Determinant of $2\times 2$ block matrices

I am trying to solve the problem : Let $A,B,C,D,$ be commuting $n\times n$ matrices over the field $F$ (it is not given whether any of these matrices are invertible). Show that the determinant of the $2n\times 2n$ matrix $$\begin{bmatrix} A&B\\C&D \end{bmatrix}$$ is $\det(AD-BC)$.  I know that there is an answer given in a paper, which mentions working over $F[x]$. However, I have come up with the following idea:     Motivated by the adjoint formula for the inverse, we get that   $$\begin{bmatrix} A&B\\ C&D \end{bmatrix} \begin{bmatrix} D&-B\\ -C&A \end{bmatrix}= \begin{bmatrix} AD-BC & BA-AB\\ CD-DC&AD-BC \end{bmatrix} = \begin{bmatrix} AD-BC & 0\\ 0&AD-BC \end{bmatrix} $$   Hence   $$\det \left(\begin{bmatrix} A&B\\ C&D \end{bmatrix}\right)\det\left(\begin{bmatrix} D&-B\\ -C&A \end{bmatrix}\right)= \det(AD-BC)^2$$   But then    $$\det\left( \begin{bmatrix} A&B\\ C&D \end{bmatrix}\right)= -\det\left(\begin{bmatrix} B&A\\ D&C \end{bmatrix}\right)= -\det\left(\begin{bmatrix} B&D\\ A&C \end{bmatrix}\right)= \det\left(\begin{bmatrix} D&B\\ C&A \end{bmatrix}\right) $$   Now, thinking of $\det$ in terms of permutations, suppose for a given permutation in the $\det$ sum that we pick $m$ elements in the first $n$ rows from the $-B$ side. Then we must also pick $m$ elements from the last $n$ rows from the $-C$ side; i.e. the sign changes must cancel out. Thus,   $$\det\left(\begin{bmatrix} D&B\\ C&A \end{bmatrix}\right)=\det\left(\begin{bmatrix} D&-B\\ -C&A \end{bmatrix}\right)$$   which shows that   $$\det \left(\begin{bmatrix} A&B\\ C&D \end{bmatrix}\right)=\pm \det(AD-BC)$$   Is there a way complete the proof from here? All I need to show is that $$\det \left(\begin{bmatrix} A&B\\ C&D \end{bmatrix}\right)\quad\text{ and }\quad \det(AD-BC)$$ have the same sign.


Got a weird (or neat) bug here.   was migrated from music.SE to sound design beta.  I happen to remember that I upvoted if not all, all but one of the other answers on the question.  However, since it has been migrated to sound.SE, although the answers preserved their votes from music.SE, I am able to upvote them again.    I remember, for instance, that I was the only one to have upvote the accepted answer.  My upvote is still there, but I can upvote it again, giving me a double-vote power.  Not a critical bug, but still a bug that could use working out.


What is Front Porch and Back Porch of a video signal in CRT display?

What is a Front Porch used for?  What is a Back Porch used for?  What does it mean by active video?


How to round a number to n decimal places in Java

What I would like is a method to convert a double to a string which rounds using the half-up method - i.e. if the decimal to be rounded is 5, it always rounds up to the next number. This is the standard method of rounding most people expect in most situations.  I also would like only significant digits to be displayed - i.e. there should not be any trailing zeroes.  I know one method of doing this is to use the String.format method:  String.format("%.5g%n", 0.912385);   returns:  0.91239   which is great, however it always displays numbers with 5 decimal places even if they are not significant:   String.format("%.5g%n", 0.912300);   returns:  0.91230   Another method is to use the DecimalFormatter:  DecimalFormat df = new DecimalFormat("#.#####"); df.format(0.912385);   returns:  0.91238   However as you can see this uses half-even rounding. That is it will round down if the previous digit is even. What I'd like is this:  0.912385 -> 0.91239 0.912300 -> 0.9123   What is the best way to achieve this in Java?


How can find location of PHP session save path?

I want to know the function name that tells the location of where the session is stored.


Can someone explain the outcome to the follow scenario:  Buyer A places a limit order to buy 100 shares at $8.00, Seller B places a sale limit order at 7.50 for 40 shares.  What price would Seller B receive for his shares?  I suspect $8.00, is that correct?  B was the last to place the order so I presume $8.00.  Whereas if the placement of the orders was reversed and B placed sale order at $7.50 and A placed a buy order at $8.00 that A would received 40 shares at $7.50.  Clarification anyone?


How do I install the latest Python 2.7.X or 3.X on Ubuntu?

I want to install the latest Python tarball on Ubuntu, downloaded from .  Is this is a correct way to install?  ./configure make make install   If not, how do I do that?


How does one effectively assign mathematics homework when all answers to all questions are available online?

In my department, we typically adopt textbooks that are very refined, sometimes in their 7th or 8th edition. Because these books have been around for so long, all of the homework problems have been worked out in full detail, and are easily found online. So it seems pointless to assign and grade homework since student can so easily copy the answers instead of working them out themselves. But if we do that, it seems like we're then eliminating a very important learning activity.  Many of my colleagues address this by not giving very many (if any) points for homework in the final grade. They sometimes give quizzes (which takes a lot of class time) to check whether the homework was absorbed. One feature of homework is that it is done outside of class, so that the class period can be used to discuss new material. I'm concerned that taking class time to force the issue of actually "doing" the homework will detract from the other aspects of the course.  I still think that mathematics is not a spectator sport, and most of the learning occurs when the students struggle with a good set of exercises and eventually find the answers on their own. This is especially true in courses that require proofs.  I've explained to my students that if they short-cut this self-discovery process, then they're limiting their learning opportunities. Still, many students copy answers.   So, in this age where all information is so easily accessible, how should we respond with how we assign homework so that students will produce their own ideas rather than copying the work of others? How do we re-enforce the idea that learning mathematics is learning how to find answers rather than just getting a copy of the answers?


Is there really no way to integrate $e^{-x^2}$?

Today in my calculus class, we encountered the function $e^{-x^2}$, and I was told that it was not integrable.  I was very surprised. Is there really no way to find the integral of $e^{-x^2}$? Graphing $e^{-x^2}$, it appears as though it should be.   A  on Gaussian Functions states that   $$\int_{-\infty}^{\infty} e^{-x^2} dx = \sqrt{\pi}$$  This is from -infinity to infinity. If the function can be integrated within these bounds, I'm unsure why it can't be integrated with respect to $(a, b)$.  Is there really no way to find the integral of $e^{-x^2}$, or are the methods to finding it found in branches higher than second semester calculus?


How to calculate determinant of matrix with 9's everywhere off-diagonal?

I need help about this question for my algebra exam. I would be very thankful if someone could help me solve this. I should calculate determinant of this $n \times n$-matrix: $$     \begin{pmatrix}     1 & 9 & \cdots & 9 \\     9 & 2 & \cdots & 9 \\     9 & 9 & \cdots & 9 \\     \vdots & \vdots & \ddots & \vdots \\     9 & 9 & \cdots & n \\     \end{pmatrix} $$ where $n$ is a nonnegative integer.


Why is the gold color code not used for Gold Materials

I am looking at how to create a realistic looking gold material (for instance for ingots). So I am looking at a "pure gold" material. When I google I find this #FFD700 hex value for the . This is a very saturated color of red and green (and NO blue). When I use that color for a simple glossy shader then I get this image. Somehow this color does not feel right ...    I also found a  at blend swap.     The shader is much more complex and a mix of colours is used (mixing forecolor and middle color and then mixing again with a back color).   Can someone explain this? Why this mixing of colors? And why is the Gold color code (#FFD700) not being used in this shader setup? Most people use a color with some blue in it.  How to construct a realistic gold shader? And what color to be used?


Is there somewhere I can buy a 20.04 disk

I updated my HP computer from 18 to 20.04.  Google Chrome crashes, I have no sound.  I have read thru many of the questions and tried the given solutions.  When I try command line nothing seems to work.  Someone suggested reinstalling from disk.  I downloaded and unetbootlin but because I cant do anything command line I cant create a bootable disk.  So is there somewhere I can buy a disk?


Is there a word out there describing an overly caring parent? E.g. a mother who is constantly calling her daughter, asking where she is, etc.


Null deviance & Residual deviance meanings?

My model is as follows: model2 <- glm(cbind(ncases, ncontrols) ~ agegp + unclass(tobgp)                                          + unclass(alcgp),               data = esoph, family = binomial()) summary(model2)  and my result is: Call: glm(formula = cbind(ncases, ncontrols) ~ agegp + unclass(tobgp) +       unclass(alcgp), family = binomial(), data = esoph)    Deviance Residuals:       Min       1Q   Median       3Q      Max    -1.7628  -0.6426  -0.2709   0.3043   2.0421      Coefficients:                 Estimate Std. Error z value Pr(>|z|)      (Intercept)    -4.01097    0.31224 -12.846  < 2e-16 ***  agegp.L         2.96113    0.65092   4.549 5.39e-06 ***  agegp.Q        -1.33735    0.58918  -2.270  0.02322 *    agegp.C         0.15292    0.44792   0.341  0.73281      agegp^4         0.06668    0.30776   0.217  0.82848      agegp^5        -0.20288    0.19523  -1.039  0.29872      unclass(tobgp)  0.26162    0.08198   3.191  0.00142 **   unclass(alcgp)  0.65308    0.08452   7.727 1.10e-14 ***  ---  Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1    (Dispersion parameter for binomial family taken to be 1)        Null deviance: 227.241  on 87  degrees of freedom  Residual deviance:  59.277  on 80  degrees of freedom  AIC: 222.76    Number of Fisher Scoring iterations: 6  With this results of null  deviance being higher than residual deviance, can I conclude that it is a good sign since more than a single parameter explains the model better? Or how else can i interpret this result?


Have the question voting patterns changed after increasing question upvote points to 10?

Are there any statistics that would show changes in voting patterns across SE sites since there was a change in the reputation system rewarding question upvotes with 10 points?  I am asking about voting patterns - numbers of votes cast up or down, not impact on users' reputation.   There are few possible outcomes:   Nothing has changed; voting counts on questions have not significantly changed There are more upvotes cast to questions There are more downvotes cast to questions   Are there any significant differences between different sites?


What's the key difference between HTML 4 and HTML 5?

What are the key differences between  and ?  Please keep the answers related to changed syntax and added/removed html elements.


Let $G$ be a group of order 35. Show that $G \cong Z_{35}$  Now, I am going to assume that this is a LaGrange based question. Also, I know that in order to be isomorphic, it must be one to one and onto.


Proof in Intuitionistic logic: $\neg \neg A \to \neg \neg B \vdash \neg \neg (A \to B)$

I have a problem with proving the below sequent in intuitionistic logic: $$ \neg \neg A \to \neg \neg B \vdash \neg \neg (A \to B) $$ I stuck here:  What should I put in $6th$ line? Is my approach even correct? I noticed that Generally, I have problems with proving sequents with double negation in intuitionistic logic. Is there any pattern for solving such examples?


Wormhole time machine and violation of uncertainty?

Let's asssume we have a wormhole that allows sending info to the past and receiving information from the future.  Next, we have a particle moving in two dimensions, for which we can evaluate $ p_{y} $ and $ x $ at every instant of time.  Also we can receive from the future the values of $ p_{x} $ and $ y$, so we can know without uncertainty the values $ x, p_{x}, y , p_{y} $. It is an apparent violation of uncertainty principle ??, or not ? :)


How to launch a command on network connection/disconnection?

I have a wifi connection that requires to authenticate using a web form once the wireless link is established. I know how to automate the authentication with a script that uses curl/.  But how can I ask Windows to call my script every time I connect to a particular network connection?  I would be also interested in receiving the name of the wireless profile or the ESSID on the command-line of my script.


Refresh jQuery functions of the page after Ajax call.

I am implementing comments section using ajax. Comments have options reply and delete. When they are clicked, reply form or delete confirm options are shown.    After clicking delete, it expands :    The problem is that after a new comment is posted through ajax, jquery for the new comments aren't loaded and so these buttons don't work.  How do I reload the jquery of the page without page refresh and get these new comments to work? Any solution? Thanks !


I am running an intel built machine but the 13.10 download file has AMD on it. Will this cause me any issues when trying to install 13.10 on the machine?  Is there an Intel specific download?  Thank you.


I'm looking for a way to force SSL and www.  I've been able to force both separately but together I keep running into redirection issues. The following code works when handling a URL in this format: http://example.com and properly redirects to https://www.example.com but when the incoming URL is https://example.com it will not forward to https://www.example.com - Any suggestions?  EDIT: it should also send http://www.example.com to https://www.example.com.  RewriteCond %{REMOTE_ADDR} !127\.0\.0\.0 RewriteCond %{SERVER_PORT} 80 RewriteCond %{HTTP_HOST} !^www.example\.com$ RewriteRule ^(.*)$ https://www.example.com/$1 [R,L]


I have noticed that zsh has a lot of things I see in emacs. I can make a selection with ctrl+space and selecting a region. I can make copies just like in emacs while I stay inside zsh. In emacs I'm able to use my system clipboard (previously with some additional configuration needed but this works out of the box now in emacs). In zsh I can't seem to paste from my clipboard using C-y and copying from zsh to my system cliipboard has the same issue. Is there a way around this?


I am trying to remove comments from a file which may be in any part of a line and span multiple lines.   struct my_struct{   field1;   field2; /** comment 1   */ field3;   /* comment 2 */  } struct_name;   I need to get   struct my_struct{   field1;   field2;    field3;  } struct_name;   I tried using   grep -o '[^/*]*[^*/]'    to remove any text between matching /* and */, but it is eliminating the comment symbols but not the text in between. What is the correct way? If there is another way using 'sed', it would be nice to know that too.


Is `\[` equivalent to \begin{displaymath}?

Are the following two code snippets equivalent?  Snippet One  \[     a + b = c  \]   Snippet Two  \begin{displaymath}     a + b = c  \end{displaymath}


when I ran TOP command in Busy box, I just wanted to know if VSZ% is MEM%, if not how can get MEM% with TOP command in Busy box


Encouraged by the zeitgeist let me ask the following:  Is it feasible (now or in the future) to build systems a certain distance of a vulnerable coastline which can serve to dampen a tsunami before it reaches the coast itself?  The following picture comes to mind. We have some device which is small enough to be mounted on a buoy. An array of such buoys can be anchored some distance off the coastline, controlled by computers which are linked into the global tsunami warning network. This setup is quite feasible given what a cell phone can do today.  On the detection of an oceanic earthquake or other tsunami generating event (such as a piece of the Rock of Gibraltar falling into the sea) and given present environmental conditions one can calculate the expected path of the tsunami and its intensity. If a TDS (Tsunami Dampening System) of the type I describe above happens to be deployed in range of the tsunami, all relevant information is conveyed to the TDS controllers by the global tsunami warning system. All this happen in a matter of moments.  This leaves plenty of time (25min - 2hr) for the devices in the TDS array to be activated and to do their job. The question in this case would be - what form could such devices take? Perhaps mini-turbines which could dissipate the incoming energy into the ocean by first converting it to electrical energy.  Any such undertaking involves physical estimates for the size and shape of such an array, the precise capabilities of each device, etc. Many of these concerns involve simple physical questions.  Can you come up with the details of such a system or alternatively outline your own design? If you think that this idea would never work in the first place - for technological, physical or some other reasons - please explain what you think would be the prime obstacle and why?


Is exon order always preserved in splicing?

Are there any cases in which the splicing machinery constructs an mRNA in which the exons are not in the 5' -> 3' genomic order? I'm interested any such cases, whether they involve constitutive or alternative splicing.


how to install google gadgets in ubuntu 11.10? Any ppa s available? .Source code is available on their website how to package it? If it is not packaged yet ,how can i build it from source code?


Any good ConTeXt tutorials / beginner guides out there?

I've been wanting to learn ConTeXt for a while, mainly due to its promises of finer typographic control than what LaTeX offers. However, every time I try, I fail and eventually give up due to some insurmountable difficulty that I can't seem to get out of. I found that I have an extremely hard time navigating the ConTeXt documentation (what I can find anyway).   The ConTeXt website isn't really that helpful. I find it kind of messy, confusing, frequently out of date, and often riddled contradicting information. While I've been able to find some up-to-date documentation detailing certain things, they're not really useful unless I'm trying to do that specific thing---and even then, very often I fail because I'm missing something else the document doesn't cover.   EDIT: The post: , which brings attention to some ConTeXt documentation is a great resource, but I still don't think it's sufficiently beginner-friendly. There's only one tutorial there about creating a 'presentation,' which is helpful, but also limited. And, even going through it, I ran into compilation issues which I wasn't able to figure out.   So I'm looking for any good beginner's tutorials or guides into ConTeXt. More than the above link offers. Similarly, for those of you who moved from LaTeX to ConTeXt, how did you go about it? What was your process and what steps did you take to make the transition? Any advice on how to go about it?  ps: Even the name itself "ConTeXt" seems to be a deterrent to my learning it, lol. Whenever I try to search for some ConTeXt-related issue, search engines almost always confuse it with the dictionary word "context." I find that both hilarious and extremely frustrating.


Which was the comic where Steve Rogers was able to hold Thor's hammer?

Which was the comic book where Captain America became worthy to hold Mjolnir ?


Whenever I travel to the Nether in Minecraft, I almost instantly get blasted to smithereens and chopped up into little pieces.  How do I survive in the Nether, at least long enough to build some sort of shelter and get situated?


Integral inequality with a strange condition

Let $f$ be a continuously differentiable real valued function on $[0,1]$.  It is given that $\displaystyle \int_{\frac{1}{3}}^{\frac{2}{3}}f(x) dx=0$     Find the minimum value of $\dfrac{\int_{0}^{1} (f'(x))^2 dx}{\left( \int_{0}^{1} f(x) dx \right)^2}$   I tried to use Cauchy-Schwarz to show that  $$\frac{\int_{0}^{1} (f'(x))^2 dx}{\left( \int_0^1 f(x) dx \right)^2} \ge \frac{\left( \int_0^1 \bigl| f(x)f'(x) \bigr| dx \right)^2}{ \left( \int_0^1 f(x) dx \right)^2} \ge \frac{ f(1)^2 - f(0)^2}{2 \left( \int_0^1 f^2 (x) dx \right)^2}$$ But I can't proceed from here.  Also, I don't know how to use the condition  $\int_{1/3}^{2/3}f(x) dx=0$


Attaching Custom Data to the blend file, scene, objects

I see many examples that attach custom properties to objects eg.  bpy.types.Object.mytype = bpy.props.StringProperty()   What are the other useful places to put custom properties. In particular I want to store a global to the blend file itself?   len(dir(bpy.types)) # -> 3282!   I see there is a type BlendData


I have a 1kg beef brisket, still in store packaging, sitting at room temp for 24 hours. Is it safe?


No icons or bars show up in the desktop, after a recent Ubuntu 13 update

Since a recent Ubuntu update, I have the problem that no icons show up in the desktop (no possibility for me to launch any program / software centre from the desktop...  How could I solve this? Would installing "vanilla Ubuntu 13.04" work?   How to do this from terminal?  I tried typing sudo apt-get vanilla Ubuntu 13.04  but does not work.


Legitimate edits of less than 6 characters

I recently came across an  by  which contained a link to a specification that has since been moved. When attempting to edit the link, a change which involved the subtraction of only 4 characters, I ran up against the 6 character minimum requirement.  Ordinarily this would not be an issue. A less experienced poster would likely have other things within the answer that could be changed (). In fact, this seems to be the answer on every meta post relating to this topic (, , etc...).  The problem here, since I don't have 2k reputation, is that BalusC writes excellent answers... with the reputation to back them up. I don't feel there is anything in the post (besides the link) that would benefit from me editing.  What is the standard practice here?   Flag the post and explain my situation in the notes (for someone with higher reputation)? Comment on the post and hope that a) visitors read the comments or b) the OP gets notified and updates their post? Make edits, for the sole purpose of increasing characters, providing no benefit and possibly hurting the quality of the post?   For reference, the EL Specification in the post should be changed to , if someone wants to go ahead and take care of this.


If $a,b,c$ and $d$ are positive integers such that    $$a+b+c+d = 63$$   Find the maximum value of $$ab +bc +cd$$   My turn : Using AM-GM $$4ab \leq (a+b)^2$$ Then $$4(ab + bc + cd) \leq (a+b)^2 + (b+c)^2 + (c+d)^2$$ But i did not go on any more


What is the purpose of the chains hanging from the shelves at the Citadel?

Question  Since the Citadel gets decent screen time the first two episodes this season I happened to notice and wonder about the chains tangling from certain book shelves.  What is the purpose of those chains?  Research findings  I came across an explanation , that says that similar chains served as some ancient version of an anti-theft device. But there are some points that leave me thinking:   The Citadel library already has dedicated departments for valuable books.  The books do not show any obvious fittings to connect chains to. As far as I know the Citadel library is not a public library, thus reducing the pool of suspects.   Screenshot


What can be done to make a trainer work quieter?

I use a trainer at home. It works quiet. But living in an apartment I would like to make it work quieter. What can I do to minimize noise of a trainer?


Linear Algebra munkres analysis on manifolds question.

If $A$ is an $n$ by $m$ matrix and $B$ is an $m$ by $p$ matrix, then  $$ |AB| \leq m|A||B|$$ where $|A| = \max\{|a_{ij}| : i = 1,\ldots,n \text{ and} j = 1,\ldots,m\}$  Attempt: $ |AB| = \max\{| \sum_{j=1}^{m}a_{ij}b_{jk} |: i = 1,\ldots,n \text{ and } k = 1,\ldots,p\} \leq \max\{ \sum_{j=1}^{m}|a_{ij}b_{jk}| : i = 1,\ldots,n \text{ and } k = 1,\ldots,p\}  \leq m\max\{|a_ij|\}\max\{|b_{jk}|\} = m|A||B| $  Is this correct?


How to use newenvironment inside a table?

How to define a formatting to use for (individual) rows of a table?  Example: (For each row) the first column is always bold, and the second column has an italic "title" and some text and possibly something more (e.g. a list). After each row I want to add some additional vertical space. Like so:  \documentclass[a4paper, 10pt]{scrartcl}  \begin{document}   \begin{tabular*}{\textwidth}{p{0.4\textwidth}@{}p{0.6\textwidth}@{}}       \textbf{1st column entry, row 1} &  \textit{2nd column title} -- 2nd column entry, row 1                                          \begin{itemize}                                             \item{some list}                                             \item{items here}                                         \end{itemize} \\     \multicolumn{2}{c}{\vspace{2.0em}} \\     \textbf{1st column entry, row 2} &  \textit{2nd column title} -- 2nd column entry, row 2                                         \newline (maybe only a note here) \\     \multicolumn{2}{c}{\vspace{2.0em}} \\   \end{tabular*} \end{document}   For a large document with a lot of these tables, it is quite tedious to write all of these formatting commands. What I would like to do is to define a \newenvironment such that each row of the table can be entered like this  \begin{TableRow}{1st column entry}{2nd column title}{2nd column entry}   %more stuff here, like, e.g., a list:   \begin{itemize}     \item{some}     \item{items}   \end{itemize} \end{TableRow}   Note that I want to define the layout just for the text of the rows. Such that I can use the environment in each 2-column table, regardless of the column-widths.  This is my non-working attempt so far:  \documentclass[a4paper, 10pt]{scrartcl}  \newenvironment{TableRow}[3] {   \textbf{#1} & \textit{#2} -- #3 } {   \\   \multicolumn{2}{c}{\vspace{2.0em}} \\ }  \begin{document}   \begin{tabular*}{\textwidth}{p{0.4\textwidth}@{}p{0.6\textwidth}@{}}       \begin{TableRow}{1st column entry, row 1}{2nd column title}{2nd column entry, row 1}       \begin{itemize}         \item{some}         \item{items}       \end{itemize} \\     \end{TableRow}      \begin{TableRow}{1st column entry, row 2}{2nd column title}{2nd column entry, row 2}         \newline (maybe only a note here) \\     \end{TableRow}    \end{tabular*} \end{document}   In my minimal example, there are 24 errors, the first of which is "! Extra } or forgotten \endgroup".  (I suspect, that the 2nd block of my \newenvironment definition is also faulty ("\\"?) but I also get this error, when I leave the 2nd block empty.)


This is not a duplicate of , as while that's the same issue, it was fixed in version 1.0.93; this is a fresh regression in 1.0.95. The team prefers that users file new bug reports for regressions.  Massive gaps between items    App Version: 1.0.95 Device Manufacturer: samsung Device Model: SM-P585   OS Version: 7.0 (P585JXU2BQF1)


Links removed from google search results

For my website www.trickwarehouse.com i have created one post on keyloggers. When i search in google that what are keyloggers? then my website's post position was 16 but after 1 hour, when i checked once again then BOOOM!!!! nothing found for my website within top 100 results. and also other keywords which was in top 100 results was shifted behind by 2-3 results...... Why it is happening?Any answers?


Is $(\mathbb{Q},+)$ isomorphic to $(\mathbb{Q}^n,+)$?

Is easy to show that $\mathbb{R}$ is isomorphic to $\mathbb{R}^n$ as $\mathbb{Q}$-vector spaces and then $(\mathbb{R},+)$ is isomorphic to $(\mathbb{R}^n,+)$ as abelian groups. This result might suggest that we also have $(\mathbb{Q},+) \cong (\mathbb{Q}^n,+)$ as abelian groups, but a similar approach to this dosen't work.  How can I prove or disprove this?


How can I recreate geometry using a photograph?

I am trying to change the floor covering using a picture. How can I define the floor?


How do I revert from 4.15.0-72 generic back to 4.15.0.70 generic?

Running Ubuntu 18.04.3 --------------------- I think the 4.15.0-72 generic kernel is corrupt or perhaps just incapable of working properly on my older laptop - it will freeze on shutdown every time when using the default 4.15.0-72 generic, but will shutdown fine when I interrupt boot-up and select 4.15.0-70 generic to boot instead... or is there something else going on?


Groups with Same Number Of Elements and Subgroups

Say I have a finite group and I tell you how many elements and how many subgroups it has. Do you now know what group it is? Or could two groups which are not isomorphic to each other have the same amount of elements and subgroups? In other words, does the amount of elements and subgroups of a group define it completely? It is interesting because if I give you just the number of elements there are several possibilities and if I give you the number of subgroups also but perhaps both combined are enough to define the group.


I am a beginner developer who knows HTML, CSS  and lately have entered in web development world with learning some beginning php scripts. I just want to know is there a clean CMS that allows me to lunch a dynamic website including forms and registration with my current knowlege? (i don't want a CMS limit my created HTML page in design.)  And for last, it is very useful if this CMS be rich in functional developments, maybe in future i can develop bigger projects, and just for mention i don't like using too many plugins for sample things, i just want this CMS be functionaly easy and do not limit me.  thanks


I'm trying to find a set which is Lebesgue measurable but not Borel measurable.  So I was thinking of taking a Lebesgue set of measure zero and intersecting it with something so that the result is not Borel measurable.  Is this a good approach? Can someone give a hint what set I would take (so please no full answers, I want to find it myself in the end ;-))  Also, I seem to remember that to construct a non-Lebesgue measurable set one needs to use the axiom of choice. Is this also the case for non-Borel measurable sets?


VWP/B1 as foreign employee of a US company for meetings and getting to know the team

I'm a German citizen and currently waiting for my H1B application to come through. Now my employer, a US company, has asked me to come to the US for 2-3 weeks in August already, in order to get to know the team and hear more about the system I will be working on.   Their lawyers say I can do so under the Visa Waiver Program/B1 visa, but all information I can find say that I should not be employed by a US company/receive salary directly from them if I want to enter on the VWP/B1.  Other online sources however say that it's totally fine to go to the US on VWP/B1 for just a couple of meetings, so the more I read, the more I get confused. Can someone help me shed some light on this?


Ubuntu 20.04 LTS Facing problem with wine

I a new user of Ubuntu 20.04 LTS facing some problem. I don't have any idea about commands, but know only a little because of youtube. Whenever I try to update the below mentioned results pop ups. robin@Eddy:~$ sudo apt-get update [sudo] password for robin:  E: Malformed entry 1 in list file /etc/apt/sources.list.d/sbt.list (Suite) E: Malformed entry 1 in list file /etc/apt/sources.list.d/wine-obs.list (Suite) E: The list of sources could not be read. robin@Eddy:~$ sudo apt-get update wine E: The update command takes no arguments robin@Eddy:~$ sudo apt-get install wine E: Malformed entry 1 in list file /etc/apt/sources.list.d/sbt.list (Suite) E: Malformed entry 1 in list file /etc/apt/sources.list.d/wine-obs.list (Suite) E: The list of sources could not be read. E: Malformed entry 1 in list file /etc/apt/sources.list.d/sbt.list (Suite) E: Malformed entry 1 in list file /etc/apt/sources.list.d/wine-obs.list (Suite) E: The list of sources could not be read. robin@Eddy:~$ wine --version wine-5.19


PyQGIS - Retrieve WMS and ArcGIS services capabilities (layers, styles, crs...)

I would like to know how to bind the methods used by the "Connect" button which retrieve services capabilities through the OWSConnect to correctly build the URL with paramas (or QgsDataSourceURI) from each layer capacity without opening the dialog or request the GetCapabilities URL by myself.  I'm looking for a "pure" PyQGIS solution, not using a dependency like OWSLib because I need parse ArcGIS Server services (Map and Features).  Any idea?    I'm interested in PyQGIS 2.18.x and 3.x.


typing "full" using $\mathcal{full}$ gives weird thing?

Just a quick question:  Why is it that when I write $\mathcal{full}$ the word full is not desplayed at all, instead parenthesis, product and vertical arrows come out? And when I tryed to copy that pdf output and paste it in  this window, the paste result was the word "full"?  Thanks to everyone!


I am running chrome Version 77.0.3865.120 on macOS.  when chrome finished to load a page, it looks like this figure    when I try to select part of the URL, it becomes like this    It takes and wastes me another click/tap, which is boring and inefficient. Is there a way to force chrome keep showing or hiding the "https://" part?


Screen text reads: Error reading block 23108274 (input/output error).  /dev/sda5: UNEXPECTED INCONSISTENCY; run fsck MANUALLY  and: fsck excited with status code 4 done Failure: file system check of the root filesystem failed The root filesystem on /dev/sda5 requires a manual fsck  At browsing Ask Ubuntu, I found similar problems mentioned but none of the previous solutions work. After I tried the exit command, this was the result:  However, I retried the exit command, and then used "reboot", which got me stuck on the following screen :  As I'm told that each reboot aggravates the problem, I feel hesitant to force a shutdown. I had no other option but to pull the plug. At restart, I got to an "enter setup f2" message on the bottom left, which I did. Within setup, I hit some of the keys to navigate. The system responded so slow that I doubt whether it did so at all and instead shifted through the different tabs at random. I managed to exit setup, and now find myself staring at this:  It took me some time but I now have an Ubuntu Live USB.


Any practical uses of machine learning for cryptography?

I am about to go study for my masters in machine learning, data mining and high performance computing, but have recently become very interested in cryptography after taking Dan Boneh's Cryptography course on coursera.com.   I was wondering if there are any practical applications for machine learning in cryptography? A quick google search didn't seem to reveal much for me so i was wondering if someone here knows something.  My first impression would be that machine learning techniques could be used to learn the inverse function for some cipher and passphrase given enough plaintext/ciphertext pairs, but i am not sure how capable things like neural networks are at learning functions which are not linearly separable.


If you haven't already watched my first video, there's a link to it in the description below. Ungrammatical?

I just finished recording an audio file for one of my podcasts.  And I'm debating whether I should delete the following sentence:      If you haven't already watched my first video, there's a link to it in the description below.     I am trying to suggest to viewers that they watch my videos in order, which I think the sentence does.  But I think this sentence is also ungrammatical and nonsensical.   Whether or not my viewers have watched my first video, a link to that video will be in the description.    I suppose I could change it to      If you haven't already watched my first video, please watch that first. You can find a link to it in the description below.     But changing audio files is such a pain.  Would it be ok to leave the sentence as is?


I recently brought Western Digital's , and will be using with my MacBook (running Snow Leopard), MacBook Air (running Lion) and Windows 7 Desktop. I should be able to read-write data using each machine/OS.  Moreover, I need to store and move files larger than 4GB.  So, what should be preferred file-system type: FAT, exFAT or NTFS? Will my portable drive support exFAT?


GIMP 2.8.22 How to SELECT ALL text objects in all layers and change font size of all at once?

(GIMP 2.8.22)  I have several text objects labeling parts of the human body and I want to increase the font size of all of them to 20 pts. Each text object was automatically put into its own layer, and I want to leave it like that, if possible. How do I SELECT ALL of the individual text objects in the entire drawing (all layers) and change them all at once?  Thank you in advance!


I'm trying to model my face on Blender using  and it gives links to reference photos.  The thing is, as I mentioned above, I want to try and model my face.  So I've decided to take photos of my face. But it doesn't seem to be working well (not symmetrical enough and stuff), so how exactly should I take my reference photos so that it would work well when I try to model it with the Mirror modifier?  Note: I only have the 'webcam' on my Macbook Pro and the camera on my Hongmi phone and I don't want to spend money on a new camera.


Is it necessary to dispose System.Timers.Timer if you use one in your application?

I am using System.Timers.Timer class in one of the classes in my application. I know that Timer class has Dispose method inherited from the parent Component class that implements IDisposable interface. Instances of the class below are created many times during my application lifecycle; each of them has an instance of Timer class that generates Elapsed events continuously during the class's lifecycle. Should I implement IDisposable interface in the class that uses Timer class to dispose the timer object? (I have seen code that doesn't do this at all). I am afraid that some unmanaged resources will not be freed if I use the class below like this:  SomeClass someClass = new SomeClass(); someClass.DoSomething(); someClass = null;   The class:  using System.Timers;  public class SomeClass {     private Timer m_timer;      public SomeClass()     {                    m_timer = new Timer();         m_timer.Interval = 1000;         m_timer.Elapsed += new ElapsedEventHandler(m_timer_Elapsed);         m_timer.AutoReset = false;         m_timer.Start();                            }      public void DoSomething()     {      }      private void m_timer_Elapsed(object sender, ElapsedEventArgs e)     {         try         {             //Do some task         }         catch (Exception ex)         {             //Ignore         }         finally         {             if (m_timer != null)             {                 //Restart the timer                 m_timer.Enabled = true;             }         }     } }


Exponential growth with growth factor <2

Is there an $a$ with $1<a<2$ such that $y=a^x$ can be bounded (or eventually dominated) by a polynomial?


how to create a cron job that runs on the first day of month

There are fields on my server's control panel like this  Minute -  Hour -  Day of month - Month - Day of the week - Command  How can I create a cron job runs on first day of the month with this fields?


Downgrade Nexus 9 running lollipop to KitKat

I'd like to downgrade my Nexus 9 to android 4.X (KitKat). Is this possible? I'm not the pro doing something like that and I could not find something with google.  Can you help me please? Thank you


Is it safe to use these chargers to replace my lost laptop charger?  Original charger: 19V, 4.74A   Replacement 1: 19V, 4.5A Replacement 2: 20V, 4.5A


Error while deleting .zip file in Ubuntu 16.04

I'm getting this error while trying to delete the zip file  Error when getting information for file '/home/silver/Downloads/Compressed/f65300fc-d02a-447f-99e0-064cae003c17_our-little.zip': No such file or directory   How do I solve this?


Log4j, configuring a Web App to use a relative path

I have a java webapp that has to be deployed on either Win or Linux machines. I now want to add log4j for logging and I'd like to use a relative path for the log file as I don't want to change the file path on every deployment. The container will most likely be Tomcat but not necessarily.  What's the best way of doing this?


Javascript : optional parameters in function

Let's say I have this :   function concatenate(a, b, c) {     // Concatenate a, b, and c }     How do I handle those calls ?   x = concatenate(a)  x = concatenate(a, b)  x = concatenate(a, c)     How can I make my function aware of the parameter I gave to it ?


How to get matrix $A$ from $A^\top A=B$ with given symmetric matrix $b$?

Given a symmetric matrix $B \in \mathbb{C}^{n\times n}$.  How many coefficients of  $A \in \mathbb{C}^{n\times n}$ can you obtain from the following equation? $$A^\top A=B$$  I think this problem is under determined? Isn't it? Sure $B$ must be symmetric. Thus  only $\frac{n(n+1)}{2}$ complex equations remain for $n\times n$ coefficients.


Why does AES_GCM sometimes has a SHA for integrity?

For example the following suite: TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 From what I understand the SHA384 at the end is used to authenticate the message, which is exactly what MAC does, and the mode GCM already creates a MAC, then why is the cipher suite followed by SHA384?


biblatex/multicol: Incorrect vertical space after bibliography heading

I'm trying to typeset a bibliography inside a multicols environment, but with the heading as a single column (using multicols' optional argument). I've noticed that the vertical space between the heading and the actual bibliography is larger than with a bibliography typeset in one-column mode. On closer inspection, it seems that the spacing after headings is also somewhat larger for "normal" text when using multicols, but that the combination biblatex/multicol results in even more additional vertical space.  The multicol  states on p. 2 that \addvspace is used for the spacing before and after the multicols environment (the length is \multicolsep). This seems to be consistent with the observed behaviour after "normal" headings because the default value of \multicolsep (12pt) is larger than the vertical space after sections in the standard classes (2.3ex, i.e. about 9.9pt for a fontsize of 10pt). My current workaround is to set \multicolsep to 0pt, but this will negatively affect in-text multicols environments. So I'd like to know what is the cause of the "on-top" additional vertical space after bibliography headings.  \documentclass{article}  \usepackage[english]{babel} \usepackage{blindtext}  \usepackage{biblatex} \defbibheading{none}{}% for biblatex v<1.5  \usepackage{multicol}  % My current workaround % \setlength{\multicolsep}{0pt}  \usepackage{filecontents}  \begin{filecontents}{\jobname.bib} @misc{A01,   author = {Author, A.},   year = {2001},   title = {Alpha}, } @misc{B02,   author = {Buthor, B.},   year = {2002},   title = {Bravo}, } @misc{C03,   author = {Cuthor, C.},   year = {2003},   title = {Charlie}, } \end{filecontents}  \addbibresource{\jobname.bib}  \nocite{*}  \begin{document}  \section{First Section }  \blindtext  \begin{multicols}{2}[\section{Second Section}] \blindtext \end{multicols}  \printbibliography[title={First Bibliography}]  \begin{multicols}{2}[{\printbibheading[title={Second Bibliography}]}] \printbibliography[heading=none] \end{multicols}  \end{document}


The question is specific to Tex Live 2016.  I use Tex Live 2016:  tex --version TeX 3.14159265 (TeX Live 2016)   Upon running   pdflatex file.tex   I encounter an error of this type   ! LaTeX Error: File `pgf-pie.sty' not found.   How to install a package in Tex Live 2016?


Calculate this limit without L'Hopital's rule

I have to calculate this limit whitout using L'Hopital's rule or Taylor polynomials: $$ \lim_{x \to 0} f(x) = (1+\frac{x}{2})^{\frac{1}{x}} $$ I know how to make it using L'Hopital and that the result is $ e^{\frac{1}{2}} $ ,but I'm getting nowhere when I try without it. Any advice?


How to selected a div inside a selector?

I want to select the div nameMachine using this.but I can't find how to select it:   I can get this element with this code :  $(".switch").each(function(){    console.log(this);    $(this).css({       'background-color': 'white',       'border-style': 'solid',       'border-color': 'inherit',       'border-width': '3px',    }); });


If $2^{\aleph_0}=\aleph_2$, what is known about $2^{\aleph_1}$?

This means: if $V\models{\sf ZFC}$ in such a way that $2^{\aleph_0}=\aleph_2$, can $2^{\aleph_1}$ be anything it ought to be? By the way, can $2^{\aleph_0}=\aleph_2$ be considered the 'simplest' case of $\lnot{\sf CH}$ in some sense?


Existence of an inverse number to zero (null)? Existence a meta of number?

Sorry for the structure and maybe some mistakes in the post - I'm not a Mathematician and not a native English speaker, so I will use Google Translator + Grammarly for help. Please, if you want and can - help me to find an answer to this sequence of questions:  Does an inverse number to zero (null) exist? 1.1) If yes - what is it? 1.2) Or/And - is the one solution or several? 1.3) Or/And - is there an equal or different weight of these solution/-s in mathematical society? Does a meta of number exist?  My own naive thoughts (briefly and simply): About 1 question: if we can imagine that "zero" (null) is a mathematical concept of "nothing", so maybe exists a mathematical concept of "everything"? Maybe if I call "zero" (null) an "Absolute Emptiness", so maybe we should create "Absolute Fullness"? Remark - I don't mean any sort of infinities, like infinity small values (maybe they called "infinitesimals") and their opposites - infinite big values (plus or minus, I suppose it doesn't matter in this context, and don't know their right definitions, sorry) - because these entities have values and they have some sort of scope of properties, let's call them "Relatives". About 2 question: if we can operate not just different values, but also their "Absolute Emptiness" (which for me looks confusing, because if I have the right understanding, we trying to operate by "nothing" with serious faces =))) - maybe there is an existing core property of a number, lets call it's "meta". This "meta" means the existence of some object, which we want to operate. Or maybe, it would be useful to separate operating of "Absolutes" (like only two objects - "zero" (null) and it's inverse) and "Relatives" which has a range from infinity small number (no matter of sign) to infinity big number (also not matter of sign)? If we do this separation, maybe we displace problems like division by zero or just will look at the problem from another angle - because it seems like when we dividing the non-zero value by zero (or do other 3 arithmetic operations) we work with 2 types of entities/properties ("Relative" and "Absolute") which maybe require a different approach, because for my understanding (of course with Dunning–Kruger effect xDD) there is no fundamental/crucial/disbalance problem to divide non-zero infinity small/big/mediocre value by non-zero infinity small/big/mediocre value (or do other 3 arithmetic operations, or other general operations), are you agree? It would be so nice if you give me answers to those questions because I even don't how trivial these questions are. P.S. If there are no one/multiple clear answers, maybe you can suggest a path/sequence of books (from zero to goal) which I must read/understand and that is will help me solo find answers to the questions above. Thanks you in advance.


What determines the size of a straw/pipe to stop a liquid running out of it when closing one end of it?

When I put a finger on a straw with water in it, it wouldn't fall out of this straw. But is there maximum size (length and diameter) of this straw/pipe to get this effect and what causes this limit?


Philippine passport transit in UK, need help

Im a filipino with a tourist visa in canada, I have a flight from Doha to London LHR then London Gatwick airport to Vancouver, Do i need a transit visa knowing that Im transfering airport in UK. Thanks advance your replies


Why can't I accept my own answer straight away?

I had a question, nobody else posted any answers, and I worked out the solution myself.  Why do I have to wait 24 hours to accept my own answer. When I don't have to wait before accepting anybody else's answer?


Does every non-trivial subgroup of $S_9$ containing an odd permutation necessarily contain a transposition?    Here $S_9$ denotes the group of all permutations (i.e. bijections with itself) of the set $\{1,2, \ldots, 9 \}$ under the binary operation of composition of functions.   By a transposition is meant a permutation that leaves all elements except two fixed, mapping either of these two onto the other.   A permutation can only be expressed either as a product of an even number of transpositions or as a product of an odd number of transpositions (but not both) and as such is defined to be even or odd, respectively.   Reference: Fraleigh p. 95  Question 23d. in A First Course in Abstract Algebra


Forgot to provide details of children on an Indian railways booking

IRCTC (The Indian Railway online ticket booking agency) provides an option to specify details of children under five years of age who are travelling with the ticketed passengers.  While booking a ticket through IRCTC, I have forgotten to fill in the personal information of my children (both under 5) in the form. One child is 3 years and another is 4.5 years old. Will they be allowed to travel with me or can it lead to a problem during boarding/journey?


What's the name for a part of speech which is not quite rhetorical, but not expected to be answered directly, either? I know the word exists, it refers to greetings such as "How are you" and similar. There's a very specific term for those greetings and I cannot recall it.  It's not perfunctory or pro forma; it very specifically refers to a common query that isn't really a question but a conversation opener. Might be from a specialized field like linguistics.  Frustrating!


I am referring to Rudin's definition 2.32 of compactness here: A subset K of a metric space X is said to be compact if every open cover of K contains a finite subcover.  Obviously X is a subset of X itself. We also knew that any metric space is both open and closed relative to itself. Then {X} is an open cover of X that contains a finite subcover which is also {X}. It seems to me that {X} is the only open cover X has.   If it really is the case that X is compact, it would follow that X is closed and bounded. Closed indeed, but being bounded would be troublesome.   I am sure one of the above statement is false, but I don't know which one.


using nulls in a mysqli prepared statement

In a mysqli prepared statement, a NULL gets turned into '' (in the case of a string) or 0 (in the case of an integer). I would like to store it as a true NULL.  Is there any way of doing this?


Text annotating process, quality vs quantity?

I have a question regarding annotating text data for classification.  Assume we have ten volunteers who are about to annotate a large number of texts into label A or B. They probably won't have time to go through all the text samples, but at least a significant portion of them.   Should we focus on generating new samples for each annotator? (They never see the same text samples as any other annotator) (quantity approach). Or should all annotators see the same samples and the annotator agreement is taken to account? (quality approach).   Thoughts,   will generate more unique samples than 2. (more training samples for a classifier) - and hoping that in the feature extraction part, the useful features will appear by themselves. will generate less unique samples, but with the annotator agreement taken into account. (less training samples for a classifier, but with higher quality)


If $A$ is an $n\times n$ matrix such that $\|A\|<1$,   show that $(I-A)$ is invertible and    $$ \frac{1}{1+\|A\|}  < \|(I-A)^{-1}\| <\frac{1}{1-\|A\|} $$   My trial:  First  to show $I-A$ is invertible: if not, then there exists nonzero vector $x$ such that  $(I-A)x =0 $ Hence  $Ax=x$ So $\|x\|=\|Ax\|\le\|A\| \|x\|$ and since $x$ is a non zero vector we get $\|A\|\ge\|x\|$ which contradicts the assumption.  To prove the second part, by the triangle inequality we have $$ \|I\|-\|A\| \le \|I-A\|\le\|I\|+\|A\| $$ But the norm of the identity is equal to 1.  I stopped here since I know $\|(I-A)^{-1}\|$ doesn't equal $\|I-A\|^{-1}$  Any help?  The norm here is the spectral norm or the operator norm.


Choosing site for question about deleting contacts of Gmail account?

I'm having trouble deleting contacts on my  account.   Which Stack Exchange site would this question be best suited for?


Generally, what are the core things that one should do in the game loop, and what are some things that one shouldn't do in the game loop?


Is Transformers anime series or western cartoon? I watched a old Transformers series but it looks like anime and I found that Marvel inc that made Transformers so whats going on?


When is the "Match Finish" XP actually awarded?

Can you quit during the Play of the Game and still get it? Or when the cards are shown, but before the XP screen? Or do you have to wait past everything?


I want to see CPU usage. I used this command :  top -bn1 | grep "Cpu(s)" |             sed "s/.*, *\([0-9.]*\)%* id.*/\1/" |             awk '{print 100 - $1}'   But it returns 100%. What's the correct way?


Can find the determinant of a matrix A of size $n$ in terms of the traces of $A^m$

We can find the determinant of a matrix A of size $n$ in terms of the traces of $A^m$, for $m=1,…,n$ ?  It's det of a matrix with term are traces, but i saw  but i can't remember   when $n=2$.


I am a new Ubuntu user. I just keep seeing "-" in every command line, such $lsb_release -a $sudo apt install catkin -y $rm -v!("filename") ... this keeps happening, does anybody have any references so I can study them all? Thanks


You are given two points and a circle. Construct a circle passing through the given two points and tangent to the given circle. You are allowed to use a straightedge and a compass.


Is short-circuiting logical operators mandated? And evaluation order?

Does the ANSI standard mandate the logical operators to be short-circuited, in either C or C++?  I'm confused for I recall the K&R book saying your code shouldn't depend on these operations being short circuited, for they may not. Could someone please point out where in the standard it's said logic ops are always short-circuited? I'm mostly interested on C++, an answer also for C would be great.  I also remember reading (can't remember where) that evaluation order isn't strictly defined, so your code shouldn't depend or assume functions within an expression would be executed in a specific order: by the end of a statement all referenced functions will have been called, but the compiler has freedom in selecting the most efficient order.  Does the standard indicate the evaluation order of this expression?  if( functionA() && functionB() && functionC() ) cout<<"Hello world";


Sometimes show highest answer before accepted answer?

For some questions the accepted answer is not that useful but the OP likes the answer for whatever reason. Later possibly, someone else comes along and provides a better answer (which ends up being rated much higher). For examples you can just look at the .  I wondered - if an answer has more than 20 votes and more than 2x the votes of the accepted answer should it show first in the list?  Justification  A great deal of the popular questions are hits directly from google. The user is going to read the answer, try it and move on to searching google further. Occasionally you will have users that want to read further into the other answers but that isn't always the case. This is still probably important because I'm guessing a good percentage of stack users operate this way. Just theorizing a bit.  One More Thought  The OP is may not be an expert (tons of questions are asked by first time users). So we are putting the first answer that appears in the hands of someone who probably doesn't care all too much. I agree their vote needs to count more than others (Since they know what they needed), but to always show it first may give them too much power.


My ubuntu terminal is opening as "gdhobe@vfroot-Thinkpad-T440:~$" I want to open it as "vfroot-Thinkpad-T440:~$"  Usually terminal opens as vfroot-Thinkpad-T440:~$  How this issue could be solved.


What is the statistical method that I should use for the following problem?

I have been given a problem and need to find the best statistical method that would help. The problem is as follows: A business has approx. 100,000 active customers who spend between £500 per annum and £200,000 per annum.  The smaller ones transact irregularly, once per year, the larger ones maybe once per week.  They are distributed across 15 different market sectors. The business has started to decline, and whilst we have implemented a process for making offers to customers once they have closed their account, it is thought this would be much more effective if we could predict which customers are likely to close, and make offers to keep them before they close.  How would you go about determining which customers to make offers to?


Are Ubuntu 20.04 updates failing on in.archive.ubuntu.com

apt-get update is failing on India location. Its not able to reach out to in.archive.ubuntu.com. Below is the error : # apt-get update  Hit:1 http://dl.google.com/linux/chrome/deb stable InRelease Hit:2 http://security.ubuntu.com/ubuntu focal-security InRelease                   Err:3 http://in.archive.ubuntu.com/ubuntu focal InRelease                            Cannot initiate the connection to in.archive.ubuntu.com:80 (2403:8940:ffff::f). - connect (101: Network is unreachable) Could not connect to in.archive.ubuntu.com:80 (103.97.84.254), connection timed out Err:4 http://in.archive.ubuntu.com/ubuntu focal-updates InRelease   Cannot initiate the connection to in.archive.ubuntu.com:80 (2403:8940:ffff::f). - connect (101: Network is unreachable) Err:5 http://in.archive.ubuntu.com/ubuntu focal-backports InRelease   Cannot initiate the connection to in.archive.ubuntu.com:80 (2403:8940:ffff::f). - connect (101: Network is unreachable) Reading package lists... Done W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/focal/InRelease  Cannot initiate the connection to in.archive.ubuntu.com:80 (2403:8940:ffff::f). - connect (101: Network is unreachable) Could not connect to in.archive.ubuntu.com:80 (103.97.84.254), connection timed out W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/focal-updates/InRelease  Cannot initiate the connection to in.archive.ubuntu.com:80 (2403:8940:ffff::f). - connect (101: Network is unreachable) W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/focal-backports/InRelease  Cannot initiate the connection to in.archive.ubuntu.com:80 (2403:8940:ffff::f). - connect (101: Network is unreachable) W: Some index files failed to download. They have been ignored, or old ones used instead.   Can someone please suggest / help here.


Will paying off an old $8 collection hurt my credit?

Let me explain a little more. I was the victim of a car accident and medical bills went through the roof. I had about $16k racked up, then my settlement finally kicked in 3 years later and paid it all off (except for that pesky $8). What happened was when we queried the debt from the hospital I went to, they somehow missed that $8 (out of the $16k) and sent it to collections. This all happened about 4 years ago. I didn't receive any letters in the mail for some reason as well. I did a credit check a few months ago to get a car loan, and my banker found the collection. I need to get rid of it, because a job I want to apply for also looks at my credit.    Should I pay it off? I would not like it to be on my credit history... Can I dispute it since they failed to bill me for it in the first place?


Why is this environment texture image showing only a solid color in the 3D view, using Cycles?

I'm having a problem rendering the environment map. I downloaded a sample project that has the same settings as my project but it renders without a problem. I tried using both a .hdr and .png image. Attached are screenshots with node settings. First is the incorrect render and 2nd image is the project the renders correctly. How do I go about fixing this?


Good evening everybody,  I have a question about the red tagged argument in : Let $g$ be a semisimple Lie subalgebra of $gl(V )$.  For $x \in g$ we have J-C decomposion $ x= x_s +x_n$ but that's not clear to me why $ x_s ,x_n  \in n_{gl(V)}(g) $ where $  n_{gl(V)}(g) = \{y \in gl(V) | [y,x] \in g $ for every $ x \in g \} $.  My idea: We know that $ x_s = P(x) ,x_n = S(x) $ for appropriate polynomials without constant terms. Thats clear that $x \in n_{gl(V)} $ so because $ g$ is a subspace it would be enough to show that $[z,x^n] \in g $ for every $z \in g$. But how?


I am reading books about linear regression. There are some sentences about the L1 and L2 norm. I know the formulas, but I don't understand why the L1 norm enforces sparsity in models. Can someone give a simple explanation?


I can't remember my iCloud username or password

I can't turn on my iPhone because I don't remember my iCloud username or password.  What can I do to log into my iPhone?


Group Theory and Lagrange's Theorem: coprime subgroups.

Let $G_1$ and $G_2$ be finite groups, and let $K≤G_1 \times G_2$. Let $H_1 = \{ g \in G_1 : (g,e) \in K\}$ and $H_2 = \{g \in G_2 : (e,g) \in K\}$ and suppose $|G_1|$ and $|G_2|$ are coprime. Then show that $H_1 \times H_2 = K$. Show that if $|G_1|$ and $|G_2|$ are not coprime then this does not have to be the case.   My working: I have proved that $H_1 ≤ G_1$, $H_2 ≤ G_2$ and $H_1 \times H_2 ≤ K$. And since $|G_1|, |G_2|$ are coprime, we must have $|H_1|, |H_2|$ are also coprime. Then given that $|G_1 \times G_2|$ = $|G_1||G_2|$, I am trying to use Bézout's Lemma or some similar thing to show that $H_1 \times H_2 = K$.   As for the second part, I have no idea.


How to find the following limit $$\lim_{n \rightarrow \infty} n \sin(2 \pi e n!)$$  Its answer is $2 \pi$. I am not seeing any clue to find it out.  Thank you for your help. If it discussed earlier please mention link.


I'm a new Ubuntu user. I am reading this book "The Linux Command Line: A Complete Introduction" and practicing the code. That's fun, but I have trouble in Chapter 8:  ➜  ~ echo {1..10} 1 2 3 4 5 6 7 8 9 10 ➜  ~ echo {z..a} {z..a} ➜  ~ echo {Z..A} {Z..A} ➜  ~ echo {a..z} {a..z} ➜  ~    I can't get a range of letters. Why? How do I fix it? My shell is oh-my-zsh.


How to prove that: $\lim_{n\to\infty} \frac{1^n+2^n+\cdots+n^n}{n^n} = \frac{e}{e-1}$

How to prove that:  $$\lim_{n\to\infty} \frac{1^n+2^n+\cdots+n^n}{n^n} = \frac{e}{e-1}$$  Any help is appreciated.


Why does this div goes way below 50% of the page instead of going straight to the center?

.try {     background-color: aqua;     width: 100px;     height: 100px;     margin: 0 auto;     margin-top: 50%;     position:relative; }

     Hello sorry for a dumb question, but is it possible to make this div go to the center of the page without using flexbox maybe?


I'm an Indian citizen. Traveling between New Delhi and Toronto via London. Do I require a transit visa for UK although I'll not be leaving the airport.


Why null pointer exception for the below code

public class IbiboTest {  static WebDriver driver;  @BeforeClass public void setUp() throws InterruptedException{     System.setProperty("webdriver.chrome.driver","C:\\Program Files (x86)\\Google\\Chrome\\Application\\chromedriver.exe");     WebDriver driver = new ChromeDriver();      //driver= new FirefoxDriver();     driver.get("https://www.goibibo.com/");     Thread.sleep(5000);     driver.manage().window().maximize();  }   @Test public void testIbiboHomePage(){     IbiboHomePage home = PageFactory.initElements(driver, com.Nalini.Ibibo.IbiboHomePage.class);     home.clickRoundTripRadioButton();  }  public class IbiboHomePage {  WebDriver driver; @FindBy(css = "input[id='gi_roundtrip_label']") WebElement iRoundTrip;   public IbiboHomePage(WebDriver driver){     this.driver = driver;     PageFactory.initElements(driver, this);  }  public void clickRoundTripRadioButton(){ iRoundTrip.click(); }   }  I am just trying to automate ibibo website.I am getting nullpointer exception for the above code.I am not able to understand where it is passing a null value.Pls help.Thank you


Finding correlation between CDF of two normal distributions

Suppose that $X\sim N(0,1)$, $Y\sim N(0,1)$ with correlation $(X, Y) =ρ$ where $ρ ∈ (−1, 1)$.  Show the following,   Correlation $(Φ(X),Φ(Y))=\dfrac6π \arcsin\dfrac ρ2 $.  Here $Φ(X)$, and $Φ(Y)$ denote the CDF of Random variables $X$ and $Y$ respectively.  What I know so far:  $$\text{Cov}( Φ(X),Φ(Y)) =E(Φ(X)Φ(Y)) - E(Φ(X)) ×E(Φ(Y)) $$  We also know since  $X \sim N(0,1)$ and $Y\sim N(0,1)$;  $Φ(X)\sim\text{unif}(0,1)$, $Φ(Y)\sim\text{unif}(0,1)$. Hence $$E(Φ(X)) =E(Φ(Y)) =\frac12.$$  I am stuck in finding $E(Φ(X)Φ(Y))$ [I tried to find it using double expectation].  What I have written may be the wrong way of attempting the question. So I am thankful for any help.


Add an option for side-by-side diff before posting an edit

Now we have a nice side-by-side diff in the 'suggested edits' review pages, and as an , could something similar be made available as an option when editing a post?  It wouldn't need to be interactive - a button to get the side-by-side diff of the current state of your edit, versus the original would do.  This would be useful when shuffling lots of whitespace around - a final check that you haven't broken some embedded code.  A workaround at the moment is to submit the edit, then check the side-by-side view in the edit history.


"Tab Tree" or "Tabs Tree" (-s at the end)

I created an extension for Firefox and named it "Tabs Tree". The extension is for managing browser tabs and representing them in the form of a tree structure. But now I think that I should have named it "Tab Tree" (without "-s"). Like "apple tree" or "orange tree". But I used google and found usages of "Elements Tree" () and "Nodes Tree" () expressions. But also usage of "Element Tree" and "Node Tree".  Are both variants correct to use with that meaning? Or those people who used "Elements Tree" and "Nodes Tree" were wrong? And can I leave "Tabs Tree" as it is as it would be troublesome to change the name now?


How do I delete my previous queries (at DATA.SE)?

I accidentally made many queries at  (forked and generated permalinks for same query many times..) and now they are listed in "my queries" history.   How do I delete any of my made queries? There seems to be no button for that...


I read that z-index positive and greater than other divs should stack the div on top of others with lower z-index.  Why does the identified div move, and how do I prevent this?   This question different from asking about display:none vs visibility because the z-index should allow for layering divs from an x, y 2-dimension plane to a third dimension, z.        var mouseX; var mouseY; $(document).mousemove(function(e) {   mouseX = e.pageX + 20;   mouseY = e.pageY - 20; });   $(".dimoption").click(function() {    var $maxdim = $("#msgmaxdim");   $maxdim.css({     'top': mouseY,     'left': mouseX   }).fadeIn('slow');   setTimeout(function() {     $maxdim.fadeOut('slow');   }, 3000);  }); .description {   display: none;   position: relative;   border: 1px solid #000;   width: 400px;   background-color: white;   z-index: 1; }  <input type="checkbox" class="dimoption">Text
Popup overlay

   Why does this div move?


I'm having a problem using the group function in TraMineR. I have a data set that contains SPELL data, so multiple rows per case. I also have demographic data per case, at one row per case. I merge these together and end up with data that has a demographic covariate per row, so multiple rows per case. An example of this data would be:  id startmin stopmin activity educ4 4      1      20       work    HS 4      20     40       play    HS 8      1      15       sleep   College 8      15     40       work    College   I can make sequence data from this, but when I try to run a plot using the group command        seqiplot(atus.seq, group = atus.seqdata$educ4, border=NA,                 withlegend="right",  cex.plot=.55)   it tells me:       >"Error: group must contain one value for each row in the sequence object".   I have gotten this to work with the example of the mvad data in the training manual, but I can't seem to get it to work with the groups, whether I link to the original demographic data, the merged data, or try to pass the covariates by seqformat and seqdef. Ideas?


Find the last three digits of $6^{2002}$. I did some work and figured out that the last two digits is 36. Can anyone help me with the hundredth digit? By the way, I used modular arithmetic and the recursion method for the tens digit, but it fell short when I attempted to do the hundreds digit. Thank you in advance!  How I figured out the last two digits: I used the formula $\frac {1}{10^k} [n-a_k (n)]$. The last digit is obviously 6. I obtained the tens digit this way: $\frac {1}{10}(6^{2002}-6)=\frac {6}{10}(6^{2001}-1)=\frac {3}{5} (6^{2001}-1)=\frac {3}{5}(6-1)(6^{2000}+6^{1999}+...+6^2+6+1)=3(6^{2000}+6^{1999}+...+6^2+6+1)\equiv3(6+6+...+6+6+1)=3(2000\cdot6+1)\equiv3 (mod 10)$ Therefore, the last two digits of $6^{2002}$ are $36$.


Static solution to the Friedmann equation

I want to find the static solution for the : $$ \bigg(\frac{\dot{a}}{a}\bigg)^2=H_0^2\bigg(\Omega_m\bigg(\frac{a_0}{a}\bigg)^3+\Omega_v+\Omega_k\bigg(\frac{a_0}{a}\bigg)^2\bigg) $$ When there is no radiation. $\Omega_m$ is the matter parameter, $\Omega_v$ is the vacuum energy and $\Omega_k$ is the curvature parameter. Since I wanted a static solution I tried $\dot{a}=0$ and tried to solve for $a$, but this gives me a horrible equation with no clear solution. Any suggestions?


How do I find the build dependencies of a package?

I'd like to find out which packages  sudo apt-get build-dep <package>   would install (if I already got some dependencies installed, I'd also like to see those → so running or simulating the above is not enough). Command line preferred.


Suppose we consider a point dipole i.e. an ideal dipole. At the origin the potential:  $$ \phi(\mathbf r) = \frac{1}{4\pi\epsilon_0} \frac{\mathbf p\cdot\hat{\mathbf r}}{r^2}$$  is undefined due to the $1/r^2$ term in the potential, but electric field:  $$ \mathbf E = \frac{1}{4\pi\epsilon_0}\frac{3(\mathbf p\cdot\hat{\mathbf r})\hat{\mathbf r} - \mathbf p}{r^3} - \frac{1}{3\epsilon_0}\mathbf p\delta^3(\mathbf r) $$  remains well defined. How can we calculate electric field at the origin by equation $\mathbf E=-\nabla\phi$?


When I type sudo apt update I get this response:   Get:1 https://dl.winehq.org/wine-builds/ubuntu bionic InRelease [6,242 B] Ign:2 http://dl.google.com/linux/chrome/deb stable InRelease                    Hit:3 http://dl.google.com/linux/chrome/deb stable Release                      Err:1 https://dl.winehq.org/wine-builds/ubuntu bionic InRelease                   The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 76F1A20FF987672F Hit:5 http://ppa.launchpad.net/graphics-drivers/ppa/ubuntu bionic InRelease     Hit:6 http://archive.ubuntu.com/ubuntu bionic InRelease                         Hit:7 http://archive.ubuntu.com/ubuntu bionic-updates InRelease Hit:8 http://archive.ubuntu.com/ubuntu bionic-backports InRelease Hit:9 http://archive.ubuntu.com/ubuntu bionic-security InRelease Reading package lists... Done Building dependency tree        Reading state information... Done All packages are up to date. W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://dl.winehq.org/wine-builds/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 76F1A20FF987672F W: Failed to fetch https://dl.winehq.org/wine-builds/ubuntu/dists/bionic/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 76F1A20FF987672F W: Some index files failed to download. They have been ignored, or old ones used instead.   I've try to use sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-key 76F1A20FF987672F to fix it, but noting is fixed:  gpg:keyserver receive failed: No data   How can I fix this? I uninstalled wine last week; have I not fully uninstalled it?


If $G$ is a group of order $4n+2$, then $G$ contains a subgroup of order $2n+1$

This question comes from M.A. Armstongs book Groups & Symmetry, Chapter 13, #5.  I came across a similar question , but I am not familiar with the language yet and would rather solve using the tools I've amassed to this point in my learning.  The question tells us to use Cayley's and Cauchy's Theorem, as well as the fact that if a subgroup $H$ of $S_n$ is not contained in the alternating group $A_n$, then half the elements of $H$ are even.  At the moment a promising approach (to me) is to examine the two cases: $2n+1$ is prime or $2n+1$ is not prime. The former leads directly to the conclusion via Cauchy, but the more difficult one tells me nothing other than $2n+1$ is a product of primes.  Any suggestions or hints to pursue this course or another one is appreciated.


Why do we use the ?  Why did it come to be the electron volt and not, say, just a prefix of the joule, like the nanojoule?  Does the electron volt represent anything particular as far as the mathematics goes? I am guessing that it does, and if so, what is it that the electron volt exactly represents in terms of the mass of a particle, as I have seen it used for both the energy of a photon and the mass of subatomic particles?


What is the MCU film "Critical Path" to get proper backstory before watching Avengers: Endgame?

I'm a casual Marvel Cinematic Universe (MCU) film fan and have probably watched about a third of the MCU films that came out since .  Is there a "" of MCU films I should watch (or have watched) prior to watching Avengers: Endgame?  I know Avengers: Endgame has not yet come out, but I'm hoping that by the time it's released (April 26, 2019 here in the US), I'll have caught up with those movies I've missed to ensure I'm minimizing any plot holes due to missing a prior film.  Side Note: If this question belongs on a different SE site (such as ), please feel free to migrate it on my behalf.


Maximal ideal in the ring of real valued continuous functions

Let R be the ring of continuous functions  f:[0,1]→R   with pointwise addition and multiplication, and suppose M is a maximal ideal. Prove that there is  a∈[0,1]  such that  M={f $\in $ R:f(a)=0}. I know how to prove its converse. I am trying to use the fact that since M is a maximal ideal then R/M is a field ; but can't really make any progress with it. Is there any alternative way of doing this?


Let $z_1$ and $z_2$ be two complex numbers. Show that there exists $C > 0$ with   $$  |z_1 + z_2|^2 < (1+C)|z_1|^2 + \left(1 + \frac{1}{C}\right) |z_2|^2. $$   I tried to simplify the L.H.S and R.H.S, SNF I was finally left to compare between a real number and a complex number  I really couldn't think of anything else. Please help.


I do a RayCast to the terrain and then use the RaycastHit.normal to plant flags.  I would like to have the flags to point up with the normal, but have them all face the same direction. As seen in the image flag 1 points to left of the screen and flag 5 to the right. I understand why, but do not know how to rotate it. I saw LookRotation (Unity) has an override that takes a forward direction too. I thought it would work with say Vector3.Forward, but if a flag is placed on a wall it points into the wall. The direction or angle they face can be set by the player. I have a hard time understanding quaternions, every time I think I do, I get stuck. Any tips ?


In python, how do I invert a 2D dictionary?

I have a dictionary in the following form  dict = {    "a" : {"a1" : 1},    "b" : {"a2" : 1, "a3" : 2},    "c" : {"a2" : 3, "a4" : 3} }   and I need the reverse index dictionary, in this form:  inverseDict = {     "a1" : {"a" : 1},     "a2" : {"b" : 1, "c" : 3},     "a3" : {"b" : 2},     "a4" : {"c" : 3} }   Basically  inverseDict = {dict.value.key : { dict.key : dict.value.value}}   So essentially, I need the keys of the values as keys, and the keys as keys of values, while at the same time joining results for duplicate new keys etc.  I've tried to do   ks = dict.keys() vals = dict.values()  ks2 = vals.keys() vals2 = vals.values()   if this makes any sense  But I'm getting an error   'dict_values' object has no attribute 'keys'   Which from what I understand is because dict.values() .keys() .items() return "views" instead of the actual element itself, but I don't know hot to go about fixing this problem.  Also is there a more efficient solution I should consider, because my actual dict is pretty large (~10k keys), and the resulting inverse dict will also be large  ( >3k keys)


Does someone know if SCII allow finally play trough LAN only ? (without internet) I know in the past (10 years ago : ) it's was not possible. is this has finally changed ?


Are answers that contain advertisements allowed?

So I just found  in which the accepted answer is only about an advertisement to an app that solves the problem. No offense to anyone, but isn't it too subjective? If the problem can't be solved without app, in my opinion, they should've just say something like:  Sorry, this problem cannot be solved without an extension or external app.  In my opinion, advertising in an answer is against the antitrust law, because accepted answers are always on top AND there is only one seat for an accepted answer. Why wasn't this answer moderated?


Why are there two different Ubuntu Software apps?

I came across the Ubuntu Software Center application while I was looking through Ubuntu Software in Ubuntu 16.04. It had the same icon and a lot of the same apps as the Software app. Can anyone explain this to me?


The titles of freestanding works (books, movies, plays, albums, etc.) are italicized; smaller parts within these works (chapters in a book, articles in a magazine, songs within an album) are not (they are put in quotes, instead).  How are software titles treated?  My understanding is that if a particular program resembles a book or a dramatic work (like a video game), its title is italicized -- otherwise, it is treated as a proper noun, just like any other product.     I played Grand Theft Auto, instead of reading "Democracy in Ancient Greece" in Microsoft Encarta and preparing my presentation in PowerPoint.   Is this approach correct?


Show with only elementary methods that the ODE $f(x)=f'(x), f(0)= 0$ has only the constant function as solution

Given the ODE $f(x)=f'(x)$ one obtains that its only solution is $ce^x$ for some constant $c$.  So if one adds the constraint $f(0) = 0$, it's easy to check that there's no way to bend the particular solution to generate this value besides setting $c=0$.  Technically, we should have enough information to reason this without any use of our knowledge about ODEs, simply by proving that the function can't be not constant.  So by basic method, I mean a method as simple as possible, but at least one that's not using knowledge about the possible functions solving the ODE.  A few examples of possible answers, which in my opinion still use too much machinery for the simplicity of the problem:  1) If the solution were analytical, its Taylor polynomial simply would be 0.  2) We can make an iterative approximation by splitting the interval $[0,b]$ into $n$ pieces, and for every piece add the increase caused by $f$'s gradient to the function (which trivially means $f$ will stay constant throughout the whole iteration). We can then show that if we let $n\to\infty$, the error of the approximation goes to 0.  I really feel like there should be a simply and easy solution to this: After all, we know no less than  $0=f(0)= f'(0)= f''(0)= ...$  Which intuitively, combined with $f$'s continuity already seems to force $0$ to be the only solution.


Limit of function with natural logarithm

I need help solving this problem. I tried L'hospital and rearranging but nothing worked. $$ \lim_\limits{x→∞} x^2\left(\ln\left(1 + \frac{1}{x}\right)- \frac{1}{x+1}\right) $$


When I clicked to open calculator app then for few seconds it is keep on loading. Then automatically it closes.


How does the number of eyes represent the number of persons?

I had an exam today (Egyptian GSEC english exam) and in a passage about library it said:     The book slipped from his hands and fell on the floor with loud noise, 20 eyes looked at him and his face turned red.....   It then asked: approximately,how many persons where at the library?  Ten or twenty or forty  But I would like to know if twenty eyes represent 10 persons or is it like a metaphor and represents 20 persons?  Is this expression even correct?  Edit : in the passage it was obvious that it is a normal library with normal people i just cut a part out of its context that serves the question


Pivoting Dynamic Rows into Columns in MySQL

I have two tables Student_Attendance and Students.  I am using this query:  SELECT     sa.Student_Id,      sa.Attendance_Date,      CASE WHEN sa.Attendance_Status as Status FROM student_attendance sa  INNER JOIN courses c      ON c.Course_Id = sa.Course_Id INNER JOIN students es      ON es.Student_Id =  sa.Student_Id WHERE sa.Course_Id = 1  ORDER BY sa.Attendance_Date DESC;   I am getting this result from above query:         But I want something like below:        In the student_attendance table there are more than 50 rows.   How 7 attendance_date rows should be converted into 7 columns as I have given below?  Can someone help me please?


Does the series $\sum \frac{\sin p}{p}$, where $p$ prime, converge?

Question. Assume that $\{p_n\}$ is the sequence of prime numbers, in increasing order. Does the series $$ \sum_{n=1}^\infty \frac{\sin p_n}{p_n} $$ converge?  The only criterion to establish convergence that I can think of, which might be of any use, is the , which requires that the partial sums of the sequence $b_n=\sin p_n$ are bounded, i.e., that there exists an $M>0$, such that $$ |\sin p_1+\cdots+\sin p_n|\le M, \quad\text{for all $n\in\mathbb N$}. $$  Any ideas?


One element of python list changes, causes the whole column elements changed


I have terrain (ANT Landscape plugin) that I would like to cut up into chunks (don't need to be equal size) for a game engine so that I can do occlusion culling /  or load and unload chunks around the player.  I am trying the knife project feature that I saw in the answer  but it doesn't work for my terrain mesh (using the terrain plugin).  I also tried some answers here that contain some Python scripts, but couldn't get them to work.  Any ideas of how I can cut the mesh up quickly in to chunks.  I've been doing it manually so far, but it takes forever to do as some terrains can be rather big. I don't mind having to do a little clean up of the mesh after.  Picture below shows the knife project method (following instructions from linked answer).      Thanks  Edit:  Example of mesh (terrain is usually much large than this) that I am trying to break into chunks.    How I am manually doing it.    Blend file that contains terrain and grid for the knife projecting method.


How can I set up a broadband connection?

I tried to set up broadband Internet connection, started as I found   sudo pppoeconf   and shown that wifi was disabled.     Sorry, I scanned 2 interfaces, but the Access   Concentrator of your provider did not respond. Please   check your network and modem cables. Another reason for   the scan failure may also be another running pppoe   process which controls the modem.   and the result found below my command was  SIOCSIFFLAGS: Operation not possible due to RF-kill   If the same command runs after enabling wifi, no result is showing in terminal.  Then I tried another command  sudo ifconfig   And got this result:  eth0      Link encap:Ethernet  HWaddr 20:89:84:ea:68:5d             UP BROADCAST MULTICAST  MTU:1500  Metric:1           RX packets:0 errors:0 dropped:0 overruns:0 frame:0           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0           collisions:0 txqueuelen:1000            RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)           Interrupt:16   lo        Link encap:Local Loopback             inet addr:127.0.0.1  Mask:255.0.0.0           inet6 addr: ::1/128 Scope:Host           UP LOOPBACK RUNNING  MTU:65536  Metric:1           RX packets:8947 errors:0 dropped:0 overruns:0 frame:0           TX packets:8947 errors:0 dropped:0 overruns:0 carrier:0           collisions:0 txqueuelen:0            RX bytes:961374 (961.3 KB)  TX bytes:961374 (961.3 KB)   wlan0     Link encap:Ethernet  HWaddr 48:d2:24:3f:4f:3e             inet addr:192.168.59.104  Bcast:192.168.59.255  Mask:255.255.255.0           inet6 addr: fe80::4ad2:24ff:fe3f:4f3e/64 Scope:Link           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1           RX packets:241942 errors:0 dropped:0 overruns:0 frame:0           TX packets:173747 errors:0 dropped:0 overruns:0 carrier:0           collisions:0 txqueuelen:1000            RX bytes:338342037 (338.3 MB)  TX bytes:18314966 (18.3 MB)   Can anyone please explain to me what the is problem and what steps I should follow to resolve it?


Solution of the series $n^0 + n^1 + n^2 + n^3 + \cdots + n^k$

What is the formula to calculate  $$n^0 + n^1 + n^2 + n^3 + \cdots + n^k$$  Calculate example  $$185^0 + 185^1 + 185^2 + \cdots + 185^{13}$$  Any hints appreciated!


existById in JpaRepository return NullPointerException

I have an implemented interface extends from JpaRepository when I use repository.existById(); and pass unavailable id in the database. It returns NullPointerException, there is nothing saying anything about NullPointer in the documentation. It's a boolean, why it return NullPointerException?  My repository @Repository public interface AccountRepository extends JpaRepository<Account, Long> {      Boolean existsAccountByClientUsername(String username);      Account findAccountByClientUsername(String username); }  Test code that uses exsistByID @Test public void givenNotAvailableId_whenGetAccountById_thenThrowIllegalArgumentException() {     Long id = Long.MAX_VALUE;     IllegalArgumentException exception = Assertions              .assertThrows(IllegalArgumentException.class, () -> accountService.getAccountById(id));     Assertions.assertEquals("Id not found", exception.getMessage()); }  production code  @Service public class AccountService {      @Autowired     private AccountRepository accountRepository;      public AccountService(AccountRepository accountRepository) {         this.accountRepository = accountRepository;     }     public Optional<Account> getAccountById(Long id) {         throwIfNotFoundId(id);         return accountRepository.findById(id);     } }  throwIfNotFoundId method private void throwIfNotFoundId(Long id) {     if (!accountRepository.existsById(id)) {         throw new IllegalArgumentException("Id not found");     } }


Passing custom string into a Salesforce email template.

I've stumbled upon a problem at the final stage of a new feature I was building (as always)   I need to pass in a custom string into a salesforce template, however there doesnt seem to be a way of doing this through the standard methods.   I'm passing in a contact ID, to email the correct user and name to personailse the email. But I need a string to be passed to the template which is completely unrelated to the contact record, and need to be dynamic. So I cant just put it in the template.   Is there a way? I know i cant pass in a custom object as it needs to be a contact, user or lead id to email a user.   Can you help?   Here is the code if you need to see it:  public static void sendSingleMail(id objId, ID templateId, string fromaddress) {      Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();     mail.setReplyTo(fromaddress);     mail.setTemplateId(templateId);     mail.setTargetObjectId(objId);     mail.saveAsActivity = false;     mail.setReplyTo(fromaddress);     mail.setSenderDisplayName(fromaddress);      ErrLogger.logger('Email being sent to :');     ErrLogger.logger('objId found:  ' + objId);     ErrLogger.logger('templateId found:  ' + templateId);     ErrLogger.logger('fromaddress found:  ' + fromaddress);      Messaging.sendEmail(new Messaging.SingleEmailmessage[] {mail}); }


How can I make custom skins for agar.io?

How can I make agar.io skins? I don't remember how to make skins for agar.io. I want to make agar.io skins on the PC version with my friend.


Ideals of the subring $\begin{pmatrix} a & 0 \\ b & c \end{pmatrix}$ of $M_2(\mathbb Z)$

The set $A$ of all lower triangular $2\times 2$ matrices with entries in $\mathbb Z$ is a subring of $M_2(\mathbb Z)$. However, what are its ideals? I couldn't find them.   Suppose $I$ is an ideal of $A$. The elements of $I$, being also elements of $A$ have to be lower triangular and $I$ should be closed under left and right multiplication by lower triangular matrices. These facts couldn't lead me anywhere.  Edit: I saw  and the answer there went far above my head. I have no idea what a module is. Please help me do this without resorting to all of those advanced technique


Lenovo ThinkPad T440p + Ubuntu 12.04/14.04

Is there anybody, who is able to install Ubuntu 12.04 or 14.04 (64bit) on Lenovo Thinkpad T440p and get fully functional NVIDIA Optimus? This laptop model is certified by Canonical to be fully supported by Ubuntu, but install Ubuntu 14.04 is nearly impossible, due to the fact, that 14.04 desktop ISO image crash during initial boot.   Any help?  See, for exmaple:   Add info regarding bad 12.04 support:


I'v indexed my pages in search console, but Google didnt show them in search results

I have indexed all of my webpages into google search console tools.. but Google did not show the results in search results. Can you help me please.. see the latests articles, they wont show in search results


Explanation of "R Square" in terms of correlation?

In linear regression, I seemed to see (but I forgot where) that if the square sum of residuals divided by square sum of total variation equals the square of some correlation between some random variables, and hence it explains why the ratio is called "R Square".   So I was wondering what the correlation is between, and why the ratio is the square of the correlation?   What assumptions on the linear regression model are needed for the explanation of "R Square" in terms of correlation?  Thanks!


Black screen after installing Ubuntu 14.04

I installed Ubuntu 14.04 on a partition along with Windows XP, but when I start Ubuntu I only get a black screen. I repeated the installation 3 times successfully, but my screen remains black. Can someone help me?


I have a problem when I use a cross-reference from other files. I have a folder in which there is a main.tex file and a subfolder (Chapter) containing Chapter1.tex and Chapter2.tex.  In the main file, I include only the chapter files like this:      \include{Chapters/Chapter1}     \include{Chapters/Chapter2}   My problem is that in the Chapter2.tex file I need to reference a section from Chapter1.  Chapter1.tex  \documentclass{standalone} \begin{document} \chapter{chapter} \label{ch:first_chapter}  \section{first section}\label{sc:first_section}      some Text.......... \end{document}   Chapter2.tex  \documentclass{standalone} \usepackage{xr-hyper} \usepackage{hyperref} \externaldocument[C1-]{/Chapter1} \begin{document} \chapter{Second Chapter} \label{ch:second_chapter} \section{section}\label{sc:first_section_ch2}   Some text...text \ref{C1-sc:first_section}  \end{document}   When I compile the file, only ?? appears.


I have the following problem.   \documentclass[a4paper,12pt,oneside]{book} \maketitle \tableofcontents*  \chapter*{Introduction}\addcontentsline{toc}{chapter}{\textbf{Introduction}}   And the problem is that I want the running title (in the headers of pages of this chapter) to be only "Introduction"  while it is "Table of Contents". I've tried to use  \chaptermark{Introduction}   but then the running title is "Chapter 0. Introduction". I would like remove "Chapter 0" and to leave only "Introduction". The only thing I know that removes the word Chapter from running title in the page headers is   \backmatter  but it completely destroys the numbering of chapters which I don't want to change and creates unnecessary empty pages.  I would be very thankfull for any help.


The project(written in Java) is getting large and large and some code will never be used. Is there a way to detect those dead/unuseful code and clean them up. I'm open for ideas.


How can I ask a user for 4 numbers and print them out sorted (ascending / descending)?

When I use this code it asks the user for 4 numbers.   When you write in the 4 numbers it prints them as wanted.   Then I want to ask the user for ascending or descending order, but the code just ends.  import java.util.Collections; import java.util.Scanner;  //import scanner class import java.util.ArrayList;  public class task2 { public static void main(String[] args){      Scanner scanner = new Scanner (System.in);  //create a scanner object     System.out.println("Enter 4 numbers");      //numerical input     int a = scanner.nextInt();     int b = scanner.nextInt();     int c = scanner.nextInt();     int d = scanner.nextInt();      System.out.println(a + "." + b + "." + c + "." + d);      System.out.println("you want the numbers by order? (descending / ascending)");     String order = scanner.nextLine();      ArrayList<Integer>             list = new ArrayList<Integer>();      list.add (a);     list.add (b);     list.add (c);     list.add (d);      if (order == "ascending"){         Collections.sort(list);         System.out.println(list);     } if (order == "descending"){         Collections.sort(list, Collections.reverseOrder());         System.out.println(list);     } }   }


Epson WorkForce printer keeps power-cycling

When I press the power button on my Epson WorkForce WF-3520 printer, it starts up normally, but shuts down within 30 seconds. Ten seconds later, it starts itself and the stop/start cycle is repeated again and again. This has only started happening today (6th December 2016).


How to use intergrated graphics instead of dedicated

I have a recent asus motherboard with an i7 processor and i've got a nvidia 670gtx connected to it.  For various reasons/experimentation purposes i'd like to connect my monitor to the intergrated graphics adapter rather than my gtx 670 card.  If i connect it to the motherboard's DVI connector the screen does not display any image on POST, nor when i'm actually in my OS, if i move the connector to the GTX card i get an image however.  Why is this happening? how can i use the intergrated graphics port to connect my monitor? (it must not involve disconnecting the GTX card)


Why use UUIDs in /etc/fstab instead of device names?

What is the reasoning behind using UUIDs in /etc/fstab instead of device names (like /dev/sbd2)?  Device names &/or partition numbers seem substantially cleaner from an administrative viewpoint.


I was attempting to solve an MIT integration bee problem (1) when I misread the integral and wrote (2) instead.   $$\int\sqrt{x\cdot \sqrt[3]{x\cdot \sqrt[4]{x\cdot\sqrt[5]{x\ldots } }}}\,dx\tag{1}$$  $$\int\sqrt{x^2\sqrt{x^3\sqrt{x^4\sqrt{x^5\sqrt{x^6\sqrt{x^7\sqrt{x^8\ldots}}}}}}}\,dx\tag{2}$$  I was able to solve (1), as the integrand simplifies to $x^{e-2}$, however, I'm struggling with solving (2).   If we rewrite the roots as powers, we get:  $$\int x^\frac{2}{2}\cdot x^\frac{3}{4}\cdot x^\frac{4}{8}\cdot x^\frac{5}{16}\ldots\,dx$$  combining the powers we get: $$\int x^{\frac{2}{2}+\frac{3}{4}+\frac{4}{8}+\frac{5}{16}+\ldots}$$  the exponent is the infinite sum  $$\sum^{\infty}_{n=1}\frac{n+1}{2^n}\tag{3} $$ we can split this into:  $$\sum^{\infty}_{n=1}\frac{n}{2^n}+\sum^{\infty}_{n=1}\frac{1}{2^n} $$ The right sum is well known except here the sum begins at $n=1$, meaning that the right sum evaluates to 1. Messing around with desmos, the integrand appears to be $x^3,x>0$ implying that (3) converges to 3 and the $\sum^{\infty}_{n=1}\frac{n}{2^n}$ converges to 2.  Which is part I'm struggling with. Any ideas?   $$\sum^{\infty}_{n=1}\frac{n}{2^n}$$


Quantities like position and time allow us to place our origin anywhere, but can the same be said for energy? I was thinking about the way we have defined the quantity gravitational potential, and for any finite distance from a 'planet' or a body, an abject would be said to have negative gravitational potential, conveying that a negative amount of work is done (in bringing the object from 'infinity' to that position, but this seems impossible as negative energy does not seem to physically exist (as far as I know). So, does negative energy really exist, or does it not (implying that negative work done is just another mathematical argument)?  Edit: The primary reason I ask this question is because I was wondering whether negative work done is fundamentally different from negative debts (when talking about money), or are they just the same - a mathematical convenience.


Determining the general perpendicular normal

Given a vector $n \in \mathbb R^3$, how can I find (any) perpendicular normal $x$, such that $n^T\cdot x=0$ for all possible values of $n$ (i.e. with no edge cases)


Lenovo Legion Y520 with Ubuntu 17.10 – Nvidia driver and settings

I bought a new Lenovo Legion Y520 and wiped Windows 10 Home because I don't like and need it. The notebook comes with a Nvidia GTX 1050 and I was wondering what's the proper way to set up the graphics for occasional playing. With a fresh ubuntu setup, default drivers and settings I tried playing "Cities Skylines" with a lot of graphical issues (texture glitches, intolerable freezes and so on) so I assume my graphics aren't set up well. I tried a few things like simply updating Nvidia driver to 390 without any changes and started it over. Do you have any advices for me how to go on from a fresh Ubuntu 17.10 installation? Hope you guys could help me out!