Using the product formula (the formula with the prime factors of $n$), I got $$1=6\frac{(P_1-1)}{P_1}\frac{(P_2-1)}{P_2}\cdots\frac{(P_k-1)}{P_k}\,.$$

I know how to find for which $n$ $\phi(n)=n/2$ or $\phi(n)=n/3$, my method for finding those was simply to find primes $p$ that satisfy $\Pi_p$$_|$$_n$$1-1/p$ $  = 1/2$ or $1/3$.  However, I don't know how to find $\Pi_p$$_|$$_n$$1-1/p = n/6$. Intuitively it seems that if I combine results for both $\phi(n) = n/2$ and $\phi(n) = n/3$ I'll get $\phi(n) = n/6$ but it does not work, cause I get number of the form $2^a3^b$ which gives $\phi(n) = n/3$ again.  Is there a way to find $n$ for which $\phi(n)=n/6$? Or do such numbers exist at all?


Is the content for an auto-saved draft located on the server, or on the client/browser side?  When I'm writing a answer or question I see a small-sized text display, "draft saved" under that textarea. If I don't submit that form, my content remains in that textarea. And I will see it even after several days.  Is that text stored in the database? Or just a localstorage?

As per the title, curious about any implementation details that can be revealed.  I don't see any details in the  that indicate how they might be stored.  Particularly, I'm curious about whether or not it's stored on the client side, the server side, a combination of the two (e.g. a cookie that the server uses) and any underlying details that can be exposed.


Let $|\mathbb F|=q$ where $\mathbb F$ is a field. Now       $$|GL_n(\mathbb F)|=(q^n-1)(q^n-q)(q^n-q^2)\ldots(q^n-q^{n-1}).$$    How it is so?  My attempt  I just viewed in the matrix such that  $\left(\begin{array}{ccccc} a_{11}&a_{12}&\cdots&a_{1n-1}&a_{1n}\\ \vdots&&\vdots&&\vdots\\ a_{n1}&a_{n2}&\cdots&a_{nn-1}&a_{nn} \end{array}\right)$  For the first element I will have q choices and rest of the elements also have q choices. So there are $q^n$ choices and i should neglect $0$ in all at a time. So I removed one choice from the total so for the first row I will have $q^n-1$ choices. But for the second and third i am having confusion how to see the choices. And I am thinking that this will give the number of distinct basis for $GL_n(\mathbb F)$. Is it correct. Give me a diagrammatical explanation.

I don't know how to do the last task of an exercise.    Let $K$ be a field, $G=GL_n(K)$ and $X=K^n\backslash\{0\}$. First task: Show that $G \times X \to X$, $(A,x)\mapsto Ax$ defines an action of $G$ on $X$. Done. Second task: find the stabilizer of $\displaystyle x=\left(\begin{eqnarray} 1\\ 0 \\ \vdots \\0 \end{eqnarray}\right)$. Done. Third task: Show that there is only one orbit. Done. Last task: Let $|K|<\infty$. Use the last two tasks and induction to find $|G|$.    I know that $|G|=[G:St_G(x)]\cdot|St_G(x)|$ and i know that $[G:St_G(x)]=|\bar{x}|=m^n-1$ but i can't figure out what $|St_G(x)|$ is.  What should i do next? I appreciate every hint :)


I want to know what is wrong with this :  if (q == "outside" && q1 == "not alive") { System.out.println("bison"); }   This statement works perfectly:  if (q == "outside" && q1 == "alive") { System.out.println("bison"); }   All of the if statements containing "alive" works perfectly, but all of the if statements containing "not alive" does not work.  This is an exercise which I have to do without using else if or else.  full code :-  import java.util.Scanner;  class age04 { public static void main(String [] args) {  Scanner keyboard = new Scanner(System.in);  String q, q1,;  System.out.println("Two more questions, baby!"); System.out.println("Think of something and i'll try to guess it!");   System.out.println("Question 1) Does it stay inside or outside or both"); q = keyboard.next(); System.out.println("Question 1) Is it alive?"); q1 = keyboard.next();   if (q == "inside" && q1 == "alive") { System.out.println("houseplant"); }  if (q == "inside" && q1 == "not alive") { System.out.println("shower curtain"); }  if (q == "outside" && q1 == "alive") { System.out.println("bison"); } if (q == "outside" && q1 == "not alive") { System.out.println("bison"); }  if (q == "both" && q1 == "alive") { System.out.println("dog"); }  if (q == "both" && q1 == "not alive") { System.out.println("cell phone"); }  } }

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


I am a PhD students in physics, and my father is a Math researcher. One time, I asked him "Doesn't the fact that we can use math to explain things that happen in front of us, tell us that math is not a human invention but rather a discovery?" My father said that in his opinion, no - we were just able to find a very useful language to describe physical phenomena. But then, I learned about Fraunhoffer diffraction, which tells us that if a light wave passes through a slit of a given shape, on a screen really far away from the slit we actually see the Fourier transform of the slit! I was mind blown. I then went to my father and told him, "look! nature does Fourier transform, so Fourier transform cannot be man made!". He disagreed, and stated the same thing he told me before. Does my statement make sense? Can we say, based on Fraunhoffer diffraction, that Fourier transform is an act of nature rather than a human invention?

What would it mean to say that mathematics was invented and how would this be different from saying mathematics was discovered?   Is this even a serious philosophical question or just a meaningless/tautological linguistic ambiguity?


I had no problem pleasing the Pope the first time around, but now that I need to get the 5 Enlightenments, I'm stuck. I have $0, FL0, B0, T0, S0/25, W9/25, C0, E1. Workers don't count as things do they? If so, how do I get rid of workers? Do I need to get one more and then I can have 10 go to the Depot leaving me with none?

When going for a walk, eventually you run into the Pope.  He asks that you:     Come see me when you have given away all of your posessions.   This is a problem since I have millions of dollars and beads.  How can I quickly get rid of all my things?


the syntax of createUser method in samlJitHandler class is    createUser(Id samlSsoProviderId, Id communityId, Id portalId,String federationIdentifier,              Map<String, String> attributes, String assertion)   I understand that this method gets invoked automatically but I could not figure how the parameters String attributes, String assertion,String federationIdentifier,String communityId... are getting  passed to this method.  Please help me in understanding this flow.

I am having a hard time digging up some information on this as I believe it is still relatively new. If you implement SSO with Salesforce you have the ability to enable SAML. I have enabled SAML and have also enabled JIT with an automatically created class to support it.  Out of this newly generated class, there are two global methods that I am assuming are called upon SSO, but I do not know which one is called or how.   global User createUser(Id samlSsoProviderId, Id communityId, Id portalId,     String federationIdentifier, Map<String, String> attributes, String assertion) {     User u = new User();     handleJit(true, u, samlSsoProviderId, communityId, portalId,         federationIdentifier, attributes, assertion);     return u; }  global void updateUser(Id userId, Id samlSsoProviderId, Id communityId, Id portalId,     String federationIdentifier, Map<String, String> attributes, String assertion) {     User u = [SELECT Id, FirstName, ContactId FROM User WHERE Id=:userId];     handleJit(false, u, samlSsoProviderId, communityId, portalId,         federationIdentifier, attributes, assertion); }   Does Salesforce have some backend code that interprets the SAML coming over the SSO and then calls the methods appropriately?   The reason I am asking this is because I would like to cancel a user's SSO if they do not match x fields based off of the values coming across in the SAML in the SSO. If I did not want to update a user or create a user, would I be able to add in my own global class that could be called from the SSO?   Let me know if this is unclear / does not make sense.  Thanks


Given Matrix $A \sim B$ , If Matrix A, B are similar,Find the invertible matrix P such that $B=PAP^{-1}$ $$  A = \begin{bmatrix} -2 & -2 & 1  \\ 2 & 3 & -2 \\ 0 & 0& -2  \\ \end{bmatrix},\qquad\qquad B = \begin{bmatrix} 2 & 1 & 0  \\ 0 & -1 & 0 \\ 0 & 0 & -2  \\ \end{bmatrix} $$  Find the invertible matrix P such that $B=PAP^{-1}$ Seek the guidance of the great God,Best is a smarter solution

Currently I'm stuck with this problem:     The following matrices are similar to each other.      $$A=\begin{bmatrix}-3&0\\8&4\end{bmatrix},\qquad B=\begin{bmatrix}-4&4\\-2&5\end{bmatrix},\qquad C=\begin{bmatrix}k&1\\m&-2\end{bmatrix}.$$      How do you find the matrix $P$ such that $AP = PB$?       And how can you calculate the values of $k$ and $m$?      Thank you in advance.


So far I have:   P(AnB)=P(a)*P(B) because the two events are independent (given in statement). I know we need to show:  P(AnB|C)=P(A|C)*P(B|C).. Is this right?

If we know that two events $A$ and $B$ are independent, can we say that $A$ and $B$ are also conditionally independent given an arbitrary event $C$?  $$P(A\cap B) = P(A)P(B) \overset{?}{\Rightarrow} P(A\cap B|C) = P(A|C)P(B|C)$$


/boot$ ls  abi-3.8.0-19-generic         initrd.img-3.8.0-29-generic abi-3.8.0-25-generic         lost+found abi-3.8.0-26-generic         memtest86+.bin abi-3.8.0-27-generic         memtest86+_multiboot.bin abi-3.8.0-29-generic         System.map-3.8.0-19-generic abi-3.8.0-30-generic         System.map-3.8.0-25-generic abi-3.8.0-31-generic         System.map-3.8.0-26-generic config-3.8.0-19-generic      System.map-3.8.0-27-generic config-3.8.0-25-generic      System.map-3.8.0-29-generic config-3.8.0-26-generic      System.map-3.8.0-30-generic config-3.8.0-27-generic      System.map-3.8.0-31-generic config-3.8.0-29-generic      vmlinuz-3.8.0-19-generic config-3.8.0-30-generic      vmlinuz-3.8.0-25-generic config-3.8.0-31-generic      vmlinuz-3.8.0-26-generic grub                         vmlinuz-3.8.0-27-generic initrd.img-3.8.0-19-generic  vmlinuz-3.8.0-29-generic initrd.img-3.8.0-25-generic  vmlinuz-3.8.0-30-generic initrd.img-3.8.0-26-generic  vmlinuz-3.8.0-31-generic initrd.img-3.8.0-27-generic

I try to do do-release-upgrade but then I get:       Not enough free disk space      The upgrade has aborted. The upgrade needs a total of 25.7 M free   space on disk '/boot'. Please free at least an additional 25.7 M of   disk space on '/boot'. Empty your trash and remove temporary packages   of former installations using 'sudo apt-get clean'.   Output of df:                      237251272 214797108  10402504  96% / udev                    488120         4    488116   1% /dev tmpfs                   198676       668    198008   1% /run none                      5120         0      5120   0% /run/lock none                    496684         0    496684   0% /run/shm /dev/sda1               233191    225867         0 100% /boot   How come there is no space left on boot? Here's the output of ls -as /boot:  total 221839     4 .     4 ..   645 abi-2.6.32-34-generic-pae   698 abi-2.6.35-30-generic-pae   727 abi-2.6.38-12-generic-pae   727 abi-3.0.0-12-generic-pae   727 abi-3.0.0-13-generic-pae   727 abi-3.0.0-14-generic-pae   727 abi-3.0.0-15-generic-pae   727 abi-3.0.0-16-generic-pae   727 abi-3.0.0-17-generic-pae   727 abi-3.0.0-19-generic-pae   761 abi-3.0.0-20-generic-pae   115 config-2.6.32-34-generic-pae   128 config-2.6.35-30-generic-pae   136 config-2.6.38-12-generic-pae   140 config-3.0.0-12-generic-pae   140 config-3.0.0-13-generic-pae   140 config-3.0.0-14-generic-pae   140 config-3.0.0-15-generic-pae   140 config-3.0.0-16-generic-pae   140 config-3.0.0-17-generic-pae   140 config-3.0.0-19-generic-pae   140 config-3.0.0-20-generic-pae     5 grub 10773 initrd.img-2.6.32-34-generic-pae 13619 initrd.img-2.6.35-30-generic-pae 15365 initrd.img-2.6.38-12-generic-pae 16481 initrd.img-3.0.0-12-generic-pae 16487 initrd.img-3.0.0-13-generic-pae 16501 initrd.img-3.0.0-14-generic-pae 16476 initrd.img-3.0.0-15-generic-pae 16481 initrd.img-3.0.0-16-generic-pae 16478 initrd.img-3.0.0-17-generic-pae    12 lost+found   174 memtest86+.bin   176 memtest86+_multiboot.bin  1700 System.map-2.6.32-34-generic-pae  1841 System.map-2.6.35-30-generic-pae  2115 System.map-2.6.38-12-generic-pae  2141 System.map-3.0.0-12-generic-pae  2141 System.map-3.0.0-13-generic-pae  2143 System.map-3.0.0-14-generic-pae  2146 System.map-3.0.0-15-generic-pae  2147 System.map-3.0.0-16-generic-pae  2147 System.map-3.0.0-17-generic-pae  2148 System.map-3.0.0-19-generic-pae  2149 System.map-3.0.0-20-generic-pae     2 vmcoreinfo-2.6.32-34-generic-pae     2 vmcoreinfo-2.6.35-30-generic-pae     2 vmcoreinfo-2.6.38-12-generic-pae     2 vmcoreinfo-3.0.0-12-generic-pae     2 vmcoreinfo-3.0.0-13-generic-pae     2 vmcoreinfo-3.0.0-14-generic-pae     2 vmcoreinfo-3.0.0-15-generic-pae     2 vmcoreinfo-3.0.0-16-generic-pae     2 vmcoreinfo-3.0.0-17-generic-pae     2 vmcoreinfo-3.0.0-19-generic-pae     2 vmcoreinfo-3.0.0-20-generic-pae  4092 vmlinuz-2.6.32-34-generic-pae  4347 vmlinuz-2.6.35-30-generic-pae  4567 vmlinuz-2.6.38-12-generic-pae  4675 vmlinuz-3.0.0-12-generic-pae  4676 vmlinuz-3.0.0-13-generic-pae  4681 vmlinuz-3.0.0-14-generic-pae  4698 vmlinuz-3.0.0-15-generic-pae  4700 vmlinuz-3.0.0-16-generic-pae  4700 vmlinuz-3.0.0-17-generic-pae  4703 vmlinuz-3.0.0-19-generic-pae  4705 vmlinuz-3.0.0-20-generic-pae   Output of uname -a:   Linux kitsch 3.0.0-17-generic-pae #30-Ubuntu SMP Thu Mar 8 17:53:35 UTC 2012 i686 i686 i386 GNU/Linux


when I try to upgrade the system ,it always failed.   W:无法下载 http://cn.archive.ubuntu.com/ubuntu/dists/precise-updates/main/binary-i386/Packages  404  Not Found , W:无法下载 gzip:/var/lib/apt/lists/partial/cn.archive.ubuntu.com_ubuntu_dists_precise_universe_i18n_Translation-en  Encountered a section with no Package: header , E:Some index files failed to download. They have been ignored, or old ones used instead.   what should i do ?

Recently I have installed an older version of Ubuntu on my old machine. Whenever I try to install any software, I get an error saying it couldn't be found:  $ sudo apt-get install vlc Reading package lists... Done                Building dependency tree        Reading state information... Done     E: Couldn't find package vlc


I have an eigen decomposition of a 30 variable covariance matrix calculated using 5y of daily data and would like to compare it to a different 5y period to see if the eigenvalues are the same. Obviously they will not be exactly the same due to noise in the signal but can I test statistically that they are the the same?  "An asymptotic chi-square test for the equality of two correlation matrices" by R. Jennrich  The closest match I have found is a paper to test the equivalence on two correlation matrices, but as I am working in the Eigenvector space I would prefer a test that is performed on the eigenvectors (plus the paper is quite old).  Also on a similar topic what is the minimum length of time I can run a PCA analysis over for 30 variables on daily data. Clearly if i can generate more eigenvector decompositions to compare I can be more confident in my results.

Is there any methodical way to compare the directions, magnitudes, etc of PCA results for different samples drawn from the same population?  I'm leaving the nature of the test deliberately vague because I'd like to hear all the various possibilities... e.g. there might be (and I'm speculating here) a test comparing the sizes of the first principal components, or a test comparing the directions of the principal components, or there's some kind of distance measure between PCA outcomes and a test statistic for their equality.  As far as a use case goes, I don't have on in mind. Just out of curiosity, maybe as an exploratory technique.


I'm trying to find out what is the name of galaxy where Coruscant and other planets are located. Like for example our galaxy is Milky Way, what's the name of that galaxy? I'm trying to find out, but I failed in my search, I hope that someone knows what it's name is.

Has the in-universe name of the Star Wars galaxy ever mentioned in the canon?


I read a book about maybe 8-12 years ago. The book was brown and there was a black haired boy running away from two men in suits.   The book was about a boy who gets given powers at a zoo by the elephants. The powers include talking to animals and being able to mimic the abilities of anyone he thinks of (ie. he thinks bruce lee and then can fight like bruce lee) but only for a limited time.   I don't remember much about the plot but I do remember some snapshots; during the book he has to get away from the people chasing him so he plays the piano at a store well enough that he gets a crowd.  At the beginning of the book when he gets the powers the hippos object to the elephant giving them to him so the elephant kills them. (something about a gas leak the next day? maybe?)  If any of this rings a bell I would be really greatful. Its been on my mind for forever!

Young adult novel, that I read roughly 20 years ago. The main character was a teenage boy who discovers that he can wish to be someone and he would gain their skills, though he still keeps his own body (however, that doesn't seem to be a limitation).   He's playing a baseball game, and says, "I wish I was Babe Ruth(1)" and is suddenly able to play really well. His power lasted a limited time, maybe 90 minutes, and once he wishes to be someone, he can't wish to be them again.  I think his name might have been Asher or Ashton. There was also a scene in a zoo, and there might have been a picture of him at the zoo on the cover, but I'm not sure. It seemed like it was a part of a larger series, but I only ever read this book.  1 It might not have been Babe Ruth, the name meant nothing to me at the time, but I'm pretty sure it was a baseball player of some kind.


Suppose $x + 2y = k$ where $k$ is prime and $x > y > 0$.  Prove that $x|\binom{x}{y}$. That is, prove that $\binom{x}{y}$ is divisible by $x$.  The only leads I have are that, since $x$ and $y$ must be relatively prime -- or else $k$ would not be prime -- in the expansion of the binomial coefficient:  $$\frac{(x)(x-1)\dots(x-y+1)}{(y)(y-1)\dots 1}$$, there is necessarily some value in $\{x-1 \dots x-y+1\}$ that is divisible by $y$. This is true, because given any consecutive $y$ numbers, at least one must be divisible $y$, and we know that $x$ is not that number.  Edit: Apparently this is answered here   I'm not seeing how the result is obvious, however, for the particular case that $(n,k) = 1$.

Prove that for every $n\geq m \geq1$ natural numbers, the following number is an integer:  $${\gcd(n,m)\over n}\cdot{n\choose m}$$  Where $\gcd$ is the greatest common divisor.  I tried to make it simpler by cancelling the $n$ from the left side, and making it $(n-1)!$ on the right: $\gcd(n, m) \cdot \frac{(n-1)!}{m!(n-m)!}$, but can't really go further.   This was problem B-2 on the .


I know I can make tabular less cramped by changing \arraystretch, but what I really want is to make sure there are some fixed paddings above and below row contents, like what \tabcolsep does.  For example, I want to have more space for the 2nd row only:  But \def\arraystretch{2} gives me:  which IMO doesn't look elegant.

How do you guys go about controlling column padding in tables?   Update  To clarify, I'm looking for a way to control both vertical and horizontal padding. So, if I had a simple table like in the following code snippet, I could pad the columns and make them look a bit less... ugly. :P   \begin{tabular}{|l|l|}     \hline     column 1 & column 2 \\      \hline     I really would like this less & crammed\\     \hline \end{tabular}   I tried this by using the command \vspace but it leaves gaps in the vertical lines.


I'm learning python, trying to figure out how does this code actually work:  def func(**args):     class BindArgs(object):        foo = args['foo']        print 'foo is ', foo        def __init__(self,args):            print "hello i am here"     return BindArgs(args) #return an instance of the class  f = func(foo=2)   Output:  foo is  2 hello i am here  But it's very confused that in the argument of a function func(foo=2) that takes equation mark in it. Could you please explain how the flow works?

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


I understand why $n \cdot p = n_i^2$ holds for intrinsic semiconductors, but why is that the equation also holds true in the case of an extrinsic semiconductor?  Here, $n$ is the charge density of the negatively charged particles, $p$ is the density of the positively charged particles and $n_i$ is the carrier concentration.  How is it proved mathematically?

The following relation is mentioned in my text book for semiconductors in thermal equilibrium.  $$n_e ×n_h = n_i^2$$  $n_e$ stands for the number of electrons.  $n_h$ stands for the number of holes.  1) Does anyone know what $n_i$ stands for?  2) Can anyone give me intuition behind this formula, or explain how it came?   (I've already guessed that $n_i$ might stand for total current carriers.  But then would have to be $n_h$+ $n_e$, right? So I think that's wrong.)


I'm running Manjaro on my main system with a Manjaro VM in Virtualbox (will probably set up for Arch in the future). Most of my configs and setup scripts are shared between the native and VM systems. There are some things I want to run only on a native system, and others only in a VM. I'm looking for ways to make my scripts VM-aware for this. So far, the only method I've found is by using a bspwm function: mainmonitor="$(bspc query --monitors --names | grep -v LVDS | head -n 1)"  However, this wouldn't be universal enough and depends on bspwm. I'd like something that would work on any Arch Linux installation, regardless of the DE/WM. Even better if it'll  work on any virtualization software like Virtualbox or VMware. I know that there is VM-aware malware but I'm not sure what files they usually check for it. How can I make my scripts VM-aware in Arch Linux?

I have command line access to a Linux machine which may or may not be virtualized. I want to determine what kind of virtualization technology it runs on, if any (VMWare, VirtualBox, KVM, OpenVZ, Xen, ). This isn't a hostile environment: I'm not trying to work against a VM that is trying to disguise itself, I'm diagnosing a flaky server that I know little about.  More precisely, I'm helping someone diagnose the issue, I'm not sitting at the helm. So I have to convey instructions like “copy-paste this command” and not “poke around /proc somewhere”. Ideally, it would be something like lshw: an easily-installable (if not preinstalled) command that does the poking around and prints out relevant information.  What's the easiest way of determining what virtualization technology this system may be a guest of? I'd appreciate if proposals mentioned which technologies (including bare hardware) can be conclusively detected and which can be conclusively eliminated. I'm mostly interested in Linux, but if it also works for other unices that's nice.


This  explicitly says:  This question was asked a few years ago by @moggizx, here: some-existing-question I've been unable to find a similar question, or an answer for this so I thought I'd try asking it again  Natural thing; I went to "close as duplicated" - but that is not possible, because some-existing-question has no answers. I saw  on meta - but that leads to Duplicate target erroneously rejected although it has upvoted/accepted answers. Doesn't apply here. And  doesn't cover this scenario either, does it?

As you may have noticed, Jarrod's been hacking away at some design changes to the "close as duplicate" UI. These are  of some discussions we've been having internally regarding the "close" UI as a whole, with the goal being a smoother, easier-to-understand experience for all involved. Streamlined UI  The new pop-up provides four different functions:  Allow input of a specific possible duplicate ()  Display suggested duplicates (as originally implemented by )  Display search results for keyword-based searches (in the same fashion as the new suggested duplicates list)  Allow previewing the selected question with answers.   The search field reacts as you type, and there's visible, bread-crumb style navigation near the top of the dialog that allows you to quickly preview different potential duplicates (or back out of the dialog entirely). Answered questions only The search results include only answered questions (per the usual SO definition of "answered", where the question must have an accepted or up-voted answer). Additionally, close targets are restricted to answered questions even when specifying the ID or URL directly (with the exception of questions from the same author, and meta posts). Moderators can override this last restriction if necessary. The rationale here is that it can be fairly hard to discern whether or not an unanswered question is actually a duplicate, and even when it is closing doesn't really accomplish very much. When searching for a "canonical" answer in particular, duplicates without answers (or with bad answers) are just noise in the results. I think this makes sense in theory - so how is it working in practice?


I am from a country that requires to get a valid visa to enter USA. I also have a Canadian passport. Am I still required to have visa to enter USA? I have no criminal record and I'm just going there to visit a friend.

This is about entering the USA. I have   Hungarian citizenship with a 10 year B1/B2 visa in my passport I got before Hungary became part of the VWP. Real soon now, I will become a Canadian citizen (my oath is on April 5th) and will get a passport.   Since I, as a person, have a visa, am I obliged to enter into the USA with that? Or can I just forget it and use my Canadian passport? I know I could do whatever I want if I didn't have a visa but with that in the picture I am unsure.  describes a number of situations but not mine.


I need to print a lightweight version of my ToC : without the dots and without the page index numbers. I've already tried with tocloft package and so on, but nothing works.  How can I achieve that ?  I'm using the report document class.  Thanks

I am using example given here by @stephan .  Works great however I want to get rid of dots and page numbers.  I added this to the preamble   \let\Contentsline\contentsline  \renewcommand\contentsline[3]{\Contentsline{#1}{#2}{}}   that removed the page numbers, but do not know how to remove the dots. I would appreciate your help. Its hard to get result without understanding the basics.


I posted  to SO recently and by chance I noticed I had ; however I only noticed this answer by chance - I never received a notification in my inbox like I always do.  I thought I may have missed it, but I checked my inbox and it is not showing there whatsoever - my last notification is from Feb 19th.  Is there a reason I wasn't notified or is there some kind of issue here?

I posted a bug just now () and then I guess I encountered another one.  Usually, after someone else answered my question, the SE would send me a notification.  about 8 mins ago, a nice guy answered one of my questions on ELL (). I haven't received that notation since.   On the other hand, I did receive other notifications, which are for some comments on the bugged question and another question.


public void clickmea(View view)        {           EditText ed1 = (EditText) findViewById(R.id.editText4);                 EditText ed2 = (EditText) findViewById(R.id.editText5);                  String s1=ed1.getText().toString();                 String s2=ed2.getText().toString();               if ((s1 == "abc") && (s2 == "abc"))                     {                       Log.i("msg","successful");                       }                 else                    {                            Log.i("msg","unsuccessful");                  }                }   when I run above code it displays unsuccessful msg in the log even if I type abc in both text boxes.

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


I have a simple html page with file input and a fontawesome icon I'm using as a button:

       <input type="file" name="files" />

   The jquery code for adding a new button works fine  $("#addFileBtn").click(function(){          $('.block').after("<input type='file' name='files' />")   My problem is with the delete button that does not seem to do anything. (The alert is not even triggered)  $('#removeFileBtn').click(function(){     alert(this.id);     $(this).parent('.block').remove(); });   Any help is much appreciated

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


Let $(E,\left\lVert . \right\rVert)$ be a normed vector space defined on $\mathbb{R}$ .  We suppose that the norm satisfies the Parallelogram law.  Prove that:  $$f(x,y)=(1/4)[(\left\lVert x+y \right\rVert)² - (\left\lVert x-y \right\rVert)^2]$$  defines an inner product.  I don't know how to prove the linearity of the function $f(x,y)$.  In other words, how to show:  $f(kx+my,z)=k f(x,y)+m f(x,z)$.

Let $ V $ be a normed vector space (over $\mathbb{R}$, say, for simplicity) with norm $ \lVert\cdot\rVert$.  It's not hard to show that if $\lVert \cdot \rVert = \sqrt{\langle \cdot, \cdot \rangle}$ for some (real) inner product $\langle \cdot, \cdot \rangle$, then the parallelogram equality $$ 2\lVert u\rVert^2 + 2\lVert v\rVert^2 = \lVert u + v\rVert^2 + \lVert u - v\rVert^2 $$ holds for all pairs $u, v \in V$.  I'm having difficulty with the converse.  Assuming the parallelogram identity, I'm able to convince myself that the inner product should be $$ \langle u, v \rangle = \frac{\lVert u\rVert^2 + \lVert v\rVert^2 - \lVert u - v\rVert^2}{2} = \frac{\lVert u + v\rVert^2 - \lVert u\rVert^2 - \lVert v\rVert^2}{2} = \frac{\lVert u + v\rVert^2 - \lVert u - v\rVert^2}{4} $$  I cannot seem to get that $\langle \lambda u,v \rangle = \lambda \langle u,v \rangle$ for $\lambda \in \mathbb{R}$.  How would one go about proving this?


I have multiple virtual hosts on port 80 and 443. They all work. The problem comes when addressing the web server by a name not mentioned as a vhost.  The documentation says:     If the lookup fails (the IP address wasn't found) the request is   served from the default vhost if there is such a vhost for the port   to which the client sent the request. If there is no matching   default vhost the request is served from the main_server.   But in my case content is server from the main_server instead of the default vhost. I have tried using both _default_ and * for this default vh  I have  NameVirtualHost *:80 NameVirtualHost *:443   And directives like:  <VirtualHost *:80>         ServerName example.com         ServerAlias www.example.com   and   <VirtualHost *:443>         ServerName example.com         ServerAlias www.example.com   Running apachectl -S Shows my carefully named default vhost.  wildcard NameVirtualHosts and _default_ servers: *:443                  is a NameVirtualHost      default server 00default.example.com (/etc/httpd/sites.d/00default.example.com:29)      port 443 namevhost 00default.example.com (/etc/httpd/sites.d/00default.example.com:29)          alias www.00default.example.com      port 443 namevhost example.com (/etc/httpd/sites.d/example.com:29)          alias www.example.com  ...  *:80                   is a NameVirtualHost      default server 00default.example.com (/etc/httpd/sites.d/00default.example.com:1)      port 80 namevhost 00default.example.com (/etc/httpd/sites.d/00default.example.com:1)          alias www.00default.example.com      port 80 namevhost example.com (/etc/httpd/sites.d/example.com:1)         alias www.example.com   If I visit  http://www.example.com/phpinfo/   It works fine. But  https://www.example.com/phpinfo/   Fails. This is because Apache attempts to serve this request from the document root configured for the main server in the default conf file. "Main server" is defined here:   www.example.com is the actual hostname of the server and  https://www/phpinfo/   or  https://ip.address/phpinfo/   Both work.  It's my understanding that a wildcard default vhost overrides the main server config as it is doing in the case of the HTTP version. Why does it not work for the HTTPS version?  Sample Vhost config:  <VirtualHost *:443>     ServerName example.com     ServerAlias www.example.com     ServerAdmin webmaster@localhost     DocumentRoot /var/www/example.com     #ErrorLog logs/example.com/error_log     #TransferLog logs/example.com/access_log     SSLEngine on     SSLCertificateFile /etc/httpd/certs.d/example.com.crt     SSLCertificateKeyFile /etc/httpd/certs.d/example.com.key     SSLCertificateChainFile /etc/httpd/certs.d/example.com.chain     <Directory />             Options FollowSymLinks             AllowOverride None     </Directory>     <Directory /var/www/example.com/>             AddType application/x-httpd-php .php     </Directory>     <Directory /var/www/example.com/>             Options Indexes FollowSymLinks MultiViews             AllowOverride All             Order allow,deny             allow from all     </Directory> </VirtualHost>   There is also a section preceding the one above, for port 80, that is identical except for the port and the absence of the lines starting "SSL".

This is a  about Hosting multiple SSL websites on the same IP.   I was under the impression that each SSL Certificate required it's own unique IP Address/Port combination. But the  is at odds with this claim.  Using information from that Question, I was able to get multiple SSL certificates to work on the same IP address and on port 443. I am very confused as to why this works given the assumption above and reinforced by others that each SSL domain website on the same server requires its own IP/Port.  I am suspicious that I did something wrong.  Can multiple SSL Certificates be used this way?


After the events of 'the Return of the King', Frodo, Gandalf the White, Bilbo Baggins, Lady Galadriel and her husband leave Middle Earth and journey to the Undying Lands. Just out of curiosity, what becomes of them, particularly Frodo? I know that, many years later, Sam Gamgee goes to join Frodo, but can anyone tell me what the Undying Lands are? It sounds like some Tolkien version of Paradise to me.  Secondly, what sort of lives do these characters live outside of Middle Earth? Is there, perhaps, a Shire-like haven full of rolling hills and crops? Are there more Elves there than any other race? I'd just like to get a picture of what happens to Frodo once he gets there. What does he do with his time?  I'm aware of the Silmarillion, but I've never read that (not yet, anyway), so I fully welcome info from there! :)

I've heard a lot about the Undying Lands but I don't fully understand how they're different from Middle-earth and why only certain people/races are allowed to go there.  Can someone explain?


I am trying to figure out why the following holds:  Given $y_{i}=E[y_{i}|X_{i}]+\epsilon_{i}$ that  $E[\epsilon^{2}_{i}] =E[E[\epsilon^{2}_{i}|X_{i}]] = E[V[y_{i}|X_{i}]]$    Specifically I am trying to understand why $E[\epsilon^{2}_{i}|X_{i}] = V[y_{i}|X_{i}]$?  Clearly, I need a refresher on conditional variance and the rules for expected values....

I've seen the homoskedasticity assumption stated as the constant conditional variance of the error (i.e., Var(u|x)=constant).   I was wondering if I can also state the homoeskedasticity assumption as constant variance across values of a same dependent variable, conditional on the independent variable (i.e., Var(y|x)=constant)?   I remember a professor one time told me that they were essentially the same thing and you could state one or the other and they meant the same. However, I have been looking around the internet and cannot find info on the matter.


How could we solve the following equation (for (m,n)) via a combinatorial method? $1! 3! 5! ... (2n-1)! = m!$ , wherein m and n are positive integers.  Thanks in advance for your help.

Find all natural numbers $n > 1$ and $m > 1$ such that $1!3!5!\cdots(2n - 1)! = m!$   I have been thinking about coming up with some inequalities which would narrow the possible range of pairs $(n, m)$, however the best I have been able to find so far are $m \ge 2n - 1$ and $m \lt n^2$, which is clearly not enough.  Update. The question has tag combinatorics as it is from a book about combinatorics, so there must be at least partly combinatorial solution.


Prove that there are no positive integers $a$ , $b$ and $n>1$ such that  $a^{n}–b^{n}$ divides $a^{n}+b^{n}$.  Can someone provide me a proof of this and explain it to me please.

I'm working through the problems in Niven's number theory book, and problem 46 in section 1.2 (page 19) has me stumped.     Prove that there are no positive integers $a, b, n > 1$ such that $(a^n - b^n) | (a^n + b^n)$.   I've tried playing around a bit (e.g. noticing that $a^n - b^n$ must divide $2a^n$ and $2b^n$), but in general I've just been going around in circles.  Can anyone please provide a (small) hint in the right direction?


Solved!  EDIT (changed source to Minimal Working Example):  \documentclass{report}  \usepackage{polski} \usepackage[utf8]{inputenc} \usepackage[T1]{fontenc}  \usepackage{graphicx} \graphicspath{ {./obrazki/} } \usepackage{epstopdf} %eps  \begin{document} \graphicspath{ {./obrazki/wyniki_eksperymentu/Wyniki przegladu_EMG/wykresy/} }  \begin{figure}[h!]   \centering     \includegraphics[width=10cm, height=10cm]{Najlepszych_30_kombinacji} % Error here     \caption{Najlepsze kombinacje łańcuchów algorytmów ekstrakcji i klasyfikatorów} \end{figure} \end{document}   Thank you very much for replies. I was so fixed on underscores problem, that i didn't noticed white space in dir path :D  Since i can't give you any reward (only comments - no answers) :  "Best Answer Award" goes to Henri Menke for package which solves problem:  \usepackage{grffile}   Second award goes to cfr for spotting source of the problem :)

In some figures I create for my thesis I want to replace the labels and such using the same font and size as in the rest of the thesis. A couple of month ago I already used psfrag and pstool (with pdflatex). But now I cannot get it working. I did not changed any files (using a version control system, so I'm pretty sure).  The following mini example produces the same error as in my thesis:  \documentclass{article}  \usepackage{pstool}  \begin{document}    \begin{figure}      \centering   \psfragfig*{Inverses_Pendel}  \end{figure} \end{document}   In the same directory are the files Inverses_Pendel.eps and Inverses_Pendel.tex. Inverses_Pendel.tex contains the following content:  \psfrag{T}[cc][cc]{$Test$}   And here is the error:     Package pstool Warning: Execution failed during process:   ps2pdf   "-dAutoFilterColorImages=false" "-dAutoFilterGrayImages=false" "-dColo   rImageFilter=/FlateEncode" "-dGrayImageFilter=/FlateEncode"   "-dPDFSETTINGS=/pre press" "Inverses_Pendel-pstool.ps"   "Inverses_Pendel.pdf" This warning occurred on input line 7.      ! Missing $ inserted.                     $ l.7 \end           {figure} ?  ! Emergency stop.                     $ l.7 \end           {figure} End of file on the terminal!   It's such a generic error, I don't even know where to start searching.  I'm using MikTeX 2.9. I'm passing the -shell-escape option.


is a divination spell that states:     For the duration, the creature has truesight [...]   While  states:     Until the spell ends, one willing creature you touch is immune to psychic damage, any effect that would sense its emotions or read its thoughts, divination spells, and the charmed condition. The spell even foils wish spells and spells or effects of similar power used to affect the target's mind or to gain information about the target.   Let's say that the Rogue had Invisibility and Mind Blank cast on him, and the Wizard cast True Seeing on himself. How do these spells interact?  The discussion at my table hinges on the fact that True Seeing doesn't target or affect the Mind Blanked rogue, so his immunity is not relevant. The Wizard would simply gain Truesight and would spot him. Is this correct?

Nondetection says it hides the target from all divination spells. Invisibility hides you from normal sight. When combining both effects on one target, are they hidden from true seeing?


I am a new user and I need some help! I think I've figured out the basics of creating a document, but certain symbols are not transferring into the pdf: the box, the diamond and the "force" turnstile. I don't know what the error messages mean or how to address them. I've attached screen shots of this and I'm hoping it's something simple that I'm missing because I'm just new to LaTeX. If anyone could help I'd be very grateful.

I know what my symbol or character looks like, but I don't know what the command is or which math alphabet it came from. How do I go about finding this out?


I have Windows installed on my pc on partition (C), then I installed Ubuntu 14.04 on another partition. After the installation process finished successfully, Ubuntu asked to restart. Unfortunately, after the restart Windows was booted without showing a menu and asking me which OS to boot.  So how can I fix this problem and get a boot menu that allows me to boot Ubuntu?

I'm absolutely new to Linux. I would like to know how to install Ubuntu alongside the pre-installed Windows 8+ OS.  Should I do it with Wubi, or through the Live USB/DVD?  What steps do I need to take to correctly install Ubuntu?


Why didn't they define it as $$ \tilde \Gamma(x) = \int_0^\infty t^x e^{-t} \, dt ?$$ Then the definition would have two less characters than the standard definition of $\Gamma(x)$, and we would have $\tilde \Gamma(n) = n!$ for $n$ a non-negative integer.  And this would save a lot of confusion.

As a physics student, I have occasionally run across the gamma function  $$\Gamma(n) \equiv \int_0^{\infty}t^{n-1}e^{-t} \textrm{d}t = (n-1)!$$  when we want to generalize the concept of a factorial.  Why not define the gamma function so that   $$\Gamma(n) = n!$$  instead?  I realize either definition is equally good, but if someone were going to ask me to choose one, I would choose the second option.  Are there some areas of mathematics where the accepted definition looks more natural?  Are there some formulas that work out more cleanly with the accepted definition?


How can I lock vertices, so that they won't translate, even when selected by e.g. Proportional Editing? Ideally you should be able to lock all axes, or combinations X,Y or Z axis. The locked vertices should remain visible, so that certain vertices can be dragged to them, or they can be used as visual reference.

In a mesh there is a group of vertices which should not move after being positioned once. I would like to find a way to lock them in place for the whole duration of the project.   Currently I 'lock' them by hiding them and then sculpting. I imagine it is possible also to create shape keys for the vertices. Or I could write a script which would save position of the vertices.   Is there a better way to do it?


I have tried everything, Knox is on, Android device manager is on and its still not working.

On my Nexus 7 2013 Wi-Fi with Android 5.0.1 Lollipop I used the Slide setting for the lock screen. To experiment with a VPN, I switched to pattern lock.  After deleting the VPN entry I had created, I tried to switch back to Slide. However, the Slide and None options are grayed out and unusable under Settings -> Security -> Screen lock. Only the Pattern, PIN, and Password options are available.  How can I switch from Pattern to Slide?


It seems that all captions in Tufte-book are placed in the margin.  I have a full-width table where I can place the caption above the table using   \begin{table*}[b]   but how do I specify the caption to have the same width as the table?  Complete MWE:  \documentclass[b5paper,11pt,nobib,symmetric,justified,notoc]{tufte-book} \begin{document} \begin{table*}[b] \caption{Foo-bar Foo-bar Foo-bar Foo-bar Foo-bar Foo-bar} \begin{tabular}{llllllllll} Foo & bar & Foo & bar & Foo & bar & Foo & bar & Foo & bar \end{tabular} \end{table*} \end{document}

I've tried to change the caption in a full-width float with tufte-book, but to no avail. I want the caption in this figure to be like more common LaTeX classes.  Here is a MWE and the result:  \documentclass[a4paper,nohyper]{tufte-book} %abstracton \usepackage{fontspec} \defaultfontfeatures{Ligatures={TeX}} \setmainfont[Numbers={OldStyle}]{Minion Pro} %or any other font \setsansfont{Myriad Pro} % or any other font \setmonofont[Scale=MatchLowercase]{Menlo} \usepackage{graphicx} \usepackage{wrapfig} \usepackage{sidecap} \usepackage[dvipsnames]{xcolor} \usepackage{polyglossia} \setmainlanguage{brazil} \usepackage[bookmarks]{hyperref} %\usepackage[font=sf, labelfont={sf}, margin=1cm]{caption} \newfontfamily{\A}{Al Bayan}  \begin{document}  \begin{figure*} \centering \includegraphics[width=.9\textwidth]{./camp-scene} \caption{Cena de Acampamento. Mir Sayyid Ali, séc. XVII. 28,4 x 20 cm. Harvard University Art Museums, 1958.75. Os tecidos preenchiam a vida tanto dos nômades quanto dos habitantes das cidades, cobrindo o chão e definindo o espaço. O papel onipresente dos tecidos é visto numa pintura de um acampamento nômade, atribuído ao pintor persa do século XVI Mir Sayyid Ali.} \label{fig:camp-scene} \end{figure*}  \end{document}


I am just wondering how can I make the color whiter but also metal-like. the car model should have a white-painted metal shell. But I cannot make the color look like white. Although I put white color in there, it looks silver-like. Can anyone help me out to make this look like white-painted metal shell? Thanks.

This is something that has been irking me for a while, as I've been working on a car project. I'm trying to create a paint (in cycles) similar to the the material in this image:    The problem is, whenever I try to make it, it always comes out looking to diffused or too sharp.  Here's my node setup:    And here's the render:


If you assume that you have a plentiful/unlimited supply of training data, and you are using a neural network for classification, how do you deal with a situation in which a very high proportion of the data belongs to one class?    For example, if you are doing binary classification and 99% of data comes from one class and only 1% the other.  When you train the network using backpropagation, it normally uses the overall average error.  If you keep the data with the same skewness as it comes in, will that cause it not to learn the rarer class properly?  Another option is to discard data (presumably at random) from the more common class, until you have an equal proportion of data from each class, e.g. it is 50/50 in my binary example.  But if you balance the data like this, then the network is being trained on data that is not representative of real life.  The assumption that training data is plentiful (or unlimited) means that balancing the data need not reduce the size of the training set.  If extreme skewness is inadvisable, is there a threshold at which this occurs, e.g. is it ok for it to be 30/70 but not 1/99 ?

I have a very unbalanced sample set, e.g. 99% true and 1% false.   Is it reasonable to select a balanced subset with a 50/50-distribution for neural network training? The reason for this is, that I guess training on the original data set may induce a bias on the true-samples.  Can you suggest me some literature that covers this topic especially for neural networks?


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

I have a USB flash drive which is no longer recognized by my computer. Windows Disk Management and DiskPart report No Media with no storage space (0 bytes) on the drive and I cannot partition or format the drive:     If the drive appears in Windows Explorer, trying to access it returns an error message indicating that there is no disk inserted, such as the following:     Please insert a disk into drive X:.   Various disk partitioning and data recovery utilities don't recognize the drive or only give a generic name for the drive and cannot access the contents of the drive.  What can I do? How do I recover data from the drive?     This question comes up often and the answers are usually the same. This post is meant to provide a definitive, canonical answer for this problem. Feel free to edit the answer to add additional details.


Somehow my work-in-progress Python server filled the rootfs partition by logging 50gb of data to /tmp/blabla.log, which I noticed by basic commands failing like this: root@server:/# crontab -e /tmp/crontab.FfvjqH: No space left on device  So, I did rm -rf /tmp/blabla.log and the file disappeared, cannot be seen with ls or tail... but the insufficient space errors persist.  df -h still reports that rootfs is 100% used and does not reflect that I removed the 50gb file.  I could free some more space by moving some files to another parition and the system is OK but I don't have my 50gb of free space back.  What could be the problem?    my own answer: After moving some 3gb of files from the rootfs partition, I dared to restart the server, at the risk of having the server nog restart due to disk-space problems, but luckily it rebooted successfully and after reboot df -h reported the correct amount of free space. So system reboot seemed to be the answer.

Possible Duplicate:          I deleted an open file and the disk usage was not reduced.  Will it free up the space if I deleted the link in /proc/PID/fd/N ? what will happen to the process (in general)?  To be specific: The server is running Zimbra and the sync.log just gone crazily big occasionally (it's Zimbra's bug)


Find the sum $$M= \cos(2x)+\cos(4x)+\cos(6x)+\cos(8x)+\ldots+\cos(2016x)$$

I try to simplify to get rid of sum $$ \sum_{k=0}^{n-1}\cos(2 \pi fk)$$  I discover I shall use euler equation to form:  $$ \sum_{k=0}^{n-1}\frac{1}{2}(e^{2 \pi fki}+e^{-2 \pi fki})$$  but how to sum exponentials?


I am using ams1117 to convert 5v/1A DC to 3.3v/1A using - .  Can this 1 amp output (measured via ammeter) damage the esp8266 or i need to limit the input current (via resistor)?.

Power supplies are available in a wide range of voltage and current ratings.  If I have a device that has specific voltage and current ratings, how do those relate to the power ratings I need to specify?  What if I don't know the device's specs, but am replacing a previous power supply with particular ratings?  Is it OK to go lower voltage, or should it always be higher?  What about current?  I don't want a 10 A supply to damage my 1 A device.


I am trying to see all the files that are not user writeable. I know I can use the ls command to view all, but I wanted to have just the ones that are not user writeable. I am currently in unix and the find command will not work for me

How can I find all files I can not write to?  Would be good if it takes standard permissions and acls into account.  Is there an "easy" way or do I have to parse the permissions myself?


I have a Lenovo Y700 and I installed Ubuntu 16.04 yesterday. I downloaded the iso and installed it in my USB drive using YUMI. I had a problem trying to boot from the USB since it wasn't recognized. I had to go to BIOS and set it to boot from Legacy. Then it already appeared on my boot options. I installed it, restarted the computer and then GRUB appeared. Everything fine, until I tried to boot Windows. There are two options to boot Windows: Windows 10 and Windows Recovery. None of them worked, it shows a black screen saying I need to recover my Windows. Ubuntu boots fine.  However, if I switch boot in the BIOS to UEFI, Windows loads just fine (although GRUB isn't displayed).  I have two questions: Should GRUB be booted with Legacy mode? (I think so but I'm not sure about that) What can I do to fix my Windows Boot from GRUB?  Thank you in advance!

I followed this  to install Ubuntu as dual-boot with Windows 8.1 pre-installed as(UEFI),but I am not able to dual-boot and tried    I first burned an Ubuntu ISO on a blank DVD-R to create the LiveCD. Even with secure boot disabled, when I tried restarting my computer, it never booted to the installation screen, and it just skipped to Windows.  After a lot of skimming, I thought I had to put my computer in Legacy Mode in order to get give my CD/ROM drive priority. I installed Ubuntu and used my existing EFI partition. Ubuntu works, but Windows doesn't, probably because my laptop is stuck in Legacy Mode. I tried switching back to UEFI using boot-repair on the Linux Terminal, and going into Advanced Properties -> Grub Location -> Ticking the checkbox for EFI, but it says I need to be in an EFI session, and now I'm just really lost and confused at what I've all done. I can see my Windows8.1 OS on a partition but I want to dual-boot Windows 8.1 along with Ubuntu?   Did I just brick my computer?


In Star Wars, I find it weird that droids are not speaking the common language, but instead do beep-boops. And what is weird of that is that even then everybody seems to understand perfectly what they are saying. (or at least the protagonists) Is it ever explained why even if droids talk in beep boops the common man seems to be capable of understanding the droid language? Like if the 'droid language' is a language just like spanish or french in our world?

In all the Star Wars movies, R2D2 just boops and beeps his way around. And everyone understands him perfectly, though he is obviously not speaking Basic.  How do people understand him - is there like an astromech language? If so, then would one have to learn it, or is it comprised of feelings and emotions (expressed in beeps), essentially making a tonal language?  If I may be permitted to use an example from the prequels without too many lynch mobs forming, Anakin Skywalker converses frequently with Artoo while in the Naboo fighter, but he couldn't have had much schooling at the age of eleven, especially because he was a slave.  So how would people, Anakin especially, be able to understand astromechs?


This question is different according to situation, the question for which you marked my question as duplicate doesn't completely clarify my question situation answer.    import java.util.Enumeration;     import java.util.Vector;  public class EnumerationDemo {      public static void main(String[] args) {         Vector vector = new Vector();         for (int item = 1; item <= 5; item++) {             vector.addElement(item);         }         System.out.println(vector);         Enumeration enumeration = vector.elements();         while (enumeration.hasMoreElements()) {             Integer integer = (Integer) enumeration.nextElement();             System.out.println(integer);         }     } }   why are we writting integer instead of int in enumeration?

I was reading  when I came across  saying something about a particular type of programmer knowing the difference between an int and an Integer in Java/C# (Object-Oriented Programming Languages).  So, what is the difference?


I plan on making a dual wielding barbarian/fighter, and in fighter's fighting style it says that this style allows me to add modifiers to damage rolls for second weapon. But do I get a bonus for the second attack itself, or does everyone already have it? If not, is there something that allows me to add it? P.s. apologies for bad english.

I understand that you have to use the two weapon fighting style to add your ability modifier to damage, but I was wondering if there were any penalties to the offhand attack modifier?


I have a list of objects. How can I order this list using property name?  string orderbyField = "Code"; List<object> l = FillList(); l = l.OrderBy(o => orderbyField);   Can I have an extension for this problem?

I found an example in the  for Dynamic LINQ that allows you to use a sql-like string (e.g. OrderBy("Name, Age DESC")) for ordering. Unfortunately, the method included only works on IQueryable<T>. Is there any way to get this functionality on IEnumerable<T>?


I'm trying to move one of the objects, but instead of just one moving, they all move.

I'm facing this frustrating "feature" that I can't seem to remedy; when I duplicate an object (and now, even when I create two completely new objects), their transformations/scaling is synchronized. This is extremely annoying when trying to use any sort of transformation keyboard shortcut.  It should be noted by going to the properties menu (N) and manually setting the properties works just fine.  For instance, here is just the camera selected (trust me, I made sure):   And when I try to transform by clicking+dragging on the X axis OR by hitting G->X, this happens:   They are not grouped (verified by going to the Groups list up in the Scene panel) and they do not have parents (verified by going to Object->Relations).  I have tried the unlink command as well, to no avail.  I have seriously run out of options; what did I change to have my G->X shortcuts transform multiple objects? It seems completely at random, too; certain objects seemed to be "linked" to other random objects, and this "linking" is guaranteed when duplicating even when I do a non-linking duplicate (Shift+D).  What gives?


I wanted to understand dangers of lock(this) with some code example. With the code, if everything works well I expect to see 1000 at the end of program. And that's what I get every time I run it even though I am using lock(this). Why lock(this) works well here?  class Program     {         static void Main(string[] args)         {             Test t = new Test();             for (int x = 0; x < 100; x++)             {                 Thread[] threads = new Thread[10];                 for (int i = 0; i < 10; i++)                 {                     threads[i] = new Thread(t.ProtectedMethod);                     threads[i].Start();                 }                  for (int i = 0; i < 10; i++)                     threads[i].Join();                  Console.WriteLine("Done with {0}", t.i);             }          }     }      class Test     {         public int i = 0;          public void ProtectedMethod()         {             lock (this)             {                 i++;             }         }     }

The  says that public class SomeObject {   public void SomeOperation()   {     lock(this)     {       //Access instance variables     }   } }  is "a problem if the instance can be accessed publicly". I'm wondering why? Is it because the lock will be held longer than necessary? Or is there some more insidious reason?


My laptop's fan is making a loud sound similar to buzzing and even vibrates. Could someone tell me if I just have to clean the dust inside the laptop box or I have to take it to a specialist?

I got a Sony Vaio laptop VPCSA and its fan is noisy intermittently. At times it is very noisy and at other times it is pretty quite. I wonder whether this is caused by dirt on the fan that I can clean or leave the laptop to a computer repair shop so that they can service is? Or do you think that the noisiness from the fan is caused by some other factor than dirt since the noise is intermittent and not all the time?  Update  I see there're some more suggestions how to fic the problem in another question


A friend showed me this proof:  Proof: 2 = 1  $$Let \space x= y$$  Multiply both sides by x:  $$x^2= xy$$  Subtract $y^2$ from both sides:  $$x^2-y^2= xy-y^2$$  Factor:  $$(x+y)(x-y) = y(x-y)$$  Cancel out $(x-y)$ from both sides:  $$(x+y) = y$$  Simplify (Because $x=y$):  $$y+y=y$$  $$2y = y$$  $$2 = 1$$  Where does the logic break down? Everything is done to both sides.

I have a "proof" that has an error in it and my goal is to figure out what this error is. The proof:  If $x = y$, then  $$ \begin{eqnarray} x^2 &=& xy \nonumber \\ x^2 - y^2 &=& xy - y^2 \nonumber \\ (x + y)(x - y) &=& y(x-y) \nonumber \\ x + y &=& y \nonumber \\ 2y &=& y \nonumber \\ 2 &=& 1 \end{eqnarray} $$    My best guess is that the error starts with the line $2y = y$. If we accept that $x + y = y$ is true, then   $$ \begin{eqnarray} x + y &=& y \\ x &=& y - y \\ x &=& y = 0 \end{eqnarray} $$  Did I find the error? If not, am I close?


How do you ask a question on Ask Ubuntu, Server Fault, the Unix and Linux SE, and Super User all at once?  My  is about Ubuntu so I put it there, but it could easily fit at any of the others.

It is possible to migrate a question from one Stack Exchange site to another by closing, but if I have a question that I think is on-topic for multiple Stack Exchange sites, is it OK to post it on both (multipost)?   For example, I have a question that's earned me the tumbleweed badge on SO and I'm not sure what the best thing to do with it is. It's about a web server so it might be answerable on Server Fault but it's really more of a programming thing, hence the posting the question on Stack Overflow.    Is there any way to make the question visible on multiple sites (crosspost) and then accept the answer wherever it came from?


Sometimes when Integrating I end up with taking:   $$\sin \left(\tan ^{-1}\left(\frac{x}{2}\right)\right)$$, or other similar combinations however thats when I use the computer to extract:   $$\frac{x}{2 \sqrt{\frac{x^2}{4}+1}}$$  However, I want to find out how this is done and if there are any tricks I could use to evaluate similar expressions.


I am having problem with the statement:  \documentclass[12pt]{article}   When I am giving 10 as the font size, it gets smaller than 12 as expected. Again, when I am giving 14pt as the font size it is again smaller than 12pt font size. Shouldn't it increase? Why is it decreasing?

I need font size = 14 in article document, but when I change  \documentclass[a4paper,11pt]{article}   to  \documentclass[a4paper,14pt]{article}   font becomes even smaller. How to change font size?


I haven't been able to get very far in the problem at all because I can't figure out how to change it to the terms of the identity. All I have for the problem is $F_{kx}$ = $F_n$ and y$F_k$=$F_n$. But I don't understand what this has to do with the identity, where the numbers in the subscript are being added and which does not necessarily have multiples.

Question: Let $F_n$ the sequence of Fibonacci numbers, given by $F_0 = 0, F_1 = 1$ and $F_n = F_{n-1} + F_{n-2}$ for $n \geq 2$. Show for $n, m \in \mathbb{N}$: $$F_{n+m} = F_{n-1}F_m + F_n F_{m+1}$$   My (very limited) attempt so far: after creating a small list of the values $F_0=0, F_1=1, F_2=1, F_3=2, F_4=3, F_5=5, F_6=8, F_7=13, F_8=21, F_9=34, F_{10}=55$ i can see that yes it does seem to work for instance $F_{6+3}=F_5 F_3 +F_6 F_4 = 10 +24 = 34 = F_9$. However, I really don't know where to begin as showing that this must hold in general terms. Should I be looking to use limits? Or perhaps induction? What is the best way to solve this?


How do you apply the 4th order Runge Kutta method of numerical integration to the problem of projectile motion through atmosphere?

I've created a MATLAB function for solving coupled differential equation with the fourth-order Runge-Kutta method based on what is provided  (Simultaneous Equations of First Order). Here the function:  function [y] = rk4_c(f, g, h, x, y, z, n) % Runge-Kutta % Implementation of the fourth-order method for coupled equations % h = dt % x is the time here  for ii=1:(n-1)     k1 = h * f(x(ii), y(ii), z(ii));     l1 = h * g(x(ii), y(ii), z(ii));     k2 = h * f(x(ii) + 0.5*h, y(ii) + 0.5*k1, z(ii) + 0.5*l1);     l2 = h * g(x(ii) + 0.5*h, y(ii) + 0.5*k1, z(ii) + 0.5*l1);     k3 = h * f(x(ii) + 0.5*h, y(ii) + 0.5*k2, z(ii) + 0.5*l2);     l3 = h * g(x(ii) + 0.5*h, y(ii) + 0.5*k2, z(ii) + 0.5*l2);     k4 = h * f(x(ii) + h, y(ii) + k3, z(ii) + l3);     l4 = h * g(x(ii) + h, y(ii) + k3, z(ii) + l3);     y(ii+1) = y(ii) + (1/6)*(k1 + 2*k2 + 2*k3 + k4);     z(ii+1) = z(ii) + (1/6)*(l1 + 2*l2 + 2*l3 + l4); end   I would like to use this function for solving motion equations for a ball with air resistance. So starting with the basic equations (I hope they are correct): $$md^2x/dt^2 = F_{D_x}$$ and $$md^2y/dt^2 = F_{D_y}-mg$$ with $$F_{D_x} = -Dvvcos(\theta)$$ and $$F_{D_y} = -Dvvsin(\theta)$$ where $D$ is a drag coefficient. From my understanding, and from what I read, both second-order equation can be converted to two coupled equations that could be used with my coupled Runge-Kutta method function. Can someone help me understand how to convert my equation to a set of coupled equations that could be used with my MATLAB function?  EDIT  I was able to use my rk4_c function, however it only works for solving the velocities. I'm now trying to see how I could solve for the positions x and y. I'm kind of learning about Runge-Kutta methods at the same time, so sorry for the questions that may sound trivials.  % Runge Kutta code to solve projectile motion with quadratic drag % dVx/dt = -(D/m)*vx*sqrt(vx^2+vy^2) % dVy/dt = -(D/m)*vy*sqrt(vx^2+vy^2) - g  clc clear all  % Constant D = 0.24; % m = 2; % kg g = 9.80665; % m/s^2  % Define function handles fVx = @(t,vx,vy) -(D/m)*vx*sqrt(vx^2+vy^2); fVy = @(t,vx,vy) -(D/m)*vy*sqrt(vx^2+vy^2) - g;  % Initial conditions v0 = 200; % m/s theta = 30*pi/180; % rad t(1) = 0; vx(1) = v0*cos(theta); vy(1) = v0*sin(theta);  % Step size h = 0.01; % s tFinal = 2; N = ceil(tFinal/h);  % RK4 simultaneous coupled loop for ii = 1:N     % Update time     t(ii+1) = t(ii) + h;      % Update vx and vy     k1 = h * fVx(t(ii), vx(ii), vy(ii));     l1 = h * fVy(t(ii), vx(ii), vy(ii));     k2 = h * fVx(t(ii) + 0.5*h, vx(ii) + 0.5*k1, vy(ii) + 0.5*l1);     l2 = h * fVy(t(ii) + 0.5*h, vx(ii) + 0.5*k1, vy(ii) + 0.5*l1);     k3 = h * fVx(t(ii) + 0.5*h, vx(ii) + 0.5*k2, vy(ii) + 0.5*l2);     l3 = h * fVy(t(ii) + 0.5*h, vx(ii) + 0.5*k2, vy(ii) + 0.5*l2);     k4 = h * fVx(t(ii) + h, vx(ii) + k3, vy(ii) + l3);     l4 = h * fVy(t(ii) + h, vx(ii) + k3, vy(ii) + l3);     vx(ii+1) = vx(ii) + (1/6)*(k1 + 2*k2 + 2*k3 + k4);     vy(ii+1) = vy(ii) + (1/6)*(l1 + 2*l2 + 2*l3 + l4); end  % Plot the solution figure(1) plot(t, vx, t,vy) xlabel('Time (s)') ylabel('Velocities (m/s)') legend('Vx', 'Vy')


Suppose I have a sticker album which consists of $N$ stickers.  How many stickers should I buy in average to complete this album, assuming all the stickers appear with the same frequency?  More formally, let $X_1, X_2, \dots$ be independent random variables with an uniform distribution on the set $\{1, 2, \dots N\}$.  Then, what is the expected value of the random variable $$ Z=\min {\left\{n\in\mathbb N: \forall i\leq N,\,\,\exists m\leq n:\, X_m=i\right\}} $$

What is the average number of times it would it take to roll a fair 6-sided die and get all numbers on the die?  The order in which the numbers appear does not matter.  I had this questions explained to me by a professor (not math professor), but it was not clear in the explanation.  We were given the answer $(1-(\frac56)^n)^6 = .5$ or $n = 12.152$  Can someone please explain this to me, possibly with a link to a general topic?


Let$$a_n \ge 0$$ for all $n \in\Bbb N$. Show that if $$\sum_{n=1}^\infty a_n$$ converges, then $$\sum_{n=1}^\infty {\sqrt a_n\over n}$$ converges, too.  The hint is to expand $$\left(\sqrt a_n-{1\over n}\right)^2$$

Problem:      Suppose that for every $n\in\mathbb{N}$, $a_n\in\mathbb{R}$ and $a_n\ge 0$. Given that   $$\sum_0^\infty a_n$$   converges, show that    $$\sum_1^\infty \frac{\sqrt{a_n}}{n} $$   converges.   Source: Rudin, Principles of Mathematical Analysis, Chapter 3, Exercise 7.


My company offers a 401k 50% match up to 6% of salary, but I'm restricted to picking one of a set of investment portfolios.  My thinking is, could I max out the 6% every year, get the full 50% match, and then withdraw at the end of each year for the 10% penalty?  Given a 50k salary, that would be 3k that I'd invest, 1.5k match = 4.5k total, and the 10% penalty would still give me 4.05k, or a 35% yearly return that I could immediately move to my regular investment account with full flexibility.  Good idea, bad idea?  What am I missing?

I have some friends who work at a company which offers 50% 401k matching up to some amount, but they don't take advantage of it because they want to use the money for non-retirement purposes. Ignoring the problems with not saving for retirement, it seems like they're leaving money on the table. Can't they just contribute to their 401k up to the matching limit, then immediately withdraw it? I know there's a 10% early withdrawal penalty, but as long as the match is more than 11.1̅%, it seems like it would always be worth it.  Is there any reason this won't work, like limits to how soon you can withdraw from an 401k, or how you withdraw from it?  I know that you have to pay income tax on the money you withdraw, but you'd have to pay it either way so I don't think it's relevant.


I tried with below Regex  Input string = \nAddress 123 Abc st. Phone (123) 456-7890\nLine2\nLine3\nCity";  Regex  Regex rg = new Regex(@"Address(.*)Phone.*\n(.*)City", RegexOptions.Singleline);   But when I have used given regex at that time in the output I got below result set.  for first group = 123 Abc st. for second group = null.  My expected output is as below but from above regex, I got only result set one but not the second one.  expected output  Group 1 = 123 Abc st.  Group 2 = Line2\nLine3

I have this gigantic ugly string: J0000000: Transaction A0001401 started on 8/22/2008 9:49:29 AM J0000010: Project name: E:\foo.pf J0000011: Job name: MBiek Direct Mail Test J0000020: Document 1 - Completed successfully  I'm trying to extract pieces from it using regex. In this case, I want to grab everything after Project Name up to the part where it says J0000011: (the 11 is going to be a different number every time). Here's the regex I've been playing with: Project name:\s+(.*)\s+J[0-9]{7}:  The problem is that it doesn't stop until it hits the J0000020: at the end. How do I make the regex stop at the first occurrence of J[0-9]{7}?


I have two samples of same size but at least at one of them is not normal distributed (tested by Shapiro-Wilk-test). How can a compare the variances of theses samples? Especially, I want to know the p-value for the hypothesis: $\sigma_1^2 \leq \sigma_2^2$.

I have two small data sets (sizes $n_1 = 8$ and $n_2 = 21$) which look like they have significantly different variances. I know very little about the underlying distributions, but it's definitely not safe to assume they're normal or anything nice like that, which rules out the F-test. I'm aware I could use one of the other named tests (Bartlett, Brown–Forsythe, ...) although I'm not currently quite sure what they assume about the population distribution, if anything.  Instead, I've tried my hand at using a permutation test: the null hypothesis is that the two datasets have equal variance, so relabel the data points at random and measure the difference in the two variances of the relabelled sets. Out of 1,000,000 attempts, fewer than 40,000 had a larger difference in variance (<4%).  Is it correct to say that, therefore, the difference in variance of the two data sets is significant at the $p < 0.05$ level? If so, is there a well-recognised name for this kind of test?


How can I stop wrong autocorrect suggestions?

I welcome popup spelling suggestions, but I dislike the OS replacing text as I type without any real confirmation from me.   I'm aware both behaviors can be enabled/disabled together as one option in System Prefs > Keyboard > Text, but would anyone know a way to disable the autocorrect while leaving the tooltip-style suggestions intact…perhaps via the Terminal? Thank you.   Mac OS X 9.4 (Mavericks)


I know it exists a distro like Vinux, but if I have to do a course where Ubuntu is used I see myself limited by my sight issues. I find accessibility options quite limited, the high contrast does not work for me since it's white high contrast and I need black high contrase like the one in Windows, and it would be nice if applications not related to the operative system would be affected by the accessibility configuration of the OS itself so I don't have to tweak every program I have to use, if it was even possible to tweak it since some don't offer the chance.  Does exist any application to download and install that improves the accessibility of Ubuntu and adds more options and themes such a dark high contrast theme, scalable text, magnifier, etc?   Scale font Change colors of the OS menus, including folder navigation. Change colors of non OS software when OS colors are changed Include a magnifier Change mouse pointer. Use of keyboard shortcuts to change accessibility setings or access the options. All of this without extensible use of commands, just install a software that embeds in the OS, like a helper and adds it's features, and adds easy tweakings.   Is something like the thing I describe?  Thanks.

I have tried to apply dark themes from Ubuntu 14.04 on 16.04 and they do not come out entirely as expected (different colours and such). What native dark themes for Ubuntu 16.04 are out there? I would prefer a theme retaining the default Unity decorations and icons and simply tweaking colours, but other suggestions are welcome.


Say I have a test - let's say for some chemical. I have 15 fields, which I divide in half. On the left side of the field, we dump some chemical into the field, on the right side, we do not. We record the bunny population before and three months after. Is it possible to construct a statistical test to say the chemical had NO effect, rather than trying to prove the chemical had an effect? Is this just a chi-square?

As the question states - Is it possible to prove the null hypothesis? From my (limited) understanding of hypothesis, the answer is no but I can't come up with a rigorous explanation for it. Does the question have a definitive answer?


class ClassB:     def __init__(self):         self.b = "b"         self.__b = "__b"      @property     def propertyB(self):         return "B"   I know getattr,hasattr... can access the property. But why don't have the iterattr or listattr?  Expect result of ClassB object:  {'propertyB': 'B'}   Expect result of ClassB class:  ['propertyB']   Thanks @juanpa.arrivillaga 's comment. vars(obj) and vars(obj.__class__) is different!

So what I'm looking for here is something like PHP's  function.  This is so I can debug my scripts by seeing what's the state of the object in question.


I want to set a testfor commandblock. This is the command I want in the block: /testforblock 1998 10 657 glass. What is the setblock command to have this in a commandblock?

Does someone know how to set a command block with a command inside using the setblock command?  I have created this code /setblock <x> <y> <z> command_block {TileEntityData:{Command:"testfor @p[_=1]"}} but it doesn't works.  Do someone know how to do that?


So I know this is a dumb question maybe, but it has been in my head recently. I once told someone, on the topic of introductory calculus, that using l'Hopital's rule to calculate $$\lim\limits_{x\rightarrow 0} \frac{\sin(x)}{x}$$ is circular reasoning, because the limit we are looking for is the definition of the derivative of $\sin(x)$ at $x=0$. They argued that it is not because you can work out the derivative of cosine via its series representation without ever recurring to the definition.  Now, there are two ways that I know of to obtain the series representation of cosine: the obvious one is Taylor expansion, which obviously requires knowledge of all the derivatives, the other one is to prove the following statement:     If there exists two functions $f$ and $g$ such that $f'=g$ and   $g'=-f$, then they are unique.   Then you have to kind of get out of the hat the series representations and show that they respect the conditions listed above, which only involves deriving polynomials. Nonetheless, it seems to me that you still have to know the derivatives of sin and cos to then identify the two trigonometric functions with the series representations using their uniqueness.   My question is: is there really a way to obtain the series representation for sin and cos without knowing the derivatives, thus getting rid of the circularity of the reasoning?  This question is by no means practical and it's just a curiosity of mine, I'm not interested in other ways to calculate the limit, which is trivial.  EDIT:  I don't think this is a duplicate, as I said in my comment if you read the question that is linked, you will notice that what the OP means by "circular reasoning" is something on proving the limit using formulas about the area of circles, which has nothing to do with my question about series representations.

The classic proof for $\frac{\sin x}x\to1,x\to0$ is using a squeezing theorem based on arguments about areas of circles.   But as far as I know, all deduction of formula of circles' area is based on the fact $\frac{\sin x}x\to1,x\to0$. For example, using definition of definite calculus needs the fact to show limitation; using Newton-Leibniz formula needs to know $(\sin x)'=\cos x$, whose deduction also needs the fact $\frac{\sin x}x\to1,x\to0$.  So is it a circular reasoning?


I understanding that if Z1, Z2, …, Zk, are independent standard normal variables, then Z12 + Z22 + … + Zk2 has a χ² distribution with k degrees of freedom.   However, say we have a 2 rows and 3 columns, then we're taking (observed - expected)2 divided by expected for 6 cells. Why then is the degrees of freedom not 6?

From , there are three interpretations of the degrees of freedom of a statistic:     In statistics, the number of degrees of freedom is the number of   values in the final calculation of a statistic that are free to vary.      Estimates of statistical parameters can be based upon different   amounts of information or data. The number of independent pieces of   information that go into the estimate of a parameter is called the   degrees of freedom (df). In general, the degrees of freedom of an   estimate of a parameter is equal to the number of independent scores   that go into the estimate minus the number of parameters used as   intermediate steps in the estimation of the parameter itself (which,   in sample variance, is one, since the sample mean is the only   intermediate step).      Mathematically, degrees of freedom is the dimension of the domain of a   random vector, or essentially the number of 'free' components: how   many components need to be known before the vector is fully   determined.   The bold words are what I don't quite understand. If possible, some mathematical formulations will help clarify the concept.  Also do the three interpretations agree with each other?


This is the first time I'm studying those subjects (I'm still in high school) and my teacher couldn't give me an answer. I'm referring specially to Newton's law of gravitation and Coulomb's law of electrostatics.

Coulomb's Law states that the fall-off of the strength of the electrostatic force is inversely proportional to the distance squared of the charges. Gauss's law implies that the total flux through a surface completely enclosing a charge is proportional to the total amount of charge. If we imagine a two-dimensional world of people who knew Gauss's law, they would imagine a surface completely enclosing a charge as a flat circle around the charge.  Integrating the flux, they would find that the electrostatic force should be inversely proportional to the distance of the charges, if Gauss's law were true in a two-dimensional world. However, if they observed a $\frac{1}{r^2}$ fall-off, this implies a two-dimensional world is not all there is. Is this argument correct? Does the $\frac{1}{r^2}$ fall-off imply that there are only three spatial dimensions we live in? I want to make sure this is right before I tell this to my friends and they laugh at me.


I can't use my outward flight ticket but need my return ticket. If I do not show on my outward flight, I am worried that the company might cancel my return flight. I have spoken to the flight company and they say I would have to cancel both tickets but the refund is so low, it's better to keep both tickets and not show for the outward flight. Should I tell the carrier that I am not going to use the outward ticket and pray they don't cancel my return flight.

I've a friend that booked a round-trip journey. He booked A-to-B and B-to-A. Somehow he needed to be earlier at location B, so he took a train and did not take the flight from A to B.  When he went to the airport to take the "back home" flight (B-to-A), he was informed that his ticket was canceled because he did not take the A-to-B flight. They canceled the ticket and sold it to someone else.  Is this normal? The company said it was their right to do so, and he could not get the flight back. The company was Iberia.


I would like to edit the way a basic article is structured. For example, I want to place the title under the image followed by content and at last the date. Already looked at Structure -> Content Types -> Article -> Manage fields, couldnt find anything about reordering those things.

When viewing a node, I'd like the Title to display below one of the other fields in the Content Type, but it's not available to arrange in the Manage Display tab.  With all of the flexibility and power that Drupal gives me, do I really need to create a custom template for each of my content types? :(  Any help is appreciated!


I've tried to install Google Chrome for 32-bit .deb package. But it gave me the following errors:   depends: lib32gcc1 (>= 1:4.1.1) but it is not installable                         depends: lib32stdc++6 (>= 4.6) but it is not installable                         depends: libc6-i386 (>= 2.11) but it is not installable                         depends: libxss1 but it is not installable   Currently, I'm using Ubuntu 13.10 (32-bit - i386). So, when i try to install the dependency, it says me that i can't install.  I'm totally lost,I don't know what should I do.

There was an update for  today, and it wasn't installable due to unresolved dependencies. How can I correct this?


I'm taking an AP Computer Science course, and I'm having a problem with this code. We're to make a method that converts Roman Numeral Strings into decimal values.  So far, we've only gotten to if/else statements and while loops. I've seen a few answers here using switch, but our class hasn't gotten there yet. I need a way to do this without using switch. I've only written code assuming that the Roman Numerals are in non-ascending order, but whenever a string like "MM" is used, the method returns "0" as a value. Anyone know why this happens here?  Any tips on subtracting the numerals would also be appreciated.     public int decimalValue ( String roman ){      //given a Roman Numeral      int decimal =0;      int a = 0; // a and b used as to check each letter in String roman      int b = 1;       // Assuming in non-ascending order. Need to make for ascending      while ( (a <= (roman.length() - 1) ) && (b <= roman.length() ) ) {         if ( roman.substring(0,1) == "M") {            decimal = decimal + 1000;         }         else if ( roman.substring(0,1) == "D") {            decimal = decimal + 500;         }         else if ( roman.substring(0,1) == "C") {            decimal = decimal + 100;         }         else if ( roman.substring(0,1) == "L") {            decimal = decimal + 50;         }         else if ( roman.substring(0,1) == "X") {            decimal = decimal + 10;         }         else if (roman.substring(0,1) == "V") {            decimal = decimal + 5;         }         else if (roman.substring(0,1) == "I") {            decimal = decimal + 1;         }         a++;         b++;         }    return decimal;   }

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


I'm about to setup a server hosting MySQL, Apache/PHP, File Uploads, and probably CCTV Storage.     Planned Personal Server Specifications:         ASUS H97M-E     INTEL i7-4790   2 x 4GB 1600MHz RAM   KINGSTON V300 120GB SSD   2 x 3TB SEAGATE 7200RPM HDD      This will be my first time setting up a server, and I haven't decided a good Operating System for this. I'll also be setting up RAID 1 for backup.  Well, as projected, the server will host a simple EHR System, DTR System, Inventory System, Accounting System, Billing System and Cashiering System in one Web Program, with only 13 Users.   I am kinda worried about the traffic since the System will serve at least 100 clients per hour.  QUESTIONS:   Are the specs listed too overkill for its task? Is RAID 1 good for the setup? If no, what are your suggested RAID setups and how can we expand its storage later? What's the best Operating System for this?   Your suggestions and answers are highly appreciated.

This is a  about  Related:      I have a question regarding capacity planning. Can the Server Fault community please help with the following:   What kind of server do I need to handle some number of users? How many users can a server with some specifications handle? Will some server configuration be fast enough for my use case? I'm building a social networking site: what kind of hardware do I need? How much bandwidth do I need for some project? How much bandwidth will some number of users use in some application?


I want to write multiple lines of text within a TikZ rectangle. This is how I did it.  \documentclass{article} \usepackage{tikz} \begin{document}  \begin{tikzpicture} \node at (0, 0) [rectangle,draw,minimum size=2cm] {     \begin{tabular}{c} \( a^2 \) \\ \( b^2 \) \end{tabular} }; \end{tikzpicture}  \end{document}     This works fine. But I want to understand why using another environment, such as, align* environment or displayed math does not work well like the tabular environment does.  For example, the following code  \documentclass{article} \usepackage{tikz} \usepackage{amsmath} \begin{document}  \begin{tikzpicture} \node at (0, 0) [rectangle,draw,minimum size=2cm] {     \begin{align*} a^2 \\ b^2 \end{align*} }; \end{tikzpicture}  \end{document}   leads to the following error.  ! Missing \endgroup inserted. <inserted text>                  \endgroup  l.8     \begin{align*} a^2 \\ b^2 \end{align*}   The following code  \documentclass{article} \usepackage{tikz} \begin{document}  \begin{tikzpicture} \node at (0, 0) [rectangle,draw,minimum size=2cm] {     \[ a^2 \] }; \end{tikzpicture}  \end{document}   leads to the following error.  ! Missing $ inserted. <inserted text>                  $ l.8     \[ a^              2 \]   Here are my questions:   Why is special about tabular environment (compared to align* or displayed math) that makes it possible to use it as text within a node? What do the Missing \endgroup inserted or Missing $ inserted errors mean?

How can I insert a line break in a TikZ node? Simply putting \\ where I want the break doesn't work (see MWE).  Is there a way to make lines break automatically at some specified width?  And can I control the alignment of the text (left, right, centered, justified)?  \documentclass{article} \usepackage{tikz} \begin{document} \begin{tikzpicture} \node {First line\\second line}; \end{tikzpicture} \end{document}


Do you need a graphic design degree to work for a agency or company? I've researched many answers towards this question and what I found, it basically comes down to your portfolio. I don't want to do freelance and want to work for a company or agency. What are the steps? How can I be a successful graphic designer without a degree?

Is it required for people to go to design schools to become a Graphic Designer? I've heard many cases where they have started from scratch without previous education in design and are doing fine as freelancers/working in studios.  Would it be better to go to a design school to become a Graphic Designer? How much leverage would it give you if you went to one?


I have a MacBook Air Mid 2011, I tried installing an El Capitan update. During installation, it says, about 19 minutes remaining, then, "OS X COULD NOT BE INSTALLED IN YOUR COMPUTER. File Syste verify or repair failed. Quit the installer to restart your computer and try again. ", and every time I restart it, it just goes back to OS X installer.  One thing about my MacBook is, the WiFi doesn't work, so I cannot go to internet recovery. I also tried getting a TPLink Nano USB WiFi adapter, thinking it may detect wifi, but it doesn't (I think I need to install the drivers first, but to do that, I need a working OS) PLEASE HELP ME

I downloaded the new OS X Lion from the App store. I am running the latest Snow Leopard on my 2010 15" Macbook Pro. During the download, it somehow stopped while I was away from the keyboard. When I returned, I resumed it again, and after download completion, began to install it. When it rebooted, it began to install Lion, and when it was at the 33 minute mark, it failed. See pictures below:  I got the error message:  Install Failed Mac OS X could not be installed on your computer Mac OS X couldn't be installed, because the disk Macintosh HD is damaged and can't be repaired.   I read somewhere that I should put in the original install DVD, and run the Disk Utility to try to verify and repair. I put the disc in, booted it, and clicked through past the language selection, but made sure to wait for the top menu bar to appear to get to Disk Utility. I clicked on Verify Disk, and got this error message after it ran:  Invalid node structure The volume Macintosh HD could not be verified completely. Error: This disk needs to be repaired. Click Repair Disk.   After clicking Repair Disk, I got this error message:  Disk Utility stopped repairing "Macintosh HD" Disk Utility can't repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed up files.   I'm also running Bootcamp, with Windows 7 installed in it's own partition. I don't know if that has anything to do with why I'm getting these error messages or not, or if that's why it thinks the hard drive is damaged. How do I fix this? I am unable to get back into Snow Leopard. Every restart leads back into the Lion install, which results in these errors. I think many others are having this issue as well. I do have my files backed up (not in Time Machine, but manually on an external USB drive).  I don't mind wiping everything (including Bootcamp), but I rather that be a last resort. Reference:   on Apple Discussions site.


I used Drupal 7 and the  module to import a table into Drupal. I could import the orphaned table, but my table has a column of type "timestamp" which does not show up when I try to edit the schema of the data table. I get the following error:     PDOException: SQLSTATE[42000]: Syntax error or access violation: 1067 Invalid default value for 'published': ALTER TABLE {resource_profiles} CHANGE published published INT NOT NULL DEFAULT 'CURRENT_TIMESTAMP'; Array ( ) in db_change_field() (line 2988 of C:\xampp\htdocs\drupal\includes\database\database.inc).   I followed , and added the timestamp datatype to /includes/database/mysql/schema.inc.  Where can I edit the schema information for my data table?

I was trying to add the column of MYSQL Timestamp to the Database Table, the Query seems to be working correctly in mysql console.But when I execute the same in db_query() the following error is thrown.     Failed: PDOException: SQLSTATE[42000]: Syntax error or access   violation: 1067 Invalid default value for 'last_update_date': ALTER   TABLE stores ADD last_update_date TIMESTAMP NOT NULL DEFAULT   '0000-00-00 00:00:00';; Array ( ) in store_update_7100() (line 254 of   /var/www/slocamo_app/sites/all/modules/store/store.install).   Is the Query.  ALTER TABLE  `stores` ADD  `last_update_date` TIMESTAMP NOT NULL DEFAULT  '0000-00-00 00:00:00');


running java -version shows: openjdk version "14.0.2" 2020-07-14 OpenJDK Runtime Environment Zulu14.29+23-CA (build 14.0.2+12) OpenJDK 64-Bit Server VM Zulu14.29+23-CA (build 14.0.2+12, mixed mode, sharing)  ( the Java JDK with sdkman.) Before I install Netbeans with snap do I need to configure anything else to ensure that Netbeans uses JDK 14?

I'm trying to install Netbeans on my Ubuntu. It was successfully installed but was unable to create new projects or new files. I have installed JDK 12 and then I removed it because I found here a solution that recommended removal of latest versions of JDK and set JDK 8 as default. I did what solution said but now I can't install JDK 8. It is showing me this error message:   E: Package 'oracle-java8-installer' has no installation candidate    So I started searching on the Internet about the solution and I found that "Oracle Java (JDK) 8 Installer PPA (DISCONTINUED)".   What should I do now?


I have a piece of code which executes three nested for loops in the following way (written as language agnostic as possible):  for i = 0 to n - 1     for j = 0 to n - 1         for k = 0 to n - 1             [do computation in linear time]   My intuition says that this should result in N^3 complexity. I'd like to compare its complexity to the following nested loops:  for i = 0 to n - 1     for j = i + 1 to n - 1         for k = j + 1 to n - 1             [do computation in linear time]   Logically, it should be faster, because as i increases, the inner loops should compute faster; however, having seen countless other threads on the site explaining that the latter of those is also N^3 is confusing.  Is my assumption of N^3 for both correct, and if so, how do I quantify the differences, assuming there are any?

What is the Big-O time complexity of the following nested loops: for (int i = 0; i < N; i++) {     for (int j = i + 1; j < N; j++) {         System.out.println("i = " + i + " j = " + j);     } }  Would it be O(N^2) still?


I installed Ubuntu from lifehacker.com, onto my Acer Chromebook, where you access it by switching back and forth between Chrome OS and Ubuntu with ctrl alt shift and ← and →. I shut down my computer and when I turned it on, I was unable to access Ubuntu again.   I need help getting back to it to install some programs that I require.

I have installed Ubuntu 13.04 on my desktop (runs like a charm). Then I used Crouton to install Ubuntu 12. 04 on my chromebook samsung (ARM). It also works quite well.  Here comes my question. Can we have a true Ubuntu (preferably 13.04) on my ARM chromebook?  It seems that the Crouton/Ubuntu is not 100% the real thing.  The best option would be to have the full Ubuntu 13.04 and remove the Chrome OS.


The email notifications are sent in the same time of the subscriptions?  I would like to choose the period (morning, afternoon, night) or the interval (6:00-9:00, 9:00-12:00, 12:00-15:00, etc) at which to receive them.  Sometimes I ignore the notifications because are sent in bad times.

I get the New questions digest message every day at ~07:56. This means that by the time I get to view/answer them, the digest message waited in my email inbox for several long hours.  Below is the settings page, and I don't see a possibility to set the time the daily message is prepared.   Is it possible to config the time when New questions are collected and sent?


I am a US citizen born in Mexico. I am traveling to Mexico in a couple of weeks with my American passport. Do I need a visa or anything else to travel?

I'm planning a family trip to Mexico in the summer. I'm a US citizen and so are my two kids. My wife was born in Mexico, but recently became a US citizen as well.    Traveling to Cancun, Mexico our flight will be making a stop in Guadalajara, Mexico  continuing it's way to Cancun on a different plane (flight). We will be in Cancun for nine days.  Should I be aware of something? Mexican visas, or anything else?