that "normalizes" θ to be within plus or minus $π/n$. This is accomplished by the "floor" function, as follows:  $B = θ - 2 π/n \lfloor(n θ + π)/(2 π)\rfloor $  Putting it together, the equation of an n-gon is $r = \cos(A)/\cos(B)$, which is  $r = \cos(π/n)/\cos(θ - 2 π/n \lfloor(n θ + π)/(2 π)\rfloor) $  Someone can give me a help to understand the second part or show me an another solution?  Thanks in advance.

For example, the square can be described with the equation $|x| + |y| = 1$. So is there a general equation that can describe a regular polygon (in the 2D Cartesian plane?), given the number of sides required?  Using the Wolfram Alpha site, this input gave an almost-square: PolarPlot(0.75 + ArcSin(Sin(2x+Pi/2))/(Sin(2x+Pi/2)*(Pi/4))) (x from 0 to 2Pi)  This input gave an almost-octagon: PolarPlot(0.75 + ArcSin(Sin(4x+Pi/2))/(Sin(4x+Pi/2)*Pi^2)) (x from 0 to 2Pi)  The idea is that as the number of sides in a regular polygon goes to infinity, the regular polygon approaches a circle. Since a circle can be described by an equation, can a regular polygon be described by one too? For our purposes, this is a regular convex polygon (triangle, square, pentagon, hexagon and so on).  It can be assumed that the centre of the regular polygon is at the origin $(0,0)$, and the radius is $1$ unit.  If there's no such equation, can the non-existence be proven? If there are equations, but only for certain polygons (for example, only for $n < 7$ or something), can those equations be provided?


Let $a_1, a_2, ..., a_k$ are real numbers greater thah $1$. Prove that   $$\frac1{1+a_1}+\frac1{1+a_2}+...+\frac1{1+a_k}\ge\frac k{1+\sqrt[k]{a_1a_2...a_k}}$$   I have this inequality proved by Sturm's method. Is there another way? May be  Jensen's inequality.

If $x_1,x_2,\ldots,x_n$ are real numbers larger than $1$, prove that $$\dfrac{1}{1+x_1}+\dfrac{1}{1+x_2}+\cdots+\dfrac{1}{1+x_n} \geq \dfrac{n}{\sqrt[n]{x_1x_2\cdots x_n}+1}$$   Attempt  AM-GM doesn't work here since we will get an upper bound. I don't see Cauchy-Schwarz working either. Thus, I think a substitution might work, but I am unsure of which one to use.


Can we use right join instead of left join and vice versa by just flipping the table position in the query.If so then why we need both joins?

states:  "In practice, explicit right outer joins are rarely used, since they can always be replaced with left outer joins and provide no additional functionality."  Can anyone provide a situation where they have preferred to use the RIGHT notation, and why? I can't think of a reason to ever use it. To me, it wouldn't ever make things more clear.  Edit: I'm an Oracle veteran making the New Year's Resolution to wean myself from the (+) syntax. I want to do it right


Let $R$ be a ring. The center of $R$ is the set $C(R) = \{c ∈ R : cr = rc, ∀r ∈ R\}$.      Determine elements in the center of the $n × n$ matrix ring $M_n (R) $ for any $n ≥ 2$.   So, we have that center $C(R)=\{x \in R / cr=rc, \forall r \in R\}$  and we need to find $C(M_n(R))\,\,\,\,\, (n \ge 2)$  The only thing that I could think of is to start looking $C(M_2 (R))$, taking $M_2(R)$ for $\begin{bmatrix}a&b\\c&d\end{bmatrix} \ge 0$ and if $a, b, c, d \ge 0$ in $R$ then, $I_2=\begin{bmatrix}1&0\\0&1\end{bmatrix} \ge 0$ but then $\begin{bmatrix}1&-1\\0&2\end{bmatrix} \not\ge 0$

Show that $Z(M_n(R))$ consist of $ \operatorname{diag}\{ a, a, ..., a \} $ with $ a\in Z(R) $


I am using Adobe Illustrator CC (latest version) and although I have been working with Illustrator for many years, I only do small vector related things in it, so by no means an expert.  I would like to align a bit of text inside a rectangle object, so I select both, then I tell it to align relative to rectangle, and press the Vertically Align Center option, but this is what I get:    As you can see, it is NOT vertically centered, what am I doing wrong?  This seems to behave this way with text only! I'm sure if I changed the text to paths and did the alignment, I'd get the result I'm after, but must I do this? Is there no easier way?  UPDATE:  Following solution provided by duplication link still doesn't work for me! Am I missing something? I applied the Effect > Path > Outline Object  Here is what I get:    Thank You.

In Illustrator, how do you align text in the exact center of a shape for example without creating outlines. If I go to center text using the align palette, Illustrator aligns the text to it's bounding box.  I know you can create outlines, but I want the text to remain editable in case I need to make changes later.  Any thoughts?


The  has the following feature:     Spell Storing. A spellcaster who wears the shield guardian's amulet can cause the guardian to store one spell of 4th level or lower. To do so, the wearer must cast the spell on the guardian. The spell has no effect but is stored within the guardian. When commanded to do so by the wearer or when a situation arises that was predefined by the spellcaster, the guardian casts the stored spell with any parameters set by the original caster, requiring no components. When the spell is cast or a new spell is stored, any previously stored spell is lost.   I'm unsure what the bolded phrase requires/means. Does the spell just needs to target the Guardian for it to be stored? What counts as casting a spell on a Shield Guardian? What are the criteria for whether or not a spell can be stored in a Shield Guardian?

The "Spell Storing" ability of the Shield Guardian says:     To do so, the wearer must cast the spell on the guardian.  The spell has no effect but is stored within the guardian.   This seems to indicate you cannot cast, for instance, Fire Shield on the Guardian, because that has a range of Self.  This seems different than what is intended, as the wording for a ring of spell storing is:     This ring stores spells cast into it, holding them until the attuned   wearer uses them....Any creature can cast a spell of 1st through 5th   level into the ring by touching the ring as the spell is cast.  The spell has no effect, other than to be stored in the   ring.   The use of the word "into," which does not seem to indicate any range, versus the use of the word "on," which seems to mean the guardian is a target of the spell.    Which is the correct interpretation, grammatically, versus what is the RAI?


I've created this function, however when it runs on the website it's designed for it is returning undefined. I did some quick Googling and found that because it's an asynchronous function, it completes and returns the data before the server can respond. I'm stumped however on how to convert it to a synchronous function.   Here is my code:  render_SC = function() {       var SC_url;     $.get(Dubtrack.room.player.activeSong.url, function(f) {         SC_url = f.data.songInfo.images.thumbnail.replace('large','original');     });     return SC_url; }; console.log(render_SC());   Thanks in advance for all your responses. :)

I have a JavaScript widget which provides standard extension points. One of them is the beforecreate function. It should return false to prevent an item from being created.   I've added an Ajax call into this function using jQuery:  beforecreate: function (node, targetNode, type, to) {   jQuery.get('http://example.com/catalog/create/' + targetNode.id + '?name=' + encode(to.inp[0].value),    function (result) {     if (result.isOk == false)          alert(result.message);   }); }   But I want to prevent my widget from creating the item, so I should return false in the mother-function, not in the callback. Is there a way to perform a synchronous AJAX request using jQuery or any other in-browser API?


i want to change my hostname that appears in my router DHCP things that i already tried   sudo hostname ___   also tried to change it from /etc/hostname and /etc/hosts

When I connect to my server (ubuntu server 10.10), I get this:  name@server-name.belkin ~>   How can I remove ".belkin"?


I have a class like this in a rails app  class User < ActiveRecord::Base   .. end   The class doesn't have a method caller foo? Nor does any of the include ... files. But User.new.foo? does respond, so how can I ask where this method is defined?

We recently had a problem where, after a series of commits had occurred, a backend process failed to run. Now, we were good little boys and girls and ran rake test after every check-in but, due to some oddities in Rails' library loading, it only occurred when we ran it directly from Mongrel in production mode.  I tracked the bug down and it was due to a new Rails gem overwriting a method in the String class in a way that broke one narrow use in the runtime Rails code.  Anyway, long story short, is there a way, at runtime, to ask Ruby where a method has been defined? Something like whereami( :foo ) that returns /path/to/some/file.rb line #45? In this case, telling me that it was defined in class String would be unhelpful, because it was overloaded by some library.   I cannot guarantee the source lives in my project, so grepping for 'def foo' won't necessarily give me what I need, not to mention if I have many def foo's, sometimes I don't know until runtime which one I may be using.


As a little hobby i am creating a random number generator tool using the javascript math.random script and an html form that asks for the minimum number and maximum number. But i am experiencing a problem where sometimes the minimum number is set to zero instaid of what the user inputted. Here is my html code:   <form id="form" onsubmit="return false;"> <input type="text" id="minNumber" value="Minimum number" onfocus="if         (this.value == 'Minimum number') {this.value = '';}" onblur="if (    this.value == '') " /> <input type="text" id="maxNumber" value="Maximum number" onfocus="if        (this.value == 'Maximum number') {this.value = '';}" onblur="yes" /> <input type="submit" onclick="getNumber()" value="Get random number"> </form>   And this is my JavaScript code:  function getNumber() { var minNumber = document.getElementById("minNumber").value; var maxNumber = document.getElementById("maxNumber").value; var randomnumber = Math.floor(Math.random() *( + maxNumber) + minNumber); alert("Your random number is: " + randomnumber); }   I have tried several fixes including:   Removing some unnecisary spaces, +'s, and 1's adding more variables   Any help would be appreciated. Thanks!

How do I generate a random int value in a specific range? I have tried the following, but those do not work: Attempt 1: randomNum = minimum + (int)(Math.random() * maximum);  Bug: randomNum can be bigger than maximum. Attempt 2: Random rn = new Random(); int n = maximum - minimum + 1; int i = rn.nextInt() % n; randomNum =  minimum + i;  Bug: randomNum can be smaller than minimum.


Here is the proof:  -8 == -2 * 3 - 2   that means -8%3 should be equal to -2.  but python returns 1 and it's driving me crazy

Can you please tell me how much is (-2) % 5? According to my Python interpreter is 3, but do you have a wise explanation for this?  I've read that in some languages the result can be machine-dependent, but I'm not sure though.


I have around 100,000 files in a directory. As you can imagine, that's not an ideal situation, and I'd like to split the directory up into subdirectories. But the filenames aren't such where I can put them into subdirectories based on their names or anything, so I'd like to create, say, 10 directories and put about 1000 files in each. Is there an easy bash command or loop that would do this?

Is it possible to 'partition' a directory listing - say in to blocks of some number, to perform different actions on each 'range'?  For example, lets say I have the following directories inside another folder:  $ ls test abc/ def/ hij/ klm/ nop/ qrs/ tuv/ wxy/ zzz/   And I want to perform some action on the first 3 directories, another on the second 3, and so on.  My thought was that perhaps a loop across numbers would work, based on the output of something like ls | nl (but before anyone mentions it, I know parsing ls is a no-no!)  This obviously doesn't work, but illustrates my point I hope:  for dir in `ls | nl`;  do     do-something-with ${dir{1..3}} # Where $dir has taken on some numerical value linked to the folder)     do-something-with ${dir{4..6}}  # And so on...     do-something-with ${dir{n-3..n}}  done   The folders I intend to actually do this on, can be worked on in any order (i.e. the final splits can be totally arbitrary), but they have no logical naming consistency - by which I mean they can't be organised sensibly alphabetically or numerically based on any key within the directory name themselves.


If before the quote the word "saying" or "said" is used, does a comma always have to be used before it? When does a comma not have to be used?

Sam developed an annual sweepstakes promotion entitled “The Free Gas Punt Return Game”.    Do I need a comma after entitled or not?


Can somebody give me a hint for showing that:  The matrix $A+I$ is invertible if there is an integer $k\gt 0$ so that $A^k=0$.

Possible Duplicate:          Given $A^{2012}=0$ prove that $A+I$ is invertible and find an expression for $(A+I)^{-1}$ in terms of $A$. ($I$ is the identity matrix).


I am looking to setup a TXT spf record that has 2 included domains...individually:  v=spf1 include:hotmail.com ~all   and  v=spf1 include:servers.mcsv.net ?all   What is the proper way of combining them into a single item?

This is a  about setting up .     I have an office with many computers that share a single external ip (I'm unsure if the address is static or dynamic). Each computer connects to our mail server via IMAP using outlook. Email is sent and received by those computers, and some users send and receive email on their mobile phones as well.  I am using  to generate an SPF record and I'm unsure about some of the fields in the wizard, specifically:   Enter any other domains who may send or relay mail for this domain Enter any IP addresses in CIDR format for netblocks that originate or relay mail for this domain Enter any other hosts which can send or relay mail for this domain How stringent should SPF-aware MTA's treat this?   the first few questions i'm fairly certain about... hope i have given enough info.


Good morning,  This is my first time writting in this page, but I am finding trouble solving some exercises about first order logic. I know the tools I have but I am not sure how should I apply them. I attach some exercises and I hope someone could bring me some light about any of them. I need to prove those implications. (The last one says that x does not happen in phi.

What I am thinking was I need two formulas, AX.p(X) => something AX.p(X) => ~ something   I guess something maybe is the p(x) and the other is ~p(x) since we was given EX.~p(x)..But actually it can't work for me. And I guess maybe is EX.~p(x) and ~EX.~p(x)..But if I am doing that then the it will go to deadend..so I give up..;(  Wish someone can help me.   For note about EE: 1: EX.p(X) 2: AX.(p(X) => something) 3: something EE1,2 But something cann't have the free variable from p..in this sample, then soemthing cannot including X..so if something is p(X) it cannot use EE, but if p(Y) then can use EE.


I computed a feature x that I use to predict y which is a probability of being a certain class.  Raw data in R format for (x,y) is pasted here:   (500 samples)  plot(x,y) looks like this:    It seems similar to a  I asked, so I am tempted to try , which I understand is the "Least Squared Fit"on log(y) (because y is a probability).  Am I correct?  (My objective is to minimize the MSE.)

I do a linear regression using R lm function:  x = log(errors) plot(x,y) lm.result = lm(formula = y ~ x) abline(lm.result, col="blue") # showing the "fit" in blue     but it does not fit well. Unfortunately I can't make sense of the manual.  Can someone point me in the right direction to fit this better?  By fitting I mean I want to minimize the Root Mean Squared Error (RMSE).    Edit: I have posted a related question (it's the same problem) here:   and the raw data here:    except that on that  x is what is called errors on the present page here, and there are less samples (1000 vs 3000 in the present page plot). I wanted to make things simpler in the other question.


I have an old system with 2G ram and 64-bit CPU. I installed the X86_64 version of Kubuntu 17.10 on my machine. I am using encrypted LVM volumes. I have decided I would like to try the 32-bit version of 17.10 while keeping my ~/ directory intact if possible.   The installer I have downloaded from Kubuntu seems only to allow a full installation. Is there a good way to accomplish my goals?

How can I Change Ubuntu 14.04 from 64 bit to 32 bit ?


Let $S = \{1,2,3,4,5\}$ How many bijective functions $f:S \to S$ do we have such that $f(x) \neq x$ for all $x\in S$?  I was trying to solve by taking the total number of such functions and subtract all the cases where $f(x) = x$.  $5!$ is all cases  $4!$ is where one $f(x)=x$ and rest are not  $3!$ is where two $f(x)=x$ and rest are not  $2!$ is where three $f(x)=x$ and rest are not  $1!$ is where all five $f(x)=x$  so $5!-(4!-3!-2!-1)$.  But then I realized that, for example, $4!$ contains also the case where all $f(x)=x$ which mean I am subtracting too much.

I am not sure how to approach this problem:  $n$ people are seated in numbered chairs $1$ to $n$. Let $N$ be the number of ways the people can be reseated so that no one is in the same chair as before. Show that $N=n! \sum_{k=0}^n \frac {(-1)^k}{k!}$.  I feel like the way to do this is to come up with a way to count all the seating arrangements, yet I am not sure how to take into account the seat where the person already sat into account when counting them. Because it would seem that there is $n-1$ possible places to sit at, yet placing the first person does not eliminate one possibility for everyone...  Any help is appreciated. Thank you in advance.


Is there some special condition for this to be true or is this always true?

Is torque or moment of a couple independent of the choice of point of rotation?   Torque is given by $\tau =\vec r\times\vec F$. It depends on $\vec r$, which is the position vector from the axis of rotation to the point where force is applied.


I have a Hudson/Jenkins installation which runs on port 443, so I can access it with https://ci.mydomain.com. I do not have a webserver running on port 80 like Apache Httpd, but I want if a user types http://ci.mydomain.com  it should be redirected to https://...  I tried it with iptables:  /sbin/iptables -t nat -I PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 443 /sbin/iptables-save chkconfig --level 35 iptables on   But the browser tells me, that the connection failed. So I do not want to install Apache webserver, I only  want to have a redirect from http://ci.mydomain.com to https://ci.mydomain.com.

This is a  about Apache's mod_rewrite.   Changing a request URL or redirecting users to a different URL than the one they originally requested is done using mod_rewrite. This includes such things as:   Changing HTTP to HTTPS (or the other way around) Changing a request to a page which no longer exist to a new replacement. Modifying a URL format (such as ?id=3433 to /id/3433 ) Presenting a different page based on the browser, based on the referrer, based on anything possible under the moon and sun. Anything you want to mess around with URL   Everything You Ever Wanted to Know about Mod_Rewrite Rules but Were Afraid to Ask!  How can I become an expert at writing mod_rewrite rules?   What is the fundamental format and structure of mod_rewrite rules? What form/flavor of regular expressions do I need to have a solid grasp of? What are the most common mistakes/pitfalls when writing rewrite rules? What is a good method for testing and verifying mod_rewrite rules? Are there SEO or performance implications of mod_rewrite rules I should be aware of? Are there common situations where mod_rewrite might seem like the right tool for the job but isn't? What are some common examples?   A place to test your rules  The  web site is a great place to play around with your rules and test them. It even shows the debug output so you can see what matched and what did not.


It is given in a question that $\vec x+\vec a=(\vec a\cdot \vec x)\vec b$ and it is stated that $\vec a$, $\vec b$ and $\vec x$ are vectors.  It is also stated that $\vec a\cdot \vec b\ne 1$.  The question asks to express $\vec x$ in term $\vec a$ and $\vec b$.  How do you do this?

It is given in a question that $\vec x+\vec a=(\vec a\cdot \vec x)\vec b$ and it is stated that $\vec a$, $\vec b$ and $\vec x$ are vectors.  It is also stated that $\vec a\cdot \vec b\ne 1$.  The question asks to express $\vec x$ in term $\vec a$ and $\vec b$.  How do you this?


Im trying to understand if nowadays using AES is secure or not, after reading some arguments on Schneier’s blog (to be more exact, ) it seems like it is not secure:  Now as the NSA GCHQ et al know very well the more efficient you make the implementation of crypto code the more side channels it has unless extreme caution is observed. One thing we do know is that optimized for speed and minimized number of gates is an almost certain guarantee of side channels no matter how clever you are. Also the NSA knew that developers would not write their own code they would simply download and use the competition candidate code. As was pointed out and demonstration code exploited implementations of AES were subject to timing attacks that could fully leak the key across a network connection due to "cache hits" on the Intel x86 platform from base level pentiums upwards within weeks of the winning candidate being announced. Even today there are very side channel suseptable AES implementations in use in fact the majority of those implementations on the likes of routers and switches are timing channel cursed as are most application level software implementations that are more than a year or so old...  …at least not if the computer used is connected to external network. Is this true or just based on assumptions?

The cipher AES-256 is used among other places in  across the Internet. It's considered among the top ciphers.  In theory it's not crackable since the combinations of keys are massive.  Although NSA has categorized this in , they have also recommended using higher than 128-bit keys for encryption.  So how secure is this cipher really? Should you assume the worlds top cracker-institutions are near or have cracked it already?


I've read several sources so far. Here are the three options I have encountered:  /etc/systemd/system  /usr/lib/systemd/system  /lib/systemd/system   I was originally putting my service in /lib/systemd/system, and it seems a bunch of other services are in that directory as well. However, it's supposed to be in /etc/systemd/system?? This source never talks about the third option:   Also, this tutorial seems to put it in that directory.   Please help clarify for me. Enabling my unit is leading to an error message: "Failed to enable unit: Invalid argument" I hypothesize because the directory is wrong. (I am using Arch Linux)

I  that there are two folders for unit files (not in user mode). /usr/lib/systemd/system/: units provided by installed packages /etc/systemd/system/: units installed by the system administrator  Conflicting with this understanding is the answer to this question: . Can someone fill in the missing information so that I understand what is going on? (UPDATE: The answer has been updated, and my understanding no longer conflicts with it.) Also, it seems that the scripts are organized in subfolders within the /etc/systemd/system/ folder: getty.target.wants multi-user.target.wants  In another location I read that there are other locations. It seems these are for user-specific services. /usr/lib/systemd/user/ where services provided by installed packages go. /etc/systemd/user/ where system-wide user services are placed by the system administrator. ~/.config/systemd/user/ where the user puts its own services.   Update 2015-08-31: For the sake of others, here is a link to a related question I recently asked:


I would like to know if there is a plug-in in Quantum GIS, which can help me to generate subcatchments starting from a DTM.

I'm 90% sure this basic question has been asked before but looking through the other posts I simply do not see a useful answer.  I need to calculate polygonal(vector) catchment areas from a raster based on minimum driving distance/cost from a set of points. I've already got the raster, and for that matter, the nodes(intersections with cost attribute) used to interpolate it. What I need now are polygons for each point describing the area nearer it than any other point. This is basically like a voronoi diagram but based on network distance rather than euclidean space.   How exactly can I do this using only open-source tools? I'm comfortable with the command line if I just know what I'm looking for. I feel like GDAL is going to be the answer, but if so, what exactly is the command I'm looking for?  Thanks!


i run the following code but it kept printing "4"     why its printing "4" and not "12"? and can I use malloc and then sizeof?(if i can then how)   #include<stdio.h> int main() {     int arr1[3]={1,2,3};     int *arr2=arr1,i;     printf("%d",sizeof(arr2));     return 0; }

First off, here is some code:  int main()  {     int days[] = {1,2,3,4,5};     int *ptr = days;     printf("%u\n", sizeof(days));     printf("%u\n", sizeof(ptr));      return 0; }   Is there a way to find out the size of the array that ptr is pointing to (instead of just giving its size, which is four bytes on a 32-bit system)?


I installed gimp via snap install previously and even though window decorations were missing, I was still able to use it. Today however, I opened up gimp and it's completely unusable (fonts is missing it seems).  See the screenshot attached.

Recently, on my Ubuntu 18.04 I have noticed that at least on gnome-calculator and chromium browser the fonts are displayed as squares. I have followed instructions  and , the calculator is fixed, but the problem on chromium still exists when I open a dialog to search for a file.  Not sure if this happens on other applications as well, I haven't checked all my apps, but File managers nemo and nautilus are working fine.  Also, before few months ago, I have included some windows fonts for my libre office shown . I used the copy (cp) method, not the link (ln -s). But, was working fine until yesterday. Haven't done any major change or update, at least on my Linux partition (dual boot). But, I don't think that this has anything to do with that.  Any idea how can I fix this issue?  .


Is it possible to mix two different languages in the same bibliography made with Biblalex?  I would like to get this output:   Instead of this:   I have tried using langid field, but it localizes only hyphenation.  paper.tex:  \documentclass{article} \usepackage{polyglossia} \setdefaultlanguage{english} \usepackage[backend=biber, style=alphabetic]{biblatex} \bibliography{biblio}  \begin{document}  \cite{paperES, paperEN} \printbibliography \end{document}   biblio.bib:  @article{paperES,     author={Adan Cruz and Brisa Carmelo},     title={Titulo},     journal={Título de la revista},     year={2011},     volume={IV},     pages={8-17},     langid={spanish}, }   @article{paperEN,     author={John Smith and James Brown},     title={Title},     journal={Journal title},     year={2012},     volume={V},     pages={3-15},     langid={english}, }   Any hints would be appreciated.

According to biblatex manual (p.24), the hyphenation field in a bib-entry switches language on per-entry basis:     hyphenation field    The language of the bibliography entry. The identifier must be a language name   known to the babel package. This information may be used to switch hyphenation   patterns and localize strings in the bibliography.   This functionality seemed to not work. I just used an example of bib base that comes with biblatex documentation to print the entire bibliography.   \documentclass[a4paper]{article} \usepackage[T1]{fontenc} \usepackage[german,american]{babel} \usepackage{csquotes} \usepackage[style=numeric,backend=biber]{biblatex} \addbibresource{biblatex-examples.bib} \begin{document} \nocite{*} \printbibliography \end{document}   The bibliography contains few entries in German. However in the printed list of references they are formatted with english strings.     [8] Averroes. Drei Abhandlungen über die Conjunction des separaten Intellects   mit dem Menschen. Von Averroes (Vater und Sohn), aus dem   Arabischen übersetzt von Samuel Ibn Tibbon. Ed. and trans. by J. Hercz.   Berlin: S. Hermann, 1869.   Per-entry language switching is provided by the  bundle of bst style for BibTeX. Looking through biblatex internal code, I've got an impression that biblatex needs major re-implementation in order to provide similar functionality. Or am I wrong?


I'm just trying to connect to the server hosting my website through Finder, but it's always read only, even though I'm logging in with my username and password.  Obviously, I can connect with an FTP client (Fetch), and through the terminal, etc. – but what's the trick to FTP-uploading with Finder?

I have just found out that I can enter a built-in FTP client on my Mac by simply pressing ^ Ctrl + K. Great thing!   But after I have successfully connected to my server and a 'folder' with files located there appeared, it occurred that I can't upload files by simply drag & drop'ing them. When I checked the 'Get info' I saw that it is marked as 'You can only read', yet the ftp account itself is okay, because I could upload files there from dreamweaver (unfortunately I have only Windows licence for this app).  Why is it marked as 'You can only read' and how do I fix that?  Please help!  P.S. Could you explain it in an easy way? Because I'm new to Mac (just bought one few days ago).


Before i buy this laptop, i would like to know other people experience with Ubuntu (and Linux) using it. Can anyone help me?

I have a device on which I would like to install Ubuntu. How do I find out if Ubuntu will work on it?


I have collected more things that can be improved or that cause confusion + frustration for a lot of users and would like to be able to propose some new rules with the ability to confront directly with complete arguments the "opinion" leaders and the rule makers.   Also I am asking this because until now there are, at least in my opinion, some requests that were rejected or left without big attention because of the author's lack of maybe more strong and convincing arguments.   Specifically I ask if there is kind of form/template to complete which would be analysed more focused, rather then leaving it as a question for community's "pop corn" sake.

Note: If you're looking for a simple explanation as to why comments aren't required on downvotes, see .   I used to get "upset" (though that is too strong a term) when I got downvoted without comment. If my answer isn't good enough then I'd like to know why. Not only does it improve the answer for the OP but it improves my knowledge too.  Where the down-vote has been explained I've found it useful & it has improved my answer, or forced me to delete the answer if it was totally wrong.  So is there any way we can encourage people to leave a comment? Perhaps they don't lose rep if they explain their down-vote?  I must admit though that I haven't always explained my down-vote either so you could call me a hypocrite. I've also grown a thicker skin over the months of using SO (it seems to have come with the higher rep score ;-)), so I'm less bothered about this now.


I have been looking for a SF book about an old man (tailor) walking down the street. He steps through a wormhole and ends up in the future. His adventures start from there. I read the story back in 1970-1980, and it was from an old paperback I got from the library.  What I remember was an old tailor closing up shop to head home one evening, and as he was walking down the street he stumbled on a crack in the sidewalk and was transported into the future. That's about all I can remember right now. I have Googled it online but, with so few facts I cannot seem to find anything. I know it was an old book from about the same time as E.E. "Doc" Smith stories of the Lensmans.

I remember reading a short story (or short book?) that was at first set around the 1930s (maybe?) and an experiment goes wrong creating a very fine beam which increased in width the further out it got from its source. Whatever was hit by this beam was transported into the distant future. This included a man (the protagonist) who finds himself on Earth but an indeterminate time in the future where he has to relearn the language and reconnect with this future humanity. He's viewed as an oddity as he still has bodily hair so they permanently remove his beard. It feels like an Asimov era story. Can anyone help with this?


I want to split a vector layer based on values in a specific field. In older versions I could use the plugins 'LayersbyField' or 'Split Vector Layer', but both seem not to be available anymore in version 3.2 of QGIS.  Are there quick and easy alternatives? I don't like to 'select' and 'save as' for every value, since that takes too much time.

I am using QGIS and I created a vector grid on a crop field in order to cut it into plots. I want to save each grid cell into individual polygon shapefiles automatically.  Here is an example of a vector grid I would like to split into 117 shapefiles:    Eventually, I did it manually with the selection tool and "Save as" but it is really time-consuming when there are more than 100 plots to save.    Is there any way to do it faster and more automatically?  Each plot as an attribute named "Plot" that can discriminate against them (basically being id + 1). It's the attribute used here to label them.


I'm aware Winter Bash is ending soon, but perhaps this could be fixed for next year's WB. As seen in the image below, my hat does not display fully.    It appears that this can be fixed by removing overflow: hidden from [class * ="gravatar-wrapper-"] in primary.css. [class * ="gravatar-wrapper-"] {     padding: 0;     overflow: hidden }

Hat in profile image gets cut like the following image:  I've inspected the element:

      .

  CSS for gravatar-wrapper is like this: class*="gravatar-wrapper-"] {     padding: 0;     overflow: hidden; }  Changing overflow:hidden to overflow:visible shows avatar correctly.


Earlier today I was describing someone to a friend. I said, "I never realized how zealous he was." I meant for the meaning of zealous here to be religiously zealous. Without an adverb, I would implicitly associate the word zealous with religion. But now I am thinking about it, and perhaps this is not the case.  So does the word zealous have an implicit religious connotation? Or is the object of zealousness too ambiguous without an adverb or other context?

A zealot is a person who is fanatical and uncompromising in pursuit of their religious, political, or other ideals.  I have never seen this word used with positive connotation, but could it (without causing raised eyebrows)? For example, “Gandhi was a zealot and should be admired by all who believe in non-violence.”  Also, do “zealous” and “zeal” carry the same connotation as “zealot”?


I want to set object a equal to object b and then edit property x from object a. But, when I edit a.x, b.x gets changed too for some reason. How do I work around this?  var b = {     x: 0,     y: 3  }; var a = b; alert(b.x); //outputs 0 a.x = 1; alert(b.x); //outputs 1?

The primitive types (number, string, etc.) are passed by value, but objects are unknown, because they can be both passed-by-value (in case we consider that a variable holding an object is in fact a reference to the object) and passed-by-reference (when we consider that the variable to the object holds the object itself).  Although it doesn't really matter at the end, I want to know what is the correct way to present the arguments passing conventions. Is there an excerpt from JavaScript specification, which defines what should be the semantics regarding this?


I use R for my statistical analysis.  I want to analyse a kinetics experiment that involves measurement over 3 time points with control, genetic background 1, 2 and 3.  Can anyone suggest a test and how to arrange the data for that particular test?   I would also need to do individual comparisons between time, group and time:group.

Hi I am trying to find the non-parametric equivalent of a two-way ANOVA (3x4 design) which is capable of including interactions. From my reading in Zar 1984 "Biostatistical analysis" this is possible using a method put forth in Scheirer, Ray, and Hare (1976), however, according to other posts online it was inferred that this method is no longer appropriate (if it ever was).  Does anyone know what method would be appropriate for doing so, and if so the corresponding functions in R or Stata?


I was transfering files to my external hard drive when it stalled during the transfer.  I unplugged the hard drive.  Now when i connect it, the light on the hard drive comes on and flashes.  You can hear/feel the hard drive running.  On the pc when i go to "my computer" it no longer shows the hard drive.  Please help

I have 2 * Maxtor Onetouch 4 Lite 500GB external hard drives (part no. 9NT2A4-500). They both used to work fine on my old laptop (an Acer) but I have not used them for about a year, since my laptop was stolen and I got this one (also an Acer [Aspire 7738G]). I have one plugged into the mains with one of the leads I believe was supplied with them. It appears to be receiving power as it is warm and the power light (on the unit itself) is on; also the mains adapter is fairly warm.  I also have it plugged into my laptop with a USB lead which I have tested on my mp3 player (so I know it works). However my hard drive is not showing on my computer. I have tried checking for new hardware, installing the software that was supplied with it, checking drive letters in case it is registered as C: or something stupid, checking for problems etc... I can't find any cause for it to do this. It does appear to be starting up and, possibly, shutting down and restarting constantly (that's what it sounds like altho I can't be certain).  I have had both hard drives stored in different places for the last year and they're both doing the same thing.. if it was only one then I'd guess it had got damaged or corrupted or something but since it is both I doubt this is it. The only things in common with both of them are the leads and the laptop, however I know the USB lead works and guess the mains lead works as there is power going to the unit.  Has anyone come across this before or does anyone have any idea what the cause / solution to the problem is? Any help would be greatly appreciated.  Regards, Richard


Every time my players are exploring a dungeon, they want their characters to do perception checks for monsters, perception checks for traps and/or secret passages while being on stealth mode, all at the same time. If a monster comes or if they activate a trap, they get mad because "my character is always looking for traps".  If I say they need to declare their actions, the game goes like this:  [me describing a area, like a corridor they're walking in]  player: I check for traps and secret doors in the wall, the floor and the ceiling. I also want to hear anything unusual and walk silently.   They want to be on "automatic mode", expecting me to roll for their PCs every time they enter a new area. Otherwise they always have this phrase "I check for traps and secret doors in the wall, the floor..." that they say EVERYTIME I introduce a new area. I can't put them in "automatic" for this kind of roll. We're playing D&D 5e, but this happen in other campaigns, and it has always been a problem to me.   How do I deal with it?

I have a player who always tells me whenever he goes into a dungeon or other hazardous location,     I am always checking for traps wherever I go. Assume that I am always looking around, wary and being alert for the slightest sound. Also, assume that I am searching for secret doors as well.   And also     I always recover my spent ammo [crossbow bolts]. Unless I say otherwise, I always reload my crossbow.   For the first case, I just assume that he is being alert but the player still gets upset when I ask him to make the skill check rolls. For the second case, I told him outright that I am not his automated helper.  The player also seems to mean that "Since I am actively looking/searching etc., I should either a) automatically pass without making a check or b) get a big bonus to my checks." So what happens is things like "I am going down the alleyway, being extra careful, checking all my sides", then he rolls awfully (or the opposition rolls too well) and the player complains that he should get a free pass.  I'm not the kind of GM that says "you didn't say you put on clothes so you are now wandering outside naked", but perhaps the player picked up this habit from other games.  How should a GM deal with a player's desire for this kind of "standing orders?" Is it reasonable to have them checking for everything and doing everything automatically?  Does the burden need to be on me, the GM, to do so?


I have to find a biholomorphic map from $\{z \in \mathbb{c} : |z|<1, $Im$ z>0\}$ to the unit disk. My idea: If I can somehow map the upper half disk into the upper half plane (biholomorphically) I am done, since I can then compose it with Caley transform to get into the unit disk. If I use $f(z)=1/z$ it will only map it to outside of the upper half disk in the half plane, so can I edit it a bit to capture the interior of half disk as well?

This comes straight from Conway's Complex Analysis, VII.4, exercise 4.     Find an analytic function $f$ which maps $G:=$ {${z: |z| < 1, Re(z) > 0}$} onto $B(0; 1)$ in a one-one fashion.   $B(0;1)$ is the open unit disc.  My first intuition was to use $z^2$, which does the job splendidly, except for the segment $(-1,0] \subset B(0;1)$.  Under $z^2$, the pre-image for this segment is the segment $[-i,i]$, which is not in $G$.  My next thought is to modify $z^2$, something like $a(z-h)^2+k$.  I've yet to work out the details, but my gut tells me this isn't the right idea.  I've been teaching myself conformal maps in preparation for a qualifying exam.  So, if there's a shockingly basic, obvious solution... please patronize me.


I am getting this error:  Warning: oci_parse(): ORA-01756: quoted string not properly terminated in <DIRECTORY> on line 200 Warning: oci_execute() expects parameter 1 to be resource, boolean given in <DIRECTORY> on line 201  In reference to this code (line 200/201 marked):          $testSQL =  "insert into INTOXDM.JOINT_USE (RECEIVED,                  REGION,                  PERMIT,                  CUSTOMER,                  TO_BUSINESS,                  TO_PERMIT,                  POWER_ADDRESS,                  COMPANY,                  MAPSECTION,                  POLES,                  FEE,                  INVOICE,                  DATE_LARRY,                  DAYS_LARRY,                  PI_PON,                  DATE_PD,                  DAYS_LARRY_PD,                  RETURNED,                  DAYS_PD,                  ERRORS_PD,                  ERRORS_MULTIPLE,                  DATE_MAKEREADY_JU,                  DATE_MAKEREADY_COMPLETE,                  DAYS_MAKEREADY,                  DAYS_JU_PROCES,                  APPROVAL,                  DAYS_PERMIT_IN_JU,                  DATE_PLANNING,                  DAYS_OPEN,                  DATE_ROUTED,                  DAYS_TOTAL,                  COMMENTS) values (                 '$RECEIVED',                  '$REGION',                  '$PERMIT',                  '$CUSTOMER',                  '$TO_BUSINESS',                  '$TO_PERMIT',                  '$POWER_ADDRESS',                  '$COMPANY',                  '$MAPSECTION',                  '$POLES',                  '$FEES',                  '$INVOICE',                  '$DATE_LARRY',                  '$DAYS_LARRY',                  '$PI_PON',                  '$DATE_PD',                  '$DAYS_LARRY_PD',                  '$RETURNED',                  '$DAYS_PD',                  '$ERRORS_PD',                  '$ERRORS_MULTIPLE',                  '$DATE_MAKEREADY_JU',                  '$DATE_MAKEREADY_COMPLETE',                  '$DAYS_MAKEREADY',                  '$DAYS_JU_PROCESS',                  '$APPROVAL',                  '$DAYS_PERMIT_IN_JU',                  '$DATE_PLANNING',                  '$DAYS_OPEN',                  '$DATE_ROUTED',                  '$DAYS_TOTAL',                  '$COMMENTS')";         $testParse = oci_parse($objConnect, $testSQL); //LINE 200          $testExecute = oci_execute($testParse); } } //LINE 201   However, I cannot find what I am missing. I have been at it for an hour, it is very frustrating. Are there tools that you can post source into that assist in finding these errors?

If user input is inserted without modification into an SQL query, then the application becomes vulnerable to , like in the following example:  $unsafe_variable = $_POST['user_input'];   mysql_query("INSERT INTO `table` (`column`) VALUES ('$unsafe_variable')");   That's because the user can input something like value'); DROP TABLE table;--, and the query becomes:  INSERT INTO `table` (`column`) VALUES('value'); DROP TABLE table;--')   What can be done to prevent this from happening?


So, I am just starting out to learn Fortran programming. I am a complete newcomer to programming. I have little experience with Ubuntu. What are the recommended ways to install Fortran on Ubuntu?

I am trying to install gfortran in my computer with Ubuntu 12.04 by using these commands,  sudo -i apt-get update apt-get install gfortran   but I found the program saying "unable to locate package gfortran". Then on a Ubuntu page I found some question regarding the same problem and I went through the solution from them but again I couldn't install the gfortran package.  Can anybody tell me how to install it?


I was using the following code to search and display results from SQL. My question - Is it SQL Injection proof ? I believe it is not, I tried converting it into a prepared statement. But the SQL query itself is in 3 parts, which makes it difficult fore to fix it. if possible, someone please show me how to make add prepared statement in it. $query = " SELECT * FROM filter ";  if($_POST['query'] != '') {   $query .= '   WHERE product_name LIKE "%'.str_replace(' ', '%', $_POST['query']).'%"    '; }  $query .= 'ORDER BY releasedate DESC ';  $filter_query = $query . 'LIMIT '.$start.', '.$limit.'';  $statement = $connect->prepare($query); $statement->execute(); $total_data = $statement->rowCount();  $statement = $connect->prepare($filter_query); $statement->execute(); $result = $statement->fetchAll(); $total_filter_data = $statement->rowCount();


Apparently I can't post a question which refers to an earlier question, links to a couple of separate jsfiddle scenarios, and is illustrated, without adding code.   Error is "you can't link to jsfiddle without adding code".  So I've added a pointless bit of code.  I can understand the point is to stop people posting brief answers which link to jsfiddle, with no context.  But in  the code is a distraction.   Shouldn't questions which link to jsfiddle be excused the code requirement (especially if theyshow their effort in other ways)?

It's extremely common for people to ask and answer questions with no code other than a link to  or similar service. These of course are not appropriate. I have personally been unable to access jsfiddle for hours due to the site being down while browsing Stack Overflow.   In an effort to help educate people on why this is a bad idea and at the same time improve posts on SO, I suggest some measures be put in place to prevent it from happening.  For example, if the question or answer has:   A link to , , or any other site in a specified list (but let's be realisitic, the one that really matters the most is jsfiddle) No formatted code   ...prevent it from being posted, with a message or link explaining why. There may be edge cases where it does make sense, so perhaps we'd need to allow the user to click through the message and post anyways, but at least they will have been warned/educated.  If we need to discuss whether or not "link only, no code" posts are problematic and not appropriate, then so be it - but I think it's obvious and that topic has been well covered. Is there anything we can do to prevent them and encourage people to put their code in their post?  This issue is very specific to jsfiddle, I would like to see something that directly addresses that. If another site becomes the defacto code demo site, then we can cross that bridge when we get to it or look for more general solutions to this ever growing problem. I think that awareness of the issue is key to preventing it, and people don't read the FAQ nearly enough as it is - we need some direct intervention.  According to the owner/creator of jsfiddle, Stack Overflow makes up . That's a huge amount. Sure they aren't all "link only" posts, but I want to emphasize how much SO is using jsfiddle in particular to dump their code.  People aren't doing this to harm the site, the usually think they are helping out by making their post easier to read. They need to understand why this is actually a problem, and why relevant code must be posted on the site, not somewhere else. If more people understood, I think the problem would start to go away on it's own - but we'd still need something to deal with newer users who aren't familiar with the rules and goals of SO and Stack Exchange, don't hang out in meta, don't read the FAQ, etc. However, the less examples of jsfiddle-link-only posts there are, the less people will imitate them.  I honestly think that if people understood the problem more, it wouldn't be as much of an issue. This doesn't mean blocking jsfiddle, but preventing posts that rely on links to it. A lot of people are confused about that, and ask me "Since when is jsfiddle not allowed?". It's allowed, but your post should hold up without the link. People need to understand that - a warning message would probably be enough.  I do not feel that this specific issue is "status-completed". I think it's still a major problem that's bound to get worse as the months and years go by.  Here are some examples from the past few hours, as of 2012/10/17 6:45 PM EST:                   Here are some more from this morning, 7:30 AM 2012/10/18 (all questions, all within the last couple of hours). I could have easily found a lot more but it was getting boring:                   These were ridiculously easy to find (took me about 3-4 minutes). I don't think the recent change has done very much to help the situatuion. There are literally entire threads on SO that are just passing jsfiddle links back and forth, and it's been like that for a long time - and bound to continue unless something is done to address this specific issue.


Sorry , i have one question , how to see original photo if I download a modified photo (.jpg) from enthernet . something like this :    How to see original photo without blue font  ? Can somebody explain me how to do it ?

OK possibly a random question here, but one that is relevant to the site and regarding a hot topic nowadays: privacy.  If I load an image file (in my case a PNG photocopy of a document which contains some personal details) into Gimp, and I 'fill' with black (i.e. as if to redact) the areas of the image that contain sensitive information, and I then overwrite the original file, is there any way that the original untouched image can be recovered or gleamed? Such as low level bit analysis or...?  If so what tools and techniques are behind that, and how can I mitigate this? Is it a simple case of not overwriting the original but simply creating a new file with the changes?


I know I can install any Language and fonts by going clicking Dash->Settings->Language Support->Install/Remove Languages but how can I do this if I'm using Ubuntu Server and I do not have a GUI.

I'm trying to have everything ready to install a new desktop with a few command line instructions. Unfortunately, to install the language packages, I couldn't find how to do it.  I can run  gnome-language-selector   But it doesn't seems to be usable in command line directly. I need to go on with clicks...  An other thing that could be done is that I do those clicks and find out which packages have been installed and read the changes in /etc/environment and /etc/default/locale (and other /etc/... file?) but the list of packages is probably different depending on the packages installed (Firefox, Thunderbird, LibreOffice, Gnome, ...)  Is there a tool for that? Like let's say :  gnome-language-selector --install fr   or a package that has all necessary dependencies :  sudo apt-get install super-language-pack-fr   Thanks,


Why is pressure is considered as a scalar quantity not a vector one while we know the pressure is force exerted on a specific unit area and vector is a quantity which is defined as a magnitude and a direction. It is not like any question asked before about scalar and vector quantities

I have a final exam tomorrow for fluid mechanics and I was just looking over the practice exam questions. They do not provide solutions. But pretty much I have to define pressure at a point and also say why pressure is scalar instead of a vector.  I am thinking pressure at a point is $P=\lim_{\delta A \to 0} \frac{\delta F}{\delta A}$. Please let me know if I am wrong.   But I do not know at all why pressure is a scalar instead of a vector. I know it has something to do with $d \mathbf{F}=-Pd \mathbf{A}$


Prove that : $x^n+4$ is irreducible  on $\mathbb{Z}[x]$ if only if $n\neq 4k$ with $k\in\mathbb{N}$.

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 $F$?


I am from india and i live in poland. I have polish national visa D on my passport. My visa is valid until 29-11-2016. My girlfriend is from germany. She always come to here and live with me somedays. I want to ask that can i go to germany with this visa and how many days i can stay there?  We both want to marry each other so tell me the right procedure about marriage that where can we get married? In poland or germany? And documents i need?  Thanks

I’m going to Germany for a semester exchange and I have a long-stay visa from Germany. Can I travel to the other Schengen states during this period with this visa or do I have to apply for a separate short stay Schengen visa?  My visa is German national visa type D. It is for a duration of 4 months, i.e., longer than 90 days. It says on the visa that the long stay visa is valid in Deutschland, which is different from my earlier visa, which I had when I visited Germany earlier; that one was a short stay visa and said it was valid in Schengen Staten.  Perhaps my current visa means that I can stay in Germany for a period of longer that 90 days can visit the other Schengen states if I don’t exceed the 90 day period.


How do you show that Let $n\in\mathbb{Z}^+$ $n\mid (2^1+2^2+2^3+...+2^{n-1})$ iff $n$ is prime?

Consider the following  (I read similar thing in a couple of sources but this one illustrates the issue I'm having):     By Fermat's Theorem if $n$ is prime, then for any $a$ we have $a^{n-1} = 1 \pmod{n}$. This suggests the Fermat test for a prime: pick a random $a \in \{1,...,n-1\}$ and see if $a^{n-1} = 1 \pmod{n}$. If not, then $n$ must be composite.      However we may still get equality even when $n$ is not prime. For example, take $n = 561 = 3\times 11\times 17$. By the Chinese Remainder Theorem ... (Some explanation)      Thus no matter what $a$ we pick, $561$ always passes the Fermat test despite being composite so long as $a$ is coprime to $n$. Such numbers are called Carmichael numbers, and it turns out there are infinitely many of them.   So according to the author, no matter what $a \in \{1,...,n-1\}$ we choose, 561 will pass the test. But this is not true e.g:  $$ \begin{align} 3^{560} &\not\equiv 1 \pmod{561} \\ 6^{560} &\not\equiv 1 \pmod{561} \\ 9^{560} &\not\equiv 1 \pmod{561} \\ &... \end{align} $$  and there are many $a \in \{1,...,n-1\}$ such that $a^{560} \not\equiv 1 \pmod{561}$.  Why would we exclude $a$ such that $\gcd(a, n) = 1$ when the test works well without such condition? If we know that $\gcd(a, n) \not= 1$, we already know that $n$ is not prime, thus the test is pointless.  The best source I read so far, sadly forget it, states that if $n$ is composite, then 50% of $a \in \{1,...,n-1\}$ will not satisfy $a^{n-1} \equiv 1 \pmod{n}$. Unless it's Carmichael numbers, i.e. there are less than 50%. Which seams true in my experiences (and this is properly the reason why the probability of not being prime gets lower by $1/2$ on each iteration).


Can you please tell me if there is a handy shortcut or hotkey using CtrlR or the knife tool to cut ALL the way through an object and not just it's face? I want to make a simple cut to make the tape follow the form of the bottle.

I'm using Blender 2.66,  I find that the knife tool (K) doesn't work the way it used to.     Dragging across an obscured edge, even if selected, doesn't cut it. There seems to be no way to activate the option to do a midpoint cut or multiple cuts.


I have some anchovies dipped in olive oil and parsley. How long can they stay in fridge before going bad?

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


I'm paying for a large (56 x 45 x 25 cm) on-board luggage at WizzAir, but can't find the weight anywhere on their website.  I've been looking at other posts like  but it's seriously outdated (and doesn't give a concrete answer to the question) and wanted to know if anyone happened to know the actual numbers by any chance.

What's the weight limit on Wizz Air, for cabin baggage?    I can't find anything about the weight on their website. I know that for Ryanair is 10kg, and EasyJet say they don't have a limit for weight.


I'm totally new to photography and need your help.  I've read much about ISO, Aperture and Shutter speed. I know to get a blurred backround: use a wide aperture. Also I know the distance between camera and object is important.   But every single time I've tried to get a blurred background, I've achieved nothing! I was thinking maybe it's not possible to have this effect with a 18-55mm STM lens at all. This is on a Canon 70D  Is that right? If not, what is your recommended setting to get a blurred background?  Best shot I could get is this. f/5.6, 1/250, ISO auto:

I'm currently using an entry-level DSLR with 18-55mm lens and having great trouble trying to creating a blurred background effect in my photos. Now matter what aperture or shutter speed I choose, I'm not able to get it.  There's a general question about , but what specific things can I do to get this effect with an entry-level lens?


Considering this sentence:     Something was awry but neither Alice nor Bob knew what.   Can I omit the neither here?     Something was awry but Alice nor Bob knew what.   It sounds reasonable, but I found it strange that it requires a list to make this negation work.  When it's just Alice, more words are required to express negation:     Something was awry but Alice did not know what.

I came across this sentence:     Cummings Motors, Smith Electric nor our subcontractors can be held liable.   Is this a proper use of the word nor?  I can understand     Neither Cummings Motors nor Smith Electric nor our subcontractors can be held liable.   But nor without neither? What about neither, nor, nor? Is one nor sufficient?


A 3 × 3 matrix $A$ is such that for $X = [2, 3, 4]^\top$, $AX = 0$. Show that $\det(A) = 0$.

Show that $det(A)=0$ for a $3\times3$ matrix $A$ such that for $X=[2,3,4]^{T}$, $AX=0$  It seems most intuitive to me that $A$ would just be a matrix composed of zeros, but is 1) this what the question is really asking (as that seems like a bit of an easy way out) and 2) a way to prove this for $A$ without it being composed entirely of zeros?  For point 2 I'm unsure of what can be done other than just making arbitrary matrices that have a $det=0$, which doesn't seem like a very rigorous way to solve the problem.


While creating a query on Stack Exchange Explorer, how do you write a query to include all Stack Exchange sites?  select P.ID as [Post Link],         p.Score,         P.Title,         P.OwnerDisplayName,         P.ViewCount,         pt.Name  from  Posts as P inner join PostTypes as Pt on P.posttypeid = pt.Id  where p.Score > ##score## AND (Something like include all site) order by P.Score desc

I think it would be useful if we could join across databases in the data-explorer.  For example, I'd like to query up a list of questions that I had a hand in migrating away from SO, and see what percentage of them were subsequently closed or re-migrated.  I realise I could download the various data dumps and do this on my own machine, but it would be nice if it were allowed on the online version.  Is this possible/practical?


I would like to find the correlation between a continuous (dependent variable) and a categorical (multinomial) variable. I found that the appropriate test is Eta ($\eta$) coefficient, however, I haven't found enough resources support this test.  Is this the right test ?

I would like to find the correlation between a continuous (dependent variable) and a categorical (nominal: gender, independent variable) variable. Continuous data is not normally distributed. Before, I had computed it using the Spearman's $\rho$. However, I have been told that it is not right.  While searching on the internet, I found that the boxplot can provide an idea about how much they are associated; however, I was looking for a quantified value such as Pearson's product moment coefficient or Spearman's $\rho$. Can you please help me on how to do this? Or, inform on which method would be appropriate?  Would Point Biserial Coefficient be the right option?


How can I test than the mean of a variable is greater than or equal to -3 and less than or equal to 3? In other words I want to test if the absolute value of the mean is less than or equal to 3. Thanks!!

I just used the standard formula to determine the sample size of a sample to match the mean of a pupulation with an error margin  of 3 percentage points and with a 90% probability. I know would like to check that the mean of my sample is actually within the 3% margin of error of the mean in the population. To do so I am taking the population and appending the sample, identifying observations in the sample with a dummy called sample. Then I run the following regresion: reg var1 sample And I am testing wheter the coefficient for the dummy variable sample is less than 3 percentage points. To do so I am using a one sided t test.  But this is only ok when the coefficient of the dummy variable "sample" has the "right" sign. I would like to test the joing hypoithesis that the coefficient of the dummy variable sample is greater than -3 and lower than 3. Does anyone have any insight on how to do this test? Thanks in advance.


In LibreOffice 6, the systray Quickstarter was removed but there is a package called libreoffice-systray in the repositories.  Can this package be used to run libreoffice in the system tray? I installed this package but cannot figure out how to use it.  I am using Ubuntu 18.04 with the official LibreOffice Fresh PPA.  Previously I asked the question  and there was no positive answer. Later I saw that there is a package called libreoffiec-systray, so I am asking how to use it. So this question is not a duplicate of that, although their answer may be similar once we find how to use this package.

In LibreOffice 6, the tools>options>LibreOffice>Memory was removed.  Is there any way to use the systray Quickstarter in this version of LibreOffice? That option used to make LibreOffice much faster.  I am using Ubuntu 18.04 with the official PPA of LibreOffice.


Do these two sentences mean the same?   When I arrived, Lisa was waiting for me. When I arrived, Lisa had been waiting for me.

This is the first paragraph of an article:     The salvage operation had been a complete failure. The small ship, Elkor, which had been searching the Barents Sea for weeks, was on tis way home. A radio message from the mainland had been received by the ship's captain instructing him to give up the search. The captain knew that another attempt would be made later, for the sunken ship he was trying to find had been carrying a precious cargo of gold bullion.   Is the word "carry" here a state verb or action verb? Can we change "had been carrying" to "was carrying" or "carried"?  At the end of the article, it contains the following sentence:     The Karen ( the name of the sunken ship) had been sailing in a convoy to Russia when she was torpedoed by an enemy submarine.   Can we change "had been sailing" to "was sailing"?


If $f:\Bbb R^2\to\Bbb R$, what does $$\frac{\partial^2 f}{\partial x\, \partial y}$$ mean? Does it mean $\dfrac{\partial}{\partial x}\left(\dfrac{\partial f}{\partial y}\right)$ or $\dfrac{\partial}{\partial y}\left(\dfrac{\partial f}{\partial x}\right)$?  (I know that most of the time due to Schwarz theorem it is irrelevant.)

Does $$\frac{\partial ^2f}{\partial x \partial y}$$ mean diff it wrt $x$ THEN wrt $y$? Or diff wrt $y$ then wrt $x$?


One of my math professors (in a U.S. university) retired this semester.  He was one person that I had planned on asking to write my letters of recommendation this coming fall semester, when I send out PhD applications in math / applied math.  He is very old and he seems anti-social and seems to not communicate with our math department very much.  I am just basing this on some stuff that he says, which scares me, e.g., "tell them (our math dept.) that I said this..."  So, I wonder whether anyone external to our own math department would even know who he is - or whether admissions committees even value his opinions about grad students, at this point in his career.  Would it be best to find someone else to replace him as one of my letter writers?  Someone who is younger and currently active in research?  I do have replacements in mind, but I am somewhat attached to this particular professor, since I feel that I got my start in rigorous mathematics with him.  Edit:  To add a bit more context, he is a full professor and has served on admissions / doctoral committees at our department numerous times.  So, he's very much qualified, of course.  My main concern is that perhaps he no longer communicates actively with people internal and external to our department, but that is only my best guess.  Thanks,

I wonder is it a good idea to ask for a letter of recommendation from a emeritus professor who I took his course and knows me well?   I was wondering is it bad to get a letter from someone who is not in Academia anymore?


Calculate $$\lim_{n \to \infty}\left(\dfrac{1}{n+1}+\cdots+\dfrac{1}{2n}\right).$$   I tried relating it to a Riemann sum, but I couldn't see how to do so.

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?


A bit of an OT-question from a newbie I'm afraid...  I just hope to find some entusiasts here who may know a source.  Here goes...  Are there any good sources of sample-documents that is suitable as inspiration?  Preferbly online, but books (especially free ebooks) will also do.  Old, handwritten, typeset/printed etc. samples, is also welcome.   Letters/envelopes, resumes/cv's, business/calling-cards, invitation, letters of introduction, business-letters, applications -- all of interest.  I'm not as interested in ready-made templates, but more of examples -- of the text (language, grammar, form), the layout, the fonts/penmanship -- of various writings over time (but mostly modern), as a source of inspiration.  I guess images (jpeg) would be the most obvouous way to present such stuff online.  So, any recomendations for sites or books for inspiration?  (That said, recomendations for websites for really good sources of templates for TeX/LaTeX and LyX -- and perhaps for Scribus, Open/Libre-Office and MS-Word -- would be welcommed too.)

If you were asked to show examples of beautifully typeset documents in TeX & friends, what would you suggest? Preferably documents available online (I'm aware I could go to a bookstore and find many such documents called 'books'). Extra bonus for documents whose LaTeX source is available.  This is not an idle question. Seeing great examples of any craft is both educational and inspiring, let alone explaining why we prefer TeX to Word or other text editors.  For instance, I like how Philipp Lehman's  looks. I don't know enough LaTeX to realize how much customization was done, but the ToC looks polished.  Your nominations, please ...


I originally posted a question about removing Ubuntu and GRUB from a dual boot system. This is what my partition map looked like at the start:    My question was marked as a duplicate by moderators, and I was directed to this post: )  I followed the directions there, and performed the following: I booted into the Windows recovery console, and ran FIXMBR on my HD.  After that, to my surprise, the computer would still boot into GRUB.  (how is this possible??) However, if I selected to boot Windows, it would say on a purple background "error: no such device: 8234ceb934ceb009. Press any key to continue...". When I press a key I get in B&W: "Invalid partition table".  I was able to boot the computer using my PMAGIC recovery disc, and run Partition Editor.  This is what I saw:    Mysteriously, a few reboots later, GRUB vanished. Now I just get the message "Invalid Partition Table". If I boot from my Windows XP installation CD, it no longer sees the installed OS, nor an NTFS partition  It sort of looks like TestDisk sees that there is an NTFS partition there:    Doing a quick search with TestDisk, however, does not seems to find it.

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


Due to the expansion of the universe, the photons emitted by the stars suffer redshift, Its mean that the energy is lowered a little bit. Does this mean that the energy is lost? Does the expansion of the universe violate some conservation principles according to Noether's theorem?

In popular science books and articles, I keep running into the claim that the total energy of the Universe is zero, "because the positive energy of matter is cancelled out by the negative energy of the gravitational field".  But I can't find anything concrete to substantiate this claim. As a first check, I did a calculation to compute the gravitational potential energy of a sphere of uniform density of radius $R$ using Newton's Laws and threw in $E=mc^2$ for energy of the sphere, and it was by no means obvious that the answer is zero!  So, my questions:   What is the basis for the claim – does one require General Relativity, or can one get it from Newtonian gravity? What conditions do you require in the model, in order for this to work? Could someone please refer me to a good paper about this?


We are all on the same wi-fi in the same room. And we all have the same version of minecraft. We press play and it won't show that we have any friends playing.

We have two iPads, and both of them have Minecraft PE. My son wants to connect the two and play with me. I have absolutely no idea what I am doing here, so I do not know how to do this.   One game says "Broadcast to LAN", and the other one says "Local Server Multiplayer". I have switched both to on.   What do I need to do to be able to play joined? We are both on the same WiFi.


i have an issue,i wanna create a hotspot,but i dont have an ethernet connection,only wifi. How can i make a hotspot without ethernet?

Although many questions have already been asked regarding WiFi hotspot, I didn't get any of the solutions working for me.  I connect to the Internet using a 3G Dongle of Huawei 3772 (Vodafone). The connection type is Mobile Broadband connection. I have to share this Internet connection with my other devices like mobile phones and laptops.  How can I create a WiFi hotspot connection for this connection.  I am using Ubuntu 12.04 LTS.  I would like to note that I have already tried some help links from Ubuntu but, they are so confusing that I could not understand them.


If there's a question where a foreign user set a bounty and it's their only appearance in the thread, will they be notified when I post a comment addressed like @BountyGrantor?  In picture:

are described at length, but don't address bounties.   If I put a bounty on someone else's question, will I be notified of undirected comments? Can people notify me via @-replies even if my only involvement with the question is putting a bounty on it?   If the answer to one or both is no, could we get a new feature putting anyone with a bounty on a question on par with the question's author for the purposes of comment @-replies?  Or, if not, at least add them to the list of @-reply targets to allow messaging them?  This was all prompted by  from DanQ that had a bounty put on it by rabidsnail, presumably because she had the same problem.  Once it showed up on the Featured Questions list, people asked for more information in comments.  DanQ never responded, and may well not have cared about the question by that point.  Presumably rabidsnail cared, but did she get any notification about the comments requesting more info?  (I assume rabidsnail checked in on the question at some point, and obviously didn't add more info then, but maybe she would have had she known sooner.)  There's also the question of proper etiquette when elaborating on a question that's not yours, but that's beyond the scope of this question.


How can I find my current GTK version using Terminal ? Is there a command for that ? I use 16.04 + Unity.

Is there a way to know which GTK version is installed using the command line?   I am working on Ubuntu 11.10.


I have a problem. I dont know how to pass 2D array of pointers to fuction by reference.  class SomeClass {  //body of class }   void somefunction(SomeClass ***array) { //body of function }  int main() { SomeClass * array[10][10] someFunction(array?????) }       Anyone know how to pass this array by reference??

I am trying to pass a reference to a two-dimensional array to a function in C++. I know the size of both dimensions at compile time. Here is what I have right now:  const int board_width = 80; const int board_height = 80; void do_something(int[board_width][board_height]& array);  //function prototype   But this doesn't work. I get this error from g++:  error: expected ‘,’ or ‘...’ before ‘*’ token   What does this error mean, and how can I fix it?


Is there a way to get all attributes/methods/fields/etc. of an object in Python?  vars() is close to what I want, but it doesn't work unless an object has a __dict__, which isn't always true (e.g. it's not true for a list, a dict, etc.).

dir(re.compile(pattern))    does not return pattern as one of the lists's elements. Namely it returns:  ['__copy__', '__deepcopy__', 'findall', 'finditer', 'match', 'scanner', 'search', 'split', 'sub', 'subn']   According to the manual, it is supposed to contain      the object's attributes' names, the   names of its class's attributes, and   recursively of the attributes of its   class's base classes.   It says also that     The list is not necessarily complete.   Is there a way to get the complete list? I always assumed that dir returns a complete list but apparently it does not...  Also: is there a way to list only attributes? Or only methods?  Edit: this is actually a bug in python -> supposedly it is fixed in the 3.0 branch (and perhaps also in 2.6)


1) Let me see if I can find a match on tinder?  2) Let me see if I could find a match on tinder?  For instance, in healthy banter with your friend, you tell him he's so ugly that no one would swipe right on him. He rebuts in either of these counter statements.  (As for my own rationale: the first sentence conveys an 'ability' while second implicates a 'possibility')

When should I use can? When should I use could? What is right under what context?


Could anyone shed some light on this error for me? To a beginner of course. This will probably be no more than a simple fix for someone else.  I'm trying to read in the Product to be used in the where clause.  alter proc Proc1 @ProductID int as go select ProductName from Products where ProductID = @ProductID

What is the reasoning behind using the GO statement after every SQL statement? I understand that GO signals the end of batch and/or allows the reputation of statements but what advantage does it have using it after every statement.   I am just curious as a lot of Microsoft documentation etc. have started using it after every statement  or maybe I've just started to notice.   Also what's considered best practice?


I'm using XAMPP on linux. I reinstalled XAMPP, but I didn't know that I need to export/import databases and not copy/paste lampp/var/mysql folder. PhpMyAdmin displays my database but it has no tables. I have mysql folder with all db files before I reinstalled XAMPP.

I have previously saved a copy of /var/lib/mysql/ddms directory ("ddms" is the schema name). Now I installed a new MySQL on a freshly installed Ubuntu 10.04.3 LTS by running apt-get install mysql-server, I believe version 5.1 was installed. After I copy the ddms directory under /var/lib/mysql, some of its tables work fine, these are the tables with an associated set of three files: a .frm file, a .MYD file and a .MYI file.  However, there are two tables with a different set of files: a .frm file and a .ibd file. These two tables didn't show up in the table list in phpMyAdmin. When I look at the error log, it says:  [ERROR] Cannot find or open table ddms/dictionary_item from the internal data dictionary of InnoDB though the .frm file for the table exists. Maybe you have deleted and recreated InnoDB data files but have forgotten to delete the corresponding .frm files of InnoDB tables, or you have moved .frm files to another database? or, the table contains indexes that this version of the engine doesn't support.   Please help with restoring these two tables. Thanks.


What are the automorphisms $(\mathbb R, 0, 1, +, \cdot, \leq)\to (\mathbb R, 0, 1, +, \cdot, \leq)$ and how many are there?

Is an automorphism of the field of real numbers $\mathbb{R}$ the identity map? If yes, how can we prove it?  Remark An automorphism of $\mathbb{R}$ may not be continuous.


I read this book two years ago at a local library and can't remember the name of it. The book is really old, written in the 60s. It has a peach cover with multicolored text.  It's about a man living in a society on an alien planet where a prison ship had crashed and the survivors banded together to form a society. He gets a promotion to a telegraph operator. I think they called it semaphore operator.   There are giant squid predators that are in a relationship with the human population. They let them live in exchange for food and are worshipped by a theocracy. There is one particular big squid who is the King and he wrecks everything the protagonist had including killing his mentor after the protagonist started talking about how they were not beholden to the monsters.

I read a book a while ago ( read many years, maybe a decade ago, it was at least 20 years old then) about a watery planet ruled over by a monstrous overlord sea monster thing.   The hero rallies some of the floating villages to fight the monster and they make iron weaponry out of iron from blood as far as I can remember.   Beyond this I can't remember much about the book, but I'm sure at least one other person out there must have read it.  Edit for more potential details: I think the village folk were reluctant to trust the hero, he was maybe a stranger to them and a lot of them didn't want to upset the status quo.    The iron weapons were maybe to pierce the hide? A harpoon seems familiar, something to trap him with the aid of nets.


I want to know how to center this lightbox. Here is a link to the code -  . I scaled the image down by changing the width of the column class from 25% to 15% and the lightbox floats to the left. I want it to be centered. Thanks

How can I horizontally center a
 within another
 using CSS?

Foo foo


In Java, when we locally declare a variable, it goes in the Memory Stack, while locally defined objects goes to the Heap. public class Clazz {     private int x;      // constructors omitted for brevity }  public void method() {     Clazz clazz = new Clazz(10); // defining an object - this goes to the heap space     int y = 10; // declaring a varible - this goes to the memory stack     clazz.doSomething(); }  Why do objects goes to the heap? Yes, I know that the Memory Stack has the reference to the objects in the heap, but why, unlike the primitives, the object values are stored in the heap? In other words: why not put them all together, or in the memory stack or in the heap? Edit: Ok, got it. It's not a good idea to put the object in the memory stack, but why not put them all together in the heap, then?  provides a good explanation on what the Heap is and what the Stack is, but unfortunately, doesn't answer my question.

Programming language books explain that value types are created on the stack, and reference types are created on the heap, without explaining what these two things are. I haven't read a clear explanation of this.  I understand what a stack is. But,    Where and what are they (physically in a real computer's memory)? To what extent are they controlled by the OS or language run-time? What is their scope? What determines the size of each of them? What makes one faster?


I'm getting a linker error when I try to build a small C program on CentOS 8.1.  I'm new to Linux development, and to using make, and I haven't been able to solve the error.  The linker is failing to resolve a function that's defined in a static library.  I built the static library from the sample code for the APUE book.    I'm able to build my program, if I use a makefile that's provided with the APUE sample code.  But I'm trying to get it to build with a simpler makefile that I wrote.  The program is:  #include "apue.h"  int main(void) {     err_exit(8, "hello world");     exit(0); }   The relevant line from the header file is:  void    err_exit(int, const char *, ...) __attribute__((noreturn));   The makefile is:  runme: testprog.o     gcc -ansi -Wall -o runme -L. -lapue testprog.o  testprog.o: testprog.c     gcc -c -ansi -Wall -o testprog.o -I. -DLINUX -D_GNU_SOURCE testprog.c   The error is:  $ make gcc -ansi -Wall -o runme -L. -lapue testprog.o testprog.o: In function main': testprog.c:(.text+0x14): undefined reference toerr_exit' collect2: error: ld returned 1 exit status make: *** [Makefile:2: runme] Error 1  Any suggestions would be appreciated.

Why does the order in which libraries are linked sometimes cause errors in GCC?


Sometimes when I ask a question, I see someone posting a comment on my question "Possible duplicate of...", and I see such banner:        However, the suggested "duplicate" does not really contain any answer to my own problem. Why should I edit my question?  A more extreme example:  Imagine you ask for 'Python loops', and someone comment that your question is a possible duplicate of 'Regular expression to get a phone number'. Should it be reported? How can I avoid to edit the question?

I asked a question regarding a very specific feature of a program and whether or not it works with a larger program.  Within hours someone had marked it with "This question may already have an answer here of a similar question, but not related to my question.  The question I asked IS NOT ADDRESSED in the referred-to question. It's frustrating to spend half an hour putting together an intelligent and specific question, and then have someone mark it as a duplicate (or possible duplicate), which apparently causes people to skip over my question. I haven't received any more responses since the question was flagged.   Two questions:  (1) How do I get this flagging removed and (2) what's the best way to prevent these "helpful" flaggings in the future?


I keep getting a null pointer exception and I am not sure why. I looked at what causes this error but I still can't figure it out. I think after this error it may not be right but I can fix that after but first I have to fix this. This is the error I am getting:   ----jGRASP exec: java PostOfficeTester Exception in thread "main" java.lang.NullPointerException at PostOffice.retrieveMsg(PostOffice.java:33) at PostOffice.placeLetter(PostOffice.java:17) at PostOfficeTester.main(PostOfficeTester.java:11)  ----jGRASP wedge: exit code for process is 1. ----jGRASP: operation complete.   Here is code:  public class PostOfficeTester{ public static void main(String[] args) {   PostOffice branch = new PostOffice(5);   branch.retrieveMsg(5);   branch.placeLetter(new Letter("Arnold", "I'll be back!"),5);   branch.placeLetter(new Letter("Spock", "Live long and prosper."),4);   branch.placeLetter(new Letter("Kirk", "KHAAAAAN!"),4);   branch.retrieveMsg(4);   branch.retrieveMsg(2);   branch.retrieveMsg(-1);   branch.placeLetter(new Letter("Harry", "Make my day!"),0);   branch.placeLetter(new Letter("Ellie", "Thanks for the adventure! Now go have another one!"), 1);   branch.placeLetter(new Letter("Buzz", "To infinity... and beyond!"), 3);   branch.findSender("Kirk");   branch.findSender("Ellie"); }  }   public class PostOffice {   private Letter pobox[];   public PostOffice(int size){     pobox = new Letter[size];  }   public boolean placeLetter(Letter mail, int boxNum){     if(boxNum>=pobox.length || (!(retrieveMsg(boxNum).equals("Empty!")))){          return false;     }     else{        return true;     }  }   public String retrieveMsg(int boxNum){     if(boxNum>=pobox.length){        return "Box does not exist!";     }      else if(pobox[boxNum].equals("")){            return "Empty!";     }      else{        return pobox[boxNum].getMsg();     }       }   public Letter findSender(String name){     for(int i = 0; i<pobox.length; i++){        if(name.equals(pobox[i].getSender())){           return pobox[i];        }      }      return null;            }    }    public class Letter {     private String sender;    private String message;     public Letter(String name, String text){       sender = name;       message = text;    }     public String getSender(){       return sender;    }     public String getMsg(){       return message;     }   }

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?


Just installed on my new laptop Ubuntu 14.04 and immediately installed Chrome (for programming purposes). I havn't done anything with Mozilla Firefox yet and I want to remove it since I have Chrome. How do I remove Firefox?  Another qustions were asking how to remove Firefox after long use.. I'm sure I don't need to write all the command lines their answers suggested..  Thanks in advance.

I have been using Firefox for a long time in Ubuntu, I downloaded some add-ons but it made firefox extremely slow, even if I remove them nothing will change.  I tried to remove Firefox also, but re-installing it will somehow recover the same Firefox I had- it seems it write some info somewhere that even if you remove Firefox, it will keep them.  Moreover, I am not able to use see any flash videos or website with Firefox(chrome works fine).. Honestly I tampered with plug-in settings in Firefox that this happened. But right now I can't do anything to overwrite the setting...  My question is how I can remove Firefox in a way to remove any previous traces and re-install a new version like for the first time?


If parsing the output of ls is dangerous because it can break on some funky characters (spaces, \n, ... ), what's the best way to know the number of files in a directory?  I usualy rely on find to avoid this parsing, but similarly, find mydir | wc -l will break for the same reasons.  I'm working on Solaris right now, but I'm looking for a answer as portable across different unices and different shells as possible.

How do I move all files in a directory (including the hidden ones) to another directory?  For example, if I have a folder "Foo" with the files ".hidden" and "notHidden" inside, how do I move both files to a directory named "Bar"?  The following does not work, as the ".hidden" file stays in "Foo".  mv Foo/* Bar/   Try it yourself.  mkdir Foo mkdir Bar touch Foo/.hidden touch Foo/notHidden mv Foo/* Bar/


Show that the space of functions $f: \mathbb{N} \to \mathbb{R}$ does not have a countable basis.  This is a problem I found a few weeks ago and I'm really stuck on it... I haven't thought of a good way to do it so could someone please provide a solution?

Show that the space of functions $f: \mathbb{N} \to \mathbb{R}$ does not have a countable basis.  I really don't know where to start with this one! Could anyone help me?  Thanks