The problem statement, all variables and given/known data. I have a 2D integral that contains a delta function: $$\int_{-\infty}^{\infty}\int_{-\infty}^{\infty}\exp{-((x_2-x_1)^2+a x_2^2+b x_1^2-c x_2+d x_1+e)}\delta(p x_1^2-q x_2^2) dx_1 dx_2,$$ where $x_1$ and $x_2$ are variables, and $a,b,c,d,e,p$ and $q$ are some real constants.    Relevant equations How can one integrate this without resulting in poles. Because integral over, for example, $x_1$ leads to a pole, given the property of delta function.  The attempt at a solution If inside the delta function, the argument would be $x_1^2+x_2^2$, and not $x_1^2-x_2^2$, then one could go to polar coordinates, and get rid of the poles coming from the delta function integral. Sadly, this is not the case here. Further one can get rid of pole by going into hyperbolic coordinates $x_1=RCosh(\theta)$ and  $x_2=RSinh(\theta)$. The R integral can be done exactly because the poles cancel out due to Jacobian. However, the integral over ##\theta## then becomes unbounded. So this method also has a problem. Is there a smarter way to perform integral with quadratic argument of delta function without encountering poles?

The problem statement, all variables and given/known data  I have a 2D integral that contains a delta function:  $\int_{-\infty}^{\infty}\int_{-\infty}^{\infty}\exp{-((x_2-x_1)^2)+(a x_2^2+b x_1^2-c x_2+d x_1+e))}\delta(p x_1^2-q x_2^2) dx_1 dx_2$,  where $x_1$ and $x_2$ are variables, and a,b,c,d,e,p and q are some real constants. Relevant equations  How can one integrate this without resulting in poles. Because integral over, for example, $x_1$ leads to a pole, given the property of delta function. The attempt at a solution If inside the delta function, the argument would be $x_1^2+x_2^2$, and not $x_1^2-x_2^2$, then one could go to polar coordinates, and get rid of the poles coming from the delta function integral. Sadly, this is not the case here. Further one can get rid of pole by going into hyperbolic coordinates $x_1=RCosh(\theta)$ and  $x_2=RSinh(\theta)$. The R integral can be done exactly because the poles cancel out due to Jacobian. However, the integral over ##\theta## then becomes unbounded. So this method also has a problem. Is there a smarter way to perform integral with quadratic argument of delta function without encountering poles?


I've researched lots of places and still cannot wrap my head around the cross product.   The closest thing I have to an understanding  of the cross product is that its a measure of how orthogonal two vectors are.  But there are still lots of things about the cross product I dont understand.  Why do we make the product vector perpendicular to the plane formed by the multiplying vectors? How does that relate to the determinant of a 3x3 matrix?  I get that this is a very vague and general question, but If someone could help me understand why the cross product is defined the way it is and whats its meaning, or refer me to a good source, which again, I've tried reading several explanations, that would be highly appreciated. I'm happy to clear up anything that is unclear about my question

I don't think I ever understood the rationale behind this.  I get that the dot product $\mathbf{a} \cdot  \mathbf{b} =\lVert \mathbf{a}\rVert \cdot\lVert \mathbf{b}\rVert \cos\theta$ is derived from the cosine rule. (Do correct me if I'm wrong.)  However, I never really understood why $\mathbf{a} \times  \mathbf{b} =\lVert \mathbf{a}\rVert \cdot\lVert \mathbf{b} \rVert \sin\theta$. Is there a proof for this?  In addition, how does the vector cross product lead to orthogonal vectors?  I remember learning that they do and I know how to solve equations using the respective formulas, but I never got why is it so.


I'm doing my club's accounting in a Google spreadsheet. I am looking for a way to put a checkbox at the beginning of a line in order to tick off the members who paid their dues and then have a function that will automatically add the amount of the "dues paid" cell to a "total dues paid" cell, elsewhere in the sheet.  Right now I'm doing it with a function of the type SUM(A1:A600)-A3-A20-A120 etc.—not very elegant…  If anyone could point me to a solution or a resource to learn how to implement this, I would appreciate it!

What I'm looking for is a one click enable/disable or toggle in some form. The closest I've come is manually editing a cell to enter a 0 or 1, but I'm hoping there's a nicer pattern.  I know there's no checkbox functionality in a Google Sheets but is there a way to get equivalent functionality somehow?


If I share a site the email is not being sent.  This function does work with everything else like if you share a document or a list.  This is happening for all users and all sites. The relays on the email servers are setup correctly.

We do not have on-premise SharePoint 2013 in production but the three dev farms that I have access to all have the same odd behavior. The majority of SMTP functions work correctly (adding to groups, alerts, etc.) but the "share with" option inside of document libraries do not send an e-mail invitation. Permissions are changed correctly so you can manually send a link but this is not how we want this system to work.  There are no event log errors that I can find related to this and since other SMTP functions work, I doubt that there are firewall or mail host configuration error. They are single front-end test farms. Any suggestions on where to look?


How would you punctuate a sentence that contains a list of items, with several examples for each item. For example: "I have found an existing relationship of qualities through a certain model: words including, between and after; colors red, yellow and blue; numbers five, six and ten."  Notice how the first set seems confusing? The main qualities are words, colors and numbers; with each quality having a set of examples. How could this be made more clear, without changing the ultimate structure of the sentence?

I am wondering if I can use a list within a list. I know that the following sentence may seem as though it would be better if reworded, but I am using euphemisms and simplifications for what I am actually writing. I am trying to boil it down, so what you see below is just a microcosm of the sentence I am actually writing.      I went there because I was sad, lonely, foolish, and in need of shelter, love, and contentment.


I have made a very simple terminal game:   I have also created the Deb file.  We surely can move the source code to /usr/bin/ directory and the word file to /usr/share/t-hangman on any Linux system to get the source code running.  But the problem is that installing dependency (only Ruby) manually, and also moving the source code, changing permissions to 755 and setting root as owner may be confusing to some people.  Can I convert the Debian package into Arch Linux tar.gz package securely so that we can run pacman -U t-hangman-v3.0.tar.gz and install it?  EDIT:  A stackexchange post suggests using dpkg on Arch Linux - I think that's not a good choice, in fact the uploader of dpkg forbids "The Debian Package Manager. Don't use it instead of Arch's 'pacman'."

The problem is simple - I have a .deb package and I want to install it on my Arch Linux. Is this possible? If yes, how?


I've just upgraded from Ubuntu 16.04 where Unity Tweaks had this dialog:    (I would normally have the top and bottom "do nothing"'s set to "top" and "bottom" as well)  Working with both large monitors and portrait monitors this functionality is invaluable. It's also the default on Windows 10 which is the other operating system I get to deal with.  I can't seem to find a place to configure this (or appropriate GNOME extension) on Ubuntu 18.04, where is it?  P.S. I did find equivalent settings is CCSM but GNOME seems to be ignoring them.

Super + left/right snaps windows to fit half the screen. I'd like to be able to snap four windows in all corners. CompizConfig Settings Manager doesn't seem to be an option since 18.04 uses the GNOME desktop.


thanks for taking time to answer the question. I am confused here as to why the outputs do not match.   Operation 1:  x = [[0, 0], [0, 0]] print(type(x)) # <class 'list'> print(x) # [[0, 0], [0, 0]]  x[0][0] = 1 print(x) # [[1, 0], [0, 0]]   Operation 2:  y = [[0] * 2] * 2 print(type(y)) # <class 'list'> print(y) # [[0, 0], [0, 0]]  y[0][0] = 1 print(y) # [[1, 0], [1, 0]]   My understanding was that both x and y should be the same. But looks like they are not. What am I missing here?

I needed to create a list of lists in Python, so I typed the following: my_list = [[1] * 4] * 3  The list looked like this: [[1, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1]]    Then I changed one of the innermost values: my_list[0][0] = 5  Now my list looks like this: [[5, 1, 1, 1], [5, 1, 1, 1], [5, 1, 1, 1]]    which is not what I wanted or expected. Can someone please explain what's going on, and how to get around it?


I'm using the package pdfpages to join many PDF documents. Some of them are scanned. Is there an option to reduce quality of those documents in order to make the resulting file size smaller?

I feel that the PDFs produced by pdflatex are too huge. So for example my 50 page book with no illustrations is 500KB. I feel it should be more like 50K or even less. The .tex files together are just 40KB. Anyone knows why the final PDF is so huge and is there a way to compress it to make smaller?


I 'm using coreUi static template.  So I'm manipulating a form.   I'm stuck at this form row that should contain websites, originally it contains 1row: input text, input URl, and a closeIcon.  There's also a add web button, so when I click it, another row in created. I successfullty implemented this feature with JS.  Now, when I press the closeIcon, I want the corresponding row to be deleted.  The problem is when I click the original's row close Button, the method is called, but when I press the other rows' close Buttons, that have been created with js, the function is not being called.     $(document).ready(function(){     $("#add_web_links").click(function(){                 add_web_links();          });     $('.close').click(function(){     close_row();     });  });   function add_web_links() {  var text="
Text
<input class='form-control' type='text'>
 URL
<input class='form-control' type='url'>

 <button type='button' class='close' aria-label='Close'>   &times;</button>

";    $('.web').last().after(text);   }  function close_row() { alert("closed"); }
Web Links

    Text
     <input class="form-control" type="text">
     URL
     <input class="form-control" type="url">

 <button type="button" class="close" aria-label="Close">   &times; </button>

      <button id="add_web_links" type="button" class="btn btn-link px-0">add web links</button>

     Then I inspect the created close icons, they all have the class="close".

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.


$\langle p | x \rangle=e^\frac{ipx}{\hbar}$ can pretty easily be derived from wave mechanics. But how can it be derived without resorting to it? I've seen it be derived from the translation operator $\hat T$. It is shown that for an infinitesimal displacement $\epsilon$ the translation operator in the position eigenbasis is: $$\langle x |\hat T |\psi\rangle=\left( 1+\dfrac{\partial}{\partial x}\right)\langle x | \psi\rangle=\left( 1+\dfrac{\partial}{\partial x}\right)\psi_x$$ In which $\psi_x$ is the state vector's representation in position space, such that $$|\psi\rangle=\int^{\infty}_{-\infty}\psi_x |x\rangle dx$$ And it then assumes that because momentum generates translation, $\frac{\partial}{\partial x}=\frac{i}{\hbar}\hat p$.  Now this leaves me rather unsatisfied. Is there any way to prove the form of the momentum operator, and from it prove $\langle p | x \rangle=e^\frac{ipx}{\hbar}$ using, for example, the matrix representation of quantum mechanics?

I'm curious whether I can find the overlap $\langle q | p \rangle$ knowing only the following:   $|q\rangle$ is an eigenvector of an operator $Q$ with eigenvalue $q$. $|p\rangle$ is an eigenvector of an operator $P$ with eigenvalue $p$. $Q$ and $P$ are Hermitian. $[Q,P] = i \hbar$.   I'm asking because books and references I've looked in tend to assume that $Q$ is a differential operator when viewed in the $P$-basis, then show that it satisfies the commutation relation. (I haven't read one yet that proves that the form given for $Q$ is the only possible one.) I've heard, though, that we can work purely from the hypothesis of the commutation relation and prove the properties of $Q$ and $P$ from it.


Ok, so the details are vague but the ending gives a strong hint. What I remember is that humans are suffering and either: A) Send out humans out into space for help from other life to get help and they eventually find help but come back much later in the future to see humans barely alive. And they now have a ‘solution’ to most human problems. B) Aliens find humans in dire need of help and offer to solve most human problems. Anyway, at the end as the aliens/future humans are informing the Earth humans of all the marvelous advancements they can offer them, they mention that they: “Can also fix the humans being all white” or something along those lines. I think it’s meant to be a cheeky commentary on race but I can’t find it for the life of me.

I am trying to track the title of a short story which is written as a message from an alien race to the original colonisers of earth apologising for the collapse of the experiment and advising the colonisers they will be rescued soon. It turns out the message is meant for a particular race of people. Any help greatly appreciated.   Thanks


As I put in the title: I struggle to solve that problem. I have a green screen footage that I would like to key and insert in a 3d space. If not on plain, the keying does great but when imported as plain the video frame remains even after keying and the items behind the video footage are not visible (hidden by the video)  Thanks for advice in advance

Here's what I need to do.  I have a footage of a street. I want to add several people walking. Each person was shot using chroma.  I understand how to remove the green using nodes. I understand how to composite each element using nodes. What I don't understand is how to I manipulate them in 3D space in order to move them where I want each element to be or animate them.  I could use the video as texture on a plane and move the plane around. But I want to know if I can process that video as texture using masks and keying. Or should I key every person, render them, then add them as texture to the planes and work like that?   Thank you


How can the white spaces from the output of the following line:  $C++$   be omitted so that there is no white space between 'C' and '+' and the last '+'.  The current output is:  C + +   C and the pluses are considered operands and operators.

Writing "C++" in plain text results in an ugly setting, as the '+' signs are too big and too spaced:    I've seen around the web several marcos for typesetting the "C++" symbol, ranging from mild kerning to shrinking, raising and lowering the '+' signs.  What is your version of a \cpp{} macro?


My system's "Settings" tool can detect noise from my microphone but Discord and games can't. I changed a few settings in the system's builtin tool and in the pavucontrol, to no avail. It works fine on Windows so I know microphone is working. This was happening in 16.04 and now in 18.04. I don't know if this is relevant, but I'm using a USB sound card from a chinese brand called U Green. Any ideas?  edit:  Settings can hear my mic:   Discord can't:

In a Discord call on the desktop app and my voice cannot be heard by others. When I use Discord  through browser I can be heard. Any help appreciated.


I exported a 3D model with textures and materials from Sketchup as a .obj file. Then, I imported the .obj file in Blender, but the textures and materials from the original file are missing. Do you know what could be the issue?

I used node textures in a mesh I exported to .FBX.  I then imported it into Unreal Engine 4 and it didn't import any textures; I clicked the Upload Textures option in Unreal Engine.  Is there something I'm doing wrong or is it Blender?


I will soon release my macOS and iOS apps on the respective App Store, but before I do this I need to make sure about a few things.  Will App Store allow me to upload a paid app but still give me the right to give away free licences to people I choose? I have a few special customers who paid for it before it was on App Store, and I would like to allow them to still download from the App Store without having to pay twice. If it's possible, could you show a brief instruction on how it could be done?

I am wondering if it's possible to do "mass giveaways" on the AppStore, without lowering, changing or otherwise changing the listed application.  Is it possible to distribute hundreds to, potentially, thousands of promo codes, legally, while still leaving the "normal" distribution channel of purchasing the app open?  An example of the above would be selling physical items in a store which have a bundled digital component available. Essentially you buy a product in a store, which comes "bundles with a free app" (BB and Android have already been dealt with, iOS is unclear). It would be nice to give the option to have a promo code in the box, that the user can then use to get the application for free. Is this possible?


I'm trying to insert a Harvard reference list to my report. I'm using the Swedish language package and biblatex. However, I am having some problems with the reference list:  (1) I would like the references to be written like this:  Author1lastname, author1first name, Author2lastname, author2firstname, Author3lastname, author3firstname (year)...  However, the second and third authors names show up firstname-lastname (please see picture).  (2) I would like my references to be sorted by author last name. However, the list starts with an author whose last name starts with the letter W :(  If I add some more references, they get sorted by author last name, so I think the problem might have to do with the Swedish language package? How can I solve this problem, so that the W comes after V?  Example tex file:  \documentclass[a4paper,11pt,twoside]{article} \usepackage[T1]{fontenc} \usepackage[swedish]{babel} \usepackage[utf8]{inputenc} \usepackage{algorithmic} \usepackage[style=authoryear,backend=biber,maxbibnames=99]{biblatex} \addbibresource{reference.bib}  \begin{document}  \title{My title} \author{My name}  \maketitle  \section{I have multiple sections}  I write references like this (\cite{key1}). This shows up first in the referencelist (\cite{key2}).  \newpage  \printbibliography  \end{document}   Example bib file:  @inproceedings{key1,     author = {Author1lastname, Author1firstname and Author2lastname, Author2firstname and Author3lastname, Author3firstname},     title = {Title},     booktitle = {Booktitle},     series = {Series},     year = {Year},     isbn = {ISBN},     location = {Location},     pages = {Pages},     numpages = {Numpages},     url = {URL},     doi = {DOI},     publisher = {Publisher}, }  @inproceedings{key2,     author = {WAuthor1lastname, Author1firstname and Author2lastname, Author2firstname and Author3lastname, Author3firstname},     title = {Title},     booktitle = {Booktitle},     series = {Series},     year = {Year},     isbn = {ISBN},     location = {Location},     pages = {Pages},     numpages = {Numpages},     url = {URL},     doi = {DOI},     publisher = {Publisher}, }   I'm new to LaTex and would be very thankful for help :)

I'm having 2 problems with  references  in my thesis.  First when a last name starts with letter W, it always comes at the top. Before A. But if I change the authors lastname from Wolf to Solf it works. W isn't a special character in this context... or is it?  Second problem is when I have two names like 'Ivan and Me', in the references list I get 'Ivan, A and B Me' not 'Ivan, A and Me, B'. Does anyone have any suggestions? Thanks in advance.  My mwe is:  \documentclass[12pt,a4paper,swedish]{report} \usepackage[latin1]{inputenc} \usepackage[swedish]{babel} \usepackage[style=authoryear,natbib=true,backend=biber,sorting=nyt]{biblatex}  \addbibresource{incl/tgene.bib}  \begin{document} Foo \parencite{ivan} bar \parencite{wolf}. \printbibliography[heading=bibintoc] \end{document}   And my .bib looks like:   @book{ivan,     author = {Ivan, A and Me, B},     title = {Title A},   }   @book{wolf,   author={Wolf, Ceasar},   title={Title B},   }


What is a best way to have ability to connect Bluetooth enabled PC and cellphone all over the house? Connection possible only in same room with PC, i want to extend now.  Does passive repeater (two antennas connected with coaxial one near the PC BT and other in remote room) helps? Or can i build BT network such as Multi-AP Roaming for Wi-Fi? Which hardware i need to use in that case as cheaper as possible?

We have two Android phones (Vibrants) and a regular land-line at home.  We bought a cordless system that has Bluetooth built-in (Panasonic KX-TGA651) so that we can use the cordless phones to answer our cell phones.  Everything works well. However, we want to place the cordless base in the kitchen, but don't want to have to park our cell phones there. Do Bluetooth repeaters exist that we could use for this purpose?


It is commonly said that heat received from sun is due to the infrared part of solar radiation. But from Wikipedia i found that most of the energy is received from visible light. Then why do we say that infrared is responsible for heating of earth?

During a sunny day the walls of my house warm up (no surprise). My question: how much of this warming up (if any) comes from visible light? I associate infrared with thermal energy. If my house was floating in space (to prevent any thermal exchange with its surroundings) and I installed a giant infrared (and UV) filter between it and the sun, would it still warm up (compared to its rest temperature in full darkness)?


My question concerns teleportation effects like the  spell or  from SoP over .  When the spell is cast, would you be able to leave behind something you are touching, such as  or even worn clothing (no, I do not plan on stripping people, just if a disguise is ruined you can abandon it for the one you are wearing underneath).

I've got a warlock with Flee The Scene, a dimension door spell-like ability. He's been attacked by monstrous spiders and has 1 STR left, meaning his 15lbs of armour alone is more than a heavy load.   He's not grappled, and he's not unable to move as he would be at 0 STR. Can he use Flee The Scene to jump out of his clothes and sprint naked for freedom?


I have an 10 year old camera (Canon 400D) and primarily use a fixed Canon 1.8 50mm lens. This weekend I was using it and noticed most of my photos with that lens looking blurry and unfocused. Over this weekend I also used other lenses (Canon 10-18mm) and the photos shot with them look sharp.   I've had a growing suspicion something is wrong with the 50mm AF as lately, the focus have felt "thrown off" despite me taking care to focus at the right object (I almost always use the centre point). It hasn't been as disastrous as this weekend though. I've had this lens for 5+ years, and I've taken great, sharp photos in the past so I don't think it's all in my head.   However, some photos from this weekend are still sharp.   Can someone help me out - although I'm enthusiastic about photography, I'm not an expert of how the lens and camera work "under the hood". Is it common that a lens will lose its AF capabilities over time?   (I'd rather not post the photos I took, as they have people in them and I value their privacy)

Probably a novice question, but how do I correctly diagnose from a photo for what reason that camera wasn't able to focus properly?  It can be any 1 of the following   Unsteady hand Lens issue Metering Re-Calibration required in camera or ...   Is there a set of unsaid protocols that needs to be followed by a photographer?  Goal is to get a sharp and crisp image prior to editing.  [PS: I own a Nikon D5200.]


I am trying to interpret the three boxplots below in light of another plot before finalizing my glmer models (GLMM) in R.  The boxplots below show the relationship between a listener's group (T, TA and TQ) and whether the listeners would match a selection or mismatch it to a predicted response (the DV match is binary: match/mismatch).   Both Listgp and match are factors; thus, I first used the xtabs function, then plotted the boxplots.    My basic model is as follows.   glmer<-(match~Listgp + (1|stimulus) + (1|listener), data= msba, family= "binomial")   Now, first, I notice that there are no whiskers in the upper and lower quantiles. I read somewhere that this means that the bottom and the top of the box would be at the exact position of the lower and upper quantiles. Is this the case here too?   Second, I am trying to interpret these boxplots in light of the plot that follows them which is straightforward for me.   In the boxplots, the range of variance for the T group is bigger than the TQ or the TA. In addition, the TQ  group seems (according to the boxplots) to be matching the patterns more, followed by the T and finally the TA.   On the other hand, according to the plot, the TA group matches the patterns more than the TA and the TQ. Basically, the TA mismatches the patterns more than the two other groups.   So my question is, do the two plots give the same or different information and is my above interpretation correct?      The first 6 lines of the data are as follows.  head(msba)   list.Listgp   cond.by gender age level.of.ed. Avg.skills.T read.A comp.A speak.A 1    T1      T Qualtrics   Male  29      college           10     NA     NA      NA 2    T1      T Qualtrics   Male  29      college           10     NA     NA      NA 3    T1      T Qualtrics   Male  29      college           10     NA     NA      NA 4    T1      T Qualtrics   Male  29      college           10     NA     NA      NA 5    T1      T Qualtrics   Male  29      college           10     NA     NA      NA 6    T1      T Qualtrics   Male  29      college           10     NA     NA      NA   writ.A   st.    match st.length st.context st.nature freq. 1     NA  man     match     short      plain      Real  7.80 2     NA Dhabb mismatch     short   emphatic      Real 50.02 3     NA   qad mismatch     short          q      Real 96.57 4     NA   ?an    match     short pharyngeal      Real 15.78 5     NA   min mismatch     short      plain      Real 59.07 6     NA dhidd mismatch     short   emphatic      Real 54.50   I plotted other boxplots but this time with the variable stimulus (which is also is a factor). These ones have whiskers! (Because I don't have enough reputation points, I will have to remove the 2nd plot so that I can paste the boxplots with stimulus)      I used these codes for the xtabs.   monosbaT.xtabs <- xtabs(~ match + st. , data = monosbaT) monosbaTA.xtabs <- xtabs(~ match + st., data = monosbaTA) monosbaTQ.xtabs <- xtabs(~ match + st., data = monosbaTQ)    Then, in the lattice package I plotted them using these codes.   par(mfrow = c(1,3)) boxplot (monosbaT.xtabs, main = "T", legend.text= c("match", "mismatch"), xlab= "stimulus", ylab= "match", col= "lightblue3", ylim=c(0, 25), breaks=seq(0, 25, 8)) boxplot (monosbaTA.xtabs, main = "TA", legend.text= c("match", "mismatch"), xlab= "stimulus", ylab= "match", col= "lightblue3", ylim=c(0, 25), breaks=seq(0, 25, 8)) boxplot (monosbaTQ.xtabs, main = "TQ", legend.text= c("match", "mismatch"), xlab= "stimulus", ylab= "match", col= "lightblue3", ylim=c(0, 25), breaks=seq(0, 25, 8))  par(mfrow =c(1,1))   My dataset has 1224 obs. of  17 variables.

I have a data set that has customerID and daily visits. This dataset records the number of times customers visited the site in a day.   customerID   TotalVisits  1            6  2            17  3            20  4            25   Just to explore the data further, I tried plotting the TotalVisits values in a box plot. The plot doesn't seem to have a lower whisker. q1=1 and there are no values between q1 and  q1-1.5(IQR). The plot has q1, q2 and q3. The minimum value and q1 are the same.   Is this why the boxplot doesn't have the lower whisker? Could you please help me with the interpretation? Is it correct to draw a boxplot without any whiskers?  [I am new to the site and I am not able to post the image.]


The Friedmann Equations describe three possibilities for the shape of our using General Relativity, I read in a book that the shape of our Universe is a 3-sphere such that in any direction if you travel far enough you will end up at the same place from which you started. This solves the problem of whether the Universe is infinite or has a boundary, since in this scenario it is both infinite and has a boundary. My question is that the Mobius strip is also a 3D curve with one side one boundary and one can travel an infinite distance on its surface. Is it possible for a non euclidean 4D spacetime to be a mobius strip?

asks what constraints there are on the global topology of spacetime from the Einstein equations. It seems to me the quotient of any global solution can in turn be a global solution. In particular, there should be non-orientable solutions.  But does quantum physics place any constraint? Because it seems to me that if space by itself is non-orientable then what happens to, say, neutral kaon interactions along two different paths that come back to the same spot with opposite orientations?  So then, is there any reason why time cannot be non-orientable? For example my mental picture (two space dimensions suppressed) is of a disc. The big bang is the centre, time is the radial direction, space is the circumferential direction. A timelike geodesic that avoids black or white holes will start on the big bang, go out to the edge of the disc, continue on the opposite edge with time and orientation (and presumably matter/anti-matter) reversed, and return to the big bang (which is also therefore the same as the big crunch). The "reflection time" of the universe would be large enough that thermodynamic violations are not observed.


I am on H1 B visa since Oct 1, 2017. Last year, I was on F1 OPT. I am filing a Married filing jointly with my wife (is on H4 without any income). I am planning to fill in Form 4868 for extension and pay the necessary amt. After I meet the substantial presence test, say by May end, I will file form 1040 as Resident Alien. Is this the right thing to do? Or should I file taxes as a Non resident like I did last year? If I have both the options, which is the best?

I am currently on H1 B (since October 1, 2017). Last year when on F1 OPT, I had filed Form 1040 NR for my taxes. Which form is advisable for 2017, considering I am on H1 B now. What options do I have?


In the past when I was sitting near my laptop (from early 2015) with the Photos app open on my iPhone (from fall 2014), when I would tap share a picture, my laptop would show up in AirDrop.  Now it is not showing up anymore!   From my laptop when I click on AirDrop from the Finder, my phone appears, and I am able to share files from my laptop to the phone.   I have confirmed that Bluetooth and Wifi are enabled for both devices. From Settings>Bluetooth on the phone, I saw my laptop listed, but when I tried to connect, it failed.  I deleted it from the list of My Devices and tried to re-pair my laptop and computer using the Bluetooth File Exchange app on my laptop.  Even after seemingly going through the process correctly, it showed the laptop in the list of My Devices again, but as "Not Connected," and when I clicked on the info icon to see more, it said, "[Laptop name] is not supported."  But how could this be?!  I have the latest OS versions on both! And now when I try to send from my laptop to the phone, which was working when I started debugging this, it says that "[Phone name] does not have the necessary services."  Again -- why?!  (However, when I share through the Finder from laptop => phone, it does work, although it's the reverse direction I need to get working again.) I had the laptop under the setting "Allow me to be discovered by: Contact Only," but I switched it to "Everyone" -- no luck.   This is maddening.  Help!

I have    iPhone 5 (with iOS 8.3) MacBook Pro Early 2013 (with OS X Yosemite 10.10.3) iPad Air (with iOS 8.3)   My iPhone is paired with the MacBook, so e.g when my phone rings, I can see it in my computer. But when I want to AirDrop photos from my iPhone the MacBook, then I can't see the MacBook in my iPhone AirDrop targets.  I can see the iPad, I can see my wife's iPhone, but not the MacBook.  On MacBook, I can see the iPad, my wife's phone and even my iPhone and I can drop to there, but not the other way around.  Before I started troubleshooting, the iPhone and MacBook were mutually invisible (I only saw iPad from both). After a while of trying things and sending files back and forth, my MacBook started to see the iPhone, but I did not manage to make it work from the other way. Still, the iPhone seems to be much "less" visible than the iPad - which I see almost instantly and always, the iPhone only seems to appear after a while.  Just to make it clear:   both iPhone and MBP have BT turned on both have AirDrop visibility set to Everyone   I would be glad for any suggestions to fix this - what settings to check, logs, whatever.


I’m looking for some hints. Let J be an ideal of $R \times S$. I have already proved that  $$J_1 = \{a \in R / (a,b) \in J \; for \; some \; b \in S\}$$ $$J_1 = \{b \in S / (a,b) \in J \; for \; some \; a \in R\}$$ are ideals of R and S respectively.  Also, I proved that if $J_1$ and $J_2$ are ideals of R and S respectively, then $J_1 \times J_2$ Is an ideal of $R \times S$. But I don’t know how to conclude the proof.

$R$ and $S$ are two rings. Let $J$ be an ideal in $R\times S$. Then there are $I_{1}$, ideal of $R$, and $I_{2}$, ideal of $S$ such that $J=I_{1}\times I_{2}$.  For me it's obvious why $\left\{ r\in R\mid \left(r,s\right)\in J\text{ for some } s\in S\right\}$ is an ideal of $R$ (and the same for $S$) so I can prove $J$ is a subset of the product of two ideals and also that the product of these two ideals is an ideal. But I can't see how to prove equality without assuming existence of unity or commutativity. Trying basically to show that if $\left(r,s\right)\in J$ then also $\left(r,0\right),\left(0,s\right)\in J$. Thank you for your help!


Let $X$ be topological space, $K_{A}$ function defined with $ K_{A} (x) = 1, x \in A, K_{A} (x) = 0, x \in X\backslash A$. Prove that if $ K_{A} $ is continuous then $FrA =\emptyset$ ($FrA=ClA\backslash IntA$).  I tried by contradiction. Since $ClA= A \cup A^{'}$ I decided to separate proof in two cases. First case ($x \in (A^{'}\backslash A)$ ) I easily got contradiction, but on this second case ($x \in (A\backslash A^{'})$ ) I got stuck.

I have been stuck on this problem for a long time ...Since the definition of continuity at a *point * is given in terms of supersets ,I am at loss of how to proceed here...     Let $X$ be a topological space and let $\chi_A:X\to\mathbb{R}$ be the characteristic function for some subset $A$ of $X$.   Show that $\chi_A$ is continuous at $p\in X$, if and only if $p$ is not an element of the boundary of $A$.   (Recall $\chi_A(x)=1$ if $x\in A$, and $\chi_A(x)=0$ if $x\in A^c$.)


I have Ubuntu 18.04 installed on an offline computer. I've used apt-offline to update the system as described in the manual, but when I run sudo apt-offline install apt-offline.zip, I have keyring errors:  ERROR: Path for keyring is invalid: /etc/apt/trusted.gpg gpgv: Signature made Ср 26 фев 2020 17:41:44 MSK gpgv:                using RSA key 3B4FE6ACC0B21F32 gpgv: Good signature from "Ubuntu Archive Automatic Signing Key (2012) <ftpmaster@ubuntu.com>" gpgv: Signature made Ср 26 фев 2020 17:41:27 MSK gpgv:                using RSA key 3B4FE6ACC0B21F32 gpgv: Good signature from "Ubuntu Archive Automatic Signing Key (2012) <ftpmaster@ubuntu.com>" gpgv: Signature made Пт 27 апр 2018 02:38:40 MSK gpgv:                using RSA key 3B4FE6ACC0B21F32 gpgv: Good signature from "Ubuntu Archive Automatic Signing Key (2012) <ftpmaster@ubuntu.com>" gpgv: Signature made Ср 26 фев 2020 17:40:27 MSK gpgv:                using RSA key 3B4FE6ACC0B21F32 gpgv: Good signature from "Ubuntu Archive Automatic Signing Key (2012) <ftpmaster@ubuntu.com>"   As I understand, there is new version of apt-offline, 1.8.2. Does it fix this bug, or is there any other way to solve this problem?  I tried , but it didn't work.

working with procedure  to update Ubuntu 18.04 offline machine, the sudo apt-offline install /path_to_downloaded_package_folder do not apply any updates/upgrades. The beginning of the massage I get is :   sudo apt-offline install ./updates_path/ No changelog available (Y) Yes. Proceed with installation (N) No, Abort. (C) Display changelog (?) Display this help message. What would you like to do next:  (y, N, ?)y Proceeding with installation ERROR: Path for keyring is invalid: /etc/apt/trusted.gpg gpgv: Signature made Mon 06 Jan 2020 08:17:27 AM MST gpgv:                using RSA key 3B4FE6ACC0B21F32 gpgv: Good signature from "Ubuntu Archive Automatic Signing Key (2012) <ftpmaster@ubuntu.com>" gpgv: Signature made Mon 06 Jan 2020 08:18:52 AM MST gpgv:                using RSA key 3B4FE6ACC0B21F32 gpgv: Good signature from "Ubuntu Archive Automatic Signing Key (2012) <ftpmaster@ubuntu.com>" gpgv: Signature made Mon 06 Jan 2020 08:18:25 AM MST gpgv:                using RSA key 3B4FE6ACC0B21F32 gpgv: Good signature from "Ubuntu Archive Automatic Signing Key (2012) <ftpmaster@ubuntu.com>" gpgv: Signature made Thu 26 Apr 2018 05:38:40 PM MDT gpgv:                using RSA key 3B4FE6ACC0B21F32 gpgv: Good signature from "Ubuntu Archive Automatic Signing Key (2012) <ftpmaster@ubuntu.com>" security.ubuntu.com_ubuntu_dists_bionic-security_InRelease synced. security.ubuntu.com_ubuntu_dists_bionic-security_Release synced. security.ubuntu.com_ubuntu_dists_bionic-security_Release.gpg synced.   What am I doing wrong?


I have encountered two (?) definitions of the electric quadrupole moment. They are: $$Q_{ij}=\frac{1}{2}\int \rho(\vec{x}')x'_i x'_j\,\mathrm{d}^3x'$$ and $$Q_{ij}=\int (3x'_i x'_j-\delta_{ij}x'^2)\rho(\vec{x}')\,\mathrm{d}^3x'$$ I am trying to study radiation arising from the electric quadrupole. I am confused since sometimes the first definition is used while other times, the second. As such, which definition should be used and why?

There are two different possibilities to define the electric quadrupole tensor:  On the one hand, one can define \begin{align}Q_{kl} = \int \rho(\mathbf r') \cdot r'_k \, r'_l  d^3r',\end{align} while on the other hand most of the textbooks (for example Jackson) define \begin{align} Q_{kl} = \int \rho(\mathbf r') \cdot (3r'_k \, r'_l - (r')^2 \, \delta_{kl}) \cdot d^3r'.\end{align}  For all higher moments, these two definitions (traceless vs. nontraceless) are also possible. Is there any physical reason why one of the definitions should be preferred?


Read this as a kid in the early 80s.  Two boys in our world get in a fight at school, but when they enter the principal's office they are transported to a parallel world. As I recall, they had to work together to save that world by finding several magic items (one was a thread, I think?). And in that world math and poetry were magic?  Anyone remember this?

As a kid I read a book about two boys who hate each other and are opposites to each other (lanky red-haired runner vs. stocky black-haired wrestler). They're transported to a parallel world where they have to undertake some sort of quest. Miscellaneous memory-fragments:   I think there's a magical yin-yang amulet. There's a wolf-spirit or wolf-god. Possibly called Fenrir? What we call magic they call science; what we call poetry they call magic. They're summoned into the other world by a bald man in a robe who looks a little like Varys from GoT.   Does this sound familiar to anyone?


i am making a program that checks 20 files for the word "NULL" and if it is not present the program puts there a predefined word/ sentence When trying to run my program through the debugger is throws the exception: "Exception thrown: write access violation. _Left was 0xCCCCCCCC."  The main problem is that in the "iosfwd" file at line 506 an exception is thrown. I tried to rearrange the code and tried different snippets from here and there.  #include <fstream> #include <string> #include <Windows.h> #include <iostream> using namespace std;  string ending = ".txt"; string name = "Prog";  int main() { ofstream os; ifstream is; string a, nouse; string Progs[20]; is.open("tempstring.txt"); getline(is, nouse); is.close(); cout << "UPDATING DATABASE.. DO NOT EXIT!" << endl; cout << "String Called" << endl; for (int count = 1; count < 20 + 1; count++) {     cout << count;     string fname1 = name + to_string(count) + ending;     is.open(fname1);     getline(is, Progs[count]);     is.close(); } cout << "done 1"; system("pause"); for (int count = 1; count < 20 + 1; count++) {     string fname2 = name + to_string(count) + ending;     if (Progs[count] == "NULL")     {         os.open(fname2);         os << nouse;         os.close();          os.open("tempdone.txt");         os << 1;         os.close();         Sleep(500);         cout << "SUCCESS" << endl;         system("pause");         exit(EXIT_SUCCESS);     } } cout << "done end" << endl; system("pause"); os.open("tempdone.txt"); os << 2; os.close(); exit(EXIT_FAILURE); }   Part of iosfwd:      static _CONSTEXPR17 void assign(char& _Left, const char& _Right) noexcept     {   // assign an element     _Left = _Right;     }   i expected the program to continue through the loop normally, but instead when i try to run the program without debugging it shows until "String Called", then displays 1234567891011121314151617181920, waits around 3 seconds and then exits with code "-1073741819"

I know that the compiler will sometimes initialize memory with certain patterns such as 0xCD and 0xDD.  What I want to know is when and why this happens.  When  Is this specific to the compiler used?  Do malloc/new and free/delete work in the same way with regard to this?  Is it platform specific?  Will it occur on other operating systems, such as Linux or VxWorks?  Why  My understanding is this only occurs in Win32 debug configuration, and it is used to detect memory overruns and to help the compiler catch exceptions.  Can you give any practical examples as to how this initialization is useful?  I remember reading something (maybe in Code Complete 2) saying that it is good to initialize memory to a known pattern when allocating it, and certain patterns will trigger interrupts in Win32 which will result in exceptions showing in the debugger.  How portable is this?


My brother and I are on PC Minecraft, and I'm trying to connect to him when he opens LAN to go to his world. We're finding that whenever I connect to him, I'm getting the error io.netty.channel.AbstractChannel$AnnotatedConnectException: Connection time out: no further information:  But that's only when I try to connect to him. Using the same method, he has no problems connecting to my worlds when I open LAN.   I've looked at all the troubleshooting problems, turned off all my Firewalls, but I can't connect to him still. Anyone have an ideas?

I am getting the following error when I try to connect to a Minecraft server:  This is all servers, not just one. The error says:  io.netty.channel.AbstractChannel$AnnotatedConnectException: Connection refused: no further information: Version 1.12  I've tried:  Restarting Minecraft Restarting Computer Uninstalling and Reinstalling Mincraft Uninstalling and Reinstalling Java Altering Firewall Restarting Internet I've messed with my port, made a second windows account, reset netsh winsock Checked hosts Made a new WINDOWS account  The overlay in the bottom right is Geforce's Overlay for game capturing. I don't have any mods installed. A Mojang support ticket wouldn't help. Im desperate.


I have collected R outputs in a text file, which I insert in latex by the following command. \verbatiminput{14.txt}  How can I change the font size of it to footnotesize?

Is there a way to set an option of fontsize that would affect the command \verbatiminput ?  MWE:  \documentclass{article} \usepackage{verbatim}  % NOT WORKING %\makeatletter %\newcommand{\verbatimfont}[1]{\renewcommand{\verbatim@font}{\ttfamily#1}} %\makeatother  \begin{document}         \verbatiminput{test.txt} \end{document}


I did an "apt-get dist-upgrade" on a 16.04.2 LTS system. I did not see any kernel related packages, so I did not reboot.  To my surprise, I no longer have /sbin/init (as shown by ps -auxw as root) as process ID 1; instead PID 1 is /lib/systemd/systemd --system --deserialize 20.  Is this expected? ...or is this a side-effect of upgrading? ...and if I reboot, would I see /sbin/init return?

I am trying to examine the output from pstree command. But for some reason it always starts from something called as systemd as opposed to it being init. I have checked to see the process ID's of both init and systemd using ps aux command and init has a PID of 1, while systemd has some other PID. So why isn't init being shown in my pstree's output? Is there an option that I need to give?  Also I did read about systemd vs init controversy, but ubuntu 16.04 LTS still uses init to start everything right?  Update as to why different PIDs?  It turns out that different PIDs that I thought were part of my ignorance. The init had a PID 1, whereas systemd wasn't the thing that I was talking about. Instead when I ran ps aux|grep systemd, I found PIDs for /lib/systemd/systemd-*, where * means some extra characters. So what I was talking about was not systemd, but some other processes that were extensions(is it the correct word?) of systemd I guess.  Some of the examples for that * are as follows  /lib/systemd/systemd-journald /lib/systemd/systemd-udevd /lib/systemd/systemd-timesyncd


I'm failing at the most basic of creating a tree with tikz-qtree. If I copy the correct string with correct formatting into Overleaf everything works fine. But if I do change too much it just breaks. Resulting in an Emergency stop within the compiler. This is my current attempt: \begin{tikzpicture}[grow'=up]             \Tree[.$\emptyset$ [.B                  [.A [.E]                     [.F] ]                         [.C ]]                             [.D ]] \end{tikzpicture}  Did I mess up the formatting or something else? I'm just clueless!

I've scoured this forum and it looks to me like I'm setting up the tree correctly, but I'm still getting this error, I have   \usepackage{tikz} \usepackage{tikz-qtree}   in the header.  Here is the code that is causing the problem:  \begin{tikzpicture}  \Tree  [.{Boolean Groups}     [.{Abelian Groups}         [.Groups]     ]     [.{Class 3}          [.{Class 5}]         [.{Class 1}]         [.{Class 2}]         [.{Class 4}]     ] ]  \end{tikzpicture}


I'm learning basic Linked Lists and wanted to try my hand at writing my own implementation.  However, I keep getting the following errors when compiling:  /tmp/ccNerPXr.o: In function `main': main.cpp:(.text+0x10): undefined reference to `LinkedList<int>::LinkedList()' main.cpp:(.text+0x2c): undefined reference to `LinkedList<int>::insert(int const&)' main.cpp:(.text+0x49): undefined reference to `LinkedList<int>::displayList()' collect2: error: ld returned 1 exit status   I've looked at other stack overflow answers and couldn't find one to meet my specific issue. The name of the template class matches the instance declaration in main, I remembered to #include "LinkedList.h" properly, and I double-checked to make sure the forward declarations in *.h matched the ones in *.cpp. What else could be causing this error? Is it staring me in the face, and I'm just too blind to see it?  I feel like this might be simpler than what I'm making it...  Here is my (unfinished) source code for reference:  main.cpp       #include "LinkedList.h" #include <iostream>  using namespace std;   int main()  {      LinkedList<int> normList;     for(int i = 0; i < 5; i++)          normList.insert(i);        normList.displayList();       return 0;  }    LinkedList.h   #ifndef LINKEDLIST_H #define LINKEDLIST_H #include <cstddef>     template <class Object> class LinkedList   {      struct ListNode     {          Object element;          ListNode *next;         ListNode() : element(0), next(NULL) {};           };           ListNode *head;          ListNode *tail;       public:          LinkedList();            void insert(const Object &x);          void erase(const Object &x);          void eraseList();          void displayList();   };   #endif    LinkedList.cpp   #include "LinkedList.h"  #include <iostream>  using namespace std;   template <class Object> LinkedList<Object>::LinkedList() {      head = NULL;  }     /*This function will insert an object *using the tail-end insertion method *i.e., inserting at the end of the list   */  template <class Object> void LinkedList<Object>::insert(const Object &x)  {     ListNode *newNode = new ListNode(x, NULL);       if( !head ) {          head = newNode;        tail = head;       } else {          tail->next = newNode;         tail = newNode;               }   }//insert()   template <class Object> void LinkedList<Object>::erase(const Object &x)  {      ListNode *prev;    } //erase()  /* *Function that deletes entire list  */  template <class Object>  void LinkedList<Object>::eraseList()  {      ListNode *prev;     while(head->next)      {            prev = head;          delete head;          head = prev->next;      }   }//eraseList()  template <class Object>  void LinkedList<Object>::displayList()  {      if(!head)          cout << "The list is empty\n";       while(head->next)      {          cout << head->element << endl;          head = head->next;      }     } //displayList()    Thanks in advance to any help or input

Quote from :     The only portable way of using templates at the moment is to implement them in header files by using inline functions.   Why is this?  (Clarification: header files are not the only portable solution. But they are the most convenient portable solution.)


I'm using libcurl to fetch e-mail with IMAP. Fetching itself is successful, but the problem is that libcurl can save the result of communication only in std::string or FILE* (as far as I have searched).  This made it difficult for me to parse the result into header, mime, and so on.  So I have searched libraries which makes parsing easier, but those are for other languages not for C/C++.  Since my project only uses C/C++, I have to use only those languages. VMime is written in C/C++ but I couldn't use Vmime because it uses its own implementation on IMAP communication (which makes libcurl useless).   // code to save the IMAP communication result into std::string buffer  curl_easy_setopt(mCurl, CURLOPT_WRITEFUNCTION, callback); curl_easy_setopt(mCurl, CURLOPT_WRITEDATA, &readBuffer);    readBuffer is std::string. I want to parse the result in readBuffer into desirable data structure( ex)stl ) for easier access.  Are there good libraries for it? I have searched for a day but I couldn't find it. Or if I can use Vmime only to parse the result, not affecting other libcurl codes that I have already finished, can you guide me how to do it?  I appreciate it in advance.

I want to digest a multipart response in C++ sent back from a PHP script. Anyone know of a very lightweight MIME parser which can do this for me?


I've just upgraded to Ubuntu 19.10 especially to enable Livepatch. Unfortunately, I get the same error I had with Ubuntu 18.04:  $ sudo canonical-livepatch enable [key] 2019/10/22 17:20:20 error executing enable: Livepatchd error: The platform Ubuntu 19.10 is not supported. exiting.   Does anybody have any clue where the problem could come from?

Last night I thought to check whether Canonical Livepatch service is working fine after upgrading to Ubuntu 18.10 from Ubuntu 18.04. I know it was meaningless since it was working fine in Ubuntu 18.04. But to my surprise when I ran   sudo canonical-livepatch status --verbose   I got the error:   2018/11/03 23:11:05 error executing status: Livepatchd error: The platform Ubuntu 18.10 is not supported. exiting.   I am now confused, is the problem only on my system? OR Is Canonical Livepatch service not supported on Ubuntu 18.10?  I would therefore like to request my fellow Ubuntu 18.10 users to do the check and if someone knows the reason/solution please reply to this thread.


I need to know the exact number of downloads (count, not range) for my app hosted on Google Play Store, is it possible?

I cannot see the download counts of one app on Google Play.   How can we know that number of one app?


The default tolerance of PostGIS ST_Intersects query is "0.00001 meters" as indicated in the . I need to use the same query with another tolerance value but ST_Intersects takes only 2 input parameters (geom A and geom B).  Is there a way to change this default value?

is there anyway to set tolerance in Postgis, in Arcgis tolerance is the minimum distance which could separate two points, if the distance between them is smaller than the tolerance so the points are considered overlapped. i need to set this parameter because i get some weird results using functions like ST_Intersects, ST_equals, ST_difference. in this conditions i check intersecting points by ST_Distance(p1 , p2) < tolerance but i would like to get a more robust and general solution.  in my use case i need only 1cm to 1mm precision, but for example sometimes ST_Intersects do not give expected results because of some microns (0.000001).  SELECT ST_Intersects('POINT(0.00000000000000001 0)'::geometry, 'LINESTRING ( 0 0, 0 2 )'::geometry);


Is there a way to hook into the  function to add a custom email as hidden (BCC) copy to each email sent?  If so, how?  -edit-  It's not like I want to send an email with BCC, I would like to make the necessary hooks to add the BCC to every sent email (many different functions in my theme make use of wp_mail)

I am currently using the below code to email users when a new post is published, but I need it to BCC all users and not TO all users. Any ideas?  function email_members($post_ID)  { global $wpdb; $usersarray = $wpdb->get_results("SELECT user_email FROM $wpdb->users;"); $users = implode(",", $usersarray); mail($users, "New WordPress recipe online!", 'A new recipe have been published on http://www.wprecipes.com'); return $post_ID; }  add_action('publish_post', 'email_members');


Let $B$ be an all-ones matrix of dimension $n \times n$, and $I$ be the identity matrix of dimension $n \times n$. Define $A = \frac{1}{n}B - I$. For $n=3$, $A$ would yield  \begin{equation*} \begin{bmatrix} -2/3 & 1/3  & 1/3  \\ 1/3  & -2/3 & 1/3 \\ 1/3  & 1/3 & -2/3 \end{bmatrix}. \end{equation*}  How would one compute rank$(A)$ for any $n$?  I have noted that any row $r_i$ of $A$ can be written as a linear combination of the other $n-1$ rows. Specifically, $r_i = - \sum_{j\neq i} r_j$. This implies rank$(A) < n$, but I don’t know how to compute the exact rank of $A$.   Any hint would be appreciated.

I want to find the rank of this $n\times n$ matrix \begin{pmatrix} 1 & a & a & \cdots & \cdots & a \\ a & 1 & a & \cdots & \cdots & a \\ a & a & 1 & a & \cdots & a \\ \vdots & \vdots & a& \ddots & & \vdots\\ \vdots & \vdots & \vdots & & \ddots & \vdots \\ a & a & a & \cdots  &\cdots & 1 \end{pmatrix}  that is, the matrix whose diagonals are $1's$ and $a$ otherwise, where $a$ is any real number.  My first observation is when $a=0$ the rank is $n$ and when $a=1$ the rank is $1.$ Then I can assume $a\neq 0, 1$ and proceed row reduction to find its pivot rows. I obtain  \begin{pmatrix} 1 & a & a & \cdots  & a \\ 0 & 1+a & a & \cdots & a \\ 0 & a & 1+a & \cdots & a \\ \vdots & \vdots & \vdots & \ddots & \vdots \\ 0 & a & a & \cdots  & 1+a \end{pmatrix} by subtracting the first row multiplied $a$ for each row below the first, and then divides the factor $(1-a)$,  and stuck there. Any hints/helps?


I just finished installing Ubuntu 16.04.05 (Desktop) LTS on an acer Aspire 3690 laptop. This OS works just fine on this laptop, however I'll see the wifi symbol on top, but it wont recognize any wifi signal. Ethernet works just fine, issue is only with wifi. Is there any way I can get the laptop to recognize wifi signals?  06:02.0 Network controller [0280]: Broadcom Corporation BCM4318 [AirForce One 54g] 802.11g Wireless LAN Controller [14e4:4318] (rev 02)     Subsystem: AMBIT Microsystem Corp. TravelMate 2410 [1468:0312]     Kernel driver in use: b43-pci-bridge     Kernel modules: ssb 0: acer-wireless: Wireless LAN     Soft blocked: no     Hard blocked: no

I'm having serious problems installing the Broadcom drivers for Ubuntu. It worked perfectly on my previous version, but now, it is impossible.   What are the steps to install Broadcom wireless drivers for a BCM43xx card?  I'm a user with no advance knowledge in Linux, so I would need clear explanations on how to make, compile, etc.    lspci -vnn | grep Network showed:   Broadcom Corporation BCM4322 802.11a/b/g/n Wireless LAN Controller [14e4:432b]      iwconfig showed:  lo        no wireless extensions. eth0      no wireless extensions.   NOTE: Answer below is updated every time new information is added and confirmed working.


I'm trying to create a return object that contains a BufferReader and a BufferWriter.  Here are my two classes:  test.java  package FileIO;  import java.io.*;  public  class Test{      static String line = null;     public static void Main() {         String fileName = Input.getInput();          Object[] ioObject = new Object[2];         ioObject = OpenFile.openFileName(fileName,"READ");                BufferedReader bufferedReader = ioObject[0];            do{            //line = null;             line =  ReadLine.getLine(bufferedReader);             System.out.println(line);         } while (line != null);    }     }   OpenFile.java  package FileIO;  import java.io.*;  public class OpenFile {     static Object[] ioObject = new Object[2];     static BufferedReader bufferedReader = null;     static BufferedWriter bufferedWriter = null;     public static Object[] openFileName(String fileName, String type){          if(type == "READ"){             try{              // FileReader reads text files              FileReader fileReader =  new FileReader(fileName);              // Always wrap FileReader in BufferedReader.             bufferedReader =  new BufferedReader(fileReader);             ioObject[0] = bufferedReader;             System.out.println("you lucky dog, file " + fileName + " was found");            }catch(FileNotFoundException ex) {             System.out.println("FATAL ERROR: File " + fileName + " not found");              System.out.println(ex);          }        }else if(type == "WRITE"){               }else{          System.out.println("FATAL ERROR: type input can only be READ or WRITE");                  System.exit(0);       }        return ioObject;    } }    I'm getting an error on this line in test.java:  BufferedReader bufferedReader = ioObject[0];    incompatible types object can not be converted to BufferedReader.  I'm confused as ioObject[0] is a BufferedReader.

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?


After the update from Windows 8.1 to Windows 8.1 pro all programs were deleted.  At the update dialog they said that you have to reinstall all apps. I understood this to mean only the apps in the store.  Unfortunately windows have not created a recovery point.  Is it possible to go back to windows 8.1 preview by recovering the old partition table?

I would like to try out the  by getting the update through the Store on my current Windows 8 installation. My only concern is that I can't find any information in the  about an upgrade path to the final version.  It states that Windows RT 8.1 Preview will be upgradable to Windows RT 8.1, but how about x86 versions?


I have two files:  file1:  905894 1197693 3703749   file2:  905894   Test1 1197693   Test2 3703749  Test3   I want to get the values in the second column if elements in file 1 column 1 matches any of the words in file 2 column 1.  I know awk can do it, but stuck in reading file 1 and using a loop.

I am using Solaris 10 and so grep options involving -f don't work.  I have two pipe-separated files:   file1:  abc|123|BNY|apple| cab|234|cyx|orange| def|kumar|pki|bird|   file 2:   abc|123| kumar|pki| cab|234   I would like to compare the first two columns of file2 with file1 (search through the entire contents of file1 in first two columns) if they match print the matched line of file1. Then search for the second line of file 2 and so on.   Expected Output:  abc|123|BNY|apple| cab|234|cyx|orange|   The files I have are huge, containing about 400,000 lines, so I would like to make the execution fast.


My website is running on node.js and runs in http on port 3000 I am using NGINX to enable https access so that all pages are served as https I have placed my sitemap.xml and robots.txt inside the public folder of my express app Should the URL's inside be http or https. They say you should not have both in the same file Nginx I assume redirects HTTP traffic to HTTPS   Can someone kindly suggest?

I have changed my website from HTTP to HTTPS.  At this moment, I have the next rewrite rule working to redirect calls for HTTP to HTTPS:  RewriteEngine On  RewriteCond %{SERVER_PORT} 80  RewriteRule ^(.*)$ https://example.net/$1 [R,L]    Should I write the URLs on the sitemap with HTTP or with HTTPS? (including the homepage)


Consider the following thought experiment. Suppose we initialize a parallel plate capacitor with the plates of area $A$ separated by a distance $d$ in empty space. The energy in the capacitor is approximated as $E\approx\epsilon_0 Ad$.  Let a large amount of time pass by. Assume that the distance between the plates increases due to the expansion of the universe (and in that case $A$ increases as well.) Then it seems our capacitor has now gained some potential energy "from nowhere". Now I have read that, though the spacetime metric is observed to be expanding on large scales, it does not follow that spacetime is expanding on small scales. But it might be. Also, I know this is a silly example, as we should not expect laws of household capacitors to hold on cosmological scales. Perhaps someone could come up with a more sophisticated example. What I am getting at, is that in many physical systems, the potential energy of that system is related to the distance between the components of that system. If the distance between the components changed due to the expansion of the universe, it would seem the potential energy of the system also changed. Yet, no work was performed upon the system. What is the discrepancy here? Where did the difference in energy go? (I think this general way of looking of the problem should overcome the objection that spacetime might not be expanding on small scale. Just define our system to occur on some scale where expansion is observed.)

Is the law of conservation of energy still valid or have there been experiments showing that energy could be created or lost?


Let $\alpha =(a_1,a_2,...,a_s)$ be a cycle and $\pi$ a permutation in $S_n$. Then $\pi\alpha\pi^{-1}$ is the cycle $(\pi(a_1),...,\pi(a_s))$.  I'm having trouble understanding the proof of this:  Take $\pi(a_i)$. Then $\pi\alpha\pi^{-1}\pi(a_i)=\pi\alpha(a_i)=\pi(a_{i+1\; (\mathrm{mod}\;\mathrm{s})})$, then follows on from here.  But I'm not understanding how this proves the statement, since it feels like it's proving that $\pi\alpha=(\pi(a_1),...,\pi(a_s))$.

Prove the following in $S_n$:  Let $\alpha = (a_1,a_2,\ldots,a_s)$ be a cycle and let $\pi$ be a permutation in $S_n$. Then $\pi\alpha\pi^{-1}$ is the cycle $(\pi(a_1),\ldots,\pi(a_s)).$     I'm not sure where to even start.


#include<stdio.h> #define POOLNAME_FMT "Hello"  void main() {   printf((POOLNAME_FMT "Cannot allocate %d bytes" POOLNAME_FMT "in pool not enough memory",5));  }   Why does it give segmentation fault when I use double brackets with printf. i.e. printf(( ));?


We have a heterogenous network that has many Apple products within it.   Recently, we had an issue with a duplicate IP that appeared to be interfering with someone's work.  Simple enough, right?  Not on OS X, apparently.  After digging around the Internet and a phone call with Apple Support, who suggested it was our routers (!!), I'm hoping someone here may have a deeper understanding of what's going on here.  I released the address from our internal Linux/ISC DHCPD server manually (it was deleted, server restarted).  I found and XML file generated at /var/db/dhcpclient/leases/en2-1,18:af:61:b7:7d:0 (for whichever device/MAC). Removing this file had no effect. OS X still insists on renewing the address it has had. Our default lease is 24 hours.  Rebooting the Mac after the above had no effect.  ipconfig, unplump/plumb the interface had no effect.  This leads me to believe that OS X is storing this information in some obscure database that I'm unaware of.   As for the documentation, well it basically sucks and didn't tell me much of anything.  Does anyone know how to force the Mac to forget about it's DHCP acquired IP address, completely, and request a new address from the server?   Thanks in advance.

From the Terminal, how can I release and renew my DHCP lease?  Currently, I'm doing the following for the wireless interface, but I'm wondering if there's a better way:  sudo ifconfig en1 down sudo ifconfig en1 up   For the wired interface, replace en1 with en0.


I'm sorry I couldn't be more specific in my question title. I don't have the vocabulary to pinpoint what exactly I have difficulties with yet; therefore, I'll try to explain through examples.  I came across this exercise on College Panda and was confused:  "Neither the employees nor the owner (cares/care) about the customer."  I thought the answer was "care" because "employees" and "owner" could be summarized with the pronoun 'they'.  And you would say, "They(plural) don't care about the customer".  But apparently, the answer is, "Neither the employees nor the owner cares about the customer." Does that mean, when using two nouns in tandem, you are supposed to base the subject/verb agreement on the noun directly preceding the verb?  E.g. with "My daughters and my son play/plays together", the verb "play" must agree with "son"; with "My son and daughters play/plays together", the verb "play" must agree with "daughters"?    Sorry about any confusion.  TL;DR: Please explain why the answer isn't "care"  Thanks in advance!

We have been asked to correct the error in the sentence:     Either he or I is right.   The only possible change that I can think of goes like this:     Either I or he is right.   Am I right? It will be helpful if someone can state the rules for such sentences as I am unable to understand why the first sentence is wrong.


Consider two buttons: - OK - Cancel  Should the positive 'OK' button be placed on the right or left? Is there some rule or convention that needs to be followed in this case. Consider the following image. There's an Approve button and Decline link. - Should the Approve button be on left or right of Decline? - Should the 'Decline' option be a button as well or should it be a link?

Should OK button be on left of Cancel button or vice versa?   Are there any studies suggesting either of the solutions?


$f(x) = x + \int_{0}^{1} (xy^2 + x^2y) f(y) dy$. Find $f(x)$   I've tried taking $\int_{0}^{1} (xy^2 + x^2y) f(y) dy$ to be $k(x)$ since it comes out to be a function of $x$. That transforms our equation to $f(x) = x + k(x)$.  $f(y) = y + k(y) \implies (xy^2 + x^2y)f(y) = (xy^2 + x^2y)y + (xy^2 + x^2y)k(y)$ Now I tried integrating on both sides against $dy$ from $0$ to $1$ in an attempt to find $k(x)$   $\int_{0}^{1} (xy^2 + x^2y)f(y).dy = k(x) = \int_{0}^{1} ((xy^2 + x^2y)y + (xy^2 + x^2y)k(y)).dy$  But I got stuck trying to integrate the right hand side. Any solutions or ideas are appreciated.

If $f(x)=x+\int_{0}^{1}[xy^2+x^2y]f(y)dy$ where $x$ and$y$ are independent variable.Find $f(x).$  I tried to solve it.  $f(x)=x+\int_{0}^{1}[xy^2+x^2y]f(y)dy$  $f(x)=x+x\int_{0}^{1}y^2f(y)dy+x^2\int_{0}^{1}yf(y)dy$  I applied integration by parts but the expression did not simplify.Please guide me to reach the answer $f(x)=x+\frac{61}{119}x+\frac{80}{119}x^2.$


I’m trying to write a simple finite state automaton in TikZ/LaTeX—The code should be quite self-explanatory:  \documentclass[a4paper,10pt]{article}  \usepackage{amsmath} \usepackage{tikz}  \begin{document} \begin{tikzpicture}   \tikzstyle{state}=[circle, draw]   \tikzstyle{endstate}=[circle, draw, double]    \node (start) at (-1, -1) {};   \node (AS) at (1, 1) [state]{$A_S$};   \node (AF) at (3, 1) [endstate]{$A_F$};    \draw [->] (start) to (AS);   \draw [->] (AS) to node [auto, near start] {a} (AF); \end{tikzpicture}  \end{document}   Unfortunately, LaTeX completely ignores the node positions, i.e. all three nodes are placed on top of each other.   A similar code (which is quite long, so I won’t post it here) used to work previously (when I was using a GUI, mikTEX, I think), but now produces the same erroneous output when compiled via pdfTeX 3.1415926-2.5-1.40.14 (TeX Live 2013/Debian), which makes me think it’s not the code itself which is causing problems, but some configuration I may have missed.  How do I get the nodes to adhere to the given positioning?

I have the following Tikz picture:  \begin{tikzpicture}   \node (a) {A};   \node [below=2cm of a] (b) {B}; \end{tikzpicture}   When I compile this code with PDF-LaTeX, I get the expected result: "B" appears 2 cm below "A".  When I compile the exact same code with plain LaTeX, in the DVI file, "A" and "B" are in the same position, mashed together.  In the PS file, after another re-compilation, they appear correctly again.  Is there some way or workaround to work with PGF/Tikz with positioning straight with the DVI preview?


At the end of Interstellar when "Cooper Station" is shown orbiting around Saturn, why does the ball while playing baseball travel to a different side and the houses appear to be upside down and there seems to be a "Pipe" effect?

I'm confused about the scene where Matthew McConaughey wakes up in this new habitat of the humans. I presume that it's not earth, he's on another planet. And why does the land look like a tunnel there? Is it the black hole where all are residing now?


This morning I attempted to upgrade from 19.04 to 19.10.  However, during the upgrade my laptop went to a black screen with a blinking dot in the top right corner.  It stayed like this for hours.  I then forced a shutdown.  Now when I boot the laptop up it goes to a blank screen an will not fully boot up.  I am running a dual boot with windows 10.  I can still boot up windows. Can I attempt to do a full install of 19.10 from a USB drive?  Or what do you recommend?

Yesterday I started the upgrade from 12.10 to 13.04, but I interrupted it because it was taking too long. Now if I restart it, it doesn't proceed.  Is there any possibility to clean the mess it left when I interrupted it and make a clean restart of this update?


I recently went on to the yearly User Reputation Leagues for Puzzling, and to my surprise, some of the entries had scrollbars for seemingly no reason:    I investigated further, and it appears that these scrollbars appear on every 4th entry (though this changes with zooming in or out). Furthermore, not only Puzzling is affected, nor only the yearly rankings (here is an image of Programming Puzzles and Code Golf on quarterly rankings):       What is causing this to happen? Can this be fixed?   Specs: Windows 10, Google Chrome 62.0.3202.75, full-screen, screen resolution 1920x1080, no userscripts, only AdBlock plugin (but still occurs if disabled)

When using Chrome 62.0.3202.94 (Official Build) (64-bit) on Windows 10 Pro Fall Creators Update, I get a scroll on some of the posts in the .  Also tested Firefox 57.0 (64-bit), Edge 41.16299.15.0 and IE11, and no scroll appear on those.


What do I enter as the Username and password when I boot up Kali Linux for the first time? I have tried everything I can think of but did not work. Thanks, Lake

I installed Kali Linux OS on my hard disk and set nothing as username and password. Now at the time of login it ask for localhost username and password. I tried root and toor as default but didn’t worked for me.


I want to install the following rpm from some reason RPM is stuck or freeze and not install the RPM package also I can't stop it by control C,   root]# rpm -Uvh --repackage /var/tmp/bash-2.05b-41.8.i386.rpm   OR   root]# rpm -Uvh  /var/tmp/bash-2.05b-41.8.i386.rpm

I want to install the following rpm, but for some reason RPM is stuck or frozen and will not install the RPM package. I can't stop it by control-C.  Please advise what could be the problem?   root]# rpm -Uvh --repackage /var/tmp/bash-2.05b-41.8.i386.rpm   ..... no output here  OR   root]# rpm -Uvh  /var/tmp/bash-2.05b-41.8.i386.rpm   RPM verification  ( the last lines )    rpm -Uvvh /var/tmp/bash-2.05b-41.8.i386.rpm   .   .   .    D: installing binary packages   D: closed   db index       /var/lib/rpm/Pubkeys   D: closed   db index       /var/lib/rpm/Conflictname   D: closed   db index       /var/lib/rpm/Providename   D: closed   db index       /var/lib/rpm/Requirename   D: closed   db index       /var/lib/rpm/Packages   D: closed   db environment /var/lib/rpm/Packages   D: opening  db environment /var/lib/rpm/Packages joinenv   D: opening  db index       /var/lib/rpm/Packages create mode=0x42   D: mounted filesystems:   D:     i    dev bsize       bavail       iavail mount point


I want to get the latest N rows of a table. Something like this:  CREATE PROCEDURE [dbo].[spProducts]     @Rows int AS     SELECT TOP(50) *     FROM tblProduct   But if the number of rows is not specified in the input-param @Rows int, all rows should be outputted (select * (all)) Do I need to implement If/Else-statements, or is there maybe a shortcut that can turn the input-param @Rows intinto an asterix?

How can I have a dynamic variable setting the amount of rows to return in SQL Server? Below is not valid syntax in SQL Server 2005+:  DECLARE @count int SET @count = 20  SELECT TOP @count * FROM SomeTable


I'm tring to write a method the creates an empty rectangle inside which there is another white rectangle surrounded by a pattern of lines (contained in the for loop).  Whenever the method is run I get a null point exception on first line of the loop.  I can't work out what's going on... please help.      public void displayArea () {             Graphics g = chartPanel.getGraphics();             int Xpos = 30;             int Ypos = 50;             int displayWidth = 300;             int displayHeight = 280;             int borderPatternY = 10;             int borderPatternX = 10;               for (int count = 0; borderPatternY <= 300 || borderPatternX <= 280; count++){                 g.drawLine(30, borderPatternY, 330, borderPatternY);                 g.drawLine(borderPatternX, 50, borderPatternX, 320);                  borderPatternX = borderPatternX + 10;                 borderPatternY = borderPatternY + 10;             }              g.setColor(Color.white);             g.fillRect(Xpos + 10, Ypos + 10, displayWidth-10, displayHeight -10);              g.setColor(Color.black);             g.drawLine(Xpos, 60, Xpos + displayWidth, 60);             g.drawLine(Xpos, 120, Xpos + displayWidth, 120);             g.drawLine(Xpos, 180, Xpos + displayWidth, 180);             g.drawLine(Xpos, 240, Xpos + displayWidth, 240);         }

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


So there's a first time question, and yes surprisingly it's not that great.. what to do?   Vote to close,  Attach a snarky comment and get 10 million (exaggeration obviously)  up-votes   Sit back and edit the question (no praise) to try and enable it to get the best answer possible - which actually someone else (unless you're houdini!) will likely get the up-votes for by the time you've finished editing   see:   Q asked, Q downvoted 4 times (so far).. comments have all got huge up-votes, question has 1 close vote (that's why the comments I suppose no really good reason to close or it would be by now?) - Q has been edited 8 times (last by me) - I feel sorry for the question asker now, as I think it's lost...   yes I would now vote to close out of sympathy as people are likely only checking that question to add a snarky up-vote on a comment but really don't have a reason to close, nor can or will they answer.. and that's sad  so what to do if a "newb" q is under attack

There is a distinct decline in the level of civility on all the sites here.  Some of this is due to new users coming in and posting spam and other nonsense, but the off-topic and downvote buttons are doing a pretty good job of keeping this under control. Unfortunately, a lot of this is coming from more experienced users, and the site's built-in moderation system does not (and probably cannot) handle this very well.  Folks are rushing to pound new users down with "this belongs on meta!", "this is off topic", "this is a duplicate!" and "read the Help!". (Which is correct, but should be done nicer) All this, of course, is accompanied by a flurry of downvotes.  This is not very welcoming to new users who don't know about meta, the Help, or what counts as off-topic. Now I am not proposing that we just allow off-topic, meta, or duplicate questions.  However, I think we could be gentler in the way we express these sorts of things.  Explain what meta and the FAQ are and provide useful links.  Just using please and thank-you when asking folks to read the FAQ or post something on meta would be an improvement.  I also think we could rein in the downvoting a bit.  Not that we shouldn't vote stuff down, but unless a new user's post is clearly spam, voting it down to -1 or -2 should be sufficient to send a message without piling on. I like Stack Exchange and I want it to become a resource for everyone, not just an elitist site for high-rep users on the sites.


This question was inspired by an answer in . Suppose the Player Characters are attempting to protect their little village from a huge monster, Godzilla in this case. Obviously they'd get xp if they murdered Godzilla with their swords or banded together to sing a moving song to convince the enormous beast to seek a meal elsewhere. However, would they get Xp for luring Mothra into Godzilla's path and having the two titans duke it out (thus preventing their village from being destroyed)?  The question that inspired this was specific for 5th edition, so I'd prefer answers from that ruleset, though if any of the older systems have an interesting take on it, I'm happy to read it.

Some thug bandits set up a road block on the main road to extract a toll from passersby. It was twilight when my party encountered them. They used the Rogue to scout ahead, and they ultimately decided to bypass them by taking the long way around with some stealth to avoid the bandits.  Is there RAW justification that I should award XP as if they actually fought and killed the bandits? (5 x 1/8 CR)


recently installed Xubuntu, and upgraded to 14.04 earlier today. When I use Software Updater to search for updates it tells me there are no updates available. Here's what I did in terminal:  sudo -i apt-get update atp-get dist-upgrade (no problems so far)   restarted laptop  sudo -i    update-manager -d   At this point I get this warning:  root:estimate_kernel_size_in_boot() returned '0'?   It then continues and opens Software Updater, which tells me the system is fully up to date. How do I fix this?  EDIT: To clarify, I'm using version 14.04 right now, I'm trying to upgrade to version 14.10, and then to 15.04

So I have Ubuntu installed on my pc, and I want to upgrade to the new Ubuntu which was just released. When I check for any new updates it doesn't show any upgrades to the new release. How can I fix this? Thanks!


I have an ArrayList<String> containing a list of 'Building Key' numbers. Forgive me if this has been answered before I am struggling to find a solution by searching. public class SortKeyNumbers {          public static void main(String args[]) {                  ArrayList<String> keys = new ArrayList<>();                  keys.add("1");         keys.add("10");         keys.add("2");         keys.add("3");         keys.add("3B");         keys.add("12");         keys.add("12C");         keys.add("21");         keys.add("32");                  Collections.sort(keys);                  System.out.println(keys);              }      }  This gives me an output of [1, 10, 12, 12C, 2, 21, 3, 32,3B] I know that this is as expected from Collections.sort What I need is an output of [1, 2, 3, 3B, 10, 12, 12C, 21, 32] What I am asking is help to write the correct comparator or compareTo to achieve the desired output.

I need to write a Java Comparator class that compares Strings, however with one twist.  If the two strings it is comparing are the same at the beginning and end of the string are the same, and the middle part that differs is an integer, then compare based on the numeric values of those integers.  For example, I want the following strings to end up in order they're shown:   aaa bbb 3 ccc bbb 12 ccc ccc 11 ddd eee 3 ddd jpeg2000 eee eee 12 ddd jpeg2000 eee   As you can see, there might be other integers in the string, so I can't just use regular expressions to break out any integer.  I'm thinking of just walking the strings from the beginning until I find a bit that doesn't match, then walking in from the end until I find a bit that doesn't match, and then comparing the bit in the middle to the regular expression "[0-9]+", and if it compares, then doing a numeric comparison, otherwise doing a lexical comparison.  Is there a better way?  Update I don't think I can guarantee that the other numbers in the string, the ones that may match, don't have spaces around them, or that the ones that differ do have spaces.


I find that a lot of new users will make one of several mistakes asking questions:   failure to check Google failure to show any effort failure to read any introductory material on the language in question very bad English   Many users will respond by downvoting the question (maybe flagging or voting to close) and moving on. The idea of  is nothing new, but the upvoted comments are often something like "what have you tried?", which isn't as useful to new users as a more thorough explanation. To a new user who may barely understand English, we just look like a black-box full of jerks.  Given that any comments explaining the issues tend to get upvoted, I propose some small set of "canned" comment buttons that appear after I've downvoted a question. Clicking on them would do one of the following:   Leave an anonymous comment Leave a named comment Leave a vote for the user to be notified (via comment or something else)   These comments could include links to the FAQs, which would save us the trouble of putting links in every bad post, and would be more useful to the poster than a single snarky comment with three upvotes.

Every tag has its questions that make the same mistake(s) over and over and over again. (But some tags more than others.) That's where Benjol's  comes in. The only downside to this great script is that it uses local storage, so if you switch browsers or machine, you lose your data! The team  in incorporating it into the core (at least not at the moment) so  this question may serve to collect good snippets here in lieu of a real central repository. To use, click "edit", and fetch the snippet's markdown source code.  Note: For these snippets to be easy to copy&paste, do not use the editor's linking method, but inline links, like so: [This is a link](http://www.this.is.the.url)    might help too:  See [so].


Question:     Find all the zeros of the equation $4^x+6^{x^2}=5^x+5^{x^2}$.   Using the fact 4=5-1, 6=5+1, we can change the equation: $$f(x)=[(5-1)^x-5^x]+[(5+1)^{x^2}-5^{x^2}]=0$$  However... I cannot continue the solution from here. I tried to solve with the derivation of $f(x)$, but nothing I can find.  Actually, I found the zeros using the graphing calculator: $x_1=0$ and $x_2=1$ But, I want to know in a mathematical way. What do you think is the most important key point to the problem? Thanks for your advice.

Find all real solutions to the equation:$$4^x+6^{x^2}=5^x+5^{x^2}$$  Obviously $0$ and $1$ satisfy this equation, but here $x$ is a real number, and I do not know how to do the next step, in fact, I guess this equation is not in addition to $0$ and $1$ other than the root. But you know, I need a proof! Could anyone help me? Thanks a lot!


I like to open most sites on my portrait mode (1050 x 1680) monitor.  A few days ago, Stack Exchange sites started requiring a horizontal scroll bar when opened on this monitor in each of my installed browsers. (Firefox, Chrome, I.E.)   Did we gain any shiny new functionality to justify the wider screen requirements or is this simply a function of designers only considering presentation on landscape mode monitors? Is it reasonable for the site to have it's width requirements reduced?

Update: this change is now live across the network. You'll still see some narrow 220px ads because it's going to take us a good while to update all of the old ads, but if you see any other style issues, please report here on meta.   Stack Exchange sites are ad-supported. We run relevant, unintrusive ads that don't get in your way--but they help us keep the lights on. Even sites that don't have paid external ads usually have a few internal ones, used to promote other sites on the network and . We don't run a lot of ads, and , but the ones we do run have one crippling problem:   The sidebar ads are currently a weird non-standard size. Yes, standardized ad sizes are . And apparently if you ignore them, folks are more reluctant to advertise and have a tendency to make uglier ads. We don't like ugly ads, and we do like selling ad space. So starting next week, we will switch to the industry-standard size for sidebar ads. The new ad units will be 300x250 and the sidebar will be expanded to 300px wide to accommodate them. We won't be reducing content size or doing any sort of weird overlay; the ads and other sidebar content will just extend an additional 80 pixels to the right.  However, even though the sidebar is growing by 80 pixels, by reclaiming some margin space, the overall page width is only increasing by 60px. Here's what it's going to look like:     of Stack Exchange users won't be affected by this change. Either they already use a viewport big enough to accommodate the new width, or they already use a viewport too small to accommodate the existing width. (And those who do find themselves affected won't be losing any content, the juicy stuff we all come here to look at. They'll just see a bit of the sidebar cut off unless they scroll.)  We're planning to roll this out on Tuesday, January 12. (There will be a transition period after that date while we work on getting all ad types swapped over; you'll still see some of the old size ads during that time.) In the meantime, let us know your thoughts.


Can I try Canonical Distribution of Ubuntu OpenStack with less than 7 machines?

Looking at , I see three different ways to do this and the third option "Install Ubuntu Cloud Infrastructure from packages: the hard way" seems like the option for me, but not even basic  steps are included in the document.  The first option doesn't seem to fit my scenario because I don't want to run a live image because I have a couple machines I'd like to use if possible--one beefy for VMs and one wimpy for infrastructure services (if OpenStack will even work that way, maybe I'm confusing it with Eucalyptus)  I don't think I can use the second option because I don't have 10+ machines to set up MAAS, though that does sound pretty cool.    Is this a reasonable scenario? Where can I find at least a basic set of steps?


Edit: I am aware this question was already answered, I just didn't find it. Thanks to everyone who pointed me in the right direction.  Why is it that when I run the following code the answers are not 0?  a = .1 d = .3  x = - a - a - a + d y = a + a + a - d  print(f'x is {x}') print(f'x is {y}')   In other words -.1 - .1 - .1 + .3 and .1 + .1 + .1 - .3  Instead I get the following:  x is -5.551115123125783e-17 y is 5.551115123125783e-17   It's almost zero but it isn't zero.  Is this due to how the python language works, is it a hardware thing, or something else?  I can't seem to find anything on stack overflow concerning this and would really like to understand what is going on.

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


Sorry, I am new to this , but the app I am developing keeps on crashing after I go to a certain menu, can you teach me on how to fix it? Here is my logcat together with my coding and xml file below:  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference         at com.example.TTTTT.ifelse.alarm.onCreate(alarm.java:27)   Code:          btnAlarm1 = (Button) findViewById(R.id.btnAlarm);         btnstop = (Button) findViewById(R.id.btn1);         txtSeconds1 = (EditText) findViewById(R.id.txtSeconds);          btnAlarm1.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View view) {                 try {                     int i = Integer.parseInt(txtSeconds1.getText().toString());                     Intent intent = new Intent(alarm.this, AlarmReceiver.class);                     PendingIntent pendingIntent =                             PendingIntent.getActivity(alarm.this, 2, intent, PendingIntent.FLAG_CANCEL_CURRENT);                     AlarmManager am = (AlarmManager) getSystemService(ALARM_SERVICE);                     am.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + (i * 1000), pendingIntent);                      if (mToast != null) {                         mToast.cancel();                     }                     mToast = Toast.makeText(getApplicationContext(), "Alarm set in:" + i + "seconds", Toast.LENGTH_LONG);                     mToast.show();                  }catch (NumberFormatException e)                 {                     if (mToast != null)                     {mToast.cancel();}                     mToast = Toast.makeText(alarm.this, "Enter Number", Toast.LENGTH_LONG);                     mToast.show();                     Log.i("MainActivity", "Number format exception");                 }             }          });         btnstop.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 Intent intent = new Intent(alarm.this, AlarmReceiver.class);                 PendingIntent pendingIntent = PendingIntent.getActivity(alarm.this, 2, intent, PendingIntent.FLAG_CANCEL_CURRENT);                 AlarmManager am = (AlarmManager) getSystemService(ALARM_SERVICE);                 am.cancel(pendingIntent);                  if (mToast != null) {                     mToast.cancel();                 }                 mToast = Toast.makeText(getApplicationContext(), "Alarm Cancelled!", Toast.LENGTH_LONG);                 mToast.show();             }         });      }   }  *Xml file here    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" android:paddingBottom="@dimen/activity_vertical_margin" tools:context="com.example.TTTTT.ifelse.Alarm">     <EditText     android:id="@+id/txtSeconds"     android:inputType="number"     android:layout_width="match_parent"     android:layout_height="wrap_content" />     <Button     android:text="Set Alarm"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:id="@+id/btnAlarm"     android:layout_below="@+id/txtSeconds"     android:layout_centerHorizontal="true" />      <Button     android:text="Stop Alarm"     android:id="@+id/btn1"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_below="@+id/btnAlarm"     android:layout_centerHorizontal="true" />       </RelativeLayout>*

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


My question is basically this:     Does a maximally entangled state stay maximally entangled under the time evolution?   Assume our Hilbert space is $\mathcal{H}_A \otimes \mathcal{H}_B$. At the time $t=0$, the states is $\rho_{AB}$ such that $\text{Tr}_A \rho_{AB}=\frac{1}{n_A}id_B$ and $\text{Tr}_B \rho_{AB}=\frac{1}{n_B}id_A$. Now assume at the time $t$, the density matrix is $\rho_{AB}(t)$. Is it right that $\rho_{AB}(t)$ is a maximally entangled state? (If not, under what assumptions one can guarantee this?)  TEMP: Is it right?  $\text{Tr}_A \rho_{AB}(t)=\sum_A \left<e^A_i(t),\rho_{AB}(t)e^A_i(t)\right>=\left<U(t)e^A_i(0),U(t)\rho_{AB}(0)U^{-1}(t)U(t)e^A_i(0)\right>=\left<e^A_i(0),U^{-1}(t)U(t)\rho_{AB}(0)e^A_i(0)\right>=\left<e^A_i(0),\rho_{AB}(0)e^A_i(0)\right>=\text{Tr}_A \rho_{AB}(0)=\frac{1}{n_A}id_B$  So Maximally entangled states remains maximally entangled.

We consider two spin 1/2 systems that are described by the following Hamiltonian: $$ H^{12} = jZ^{1} \otimes Z^{2} \tag{1}  $$  The composite system is initialised in the state: $|\psi^{12}(0)\rangle=|x_+,x_+\rangle,$ which written in the $z$ basis ($z_+$ being spin up state along the z dimension), is:  $$|\psi^{12}(0)\rangle = 1/2(|z_+,z_+\rangle+|z_+,z_-\rangle+|z_-,z_+\rangle+|z_-,z_-\rangle).\tag{2} $$  Given the Hamiltonian in $(1)$, the unitary time evolution is $U(t)=e^{-iH^{12}t/\hbar},$ and after a time $t_0=\pi \hbar/4j,$ $U(t)$ becomes   $$ U(t_0)=e^{-i\frac{\pi}{4}Z^1\otimes Z^2} \tag{3} $$   Knowing $U$ at $t_0,$ the composite state evolved by this Hamiltonian upto $t_0$ becomes:  \begin{align*} |\psi^{12}(t_0)\rangle =& U(t_0)|\psi^{12}(0)\rangle \\ =& 1/2(e^{-i\pi/4}|z_+,z_+\rangle+e^{i\pi/4}|z_+,z_-\rangle+e^{i\pi/4}|z_-,z_+e^{-i\pi/4}\rangle+e^{-i\pi/4}|z_-,z_-\rangle) \tag{4} \end{align*}  So it seems that just by evolving the separable initial state $(2)$ that was not an eigenstate, for a certain amount of time, the composite system suddenly becomes entangled $(4).$    Once the system has become entangled, will further evolving the system according to $U(t)$ dis-entangle the system again at some point in time? I.e. do we expect regular transitions between separable to entangled states of the composite system? Or, once the system has become entangled, it maintains its entangled state?  If the change between separable and entangled is expected to occur during the time evolution of this system, then it means the involved subsystems are constantly undergoing transitions from pure (when in separable state) to mixed states (when the composite state is entangled), is such behaviour physically allowed?


Typically, this would involve duplicate questions. I searched SO-Meta to see if this question was already answered, and I found a few, but they all related to answering questions duplicated on the same SE site.  In this case, I'm talking about duplicate or near duplicate questions found on different SE sites. And to be clear, I'm not talking about cases where the same user might cross post the same question on multiple SE sites. I mean 2 questions by different users and not obviously copy-pasted from one to the other, but still essentially duplicates.  I don't have any specific examples at hand, but I've seen questions on Stack Overflow or Super User or Server Fault or Programmers.SE, and seen a duplicate or near duplicate on one of the other sites. I'm talking duplicate to the extent that sometimes they could both be answered with the same answer.  So my question is, if I can answer the question, is it OK to post the same or nearly same answer to the questions on both sites, or should I make significant efforts to hide the fact that the answers are the same?

I recently asked a  on security.stackexchange.com. The question was related to XSS so in my opinion it belonged to the security website.  There was a comment on the question saying that a similar question exists on SO and my question was a duplicate (I think he gave it a down vote). The guy was right but the question was asked on another website (SO). There may be a case when person asking a question might not have an account with the other website.  Is it a good practice to mark questions duplicate if you have seen a similar question on some other website?