Short story in a society where people constantly record their whole lives and receive "ratings" on their skills/abilities?

This is a recent story, probably from the 2000s.  The protagonist of the story is a teen-aged boy whose highest "rating" (based on the entirety of the world population) is in... magic, or card tricks, or something to do with cards? He laments he will never really be good enough to be famous/popular and have a shot at being in the Top 100, etc. Eventually he meets a girl who is disconnected from the "system," and when he shows her his card tricks, she is impressed because she has never seen anyone do it better, since she isn't a part of the "system."   There was a part in the story talking about how one kid who had never had sex before, had sex with someone else and instantly became the #1 rated "male intercourse with female" in the world, and how everyone was waiting for him to have sex again to see if his rating would stay high or plummet out.  I don't remember if the story was CCTV-style constant surveillance or 'eye cam' or both. I do remember that the protagonist and the girl had to go somewhere secluded (and take out their contact-cam?) to get away from being recorded.


Classification / learning with one class

My dataset contains a single class, which has noisy examples. Up to now I have been converting this to a binary classification problem and using logistic regression, however this does not feel correct, as the negative class has data which is not truly part of a single class, it is just not in the "positive" class. I stumbled upon and tried  with little success (in terms of classification performance). What are some possible techniques for learning the distribution of just one class? Am I formulating the problem in the correct manner? My specific dataset are document vectors created by a doc2vec model. EDIT: Adding more information based on comments. The task is to classify webpages that will be relevant for certain advertisers based on past performance. We have a positive class, where we know there was a positive interaction. I have been training an LR model based on this positive interaction and a sample of pages where no interaction occurred. EDIT 2: Again based on the comments I would like to provide a simpler contrived example to see if my thinking about this is wrong. Let's say we want to classify webpage as being about football, we could:  train a classifier of football VS non-football train a model to learn the distribution of football and treat all other articles as outliers  Is the second option an incorrect way of framing this problem?


I have already drawn a graphic function that isn't defined at -3 and -2. But somehow, I tried to draw the vertical asymptote, x=-3 and x=-2, then I get stuck. As I know, the \addplot is used to draw f(x), not f(y). Anybody can help me?  \documentclass{report} \usepackage{pgfplots} \begin{document}  \begin{tikzpicture} \begin{axis}[    axis lines = left, axis x line= center,    axis y line= center,    xlabel = $x$, ylabel = {$f(x)$},    xmajorgrids=true, ymajorgrids=true,    restrict y to domain=-50:50,    ymin=-40, ymax=40,] \addplot[    samples=500, color=red, thick]    {(x-1)/(x^2+5*x+6)}; \addplot[    samples=100, color=blue, thin, dashed] %   {???}; <= how can I get the x=-3 line? \end{axis} \end{tikzpicture}  \end{document}


Controlling title , bibtex, using JabRef

I'm using Jabref to manage references. I use references both in English and German.       % my Question \documentclass[12pt,twoside]{report}% Use this line for the print version of the thesis  \usepackage{natbib} \begin{filecontents}{\jobname3.bib} @INPROCEEDINGS{Talaya2004,   author = {Talaya, J. and Alamús, R. and Bosch, E. and Kornus, W},   title = {Integration of a Terrestrial Laser Scanner with {GPS/IMU} Orientation     Sensors},   booktitle = {The International Archives of the Photogrammetry, Remote Sensing     and Spatial Information Sciences 35 (Part B7)},   year = {2004},   pages = {990-995},   owner = {Say},   timestamp = {2013.09.07} } @PHDTHESIS{Gordon2008,   author = {Gordon, B},   title = {Zur Bestimmung von Messunsicherheiten terrestrischer Laserscanner},   school = {Technical University Darmstadt, http://tuprints.ulb.tu-darmstadt.de/1206/.},   year = {2008},   owner = {Say},   timestamp = {2013.09.08} } @ARTICLE{Rautenberg2002,   author = {Rautenberg, U and Wiggenhagen, M},   title = {Abnahme und Ueberwachung photogrammetrischer Messsysteme nach VDI     2634, Blatt 1},   journal = {PFG},   year = {2002},   volume = {Nr. 2/2002},   pages = {pp. 117-124},   owner = {Sayyad},   timestamp = {2013.09.08} }  \end{filecontents}  \begin{document}  %%%%%%%%%%%%% begin Bibliography %%%%%%%%%%%%%%%%% \citet{Talaya2004}\\  \citet{Gordon2008} \citet{Rautenberg2002} \bibliographystyle{apalike}  \bibliography{\jobname3}  \end{document}   Output:     Gordon, B. (2008). Zur Bestimmung von Messunsicherheiten ter-   restrischer Laserscanner. PhD thesis, Technical University Darmstadt,   .      Rautenberg, U. and Wiggenhagen, M. (2002). Abnahme und ueberwachung   photogrammetrischer messsysteme nach vdi 2634, blatt 1. PFG, Nr.   2/2002:pp. 117-124.      Talaya, J., Alams, R., Bosch, E., and Kornus, W. (2004). Integration   of a terrestrial laser scanner with GPS/IMU orientation sensors. In   The International Archives of the Photogrammetry, Remote Sensing and   Spatial Information Sciences 35 (Part B7), pp. 990-995.   I want to get     Gordon, B. (2008). Zur Bestimmung von Messunsicherheiten ter-   restrischer Laserscanner. PhD thesis, Technical University Darmstadt,   .      % Correct german, Nouns are written with capital letters      Rautenberg, U. and Wiggenhagen, M. (2002). Abnahme und   Ueberwachung photogrammetrischer Messsysteme nach VDI 2634, Blatt 1. PFG, Nr. 2/2002:pp. 117-124.      % First letter should be capital.      Talaya, J., Alams, R., Bosch, E., and Kornus, W. (2004). Integration   of a Terrestrial Laser Scanner with GPS/IMU Orientation Sensors. In   The International Archives of the Photogrammetry, Remote Sensing and   Spatial Information Sciences 35 (Part B7), pp. 990-995.   What  should include / have to change in my code. What should I change in .bst file.  I'm using JabRef to mange my code.


Are the default kernels come with official distributions of Ubuntu the most suitable for them?

Recently I realized that Ubuntu can be booted with different kernels, and downloading Official Ubuntu distributions from Ubuntu.com there are usually two kernels installed by default on the system. I realized it is possible to install more kernels. I want to know are the kernels that come with the official distribution the best ones for Ubuntu to function well, or as newer the kernel is it is better to boot the system with?


Is there a key combination to cycle through clipboard history when pasting in windows?

In Visual Studio, I can cycle through my clipboard history by pressing CTRL+SHIFT+V rather than CTRL+V. I believe it's called a clipboard ring. But that feature doesn't seem to exist outside of Visual Studio, at least not with the same key combination. Is there a key stroke combination built in to windows to do the same, i.e. be able to cycle through your clipboard history while pasting?


Heuristic derivation of Schrodinger equation

Is there a heuristic derivation of Schrodinger equation beginning with concepts from classical physics? When I say classical I mean something at the level of an engineer.


Which fonts support Cyrillic letters in TexLive?

TeXLive installs a lot of fonts. How can I know which of them support Cyrillic letters?


How to avoid the 'not properly formatted as code' alert

I've been trying for many hours to post a question in Mathematica Stack Exchange and I always get the following warning  I've done the indentation but did not work (though in the preview looks perfectly fine). I also pressed the code toolbar button and tried to use ``` and ' instead of indenting but did not work either. How can I fix the problem? I am sure it has to be a really basic mistake of mine. Here's the question I want to post: I want to compute the Christoffel-symbol for a given metric. I am using the code , but I am missing something. The Chrisfoffel-symbol formula is $$ \Gamma^{\mu}{\phantom{\mu}\nu\sigma}=\frac{1}{2}g^{\mu\alpha}\left{\frac{\partial g{\alpha\nu}} {\partial x^{\sigma}}+\frac{\partial g_{\alpha\sigma}}{\partial x^{\nu}}-\frac{\partial g_{\nu\sigma}}{\partial x^{\alpha}}\right}\quad $$ The metric is given to be $$ g_{\mu \nu} = \begin{pmatrix} 1 & 0 & 0 & 0 \ 0 & r^2+b^2 & 0 & 0 \ 0 & 0 & (r^2+b^2)\sin^2(\theta) & 0 \ 0 & 0 & 0 & -1 \end{pmatrix} $$ The provided solution is: $$ \Gamma^{1}{22}=-r $$ $$ \Gamma^{1}{33}=-r\sin^2(\theta) $$ $$ \Gamma^{2}{21}=\frac{r}{b^2+r^2} $$ $$ \Gamma^{2}{33}=-\cos(\theta)\sin(\theta) $$ $$ \Gamma^{3}{31}=\frac{r}{b^2+r^2} $$ $$ \Gamma^{3}{32}=\cot(\theta) $$ The code I'm using is     Clear [coord, metric, inversemetric, affine]       n = 4; coord = {t, x, y,z};       metric = { {1,0,0,0}, {0,r^2+b^2,0,0}, {0,0,(r^2+b^2)Sin[\[Theta]]^2,0}, {0,0,0,-1}};       inversemetric = Simplify[Inverse[metric]];       affine := affine = Simplify[ Table[(1/2)* Sum[inversemetric[[i, s]]*(D[metric[[s, j]],                          coord[[k]]] +      D[metric[[s, k]], coord[[j]]] - D[metric[[j, k]], coord[[s]]]), {s, 1, n}], {i, 1, n}, {j, 1, n},          {k, 1, n}]];       listaffine := Table[If[UnsameQ[affine[[i, j, k]], 0], {ToString[\[CapitalGamma][i - 1, j - 1, k      -1]], affine[[i, j, k]]}], {i, 1, n}, {j, 1, n}, {k, 1, j}];      TableForm[Partition[DeleteCases[Flatten[listaffine], Null], 2], TableSpacing -> {2, 2}]  I am struggling now in how to call out the specific Christoffel symbols correctly. What I do is     affine[[3,3,2]]  But I get zero instead of $\cot(\theta)$; the same happens to me with other non-zero terms. What am I missing? Besides, I'd like to learn how could I display the answer once I know how to actually get it.


Is volunteer work allowed in the US while visiting under the VWP or a B1/B2 visa?

I am going to Santa Monica for 4 weeks to polish my English in July and would like to volunteer at the Planetary Society located in Pasadena.  I am a Swiss citizen and have a biometric passport. However, I don't have any special visa, as there is no visa needed for the school I am attending and using the Visa Waiver Program, I am allowed to stay up to 90 days in the US.  Am I allowed to do volunteer work during my stay?


Use runas with a domain account on a non-domain machine in Windows 2k/XP/Vista/7

My Windows 7 computer is on LAN in an intranet with a Windows domain, but it is not a member of that domain. However, I need to run some applications under domain accounts while I'm logged on locally as a local admin.  I know you can use the runas utility to start processes under accounts different from the one under which you have logged on. The thing is that Windows needs to know or authenticate the account under which a process is starting.  When I do something like:  runas /user:DOMAIN\USERNAME cmd.exe   (and put in a correct password afterwards) I get this kind of error:  RUNAS ERROR: Unable to run - cmd.exe 1326: Logon failure: unknown user name or bad password.   Does anybody know how to cope with this?


Can I substitite iodized salt or sea salt instead of kosher salt to fry green tomatoes?

I am frying green tomatoes. The recipe calls for kosher salt. Can I use iodized salt or sea salt instead?


How long after first contact, where editor says "manuscript is still under review", is it okay to enquire again about status of manuscript?

About a year ago I submitted a paper to a very good math journal.  After 10 months I asked the editor for its status,  and he said it is still with the referee, and that he will remind him about it.  Two more months have passed. Should/could I write the editor again? or am I risking annoying the editor/referee? How much time should I wait between such inquires?


Reverse Tethering (USB) through Windows 10 using Android 4.2.2 without installing additional software

I want to use the Internet Connection of my Windows 10 PC with my Android-Device through USB-Cable.  How can I reverse tether through windows 10 using my usb-cable?  I have found some , but the question and its answers are telling me how to use the Android SDK to do USB-Tethering. I don't want to install additional software like the Android SDK.  It sounds, like there was an built in solution in windows, but the necessary sharing tab is missing:   Is there really no way to do usb-tethering using Windows 10 without installing external software like the Android SDK?


Getting a constant answer while finding patterns with neuralnet package

I'm trying to find patterns in a large dataset using the neuralnet package.  My data file looks something like this (30,204,447 rows) :  id.company,EPS.or.Sales,FQ.or.FY,fiscal,date,value  000001,EPS,FY,2001,20020201,-5.520000 000001,SAL,FQ,2000,20020401,70.300003 000001,SAL,FY,2001,20020325,49.200001 000002,EPS,FQ,2008,20071009,-4.000000 000002,SAL,FY,2008,20071009,1.400000   I have split this initial file into four new files for annual/quarterly sales/EPS and it is on those files that I want to use neural networks to see if I can use the variables id.company, fiscal and date in the case below to predict the annual sales results.  To do so, I have written the following code:  dataset <- read.table("fy_sal_data.txt",header=T, sep="\t") #my file doesn't actually use comas as separators  #extract training set and testing set trainset <- dataset[1:1000, ] testset <- dataset[1001:2000, ]  #building the NN ann <- neuralnet(value ~ id.company + fiscal + date, trainset, hidden = 3,              lifesign="minimal", threshold=0.01)  #testing the output temp_test <- subset(testset, select=c("id.company", "fiscal", "date")) ann.results <- compute(ann, temp_test)  #display the results cleanoutput <- cbind(testset$value, as.data.frame(ann.results$net.result)) colnames(cleanoutput) <- c("Expected Output", "NN Output")  head(cleanoutput, 30)   Now my problem is that the compute function returns a constant answer no matter the inputs of the testing set.       Expected Output   NN Output 1001     2006.500000 1417.796651 1002     2009.000000 1417.796651 1003     2006.500000 1417.796651 1004     2002.500000 1417.796651     I am very new to R and its neural networks packages but I have found online that some of the reasons for such results can be either:   an insufficient number of training examples (here I'm using a thousand ones but I've also tried using a million rows and the results were the same, only it took 4h to train)  or an error in the formula.   I am sure I'm doing something wrong but I can't seem to figure out what.


Can I award a bounty to my old question?

. I can't award a bounty to this question. But I need an answer to this question. Is it possible to award a bounty to questions ?   Note: I'm not fully familiar with the bounty system.


Let $M$ be a metric space, $x_n\in M$ a sequence which converges to $x\in M$  Prove: $F=\{x_n\}\cup \{x\}$ is a closed set  So we have $x_n\to x$ such that $x_n\in F$ and $x\in F$ and we know that a set is closed if it contains all of its accumulation points, so $F$ is closed  Or must I look at $F^c$ and prove that it is open?


Upgrade Kubuntu 20.04 to latest release (21.04), instead of next release (20.10)

I want to upgrade from Kubuntu 20.04 to 21.04. I have changed /etc/update-manager/release-upgrades so that Prompt=normal. Running pkexec do-release-upgrade -m desktop -f DistUpgradeViewKDE I get the option to upgrade to 21.10.  Also, sudo do-release-upgrade -m desktop [sudo] password for cip:  Checking for a new Ubuntu release Get:1 Upgrade tool signature [819 B]                                                                                Get:2 Upgrade tool [1 340 kB]                                                                                Fetched 1 341 kB in 0s (0 B/s)                                                                                authenticate 'groovy.tar.gz' against 'groovy.tar.gz.gpg'  extracting 'groovy.tar.gz'  I guess that should say hirsute instead of groovy.  How to upgrade to latest 21.04 directly?


How can I tell if a laptop's video card can be upgraded?

Some laptops have integrated video, while others have dedicated graphics.  Still others have dual graphics that change on demand.  Most laptops have the video components built into the design of the motherboard, but some have a separate video card that can be removed.  How can I identify if a laptop has a card that can be removed?


How to optimal display multiple subdivided objects with one or few clicks?

I have several objects with subdivision surface that I would like to set in optimal display option, because it is annoying to apply that setting in every single object separately.


Is there any process for informing the community about StackExchange members who have passed away?

A good friend of mine, who was also active on StackExchange, passed away a couple of days ago.  Does SE have any sort of process in this scenario, or do SE profiles sort of live on forever?  Thanks


PHP: Text transformed after being put in database

I have a form sending data to a mySQL database. But when I enter some text like "Jack&Jones", the special characters get transformed into HTML special chars (here, the & becomes "&amp;").   The data inserted in this database can later be used to generate Word documents using a template, but these HTML characters are read wrong and the resulting file is completely messed up.  I tried to resolve the problem by ensuring all my pages used the <meta charset="UTF-8"> tag and by using header("Content-Type: text/html; charset=utf-8"); to ensure that the data keeps the UTF-8 encoding during the whole process, but it did not work.  So my question is: how do I ensure the encoding consistency between my form, my database and my word document ?


How to show $f'(0)$ exist and is equal to $1$?

Assume that $f$ be continuous on $\mathbb{R}$, $f'(x)$ exists for all $x\neq 0$, and $\lim_{x\rightarrow 0} f'(x)=1$. We need to show $f'(0)$ exist and is equal to $1$.  $f'(0)=\lim_{x\rightarrow 0}\frac{f(x)-f(0)}{x}$, $\lim_{x\rightarrow 0}f'(x)=1\Rightarrow\lim_{x\rightarrow 0}\lim_{h\rightarrow 0}\frac{f(x+h)-f(x)}{h}=1$...am I going in the right direction? Please help.


In Dr.Einstein's theory of General Relativity-- he goes to great lengths to explain how the force of gravity is merely an illusion and in the case of the falling apple-- it is the earth accelerating to meet the apple's inertial frame. But it is well known that gravity is one of the four fundamental forces. I would like to know the reason for this apparent contradiction. Is it or is it not a force?


Does a pilot have to take into consideration the angular spin velocity of the earth?

First imagine a pilot takes off from a North South runway situated on a specific northern latitude, the circumference of which is 888 miles, where the angular spin velocity of the earth (and the plane) would naturally be calculated at approximately 37 miles per hour in an Easterly direction.  Then imagine that he attempts to land on a North South runway at the equator where the angular Easterly spin velocity is 1037 mph.    Explain how this 1000 mph difference of angular spin velocity is gained with enough exactitude that his plane will not flip over upon touchdown?   For extra points explain how such a plane under these conditions could lose the greater angular spin velocity if the trip were reversed and started out at the equator and landed at the northern runway?


We say $U,V$ is a splitting of a Topological space $X$ if , $$ X = U \cup V    $$  where $U,V$ are Open, disjoint , non empty subsets of $X$  In a book I'm reading it says that for any Compact Haussdorf topological space and given two distinct connected components, a splitting can be chosen such that they lie on different sides of the split.  My question is, how do we show this? I realize compact haussdorf implies Normal but I'm not able to make an explicit splitting using that.


Use induction to prove that that $8^{n} | (4n)!$ for all positive integers $n$  So far I have: Base case (n = 1) = $8^{1} | (4(1))!$  = $8 | 24$ which is true.  Induction Step:  $8^{n + 1} | (4(n + 1))!$  $8^{n + 1} | (4n + 4)!$   A bit confused as to how to close this proof out, also wanted to make sure my current progress is correct as well. Any help is appreciated.


I'm looking into a possible bug in the SE chat system.  To do this, I need to be able to send a bunch (10+) of chat messages.  I don't want to bother anyone.  Is there already a "test" chat room in which this would be appropriate, or would it be best to just create a new one?


What timeline is the post-credit scene at the end of The Wolverine in?

Through the X-Men film universe (X-Men 1-3, X-Men: First Class, X-Men: Days of Future Past, X-Men Origins: Wolverine, and The Wolverine), we see at least three distinct timelines/alternate realities.  The "Original" Timeline  Through X-Men 1-3 mutants are a largely unknown factor. X-Men 1 opens up in "the near future" (relative to the year 2000, when the film was released) with the public largely unfamiliar with mutants or their abilities. The "Mutant Registration Act" aims to identify and register mutants. The following films deal with mutants still being very much hidden, but there is no indication that they are being hunted or even identified in any large scale way until X-Men: The Last Stand when mutants voluntarily come forth. In these movies, the only mention of anything even remotely close to a Sentinel is a robot head in the Danger Room in X-Men: The Last Stand. In this timeline, when mutants appear, police are called, not Sentinels, and       Jean Grey and Cyclops both die (Jean dies twice).   The Days Of Future Past Timeline  In this timeline, Sentinels are used to hunt mutants and anyone with mutant genes.  The whole premise of the movie/Wolverine's mission is that       the assassination of Bolivar Trask in Paris in 1973 sets off anti-mutant hysteria, leading the US government to activate Trask's Sentinel project. In addition to the Sentinels, Trask has a device which can detect mutants (he has it with him at the Paris meeting which he is to be assassinated in). When the assassination fails, Trask already has a number of Sentinels built and ready to deploy, proving that while the updated Sentinels with adaptation ability are still a ways off, the technology for the Gen-1 Sentinels is largely ready - in 1973.   These two timelines are definitively different as      there are no Sentinels hunting mutants, nor is there any massive anti-mutant hysteria in X-Men 1 (at least, not to the level described in Days of Future Past)   The Altered Days of Future Past Timeline  Prior to Wolverine embarking on his mission, Kitty explains that should he succeed,       he will wake up back in their present (2023, I believe), but with history changed around him. Only he would remember the original Days of Future Past timeline with mutants having been hunted to near extinction.   In the end, we see this timeline      with Jean and Cyclops still alive and well in the 2023 present time.     Phew... Got all that?  The present story of The Wolverine opens with Wolverine having nightmares of when      he was forced to kill Jean Grey.   By itself, this doesn't mean that The Wolverine takes place in the "original" timeline, but we see a world where, as with the "original" timeline, there is no indication of mutants being hunted. Nor are there any mentions of Sentinels.  Conclusion: It is reasonable to assume that The Wolverine takes place in the same timeline/continuity as X-Men 1-3.  Right until we get to the post-credit scene  The Wolverine ends with      Logan flying off with Yukio, but only has bone claws.   The post-credit scene takes place later (2 years, IIRC). In this,      Wolverine sets off metal detectors, and is then approached by Professor Xavier and Magneto, hoping to recruit him for an upcoming battle. In the background, we see a commercial for Trask Industries playing on a TV.   The insinuation, of course, is that this scene is meant as a direct lead-in to X-Men: Days of Future Past, and that      Xavier and Magneto are recruiting him to fight the forthcoming Sentinels.   If we assume that The Wolverine and the post-credit scene are in the "original" timeline, then the post-credit scene is not a true lead-in.  If we assume that the post-credit scene is in the Days of Future Past timeline, then we are left to explain why no mutants have are being hunted by Sentinels already.  So... Which timeline does this post-credit scene take place in, or why is the history described in DOFP not reflected in X-Men 1-3?


Resolve nested aliases to their source commands

I've made several aliases for my convenience.But now I need to be helpful by sending a useful command and it is full of aliases.I've tried doing type u but all it returns is   up && ap upgrade -y --show-progress && r && ap check && ap autoclean  These are all aliases in u:  alias a='alias' a ap='apt-get' a r='ap autoremove -y' a up='ap update'


Is it necessary that if $\lim_{x \to \infty } f(x) + f'(x) = L$ , where $L$ is finite then $\lim_{x\to\infty}f(x)= L$ and $\lim_{x\to\infty}f'(x)=0$

Let $f(x)$ be differentiable in $x \in (0,\infty)$ and suppose $$\lim_{x \to \infty } f(x) + f'(x)  = L$$ , where $L$ is finite quantity then find $$\lim_{x \to \infty } f(x)  \text{ and } \lim_{x \to \infty } f'(x)$$ or can nothing definitive be said about these limits.   Intuitively it seems that $\lim_{x \to \infty } f'(x) = 0 $ because if it is not , as we approach $\infty$ , its value will keep on changing as we go farther towards right. And thus $\lim_{x \to \infty } f(x) = L $. But how to prove that this happens or if it is really this that happens.   Eg like in the function $x\sin \frac{1}{x}$, the limit approaches $0$ but it's derivative keeps oscillating. So maybe , something similar might happen at $\infty$ where the function approaches a limit but it's derivative keeps oscillating.  How do we solve it ?? Please help   Edit: As it has been pointed out that this is a possible duplicate, I must say, that the  does not have a satisfactory answer and consider the follow up argument-  If we consider the function $\frac {e^x f(x) }{e^x} $ And apply L' Hopital's Rule, as @ΜάρκοςΚαραμέρης points out Even in the case if the limit of $f(x)$ exists consider for example $f(x)=e^{-x}sin(\frac{1}{x})$, how is L Hospital applicable now? You need a formal proof that $\lim_{x\to\infty}e^xf(x)$ exists  Also as @PeterForeman point out, in the accepted answer it is assumed that $f'(x) \to 0$, instead of proving it.


Find $x$ in the equation $ax^3+bx^2+cx=d$

$\begin{equation} \tag{A} ax^3+bx^2+cx=d \end{equation}$  We can define Delta for quadratic equation to check whether  the equation has answer or not....for $f(x)$ which contains powers higher of $2$ for Is there any method to see how many acceptable roots the polynomial contains? Consider equation $(A)$. Can we say whether the equation has real root? How many roots of the function above  are acceptable?


List of IP addresses/hostnames from local network in Python

How can I get a list of the IP addresses or host names from a local network easily in Python?  It would be best if it was multi-platform, but it needs to work on Mac OS X first, then others follow.  Edit: By local I mean all active addresses within a local network, such as 192.168.xxx.xxx.  So, if the IP address of my computer (within the local network) is 192.168.1.1, and I have three other connected computers, I would want it to return the IP addresses 192.168.1.2, 192.168.1.3, 192.168.1.4, and possibly their hostnames.


Is there empty space left in the skull after the second set of human teeth grow out? What happens to it?

Reading about teeth on this website, I came across this link and picture of a human child skull, where we can see how both sets of teeth are placed. It made me wonder: after the second set of teeth move into the mouth (do they actually move?), what happens to the space they occupied before, while they were hidden? Or do they not actually move, but stay in place and the mouth/skull/bone grows in size to expose them? I'm not sure which way it is.


This is so strange, I'm using node for some time now, and I never noticed such a thing. When I try to sum something like 0.7+0.2+0.1 or 0.6+0.3+0.1, the result is 0.9999999999999999. Why isn't the result 1?  I need to validate that the sum of three variables is exactly 1, so I can't round this number, can someone help me understand why node is behaviouring like this? Here is my node version and some more examples/errors on terminal:


How can I place multiple objects on the mesh?

I am trying to make similar shoes and I don't know how to make those extruding objects on the shoe strap/ on its sides (I've thought of particles, but my output is faaaaar from what I want, I don't know how to set the orientation axis so the placement is not off like in my blend file..)  my blend file is here:


Usage of English definite article when referring to generic word

My mother language does not have articles, so I still struggle to choose when to use the indefinte and definite article. The other day, I learned:   "The dog is an animal" is acceptable. "The iron is a metal" is not acceptable. (By the iron, I mean the metal, not the device.)   Is that true? If so, could anyone explain why?


I installed Ubuntu on an HP WiFi-only PC. After Installation The OS does not find the WiFi device. This is my maiden voyage with Ubuntu. I suspect that I did something wrong.


How to solve the "The following module is missing from the file system" error?

I am getting the following error in a Drupal 8 site.     The following module is missing from the file system   It looks as if a custom module was installed and deleted without uninstalling it.   How can I fix this error?


Difference between map layer and spatial dataset (e.g. feature class, shapefile)?

What is the difference between a feature class and a feature layer?  To me they seem very similar in concept.


Is there any way to download Adobe flash?

I am trying to use Flash for habbo.com. I cannot get it to download. Is it even possible? Any recommendations or tips would be highly appreciated.


If I have a large number of SQLite databases, all with the same schema, what is the best way to merge them together in order to perform a query on all databases?   I know it is possible to use  to do this but it has  of 32 and 64 databases depending on the memory system on the machine.


for every $x$ in ring $R$, we have $x^2 = x$. Show any finitely generated ideal is cyclic.

With the given condition, $R$ should be commutative and for every $x$ in $R$, $2x = 0$. I'm trying to first solve this problem for the case where ideal $I$ is generated with only two elements, like $I = < x, y>$. In this case, I found a hint that if we consider $z = x + y + xy$, we can prove $I = < z >$ I know $xz = x$ and $yz = y$. How can I use this information to show $I = < z>$?


What is the word for a sentence that initially sounds profound or deep, that is, in fact, meaningless or empty?

I'm sure I saw, recently, a word for this, but I can no longer remember, or find, it.


Heading css styles need bigger margin-top or smaller margin-bottom

The margins for headings make my inner child cry.    Here's some text  Heading 1  The gap to this text is more than the text before it  Heading 2  Here too!    Here's an image explaining it with visual helpers:    So the request is simple; fix the css for headings and give us nicer layout! Otherwise kittens will die (or some other inappropriate Internet meme).


The page that opens vs The page that is opened

On a website I have an input field "Page" with a label / description below it: which one of the following is correct? If both are correct, is there any difference in meaning?  The page that is opened when a user clicks the notification The page that opens when a user clicks the notification


LWC datatable not rendering modified column

@track data;   @track columns = [{                 label: 'Name',                 fieldName: 'Name',                 type: 'text',                 sortable: true             }]      @wire(getAccountlist)     accountList({data,error}){     if(data){    this.data= data;    for(var i=0;i<data.length;i++){        this.columns.push({label : 'Info',                           ...this.data[i].Info__c&& {fieldName:'Info__c'},type: 'text',sortable: true})     }     } }   The column that I'm dynamically adding is not being added to the data table.


Unexpected behavior during index assignment in a Bash array

I'm having trouble assigning values to a specific bash index, but apparently only when the index variable is set using a while read loop. Taking this code as a test example: #!/bin/bash  read -d '' TESTINPUT << 'EOF' 1,100 2,200 8,300 EOF  declare -A ARRAY echo "$TESTINPUT"| while read _l; do     i=$(cut -d, -f1 <<< $_l)     j=$(expr $i + 0)     value=$(cut -d, -f2 <<< $_l)     ARRAY[$j]=$value done  for i in {4..6}; do     ARRAY[$i]=$i done  for i in {1..10}; do     echo "$i ${ARRAY[$i]}" done  The output clearly shows that in the case of the while loop, the array variables don't get set, while with the for loop, using a range of {4..6} doesn't seem to have any issue. $ ./test_array.sh 1  2  3  4 4 5 5 6 6 7  8  9  10  Notice I also tried to convert the index variable to an integer using j=$(expr $i + 0)  But that doesn't seem to work either. Any ideas?


Proving that the sequence $F_{n}(x)=\sum\limits_{k=1}^{n} \frac{\sin{kx}}{k}$ is boundedly convergent on $\mathbb{R}$

Here is an exercise, on analysis which i am stuck.    How do I prove that if $F_{n}(x)=\sum\limits_{k=1}^{n} \frac{\sin{kx}}{k}$, then the sequence $\{F_{n}(x)\}$ is boundedly convergent on $\mathbb{R}$?


Best way to parse command line arguments in C#?

When building console applications that take parameters, you can use the arguments passed to Main(string[] args).   In the past I've simply indexed/looped that array and done a few regular expressions to extract the values. However, when the commands get more complicated, the parsing can get pretty ugly.    So I'm interested in:   Libraries that you use Patterns that you use   Assume the commands always adhere to common standards such as .


I need to create a cross section of a surface (which takes the form of a cube), and therefore there are certain areas which need to be "empty". A visual description of what it would look like is below:.  Moreover, it might be necessary to include that there is a particle system that is emitted from the surface, and these particles should not be emitted from "empty area".  Things I have tried:   The cell fracture add-on... to not much success. Not sure if I am using it incorrectly. Simply deselecting 50-80% of the faces (I subdivided the cube already) and then deleting them.   None of these methods create an optimal output. Any help would be appreciated!  EDIT: Here is what I have so far:   The yellow portion is to be modeled like the green cross-section provided before. As you can see, the small black-white bits on top of the yellow is a particle system that is frozen to 1 frame. So, tying everything together, I'm trying to model yellow area to look like the green image shown earlier, however the particle system must only emit from the non-empty areas.


Origin moves instead of actual object in blender 2.9. Same applies to Rotation and Scale also. It was not so in previous versions. Tried the solution given to question raised by Nyx. But still it is not working. Old answers not working, in my version, Transform affects only the Origins is also Off / Unchecked.


I was reading a text and it had the following listed as immediate:  $\int_{0}^{1}\int_{0}^{1-x_{1}}\cdots \int_{0}^{1-x_{1}-\cdots -x_{n-1}} dx_{n}\cdots dx_{1}=\frac{1}{n!}$  I haven't actually evaluated an integral and done calculus in a while so I'm sorry if this is apparent.  But why is this immediate?


How can I get list of all running applications?

System monitor in Kubuntu can filter running processes so that I can choose Program only choice so my question is how can I get the same results by commands ?


To show a field $K$ to be algebraically closed.

Let $F \subset K$ be a separable extension such that every irreducible polynomial in $F[x]$ has a root in $K$. Show that $K$ is algebraically closed. So I just need to prove that for any polynomial with coefficients in $K$ has roots in $K$. But I've no idea how to solve the problem.


I've looked into and considered many JavaScript unit tests and testing tools, but have been unable to find a suitable option to remain fully TDD compliant. So, is there a JavaScript unit test tool that is fully TDD compliant?


I was told by a friend, that the (physically) innermost track on an HDD platter will read and write the fastest. But I think to myself that the outermost track must have more capacity for blocks and is covering more distance in one rotation, since the whole platter is spinning at a fixed RPM. So shouldn't data stored on the outer parts of a HDD platter be read and written faster than on the inside?


Does the length of a pipe influences the flow?

if I have a closed system of horizontal pipes, filled with water, where I want to create a flow at some rate by using a pump. Does the length of the system influences the flow ? (in real world not in the wonderful world of the books)


Increase resolution to 4K in VMware or Virtualbox

I have a laptop with a 4K (3860×2160) display, but there are a lot of problems. A lot of virtualization programs aren't compatible with 4K resolution.  VMware Workstation and VirtualBox don't support 4K display in the list of the display's resolution. How I can set the resolution of the display in a virtual machine to 4K?


Parents UK Visitor Visa Refused - please help!

I have recently applied for a UK Vusitor Visa for my parents who live in India and it got rejected. My parents are retired and I was going to sponsor their whole trip to UK for 3 months which I have mentioned clearly on the Invitation letter and Sponsorship letter stating my Salary, payslips and UK bank statements from my side. As for my parents' financial proof, I have added their bank statements with balance around £4.4k and a letter by Chartered Accountant, stating the property, fixed deposit and assets worth £33K ( which I think got completely neglected by the ECO). I have got the rejection with below points:  ******************** Letter *****************     The decision      I have refused your application for a visit visa because I am not   satisfied that you meet requirements of paragraph 4 2 of Appendix V   Immigration Rules for Visitors because:-       1.You have applied to travel to the UK alongside your wife for three months to visit your son i have taken into account that you have   provided details of your sponsor's financial and living circumstances   in the United Kingdom and l am very aware of the importance of family   visits and the significance which should be afforded to maintaining   family links, however, it is your circumstances as the applicant which   is of most importance.       2.You have stated on your application form that you and your wife are both retired. You have not stated in your application form or   presented documentation to suggest that you are in receipt of any   regular income. You have estimated the personal cost of this visit at   £2,000 To demonstrate your financial circumstances you have provided   an Indian Bank statement, account ending ******5190, which shows a   closing balance of Rs.360,450 (£4,291). You therefore propose to spend   over half of your savings on this visit to the UK. Given your   financial circumstances as outlined above, and that you have not   demonstrated any income, I am not satisfied that this proposed   expenditure is credible.       3.I have also considered the pattern of deposits into your bank account. I note that in the month of February 2017, this account   received a number of deposits totalling Rs.200,190 (£2,383). I am   unable to confirm from the documents submitted the origin of these   funds.      4.In light of all of the above I am not satisfied as to your intentions in wishing to travel to the United Kingdom or that you will   leave the UK at the end of your visit. Furthermore, I am not satisfied   that you have sufficient funds available to cover your costs whilst in   the UK without working or accessing public funds Your application for   a visit visa has been refused under paragraph V4.2 (a) (e)   I am considering reapplying for the Visa, but I wanted to clarify below doubts? So, can you please guide me on the below points based on their experience?  Questions  :  For point 2:  a. As my parents are retired they dont have a regular income - how should I respond to this question? b. For spending half of the amount - We can dissolve one of the properties worth 15 lakh and provide the proof of same - will that work?  For Point 3 : Also, I keep on sending money to them, is it fine to state that in my next application?  Thanks in Advance Sunny


Since the T-800 was meant to be an infiltration unit, it doesn't make much sense for there to be multiples of the same face. But somehow at least five separate terminators from the movies are all replicas of Arnold (forgiving some aging from the actor)  Are there any hints at non-Arnold T-800 models or an explanation as to why all T-800s look the same?


document.write(variable) in href attribute of  tag

due to the my lack of knowledges in javascript, i m here to please you to explain me why this line of code is not working properly, as it should do.  Firstly let me explain what I am trying to do and after that i will let you see my code. So, I'm using this guy script to check if adblock is active or not.   I changed adblock variable with adblock = ". example1. tld" and adblock = ". example2. tld".  I need to write adblock variable within href attribute of the  < a > html tag. But till now I didn't find out how. The line of code that is not working is the next one:   <script>document.write('<a href="<script> document.write(adblock)</script>"' + 'class="button-download popup">')</script>   Can somebody explain me what to do in this situation and why my code is not working properly?


Find solutions for an differential equation system

I have a differential equation system  $x_1'(t) = -x_2(t)$  $x_2'(t) = -x_1(t)$  I see that I can write $\dot{x} = Ax$ where  $A = \begin{pmatrix}0 & -1 \\ -1 & 0\end{pmatrix}$  The complete real solution will be  $x(t) = c_1 e^{-t} \begin{pmatrix}1 \\ 1\end{pmatrix} + c_2 e^t \begin{pmatrix}-1 \\ 1\end{pmatrix}$  where $c_1,c_2 \in \mathbb{R}$.  It this correct?  Now I need to find the solution such that $x_1(0) = -1$ and $x_2(0) = 1$.  How can I do this?  I think I could split my complete solution in  $x_1(t) = c_1 e^t - c_2 e^{-t}$  and  $x_2(t) = c_1 e^t + c_2 e^{-t}$  and then find $c_1$ and $c_2$ by solving $x_1(0) = -1$ and $x_2(0) = 1$ with respect to $c_1$ and $c_2$ and finally substitute these values in the complete solution $x(t)$.  Is this correct?


Linux - Sending a command to a screen through a shell script?

I'm trying to figure out how to make a script that will be able to send commands to a screen that will execute within whatever the screen is doing. Is this possible, and if so, how is it done? I've already tried screen -X etc, and it is not executing the commands.


Is electrical energy wasted when a device is fully charged?

Many a times I leave the laptop connected to the charger with the switch on for the entire day. When it becomes fully charged does it still consume electrical energy?


how to make nouveau.modeset=0 automatic on boot

I am very new in ubuntu and this will be my first question :) My laptop has an nvidia graphic card and on every boot I have to include the line nouveau.modeset=0 Is there a way to include it permanent in the kernel to have the boot automatic without having to type it everytime?  I have dual partition windows/ubuntu, not sure if this could affect on something.  Thanks


Eligibility requirements for Stack Overflow moderator elections

There is no single place where SO users can check the requirements necessary to nominate oneself to a moderator elections. There is a formal description of the requirements:  But I think they should be summarized somewhere together in a more human-friendly way (i don't mean a programmer).  Reputation should be greater than 3000  Should have all of the following badges:    Civic Duty Strunk & White Deputy Convention Yearling  Did I miss something?


Perpetual motion in electric dipole restricted to a circular path with a charge at the centre

This problem is from Griffith's Introduction to Electrodynamics (4th Ed.), Problem 4.31.  A point charge $Q$ is "nailed down" on a table. Around it, at radius $R$, is a frictionless circular track on which a dipole $\mathbf{p}$ rides, constrained always to point tangent to the circle. Use $\mathbf{F} = (\mathbf{p}\cdot\nabla)\mathbf{E}$ and show that the electric force on the dipole is $$\mathbf{F} = \frac{Q}{4\pi\epsilon_0} \frac{\mathbf{p}}{R^3}$$ Notice that this force is always in the "forward" direction (you can easily confirm this by drawing a diagram showing the forces on the two ends of the dipole). Why isn't this a perpetual motion machine?$^{21}$ $^{21}$ This charming paradox was suggested by K. Brownstein.  I have done the first part and shown that the force on the dipole indeed is equal to what is given in the question. But can anyone help me with the perpetual motion bit? And for the circular motion, where is the centripetal force coming from? Is it due to the constraint?


purchaseinventorytrigger: execution of AfterInsert caused by: System.FinalException: Record is read-only Trigger.purchaseinventorytrigger: line 8

trigger purchaseinventorytrigger on KBT_Purchase_History__c (after insert ,after update) {     for (KBT_Purchase_History__c ph: Trigger.New) {         System.debug('Trigger.New List' + Trigger.New);          List<KBT_Inventory_Stock__c> currentstock =new List<KBT_Inventory_Stock__c>();         currentstock = [SELECT Id,KBT_Products__c,Name__c,Name,Next_stock_Expected_Date__c,Stock__c FROM KBT_Inventory_Stock__c];         System.debug('The Current stock is' + currentstock);         KBT_Inventory_Stock__c s= New KBT_Inventory_Stock__c();         ph.ProductId__c=s.KBT_products__c;         s.stock__c=s.Stock__c-ph.Purchased_Quantity__c;         if (s.Stock__c==0){             s.Stock__c.addError('out of stock ');         }     } }


What is the rebel doing when the Millennium Falcon lands on the moon of Yavin?

See this image:    What is he doing there? Why is he aiming at the Millennium Falcon?


Using ShellExecuteEx and capturing standard in/out/err

I'm using ShellExecuteEx to execute a command in C. Is there a way to use ShellExecuteEx and capture standard in/out/err?  Note: I don't want to use CreateProcess.


Godox x1r x1t and canon speedlite 430exii

I was waiting for your kind reply on how to synchronise the godox x1r x1t & canon speedlite 430exii.. Thank you


(a) Let $x$ and $y$ be $n\times 1$ matrices, $n \ge 1$, and let $A=xy^T$. Show that $\det(A)=0$.  (b) Explain why the statment in part (a) is false if $n=1$.


Recover JavaScript files from deleted partition

I deleted my whole partition by mistake. To make things worse I created a new partition over it (I didn't leave it like unallocated space). However I didn't copy anything to that partition or used it in any way. I tried some data recovery software tools (only to preview what would they recover). I could restore my video files, pictures, audio, html, etc... However I couldn't find any javascript files. Is it at all possible to recover javascript files. If it is do you have any software to recommend (Windows 10 User). Thanks for your time in advance.


Any way to change screen dimensions so the left part of monitor is blank?

I'm running Ubuntu 16.04 on my laptop, but recently the left 5th of my laptop screen stopped working. Is there any way to adjust the screen dimensions so it doesn't use this portion of my screen while I figure things out?  Thanks


How does Loki survive his fall at the end of Thor?

In one of the concluding scenes of the movie Thor, it's shown that Loki deliberately let go of the Scepter, and falls deep into the vast intergalactic sea sort of thing. How does he survive and return in The Avengers?


I'm searching for a way to remap certain keys in ubuntu.  i.e.   I'd like to change PgUp to Home or PgDown to End.  Does a built-in command or a tool exist reassign keys in Ubuntu/GNOME?


My terminal is set to UTF-8. If I type this:  echo -n 'ýá' | xxd   I can see this output:  00000000: c3bd c3a1   Which is fine. Now I would like to remove the 'ý' character from the string, so I use:  echo -n 'ýá' | tr -d 'ý' | xxd   But the result will be:  00000000: a1   The tr removes also the next c3 byte, but that is part of the 'á' character. Why is working this way? Is this a bug? Or should I set something?


Prove or disprove that the language L is regular

I had an exam where I had to prove or disprove that the language $L=\{w^{|w|} | w \in \Sigma^*\}$ where $\Sigma = \{0,1\}$ is regular. On a glance, it looked regular to me so I tried using induction to prove that it is in fact, regular. Here's what I did: Let $|w|=n$. We will use induction over $n$ to prove $L$ is regular.  Base: Let $n=1$. Then we have $|w|=1$, so $w$ is made up of one letter (either 0 or 1) and $L = w^1=\{0,1\}$. Then $L$ is finite and therefore regular. Hypothesis: Let's assume that our claim is true and $L$ is regular for a given $n$ (that is $L=\{w^n\}$ is regular). We will now try to prove that $L$ is regular for $n+1$ Step: If $|w|=n+1$, then $L=\{w^{n+1}\}=\{w^n.w\}$. From our hypothesis we get that $w^n$ is regular. Since our $n$ is not infinite we know that $w$ is finite and as such there exists a regular expression that recognizes $w$. Which means that $w$ is regular as well. Now we have that $L=\{w^n.w\}$ is a concatenation of two regular languages which means that L is regular as well.  I had 0 points given for that answer. Unfortunately we are not allowed to see our mistakes or possible solutions as that problem was a part of the graduation exam in my country so I have no idea where I got wrong. I would greatly appreciate if you could point where I've made a mistake and point me to a possible solution. P.S. After the exam I came up with something proving that the language is not regular using the pumping lemma but I will probably post it a bit later


Do perception checks to locate Invisible / Hiding creatures auto fail?

The Invisibility condition states:     For the purpose of Hiding, the creature is heavily obscured.   Rules for The Environment state:     A heavily obscured area—such as Darkness, opaque fog, or dense foliage—blocks vision entirely. A creature effectively suffers from the Blinded condition (see Conditions ) when trying to see something in that area.   The Blinded condition states:     A blinded creature can’t see and automatically fails any ability check that requires sight.   A group of 3 characters is under the effects of Great Invisibility and takes the Hide action. Within a minute later, a group of hostile npcs (who do not have any abilities above darkvision and hearing) enters the area. Do they automatically fail all perception checks (thereby granting the invisible party a surprise round)?


If I have a p-value of 0.01 on a statistical test, does that mean the probability of my hypothesis being wrong is 1%?   If not, why not?


I have a very tricky question....all the veg and fruit   cells contain cell wall and it is made of cellulose when we eat how our body digest though we   don't have the enzymes to breakdown 1-4 beta glucose sugar?


Testing significance between a linear model and a linear mixed effects model

I have a number of fish measurements I want to test, for example Condition, HSI, and GSI. These are to be tested against Parasitism (A factor, 0 being non-parasitized and 1 indicating parasitized). I am hoping to see no effect from parasitism.   I did preliminary T-Tests for four lakes (pooled over three years) comparing Parasitized and Non-Parasitized fish for the three metrics. All but one lake yielded no significant difference in Parasitized and Non Parasitized fish.   Overall I want test this as a model, and since I am seeing differences in one of the lakes, I believe this means I would have to treat Lake as a RANDOM effect, and Parasitism as a FIXED effect. Please correct me if I am wrong.   My question is... how do I test for significance (where I can obtain a P-value) by comparing a linear mixed model and a simple linear model?   Can this be done similarly using likelihood ratios? For example:  anova(LMM1, LM1)  All help, suggestions and links are much appreciated...


What lens characteristics are important in star photography?

In optimal world I would buy a lens that is good in every way. But I'm on a budget and have to find a balance in quality and price. I'm looking for a lens for star photography, so in my case it will be a wide angle lens with good characteristics for capturing points of light in a dark sky. What would those characteristics be?  So far I've learned about , which seems like a thing to note when comparing different lenses for star photography. It would be quite disappointing if stars turned into long teardrops on the edges of a photograph even when every precaution was taken to make all stars sharp round points of light.  Vignetting would be an example of lens characteristic not so important in this use.  Many characteristics of a lens turn better when aperture is slightly stopped down, but I suppose I'd be wanting to use a lens with wide open aperture when trying to capture the stars in a dark night sky.  I'm not asking for lens recommendations. But, as an example of what kind of lenses I've been looking at, I name  manual focus lens. Its price level is $350'ish in Amazon and seems to run with name Rokinon too. It seems to be reasonably sharp even when wide open - my camera is an APS-C sensor camera.


Invertible Elements of $\mathbb Z[i] \subseteq \mathbb C$

How can we find all invertible elements of $\mathbb Z[i]=\{a+bi | a,b \in \mathbb Z\} \subseteq \mathbb C$?  The idea is: let $u=a+bi$ be an invertible element and let $v=c+di$ be the inverse element of $u$ over $\mathbb Z[i]$. This implies that $uv=1$, but how do i continue from here on out? Are there any more elegant solutions to this question?  And shouldn't be every element invertible in $\mathbb Z[i]$ since $\mathbb C$ is an integral domain? I appreciate your help, thank you!


I came across this code:  void f(const std::string &s);   And then a call:  f( *((std::string*)NULL) );   And I was wondering what others think of this construction, it is used to signal that function f() should use some default value (which it computes) instead of some user provided value.  I am not sure what to think of it, it looks weird but what do you think of this construction?


Using the parseFloat method converted the string value from the DB to float and multiplied by 100. But the output looks odd. Following the piece of code which I've used.  parseFloat(upliftPer) * 100 //upliftPer value read from DB and its value is 0.0099   So when it multiplied with 100 getting 0.9900000000000001 I suppose to get 0.99 but some junk values getting appended. Also I went ahead and did the same in the console log of chrome browser still the same result. I have attached screenshots for reference. Solution I needed is 0.0099 * 100 should result 0.99. I cant apply round / toFixed since I need more precision.


What are the units for rate of movement through time?

Thinking of time as the dimension orthogonal to depth, it seems logical that the rate at which a body moves through time could vary.  Do units exist for rate of movement through time?  The numerator seems clear (e.g. seconds), but what could the denominator be?


After installing fedora and Centos and other OS now I have them all showing in my Boot menu [F2] on start up not the menu form the OS even after deleting them and reinstaling other OS - Ubuntu -so It just shows one when the OS starts but when I go to UEFI setting I still find all the old ones they instruct you to use DEL to take them out but that does not work


What happens in this current branch? In circuit analysis how to deal with branches like this?


E: Problem executing scripts APT Update::Post-Invoke-Success error during apt-get update

I cannot install any package. It seems the command apt-get update must be run but it throws some errors:  $ sudo apt-get update Get:1 http://security.ubuntu.com/ubuntu xenial-security InRelease [102 kB]      Hit:2 http://ve.archive.ubuntu.com/ubuntu xenial InRelease                      Hit:3 http://ve.archive.ubuntu.com/ubuntu xenial-updates InRelease              Hit:4 http://ve.archive.ubuntu.com/ubuntu xenial-backports InRelease            Fetched 102 kB in 23s (4337 B/s)                                                *** Error in `appstreamcli': double free or corruption (fasttop): 0x000000000210f4b0 *** ======= Backtrace: ========= /lib/x86_64-linux-gnu/libc.so.6(+0x777e5)[0x7fac8d8317e5] [...] Aborted (core dumped) Reading package lists... Done E: Problem executing scripts APT::Update::Post-Invoke-Success   'if /usr/bin/test -w /var/cache/app-info -a -e /usr/bin/appstreamcli;   then appstreamcli refresh > /dev/null; fi' E: Sub-process returned an error code


I tested a few numbers of the form $10^n+1$ (i.e. $100000001$) besides $11$ and $101$ and they were all composite. Clearly some of them if we have an even number of $0$'s in between are multiples of $11$, but is it just a coincidence that the ones with odd number of $0$'s are also composite?


How to write LINQ query row numbers in C#?

SQL:  Select top percent a,b,ROW_NUMBER() over(PARTITION BY a,b order by a,b) as rowsnumber from Students as s group by a,b   LINQ:  var students=from p in Students group p by new{p.a,p.b} into grp order by grp.Key.a,grp.Key.b .Select(s=>s.a,s.b).ToList();   I want to this SQL query convert to LINQ but not convert.


Changing the default shell without chsh or administrator privileges

I saw the following snippet in this thread:   sleep 2 if (-x /usr/local/bin/bash) then   exec /bin/sh -c '. ~/.profile; exec /usr/local/bin/bash' endif   My understanding is that if you place this snippet in ~/.login it will invoke bash when you login.  I have a similar situation where I would like to use a similar snippet to invoke a  version of zsh that is different from the default one with which I log in. Part of the reason why I am going through this trouble is because I can't choose my desired version of zsh in the options allowed in chsh, and I don't have administrator privileges.  With this:   How would I change the snippet above to do this when switching between different versions of zsh?  Why are two exec commands needed in the snippet above? What do they do? Also, why does the snippet above use sh and bash (the user is supposed to login with csh)


In a hash function, you map an input of arbitrary length to an output of finite length such that the relationship is one-to-one (or at least that's what you are trying to achieve).  Hence, isn't it impossible to have a perfect hashing algorithm? Aren't MD5, SHA-*, all flawed in this respect?  Is an "ideal hash" impossible to achieve?


Epiphany hat in another language except on Winterbash Hat List

I just got the Epiphany hat, but it had a weird description:    Seeing this, I went to the hat list on the Winter Bash page to see if this was just a secret hat with a different description since these descriptions are the unlocking requirements except for secret hats (but generally it's "this is a secret hat")    So I decided to click on it here, and the weird text has appeared again:    I get the feeling this is another language, but why is this hat doing this?


Ubuntu 16.04 LTS black screen after suspension on Dell

I have a Dell Inspiron 15R with Intel® Ivybridge Mobile Graphics. I upgraded to Ubuntu vanilla and the latest version (16.04) few days back. Each time I close the laptop lid with the power source plugged in, and reopen it, a blank screen appears. A forced restart using the hardware button is necessary at this point.  If the lock screen is activated, after a time it goes black.  Even when on plugged on or on battery, if unused or locked, the same happens and a manual reboot is required for it to start. The CPU is running but I cant get to the login screen


computing confidence curves around the fitting line

I am reading a book about linear regression in which there is a plot showing the regression line and two curves they call a confidence band (also can be seen ). As I learn something last week that a set of samples may result in a statistical quantity called the confidence level which used to describe the "precision" of estimation of the population. However,  shows two curves of confidence level at each variable X of the fitting line. It is quite confusing why there will be a curve instead of a single number. My best guess is at each X, there could be tons of measurement so many $\hat{Y}$'s returned, and there will be confidence level for those $\hat{Y}$'s. If this is correct, why there are local minima of confidence curves. The local minima indicate there is some point at which you do the measurement, results will be more "precise"? I don't see how this happen.  My second question is how to compute the confidence curves. Though many software like R and Mplus work out the problem easily, I want to know how to compute that by hand calculation. I know the  states the algebra and I borrow the math here  $$ s_{\hat{Y}_{X}} = s_{Y|X}\sqrt{\frac{1}{n}+\frac{\left(X-\bar{X}\right)^{2}}{\sum_{i=1}^{n}{\left(X_{i}-\bar{X}\right)^{2}}}} $$  $$ s_{Y|X} = \sqrt{\frac{\sum_{i=1}^{n}{\left(Y_{i}-\hat{Y}\right)^{2}}}{n-2}} $$  $$ \hat{Y} \pm t_{\nu=n-2, \alpha/2}s_{\hat{Y}} $$  I am trying to understand those expressions and notation. My understanding is $X$ is the independent variable we choose for the fitting line and $X_i$ is the independent variable from data. $\hat{Y}$ is the measurement on the fitted line when $X$ is given while $Y_i$ is the measurement from data. I don't understand what $Y$ stands for. From the math, it seems that we compute something called $S_{\hat{Y}_X}$ from data and fitted values then use the very last formula to compute the curve. In the last expression, the $t$ is the student distribution and $\alpha$ related to the confidence level we choose and I assume there is a typo that $S_\hat{Y}$ should be $S_{\hat{Y}_X}$?  Very last question. I don't remember which book I read before but there is an example to introduce a cross term in the regression model something like  $$   Y = a_0 + a_1X + a_2TX $$   Where $Y$, $X$ and $T$ are given as data and by regression, $a_0$, $a_1$ and $a_2$ are computed. But instead of plotting Y again X, the author concerns the plot $Z=a_2T$ against $T$ only. In this case, if we want to plot the confidence band as well, should I just repeat the same calculation but replace $\hat{Y}$ with $\hat{Z}$, $X$ with $T$ and $\overline{X}$ with $\overline{T}$?


Where were the capital ships and bombers?

During the     attack on Starkiller Base,   Mon Calamari cruisers, Star Destroyers and all the other capital ships were conspicuously absent. In fact, the only spaceships I saw in that scene were X-wings and TIE fighters.  I understand that the Resistance is underfunded, but are they really so poor they can't afford a corvette or something? Or at least a few Y-wing bombers to     take out the oscillator?   For a major military installation,     Starkiller Base seems very poorly defended as well. Is the Finalizer the only star destroyer the First Order has left? If the Order can turn an entire planet into a weapons platform, they must be able to crank out something better than TIE fighters.   TFA fighters are significantly improved over their OT equivalents, but the lack of bomber cover, capital ships or light cruisers are highly unusual.  Does the novelization/other sources clarify this?


This might be a completely wrong question, but this is bothering me since many days ago. Given the mass (Sun) curves the space around it, gravitation is the result of such curved space (Correct me if I am wrong, source: A Documentary film). Given any point on a circle with center same as center of the mass, curvature in the space should be equal (Intuition).   Planets rotate around the Sun because of the curve in the space they should follow a circular path and the distance between planet and Sun should be at a distance.  Given the fact that earth has a elliptical orbit around the sun, and the distance between Earth and Sun varies according to position of the earth. Why do we have a elliptical orbit not a circular orbit.


How to prove that $(A×B) ∩ (B×A)=(A ∩ B) × (B ∩ A)$?

It is known that, to prove that two sets are equal, we need to show that they are subset of each other. Here we have, intersection of cartesian products on the left side and cartesian product of intersections of sets on the right side, I know the definitions here that is:  Cartesian Product: If $A$ and $B$ are any two sets, then $A\times B=$ {$ (a,b), a \in A, b \in B$ }. Intersection of sets: $A \cap B=${$ x\colon x \in A, x \in B $}.  but don't know how to prove that.


Possible non geometric intuition for the mean value theorem?

Is it possible to "see" the mean value theorem when one is only thinking of numerical values without visualizing a graph? Perhaps through a real world problem?


All values $n$ s.t. ${1 \over x} + {1 \over y} = {1 \over n}$ has exactly 5 solutions

Given  ${1 \over x} + {1 \over y} = {1 \over n}$  where $x,y,n$ are positive integers.  Find all possible values of $n$ such that there are only $5$ ordered pairs of $(x,y)$ which satisfies the equation.  I tried taking LCM and trying to factorize it, but I am unable to do so. Please help.   PS- Do not use calculus in your reasoning or solution as I am preparing for an Olympiad which does not allow calculus. You can still upload an answer involving calculus for other's to understand.


Pilot light on switch comes on when light is off

First off I know the switch the works I plugged it into a different circuit where I have another one and the pilot light turned on when the switch was on. However when I have it installed in the problem circuit the indicator light is switched and is illuminated when the light is off instead of it being illuminated when the light is on.  The circuit is for the downstairs lights in an older building so I am thinking it has to be something with how the lights are wired. The switch works the lights just fine so I am figuring it is something to do with the neutral side. I am unfamiliar with this light switch and how it works internally.   What would make the light come on one way in one circuit and opposite in another? I am unsure the exact brand I am an amateur electrician just helping a friend, but it is similar to the Leviton 15 Amp Combination Switch with 25-Watt Neon Pilot Light found on the home depot website. any help or ideas would be greatly appreciated


$\int_{0}^{\frac{\pi}{2}} \frac{\cos \left(s \arctan \left(-\frac{x}{\ln \cos x}\right)\right)}{\left(x^{2}+\ln ^{2} \cos x\right)^{\frac{s}{2}}}d x$

In the middle of solving for  $\int_{0}^{\frac{\pi}{2}} \frac{\cos \left(s \arctan \left(-\frac{x}{\ln \cos x}\right)\right)}{\left(x^{2}+\ln ^{2} \cos x\right)^{\frac{s}{2}}} d x, 0<s<1$,  I encountered the following substitution: $$\int_{0}^{\frac{\pi}{2}} \frac{\cos \left(\operatorname{sarctan}\left(-\frac{x}{\ln \cos x}\right)\right)}{\left(x^{2}+\ln ^{2} \cos x\right)^{\frac{5}{2}}} d x=\frac{1}{\Gamma(s)} \int_{0}^{\frac{\pi}{2}} \int_{0}^{\infty} u^{s-1} \cos (u x) e^{u \ln \cos x} d u d x$$ However, I'm not sure of how it is done. I tried \begin{aligned} &=\frac{1}{\Gamma(s)} \int_{0}^{\frac{\pi}{2}} \int_{0}^{\infty} t^{s-1} \cos \left(s \arctan \left(-\frac{x}{\ln \cos x}\right)\right) e^{-t \sqrt{x^{2}+\ln ^{2} \cos x}} d t d x \\ &=\frac{1}{\Gamma(s)} \int_{0}^{\frac{\pi}{2}} \int_{0}^{\infty} t^{s-1} \cos \left(s \arctan \left(-\frac{x}{\ln \cos x}\right)\right) e^{\frac{t \cos x}{\cos \left(\arctan \left(-\frac{x}{\ln \cos x}\right)\right)}}  d t d x\end{aligned} But I still can't figure out how to transfer this to the ideal form. Please, help me out.


How to make crontab email me with output?

How can I make crontab email me with the output of its jobs? I have MAILTO=redacted@yahoo.com.au above the jobs, but it doesn't work.  I know I need to use something like Postfix or Sendmail but for the life of me I cannot find out how to achieve this. I've searched and searched for a simple guide on setting up Postfix but they're all insanely complicated and expect you to be setting up a whole server to send and receive email and to know all the terms (like, what is a domain name for outgoing emails?).  All I want to do is have crontab email me. Why is this so difficult??  Additional Info:  My crontab file looks like this:  MAILTO=redacted@yahoo.com.au 1 0 * * * ~/Desktop/toskymesh.sh 59 6 * * * ~/Desktop/tooptus.sh 0 3 * * * snapraid sync   More Additional Info:  The output of ps -ef | grep '[s]endmail'  root 6840 1370 0 10:26 ? 00:00:00 sendmail: MTA: accepting connections   I know for sure cron is working, but I'm testing the mail command with echo Test | mail -s Test redacted@yahoo.com.au anyway.


Is there a place or software in ubuntu like controol panel add/remove programs

is there a software or add/remove programs like windows that keeps a list of all installed used programs list on ubuntu. gui is prefered here.  so that its easy. we do not have to use terminal.


Why the principal components correspond to the eigenvalues?

Suppose ${\bf{X}} = ({X_1},{X_2},\ldots,{X_n})$ are the original components (also random variables) and ${{\bf{w}}_j} = ({\omega _1},{\omega _2},\ldots,{\omega _n})$ are loadings for the $j$th principal component satisfying ${\bf{w}}_j^\rm{T}{{\bf{w}}_j} = 1$ and ${\bf{w}}_\rm{i}^\rm{T}{\bf{w}}_j = 0$ for $i\neq j$, thus ${z_j} = {\bf{w }}_j^{\rm{T}}{\bf{X}}$ is the $j$th component.  To find out the first principal component, we try to maximize the variance of $z_1$, which is $\rm{var}(z_1)=\rm{var}({\bf{w }}_1^{\rm{T}}{\bf{X}})=\bf{w}_\rm{1}^\rm{T}\rm{var}(\bf{X})\bf{w}_\rm{1}$. We estimate $\rm{var}(\bf{X}\rm{)}$ by the sample co-variance matrix $\bf{S}$, we maximize $L=\bf{w}_\rm{1}^\rm{T}\bf{S}\bf{w}_\rm{1}-\lambda({\bf{w}}_1^\rm{T}{{\bf{w}}_1} - 1)$ where $\lambda$ is the Lagrange multiplier. By taking derivative we arrive at $(\bf{S}-\lambda\bf{I})\bf{w}_\rm{1}=0$. It is obvious $\bf{w}_1$ is an eigenvector of the sample co-variance matrix $\bf{S}$.  Now the problem comes. Solving the equation gets you all eignenvalues and eigenvectors. I searched the internet all materials I found simply tell you to rank the eigenvalues and the eigenvector of the largest eigenvalue is the first principal component, and the eigenvector of the second eigenvalue is the second principal component, and so one so forth.   My question is how do we show or prove the largest eigenvalue corresponds to the largest variance and the second largest eigenvalue corresponds to the second largest variance and so on. Thank you.


Notify when some grouped services fail in Nagios

I have three DNS services, each on different hosts configured in Nagios. Each service notifies me whenever it is failing (DNS on host A down).  Is it possible to configure Nagios so that I'm only getting a (customized) notification when all three DNS services are down via pager (DNS is not working) and a mail in case only a single service goes down (DNS on host A down).  The only way I see how I could achieve something like this is with service dependencies, which are cumbersome to use. They also do not have their own notifications.  How would you do that?


Is the total angular momentum of the universe zero?

I know that having a net angular momentum will contradict isotropy of the universe by preferring a specific direction. But is there any experimental data on the total angular momentum of the universe and how much it deviates from zero (perhaps according to the CM frame)?


Issue wish visualization / Jagged faces at cube edges

When I createa a solid, this is the way that it appears on the screen. Actually faces are planes but this is what I see, the edge seems to be jagged from far and as soon as I zoom in it becomes perfectly sharp. It never happened to me before. I use 2.9 in solid mode. Maybe I have done something wrong?


Manually generate password for /etc/shadow

I need to manually edit /etc/shadow to change the root password inside of a virtual machine image.  Is there a command-line tool that takes a password and generates an /etc/shadow compatible password hash on standard out?


How to measure disk-performance under Windows?

I'm trying to find out why my application is very slow on a certain machine (runs fine everywhere else). I think i have traced the performance-problems to hard-disk reads and writes and i think it's simply the very slow disk.  What tool could i use to measure hd read and write performance under Windows 2003 in a non-destructive way (the partitions on the drives have to remain intact)?


How should I determine how many lands of each different color to put in my deck?

Situation: You've built your at least 2 color deck, know exactly what number of lands you want in it, but don't know how many to put in of each basic-land type.   How do pro-players figure this out? Obviously it seems like a deck that is about 50-50 color-wise would have equal numbers of each basic-land for those colors, but what if the deck is 60-40, 70-30, 80-20, etcetera? Or perhaps its a tri-color deck with a 40-30-30 or a 50-40-10 color distribution? Obviously it will depend on the mana-curve and the cards in the deck, but I'm just looking for some general guidelines.  Not getting any land in your side-color is bad, but not getting any in your main color is even worse. How do you manage these problems to get the best chance of success?    , and  but I'm specifically interested in color distribution of lands. It would be awesome if answers could address both 40 and 60 card decks. I'm talking only about basic lands, as I believe addressing the entire issue of "What lands should I put in my deck?" is far too big for one question.


How to Automatically Center Ellipses in Justified Text

Consider the following excerpt from Plato's Republic:  See how nicely centered the elipsis is on the second to last line. However (and frequently encounter this), when I try to produce such a paragraph in Latex (using Pdflatex): \documentclass{article} \begin{document} \large  In \emph{Laws} 731 {\small{\scshape{B-C}}} Plato tells us again that the soul cannot combat injustice without the capacity for righteous indignation. The Stoics affected to deprecate anger always, and the difference remained a theme of controversy between them and the Platonists. \textit{Cf.} Schmidt, \textit{Ethik der Griechen}, ii. pp. 321 ff., Seneca, \textit{De ira}, i. 9, and \textit{passim.} Moralists are still divided on the point. \textit{Cf.} Bagehot, \textit{Lord Brougham :} ``Another faculty of Brougham \ldots is the faculty of easy anger. 398 \end{document}  I get this:  Notice how far to the right of center the ellipsis is. QUESTION: Is there a way to correct this using Pdflatex so that the ellipses always appear "centered" in justified text? Thank you.


How do I apply for a UK standard visit visa for a 2-year-old child?

My husband holds a UK business visa and asked me to apply for a visit visa.   I have filled in my application and entered my uncle's address under the question of where I plan to stay. I am trying to give the same address for my child, as well, but it keeps asking me the relationship between my uncle and my child. As it isn't an option for direct family, I cannot proceed further.  I read previous answers here that mention a GWF number, but I don't understand where to mention it in the online application.   Also, what do I put in for the question about how much I plan to spend in the UK?


I have gotten into checking my credit scores recently. I have it setup to check once a month on mint, and I also check it about once a week on credit Karma.  Today I noticed a discrepency. On my mint.com credit score (Equifax) it shows as a 738 with all of the correct details. On credit karma it shows a 792 (Equifax) and 797 (Transunion), again with all of the correct data. The credit karma was updated today, and the mint.com data updated on the 19th.  What could cause this discrepancy?


What's the added value of SD line over regression line when examining association between 2 variables?

I'm trying to incorporate different practices to use when exploring a new data set. Especially, how to examine the association between two variables.  Steps for example (not necessarily by order):   plot a y-by-x scatter plot of the raw data to see the relationship visually. compute summary statistics for each variable (mean and sd) compute correlation coefficient r draw the OLS regression line, compute its slope and intercept etc....   I've come across the "SD line" in Freedman's Statistics book, which is defined as:     "the line that goes through the point of averages and climbs at the rate of one vertical SD for each horizontal SD" Freedman, D., Pisani, R., & Purves, R. (2007). Statistics (4th edn).   Since this book ("Statistics") is a canonical textbook, I consider its choice to discuss the SD line as an indication for the line's importance. However, a simple google search for the term "SD line" doesn't yield as many independent results. Most of them come directly from Freedman's book. This tells me it's not a central concept in bivariate analyses in general.  When comparing the SD with the OLS regression line, it seems like the regression line is more informative (than the SD line) for predicting y from x. Therefore, I'm wondering if bothering to plot the SD line has any benefit or added value that I would not already have when plotting the regression line.  Example using mtcars dataset, focusing on association between weight and mpg  data(mtcars)  ## calculate means mean_wt <- mean(mtcars$wt) mean_mpg <- mean(mtcars$mpg)  ## calculate standard deviations sd_wt <- sd(mtcars$wt) sd_mpg <- sd(mtcars$mpg)  ## scatter plot plot(x = mtcars$wt, y = mtcars$mpg)  ## add the "point of averages" points(mean_wt, mean_mpg, col = "red", cex = 1.5, pch = 16)  ## calculate the slope of the sd line slope <- -1*sd_mpg/sd_wt  ## plot the sd line curve(expr = x*slope + (mean_mpg - slope*mean_wt), add = TRUE, col = 'blue', lwd = 2, type = "l", lty = 2)  ## plot the regression line model <- lm(mpg ~ wt, data = mtcars) abline(model, col = "orange", lwd = 2)  ## legend legend("topright",        legend = c("Regression line", "SD line"),        col = c("orange", "blue"),        lty = c(1, 2),        lwd = c(2, 2))     Thus, my question: how can the SD line increase one's understanding about the relationship between two variables, in a way that's either adding or complementing on what the regression line already tells?


Hi My friend and I get 2 different answers to this question. I would like to know how to calculate the value of q. My friend says that 500/1500=q because there are 500 recessive alleles in the population and there are 1500 alleles in total. I say that p2= 500/1500 and P is the square root of that value and  q+p=1 but we both get different answers.  Please let me know which way is correct. Thank you guys in advance


Possible Duplicate:          I've always been curious because I've run a virtual machine a few times.   Can a VM infect the host with a shared drive between the two? Can a VM infect the host with absolutely no networking at all? Can something malicious "break out" of the virtual machine and infect its host?   Basically, is there any time at all that a virtual machine can pose any kind of security risk to its host?


I can't draw a particular cross symbol in LaTeX.  I tried drawing it in Dextify, but that didn't recognize the symbol.  I don't even know what it is called.  Any help with the name or the code is appreciated.  An image is below.


Connecting nine LEDs in series.. why the results?

I asked this before but I'm having problems still. I need to connect nine LEDs in parallel with a 9 volt battery. The wire leading away from the 9V separates into three and on each three are three LEDs in series. A calculator told me that if I have 2.25 volt, 28 mA LEDs on each branch I need an 82 ohm resistor. If I have an 82 ohm resistor and 9/82 is .10976... wouldn't my current be too low? I just don't know how to do it. How do I decide which resistor I need to use with an LED?


How to get Nginx to support the HTTP OPTIONS method

I have an Nginx server this is returning a 403 when a client uses the HTTP OPTIONS method. It sounds like Nginx does not support the OPTIONS method, but I couldn't find conclusive evidence of this on the Interwebs.  Right now Nginx is running on Centos5. Is it true that Nginx does not support this and is there a module that could be enabled for Nginx to support OPTIONS?  Thanks.


Proving an Olympiad type inequality $\sqrt{\frac{2a}{b+c}}+\sqrt{\frac{2b}{a+c}}+\sqrt{\frac{2c}{a+b}}\le\sqrt{3(\frac{a}b+\frac{b}c+\frac{c}a)}$

Let $a,b,c>0$ be real numbers. Prove that:  $$\sqrt{\frac{2a}{b+c}}+\sqrt{\frac{2b}{a+c}}+\sqrt{\frac{2c}{a+b}}\leq\sqrt{3\left(\frac{a}{b}+\frac{b}{c}+\frac{c}{a}\right)} $$


Do any birds beside the family Columbidae (or any reptile or mammal) feed their young "Crop Milk"

Birds from the family Columbidae (e.g., doves and pigeons) produce a fatty, milk-like substance in their crop.  The secretion is often referred to as "crop milk."  They feed crop milk to their young through regurgitation.  Does anyone know of another bird or reptile group (or even mammals) that has evolved such a mechanism; not regurgitation but secretion of a milk-like substance for feeding young?  Also, both male and female doves produce crop milk; are there cases where males of a mammal species produce milk?


public class Autoboxing { public static void main(String[] args) {    int x=10;     Integer oldValue=x;     change(oldValue);     System.out.println("value:"+oldValue); } static void change(Integer value){     value=100; }   }  Hi, I am trying to autobox a int value into Integer type. Then pass the Integer object to a method to change the number . But the number doesnt change. it still prints out 10?  Could some one spot my error. Thanks in advance.


Can anyone explain where the following expression for the electric field vector comes from? $$ \mathbf E(\mathbf r,t) = -\nabla \phi(\mathbf r,t) - \frac{\partial}{\partial t}\mathbf A(\mathbf r,t)  $$  where $\phi$ and $\mathbf A$ are the scalar and vector potentials, respectively.  Presumably it can it be derived from Maxwell's Equations?


Prove that $d$ is a gcd of $a_1, ..., a_n$ iff $\langle d\rangle = \langle a_1\rangle + \cdots + \langle a_n\rangle$.

To anyone encountering this problem: As the comments and answer correctly point out, if $R$ is a commutative ring with identity, and $\langle d\rangle = \langle a_1\rangle + \cdots + \langle a_n\rangle$, then $d$ is a gcd of $a_1, ..., a_n$. If, additionally, $R$ is Noetherian (for instance if $R$ is a PID), then this becomes an equivalence. However, if $R$ is not Noetherian this may fail (as in the example given by Exodd). Furthermore, in any commutative ring $R$ with identity, the following stronger statement is true: $d\in R$ is a gcd of $a_1, ..., a_n$ and is equal to $r_1 a_1 + \cdots + r_n a_n$ for some $r_i\in R$ iff $\langle d\rangle = \langle a_1 \rangle + \cdots + \langle a_n\rangle$.  Let $R$ be a commutative ring with identity, and let $a_1, ..., a_n\in R$. I would like to prove that $d\in R$ is a gcd of $a_1, ..., a_n$ iff $\langle d\rangle = \langle a_1\rangle + \cdots + \langle a_n\rangle$. If $\langle d\rangle = \langle a_1\rangle + \cdots + \langle a_n\rangle$, then $\langle a_i\rangle \subseteq\langle d\rangle$, so $d\mid a_i$ for all $i$. Furthermore, if $c\mid a_i$ for all $i$, then $\langle a_i\rangle\subseteq\langle c\rangle$, so $\langle a_1 \rangle + \cdots + \langle a_n\rangle\subseteq\langle c\rangle$, or $\langle d\rangle\subseteq\langle c\rangle$, so $c\mid d$, implying $d$ is a gcd of $a_1, ..., a_n$. I'm finding the other direction trickier. I thought I had an argument but I can't quite make it work. First, if $d \mid a_i$ then $\langle a_i\rangle \subseteq\langle d\rangle$ for all $i$, so $\langle a_1\rangle + \cdots +\langle a_n\rangle \subseteq \langle d\rangle$. My idea was this: let $J = \{I\subseteq \langle a_1\rangle + \cdots + \langle a_n\rangle\ |\ I\ \text{principal ideal}\}$, ordered by inclusion. $\color{red}{\text{Then $J$ has a maximal element by Zorn's lemma.}}$ This is not actually true, as only finite chains have upper bounds in $J$, unless $R$ is a PID. That is, if we have an arbitrary collection of principal ideals $\{\langle a\rangle\}_{a\in A}$, totally ordered by inclusion, then we cannot guarantee that $\bigcup_{a\in A}\langle a\rangle$ is also a principal ideal (it is an ideal however). If we roll with it, letting $\langle d\rangle$ be a maximal element of $J$, clearly as $\langle a_i\rangle\subseteq \langle a_1\rangle + \cdots + \langle a_n\rangle$ we must have $\langle a_i\rangle\subseteq\langle d\rangle$, so $d \mid a_i$. Furthermore, if $c \mid a_i$, then $\langle a_1\rangle + \cdots + \langle a_n\rangle \subseteq\langle c\rangle$, so $\langle d\rangle\subseteq\langle c\rangle$, and thus $c \mid d$. So $d$ is a gcd of $a_1, ..., a_n$. Can I modify my argument to make this work? Is there a simpler route I've missed?


Can I "upgrade" my old 32-bit IBM ThinkPad to 64-bit by installing a new hard disk?  I am running Ubuntu 14.04 but want to upgrade to a newer Ubuntu system. Can Anyone help this novice with that?


What is the reason why I get -70 of Serial upvoting reversed on Stack Overflow, -70 of doing what?  I read the document    But I want to know which why in details why I get -70. Come on this is crazy  Anyone?


storage facilities at the San Francisco airport

Hello we will be travelling onwards from San Francisco on the 30th of June and will return on the 2nd evening. We would like to leave our heavy luggage behind and travel light. What are the options of storing luggage at the airport, as we will be boarding a midnight flight on 2nd to Boston


Are unequal groups a problem for one-way ANOVA?

I have data for three unequal groups: $N = 44$, $N = 354$ and $N = 347$. Is it possible to compare all three groups running a one-way ANOVA or is the first group too small?


Solution for A/C Condensate Drain Line that doesn't require emptying a bucket of water every day?

I have a split A/C system in a room that runs on low 24 hours a day during Summer that unfortunately cannot be connected to any drain or pipe and which therefore requires a bucket outside to be used to collect the condensate from the condensate drain line in the exterior unit that sits on my balcony in my apartment building.  This is quite frustrating as the bucket has to be emptied every single day (once a day), so I'm looking for a better solution.    The bucket is already quite large and gets quite heavy at the end of the day when it's full, so maybe something that makes the water evaporate faster than normal so that I don't have to empty the water so often?  Does such a solution exist or am I condemned to a lifetime of emptying the bucket every night during Summer?  ** 14 May 2015 EDIT **  I have not yet been able to solve this issue.  Without going into details, connecting the condensation drain line to any drain of any kind, drain line, drainage hole, ground, pumps, pipes, etc. is NOT an option, so I need an outside-the-box solution.  The A/C Condensate Drain Line seems to empty about 3 Gallons / 12 L per 24 hour period.  Potential solutions:  Humidifier   Are there outdoor-friendly humidifiers that could get rid of 3 Gallons/ 12 L per day?  The tank would not have to hold that much as the drain line would just drip the water constantly into the tank. CONSIDERATIONS: Would I need to use more than 1 humidifier and serialize them?  Can a humidifier handle being on for 24 hours a day for 4 months straight?  Can a humidifier handle the elements (e.g. could rain affect the circuitry or create any electrical issues)?      My balcony has 37sqft / 3.4 m2 of area to play with but only 1 hour of direct sunlight (although plenty of indirect sunlight) per day, could I create a garden of plants/grass to absorb the water? CONSIDERATIONS:  How much garden would I need?  Which plants could meet this criteria?  Could the balcony handle the weight of soil + plants + water?   NEW: Drip Tray + Humidifier Wick   What about something like  plus several of , could that evaporate 3 Gallons / 12L per day? CONSIDERATION: Would they get clogged from dirty city air? How many wicks would I need to evaporate all that water?   Any other outside-the-box solutions?  Would any of the solutions listed above work?  If so, what specific details would I need to make it work?  Are there any other solutions?  CLIMATE:  On the hottest Summer months, the average relative humidity is about 72%, with about 9 mean daily sunshine hours, 1-2 inches of monthly rain, and daily mean temperatures of about 76 F / 24 C (with average highs of 84 F / 29 C). Remember, however, that the balcony only receives about 1 hour of direct sunlight, although plenty of hours of indirect sunlight.    As you can see, it gets VERY dirty due to this being in the inner city next to a large avenue where a lot of cars run through creating a lot of direct air pollution, so any solutions that may clog need to take this into account. This is another reason I want to avoid having to open the balcony doors to empty it every night. In case it helps, the model of the outdoor unit is Mitsubishi MXZ-18TV.


Is it possible to disable the Windows volume box that pops up when using the keyboard to change the system volume, or at the very least, make it so it's not clickable?     Running a fullscreen application, and clicking anywhere in the top left corner after changing the volume typically ends with me waking up the neighbours while I fumble over the keyboard trying to get the sound back down to a reasonable level.  I found  asked over a year ago, but all the solution does is reduce the overlay to 5 seconds, which was already my default, and a similar question asked two years ago that suggested it may be hacked out eventually.  Cheers.


I cannot change the number of vertices of added mesh, must be some changes from default settings

This is blender 2.90.1. I am not able to changes vertices count of the added mesh, might be due to changes of default settings. Pls help me solve the problem. I tried reinstalling ,but the problems remains the same.


I just got confused by seeing votes for comments. While hovering over the vote button it shows "number of useful comment votes received". So where can I give an upvote to a comment?


I am a beginner to QGIS. My problem is I tried to create sub-catchment within a basin by using provided point datasets (river gauge location). In total, I have 12 measuring points (i.e 12 pairs of x and y coordinates) within my basin. I want to delineate all catchments within basin on the basis of provided coordinates ( not on the basis of minimum or maximum cell that r.watershed has.) I am looking for the function in 'hydrology' extension tool of ArcMap.


i have been doing a programing project and i have been keeping all the files on a usb stick. To get to the point i accidentally deleted this folder in the usb with all the files in. can anyone tell me how to restore them? i have already tried the program file drill but that did not work.


copy to clipboard current path from console with no mouse

I'm wondering if it possible to copy to clipboard output of pwd command.  I often need to copy some path and I have to select it with mouse, do several clicks and that is annoying for me.  What I want is piping output of pwd command to something that will copy it to clipboard so I do not have to touch my mouse  Edit: it will be great if it is possible with some built-in


The Passive Voice when referring to time

If we say something like "More than two months have passed", would you say this is speaking in the Passive Voice? When you look at the general rules about when to use the Passive Voice, it doesn't seem to mention the passing of time, so I'm wondering why we say it this way.


What is the difference between Inference and Machine Learning?

I have seen some classes in my University labeled as an "Inference class" and others as "Machine learning" classes, but I was not sure if appreciated the core difference between these two labelings?   I normally think of machine learning as the study of systems/algorithms that are able tp extract information from data. It uses techiniques from a broad list subjects, like statistics, computer science, optimization, etc. However, I was not sure how statistical inference differed from Machine Learning.  Thanks for the help in advance! :)


Object.create(Function.prototype) => create Function which inherits properties

I am looking for a way to construct a function that has some inheritance.    What I am looking for is an object that is a function that can be instantiated in a program, but that has new properties attached to it's prototype.  So, what we shouldn't do is this:  Function.prototype.x = function(){  };  Function.prototype.y = function(){  };   so what I want to do is something like:  const proto = Object.create(Function.prototype);  proto.x = function(){};  proto.y = function(){};   however, at some point later in the program, I would like to actually define the function body for proto, so that I can actually call proto like a function:  proto();   is there a way to do this? The above definitely does not work :)  This is a little closer, and the error message is telling:  function F(){  }  F.prototype = Function.prototype;  var f = new F();  f.apply(null);   Run the above and we get:     TypeError: Function.prototype.apply was called on [object Object],   which is a object and not a function           at Object. (/Users/amills/WebstormProjects/oresoftware/suman/exp7.js:15:3)           at Module._compile (module.js:541:32)           at Object.Module._extensions..js (module.js:550:10)           at Module.load (module.js:458:32)           at tryModuleLoad (module.js:417:12)           at Function.Module._load (module.js:409:3)           at Function.Module.runMain (module.js:575:10)           at startup (node.js:160:18)           at node.js:449:3


Is there a list of error codes for Minecraft?

Similar to  on the bugs in Minecraft, I would like a complete list of what error codes exist in Minecraft and how they occur, as well as how they can be resolved.


Is the war cleric's divine strike considered non-magical damage?

Other domains give damage types that are not commonly resisted. Stat blocks list fire, cold, and other resistances separately from the "bludgeoning, piercing, and slashing damage from nonmagical weapons/attacks" that many powerful creatures have. That caveat is also never used for non-weapon types of damage (b/p/s), to my knowledge.   This means that even with a mundane weapon, a cleric with divine strike usually has a way to deal consistent, unresisted damage. They deal a different damage type, that might not be resisted. But war clerics deal the same damage as their weapon attack, and that should make it bludgeoning, piercing, or slashing from a nonmagical weapon.   Now, the flavor text says " you gain the ability to infuse your weapon strikes with divine energy." But unlike, say, monk's ki-empowered strikes, it never says "[this attack] counts as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage" under divine strike, so it should still count as mundane damage.   That makes it sound like war clerics' divine strike ends up being a little rough compared to some of the others (though trickery domain probably has it worse). Have I interpreted this correctly?


So, I'm having trouble doing this certain problem. As the title suggests I should prove that if this holds: $$x | y^2 $$ $$y^2 | x^3$$ $$x^3 | y^4$$ $$...$$ Than for each natural x and y, x is equal to y. I've tried writing the numbers x and y in form of: $$x = p_1^{\alpha_1} + p_2^{\alpha_2} + ... + a_n^{\alpha_n}$$ $$y = P_1^{\beta_1} + p_2^{\beta_2} + ... + p_n^{\beta_n}$$ Now when I try to express the given equations in this form I get: $$x \le y^2 \le x^3 \le y^4$$ Which for each $i$ yields: $$\alpha_i \le 2\beta_i \le 3\alpha_i \le 4\beta_i ...$$ I was now wondering what to do next to prove it. Thanks.


ubuntu is not getting updated when i try to update it shows:  E:Malformed line 43 in source list /etc/apt/sources.list (dist parse)   My update manager is also not working when i try to open it from terminal it also show some errors similar to this


Complex Analysis analytic function 1$f(z)=z$

if$\text{ } f:D(0,1)\longrightarrow D(0,1)$  is  analytic such that there exists  $a,b\in D(0,1)$ and $\text{ }$$f(a)=a$ , $f(b)=b$  prove that $f(z)=z$      $\forall$ $z\in D(0,1)$


What's the windows 10 equivalent of "Command `" on a mac

For those who don't use a mac, command ` cycles between windows of the same application just like alt tab.  I was wondering if there is a windows 10 equivalent ?


What tools do you use to check if your host/devices on your network are online in one glance. i have multiple companies with APs, servers and NAS. Of course I can ping one by one, but I'm sure you have a better one. I heard Nagios Core seem the solution, but it hell of overkill features.   Same question here asked by  but yet to be answered.   Newbie here.   Thank you in advance,


Force Github account to show up in google search

Is there any way to index my Github account to google search. I see that many people's account show up as soon as I type their name, but mine doesn't show up even after I type my name followed by github n search.