If I    open any post on any Stack Exchange site in mobile version (Chrome 63 on Android) then click "add a comment" then type @ then type first letter of user name which already commented to this post   Then no username autocomplete happens.   Here is gif where I try to autocomplete @Mureinik in :        In desktop Chrome autocomplete works as expected (that is after typing @ and first letter of username, popup with username appears):        Sorry if this question is duplicate.  I don't know exactly why this is not a bug (@iDebug says so), so I put both  and  labels.

Yesterday, I was browsing the mobile Stack Overflow site. I noticed one thing: the textareas where you write your comments/answers are very buggy. I'm using a Samsung Galaxy S2, with the standard Android browser (Android version 4.1.2). There are a number of things that aren't working when typing your comment/answer.   Automatic spacing with Swype is disabled (however this might be because of Swype, not the site). Text navigation buttons (step left, step right, select text, copy text etc.) doesn't work with the on-screen keyboard, and selecting text by holding your finger over text is extremely difficult. When you paste something it always seems to be pasted at the top of your text, no matter where you try to paste it. Replying to another comment ("@Example User") does not show suggested people to reply to, like the full site does.   Is there anything I can do to solve these issues/bugs, or is it in the hands of Stack Overflow itself, and if so, should it be looked into?  Edit: I was using the mobile version of the site when noticing these bugs.


the Schwarzschild metric describes the geometry of a black hole for an observer infinitely far away. My question is simply: How does one find the geometry of the same black hole except that the observer also has a radial velocity? Giving the observer a velocity breaks spherical symmetry and might be non-trivial. But what is the procedure of finding such a metric? Can you simply add a Lorentz transformation boost since the geometry around the observer is flat? Also, the geometry necessarily has to change to include the Doppler effect, right?

Let $\Phi(0, t)$ be the gravitational potential at the origin and $t$ the clock ticking at infinity, i.e. not influenced by any gravitation.  Let a mass $m$ approach the origin with constant velocity such that its distance to the origin is $r(t)$. What is $\Phi(0,t)$?   The naive answer would be $\Phi(0,t) = -Gm/r(t)$. But this would mean instantaneous influence. My next best guess is $$\Phi(0, t+\frac{r(t)}{c}) = -Gm/r(t)$$ which assumes that the influence of the mass on the origin can only travel at the speed of light.  But for the observer at infinity (that's were the $t$ clock ticks), the gravitational influence travels not with $c$ in empty space, but with a $c_{\Phi}$ that depends on the gravitational potential or (even worse) the metric along the path which, for the observer at infinity, is less than the constant $c$.  While bringing in the word 'metric' I immediately concede that I have no idea in which metric to measure $r$ anyway.  Short Version  What is the time dependent gravitational potential at the origin when a mass approaches it with constant velocity in terms of General Relativity. (It may turn out that gravitational potential is not the right thing to talk about, but rather metric or stress-energy tensor. I am happy to get answers as such.)


With macOS Sierra's iCloud Drive feature, it seems the promise of automatic space management is that:   it will fill your hard drive's free space by downloaing iCloud drive files automatically it only clears the local copies when you select other iCloud drive files to download instead   This works to keep your HDD constantly full to capacity, causing many issues with other programs, including Terminal and iTunes complaining there is not enough free space to continue. Despite Finder reporting there is plenty (due to point 2).  Is there a way to tell iCloud  Drive to stop attempting to download more files (fixing point 1), and to delete the local copies of files it has insisted on downloading (fixing point 2)?    The below image captures the problem. Finder reports 157.99GB available, yet I can't download a 773.1MB folder because there isn't enough free space, because iCloud Drive is insisting on filling my hard drive with 164.63GB of data.

How do I stop iCloud from downloading files to my hard drive? I opened up a folder and it immediately started downloading all contents


How is it possible to make a table note for the table caption?  Something like  \begin{table} ... \caption{...\tnote{1}.} ... \begin{tablenotes}    \item [1] : blabla. \end{tablenotes} \end{table}   does not work in the sense, that no '1' is added after the caption to refer to the table note - which is written as expected.

I have these \footnotetext and \footnotemark as illustrated in the figure below. I used these tags to enforce my own numbering (and because using only \footnote was not working the way I expected).    The code I use for generating the mark is:   \caption{Lista de notas presentes em um piano de 88 teclas,  com notação em Inglês, frequência em Hertz e comprimento de  onda em centímetros.\protect\footnotemark[1]}   Is there any way I can enforce my \footnotetext to appear in the same page as my \footnotemark?


I do not know how to login as a different user except for guest.I want to change my user name because I misspelled it during installation. Please advise.

Some time ago, when I installed Ubuntu, I chose a rather stupid username for my account that I do not want to use anymore. How do I change this (including the name of my home directory, and the name in the terminal) without losing settings for applications? How do I keep permissions and my keys for various authentification (e.g. email, SSH, GPG and more)? What settings could possibly get lost if I changed my username?


Recently I started leveling up in Ranger class, and I looked into the Beast master Ranger archetype and something bothered me. If a character decides to have a Pony as a Companion, would commanding him to Dash (Dodge or Disengage)  take an action.     Ranger's Companion      At 3rd level, you gain a beast companion that accompanies you on your   adventures and is trained to fight alongside you.       Choose a beast that is no larger than Medium and that has a challenge   rating of 1/4 or lower. Add your proficiency bonus to the beast’s AC,   attack rolls, and damage rolls, as well as to any saving throws and   skills it is proficient in.      The beast obeys your commands as best as it can. It takes its turn on   your initiative, though it doesn't take an action unless you command   it to. On your turn, you can verbally command the beast where to move   (no action required by you).   Commanding it to move would not take an action but commanding something else would. And it can be a Ranger's companion since it is medium, has a 1/8 challenge and it can even be a mount since my character is a Halfling.

I'm trying to parse out mounted combat as a ranger with a ranger's companion.  From Controlling a Mount (PHB pg. 198):     You can control a mount only if it has been trained to accept a rider. ... It moves as you direct it and it only has three action options: Dash, Disengage, and Dodge   From Ranger's Companion (PHB pg. 93):     The beast obeys your commands as best as it can. On your turn, you can verbally command the beast where to move (no action required by you). You can use your action to verbally command it to take the Attack, Dash, Disengage, Dodge, or Help action.   Assuming a ranger's companion has been trained to accept a rider, what's the action cost to the ranger of commanding it to Dash, Disengage, or Dodge? I assume it would be free while mounted and cost one action when not mounted.


Imagine a dual Chilean-Canadian national who wishes to fly from Chile to Canada in September, 2020. There are currently no flights directly from Chile to Canada (in better times there was an SCL-YYZ route). Can this person safely use a ticket that transits through US airports given restrictions on entry due to COVID-19, assuming they meet the usual entry requirements for a Chilean (e.g., eligible for visa waiver program)?

This community wiki explains the current restrictions by the United States of America on the entry of individuals who may pose a risk of transmission of the SARS-Cov2, the virus which causes the Covid-19 disease.


Hi guys can anyone help me with the following problem Let it be that $R=\Bbb Z/m\Bbb Z$. I must show the following equivalences $ā∈R^ˣ⟺\gcd(a,m)=1⟺ā$ is not a zero divisor in $R$ I already know that to solve this question i must show 3 or 4 separate (small) proofs of implications. For example "a∈Rˣ⇒gcd(a,m)=1" and "gcd(a,m)=1⇒a∈Rˣ". But I can't  solve any of them. I also tried to use "Bézout's identity" for some of the implications but I can't seem to get anywhere. Thanks for your help

Let us consider the ring $\mathbb{Z}_n$ where $\bar{m}\in\mathbb{Z}_n$  Could anyone help me prove that $\bar{m}$ is a zero divisor in $\mathbb{Z}_n$ if and only if $m,n$ are not coprime  So far I have:  Assume $\exists \bar{a}: \bar{m} \bar{n}=n \mathbb{Z} \Rightarrow$ for some $b\in\mathbb{Z}:am=bn$  I then assumed $n,m$ were coprime and attempted to use $\exists a',b'\in \mathbb{Z}:a'm+b'n=1$ to come to a contradiction, however haven't found one, the most promising thing I have found so far is that  $a=n(a'b+ab')$ and $b=m(a'b+ab')$ $\Rightarrow n|a$ and $m|b$


I download kernel source from git://kernel.ubuntu.com/.../ubuntu/ubuntu-trusty.git. I need to compile version 4.4.0-31-generic on 14.04.4 lts 64bit, so I clone and checkout branch Ubuntu-lts-4.4.0-31.50-xxx-14.04.1.I use config-4.4.0-31-generic as config file from linux-image-4.4.0-31-generic package. After I compiled, I realize kernel version is 4.4.13 in Makefile and I found arbitrary kernel version config item seems not take effect and installed modules is more than 5000 but package in linux-image-4.4.0-31-generic just contain about 1000 modules. The modules I installed size is around 3G, the package just 39M. Am I did it a wrong way?

I'm interested in compiling a new kernel under Ubuntu 12.04 x86 64 bit.  I found  which is basically a mirror for  and there are a lot of steps (git, etc.) that appear useless to me.  With earlier releases/distros, I used to create a .config file and modify a Makefile if I needed to, then just run make and it's done.  Is there is a simple way to do this under Ubuntu?


Consider the subring  $$  \mathbb Z\left[\frac{1}{2}\right] = \left\{ \frac{k}{2^n} : n \ge 0 \right\}. $$ As $1/2$ is the root of $2X - 1$, this is an intergral extension. Now according to  we have the equivalence  that if $A \subseteq B$ are rings with $b \in B$ $$  \mbox{$b$ is integral over $A$} \Leftrightarrow  \mbox{the subring $A[b]$ is a finitely generated $A$-module}. $$ But why is $\mathbb Z[1/2]$ a finitely generated $\mathbb Z$-module, as I see it the elements $1, 1/2, 1/4, \ldots$ are infinitely many generators?

$\mathbb Z[1/2]$ is not finitely generated ?   Maybe I misunderstood, what finitely generated means.  it says, we need finitely many elements and I think $1$ and $1/2$ suffices as generators.  But , at the end of Proposition $5.1.4$, from the fact that $\mathbb Z[1/2]$ is not finitely generated it is concluded that $1/2$ is not integral.


I have built a model on log(units) sold and want to measure the contribution of each independent variable in the model (which are also in log) i.e. proportions of predicted units explained by independent variables.  So, basically I have a log-log model and want these contributions to be in actual units.  Under usual circumstances, I would be using an additive model but since now I am using a log-log transformation (multiplicative model) I think the process of calculating contribution will be different than additive.  How should I go about it?

I'm wondering if it makes a difference in interpretation whether only the dependent, both the dependent and independent, or only the independent variables are log transformed.  Consider the case of  log(DV) = Intercept + B1*IV + Error    I can interpret the IV as the percent increase but how does this change when I have   log(DV) = Intercept + B1*log(IV) + Error   or when I have   DV = Intercept + B1*log(IV) + Error   ?


I know very well that the sum of integers from $1$ to $n$ is $\dfrac{n\times(n+1)}2$. What I'm interested in today, and cannot find a solution for, is performing the opposite operation.  Let $m = \dfrac{n^2 + n} 2$. Knowing the value of $m$, how do I figure out the value of $n$? I could easily program a solution but I'd much prefer an algebraic one.

Can someone reverse this formula? Sorry if it's too basic, I'm an old guy and my math is rusty :-D  $s =\frac{n(n+1)}{2}$  If it ain't clear, by reverse I mean obtaining the value of n by providing s  Thanks


I have this finction:   var msec = 100;    setInterval(function () {             if (childNodeDocument.readyState == "complete") {                 parent.parent.mapFrame.hideModal;                 alert("complete");                 clearInterval();             }         }, msec);   when this condition is satisfied:  childNodeDocument.readyState == "complete"   I want to stop executing setInterval().  But the way I am doing above not working.  Any idea what I am missing?

I am using setInterval(fname, 10000); to call a function every 10 seconds in JavaScript. Is it possible to stop calling it on some event?   I want the user to be able to stop the repeated refresh of data.


Currently I am using the Ubuntu 20.04 operating system and I would like to erase it and install windows 10 but how?

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


I have a layover in Stockholm from the US on my way to the Czech Republic. I have both Czech and US passports. I need to pick up and recheck my bags. Will I need a transit visa?

I found many related questions on this site but I am still not sure about the rules. How can I decide if I need a visa to transit? Schengen members as of May 2021 are as follows:  Austria Belgium Czech Republic Denmark (excluding Greenland and the Faroe Islands - but an open border with the Schengen Area is maintained) Estonia Finland France (excluding overseas departments and collectivities) Germany Greece Hungary Iceland Italy Latvia Liechtenstein Lithuania Luxembourg Malta Netherlands (excluding Aruba, Curaçao, Sint Maarten and the Caribbean Netherlands) Norway (excluding Svalbard) Poland Portugal Slovakia Slovenia Spain (except Ceuta and Melilla) Sweden Switzerland


What I would like to be able to do is ask a user a question using input. For example:  print('some scenario') prompt = input("You have 10 seconds to choose the correct answer...\n")   and then if the time elapses print something like  print('Sorry, times up.')   Any help pointing me in the right direction would be greatly appreciated.

I'm calling a function in Python which I know may stall and force me to restart the script.   How do I call the function or what do I wrap it in so that if it takes longer than 5 seconds the script cancels it and does something else?


I am using Time Machine to backup an external HDD (A) (2 TB) linked to my computer to an external 6 TB HDD drive.   I now had to shift the data from HDD (A) to a new 3 TB one (B). Is there a way to continue the backup of the data so that Time Machine doesn't think it has to start the backup of (B) from scratch? Does TM automatically detect that the data on the new hard drive (B) are the same as the ones previously backed up on the old hard drive (A)?   Given how flimsy HDD are, I thought this would be a common problem. But I didn't find anything in the questions.

I replaced my HD with an SSD (256 GB), and restored the contents from my Time Machine backup (external HD 320 GB).  Now, after a day of working, I plugged in my external HD to make the next backup. Time Machine now started to scan my files, prepared the files etc. (took rather long, because it somehow needed to scan everything), then entered the "Deleting old backups" phase. Everything looked normal, but just when it was about to finish, it failed with "This backup is too large for the backup disk.".  Only about 200 GB of my SSD are used, so this should easily fit on the external 320 GB HD: Not many files have changed since the time I restored the backup.  When I look into the Time Machine drive, I see, that it has automatically deleted all my old versions already I'm really not happy about that! Only the latest one is left - the one I restored from yesterday, and now it seems to create a separate backup for my new disk? Ok, "200 GB x 2 > 320 GB", but that's not what it should do. It should just continue writing the differences, as it has always managed to keep several old versions, so why would it be any different just because I moved the contents to an SSD?   Is there a way to make Time Machine "reconnect" to the new SSD (I assume, it is still somehow "connected" to the old HD, and therefore doesn't treat the changes on my new SSD as changes to the backup?)  I wonder, if I should have rather cloned my HD (e.g. with a third party tool), without Time Machine knowing about it?


Consider a function $g(x)$ such that the delta-function is given by $\delta(g(x))$, with $g(x)=0$ at $x_i$. Then we have that $$\sum_i=\frac{\delta(x-x_i)}{|g(x_i)|}.$$  Can someone suggest me a page with a good proof or show me the proof themselves? Thanks.

Firstly, apologies in advance for using an abuse of notation by placing the Dirac-delta inside an integral. But for my level of understanding, I have no choice.  This question involves one of the Dirac-delta properties: $$\delta(bt)=\frac{1}{\mid b \mid}\delta(t)$$ where $b \gt 0$ and $b \in \mathbb{R^+}$; which was proven in this  asked by myself.  This is essentially a word by word copy of a  given on page 470:      Given $$\delta(bt)=\frac{1}{\mid b \mid}\delta(t)$$ and by    considering an integral of the form  $$\int  f(t)\delta(h(t))\mathrm{d}t$$ then making a change of variables to $z =  h(t)$, we may show that $$\displaystyle\delta(h(t)) =  \operatorname*{\Large\sum}\limits_{i}\cfrac{\delta(t − t_i)}{\mid  h^{\prime}(t_i)\mid}$$ where the $t_i$ are those values of $t$ for    which $h(t) = 0$ and $h^{\prime}(t)$ stands for   $\cfrac{\mathrm{d}h}{\mathrm{d}t}$.   Could someone please show the steps in this derivation as I have no idea how they reached $$\color{#180}{\displaystyle\delta(h(t)) = \operatorname*{\Large\sum}\limits_{i}\cfrac{\delta(t − t_i)}{\mid h^{\prime}(t_i)\mid}}$$   Many thanks.


I installed Ubuntu on VirtualBox today. In order to have a shared folder with my host OS (Win 7) I followed the advise listed here:    When I start the VM now I get :  VBoxClient: the VirtualBox kernel service is not running. Exiting   at the top of the screen and I am unable to change the screen size to the full resolution of my Monitor. This was possible before.  I already tried the solution supplied here:    But it does not work. My virtual box installation is not updated to the current version for various reasons.

I've recently installed Ubuntu on Oracle's Virtualbox.  Now I want to install the guest additions.  I started up my Ubuntu guest OS, clicked "Devices" and chose "Install Guest Additions". Nothing happened, and I don't see the CD icon on my desktop.  How can I make this work?


W:The repository 'http://ppa.launchpad.net/tualatrix/next/ubuntu xenial Release' does not have a Release file.,  W:Data from such a repository can't be authenticated and is therefore potentially dangerous to use., W:See apt-secure(8) manpage for repository creation and user configuration details.,  E:Failed to fetch http://ppa.launchpad.net/tualatrix/next/ubuntu/dists/xenial/main/binary-amd64/Packages  404  Not Found,  E:Some index files failed to download. They have been ignored, or old ones used instead.

PPA seems to be constantly offline. Whenever I use sudo apt-get update, this error is shown:  W: Failed to fetch http://ppa.launchpad.net/ 404  Not Found   How do I fix these errors?


I have an array of players, which are arrays themselves and I want to sort by score.   [player_info] => Array (     [0] => Array         (             [player_] => âlêj!!tâ~ôk             [score_] => 66             [ping_] =>              [team_] => Blue         )      [1] => Array         (             [player_] => alejitbella             [score_] => 3             [ping_] =>              [team_] => Blue         )      [2] => Array         (             [player_] => §Uph§£lMejo             [score_] => 34             [ping_] =>              [team_] => Red         )      [3] => Array         (             [player_] => timoleon             [score_] => 10             [ping_] =>              [team_] => Red         )  )   I've already managed to get usort working properly (not shown in the example above) however I need to preserve placement of teams. Let's say Simon, Becky, Alek, and George are here.  Simon 25 Red Becky 13 Red Alek 3 Blue George 5 Blue   I want to be able to arrange them by score high to low, while preserving their location in the array based on team.  How might I accomplish this?  EDIT:  Due to people thinking this is a duplicate I need to clarify.  I want to order these by score while preserving the order of the team "Red" and "Blue"  Basically I want to turn the above example into     Simon 25 Red     Becky 13 Red     George 5 Blue     Alek 3 Blue

I have CSV data loaded into a multidimensional array. In this way each "row" is a record and each "column" contains the same type of data.  I am using the function below to load my CSV file.  function f_parse_csv($file, $longest, $delimiter) {   $mdarray = array();   $file    = fopen($file, "r");   while ($line = fgetcsv($file, $longest, $delimiter))   {     array_push($mdarray, $line);   }   fclose($file);   return $mdarray; }   I need to be able to specify a column to sort so that it rearranges the rows.  One of the columns contains date information in the format of Y-m-d H:i:s and I would like to be able to sort with the most recent date being the first row.


I'm very new to using regular expressions and am trying to allow only A-Z, a-z, 0-9, -, _  I'm using the following expression which is working:  preg_match('/^[a-zA-Z0-9-_]+$/i', $_POST['sign_up_username'])   My question is if this is the correct way to go about doing this. I'm not sure if this is the right place to post this. Any help would be great. Thanks.

I don't really understand regular expressions.  Can you explain them to me in an easy-to-follow manner?  If there are any online tools or books, could you also link to them?


I know that: $\sqrt{1+2\sqrt{1+3\sqrt{1+4\sqrt{1+\cdots}}}}=3,$ which is one of Ramanujan's infinite radicals. So surely the expression in question is less than $3.$ But how can I prove this without mentioning this or in general how to prove: $\sqrt{2\sqrt{3\sqrt{4\sqrt{\cdots\infty}}}}<3$ ? I'm not quite sure, how to approach this? Expressing the expression as an infinite product: $$\prod_{i=1}^{n} i^{\frac1{2^{i-1}}},\text{ as }n\to\infty$$ and then using some sort underlying inequalities might help! Please suggest. Thanks in advance.

Problem: prove $\sqrt{2\sqrt{3\sqrt{\cdots\sqrt{n}}}}<3$ by induction. I tried some, but stopped in $\sqrt[2^n]{n+1}$. Also tried with $2\sqrt{3\cdots}<3^2$ and so on.


I would like to be able to make every other page in a double-sided document be a float page or empty (apart from header w/page number). Ideally this would be the verso page and all floats (unless there are too many, of course) of the facing recto page would be there.  If this works, what is the best way to make the margin of these pages smaller?  (This is for course notes: the empty pages can be used by students for their own notes.)

My problem is that I would like to have either blank or figures on the left pages, and text on the right ones, with the numbering of the right pages to be 1,2,3,4,5 and not 1,3,5,7.   It means, in a book-derived class, to have right pages, with the odd layout, but with also an even number half the time.   It also means that I would like to have, by default, a blank page everywhere on a left page, except if a picture has been defined somehow before on the previous page.     Update:  I've tried it. There is a little \makeatother missing, but I spotted it right away. It seems to work fine alternating pages and inserting blank or figure pages. However, I have two problems:   The class (book-derived) sometimes introduces blank pages of its own. I can tweak it, but would prefer to be able to turn on/ turn off the action of the blankpage routine along the course of the document.  The layout of the text pages depends on the odd/even number of the page. Since my text pages have odd and even numbers (which is the intended result), the layout is now alternatively odd or even, which is not what I would like, since there they will all be on the right hand side of the doc when open...   Do you have any clue as to how to manage this? I think the second problem is way more difficult...  Thank you already for this answer both simple and effective for achieving the result.   EDIT 2 (19/12/2011) : The answer from Bruno Le Floch seems to me more complete and I recommend it.


We have a 6th druid in the party.  He can wildshape twice per short rest, and for each use, maintain his shape for half his level, thus for 3 hours.    Can a druid effectively stay wildshaped indefinitely by taking short rests in wildshape form, thus allowing them to regain their wildshape uses?  For example, the fore-mentioned druid wants to wildshape into a cat and sit on the back of the horse while the party is traveling.  Would the druid be able to simply continue his wildshape form every 3 hours while resting on in a cart or on a horse?  Thanks.

Do the druid's uses of the Wild Shape feature recharge while still in Wild Shape?  Say a 10th-level Circle of the Moon Druid spends two uses of Wild Shape to transform into an Air Elemental, whose form she can stay in for the next 5 hours. After 2 hours, she takes a short rest, but does not drop the Wild Shape. She has another couple of hours to keep the Air Elemental form.  My main concern: Does she get her two uses of Wild Shape back with that short rest? Or, does she have to drop the Air Elemental form first before taking the short rest to recharge Wild Shape?


I have object in typescript:  export class A {  public var1: boolean = false;  public var2: boolean = false;  public b: B = new B();   }  export class B {    public v: boolean = false; }   And declare and exist object:  ... public a: A = new A(); ...   When I use jQuery:   const myCopy: A = $.extend(true, {}, this.a); this.a.b.v = true;   When I change variable object this.a  I see change in copy. How Can I deep copy in this situation.

What is the most efficient way to clone a JavaScript object? I've seen obj = eval(uneval(o)); being used, but . I've done things like obj = JSON.parse(JSON.stringify(o)); but question the efficiency.  I've also seen recursive copying functions with various flaws.  I'm surprised no canonical solution exists.


I am looking for climate rasters (temperature, precipitation) for European continent.   I know WorldClim (1km/pixel) but it is too coarse.   Do you know, where can I download finer data, for example 500m/pixel or more.

I am looking for the best available climate data in Europe. Worldclim seems to be the best source of information for global data, but I am wondering if there is a higher resolution (better than 1km cell size and/or 1 month temporal resolution) product in Europe. (I've seen on this site that PRISM is great for the USA, but I couldn't find anything similar for Europe).    EDIT : my purpose is to use the dataset for ecological modeling.  EDIT: if you use another dataset, I am very interested in knowing why it is used instead of worldclim.


Every which way I try to correct unmet dependencies it gives me some long error. Trying to install packages I get   evas-loaders : Depends: libefl (>= 201312241217) but it is not going to be installed libedbus1 : Depends: libefl (>= 201312241217) but it is not going to be installed E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).   If I try to open software-proporties-gtk its a grey icon that cannot be opened. Trying Synaptic package manager to fix broken packages evas-loaders/libedbus1 it says   Failed to fetch http://packages.enlightenment.org/ubuntu/dists/jaunty/Release.gpg Something wicked happened resolving 'packages.enlightenment.**org:http' (-5 - No address associated with hostname)   and another thirty something like that.

There are now errors when updating and I cannot install most software due to a corrupted  /etc/apt/sources.list   file. Is there a copy I can download to replace it?  The file would be for Ubuntu 12.04 (Final Beta) in the United States.


What is the red confetti for on my nearby PokeStop?  It appears to have confetti flying around it.

I was walking about and I loaded up Pokemon Go to check if there were any Pokestops in my area. There were two, but one looked different than normal. When I clicked on the Pokestop, there were floating hearts around it.   Are there anything special significance to these hearts?


I have this property:  int? firstClientID;   Why does this  firstClientID = dataRow.IsFirstClientIDNull()                      ? null                      : (int.TryParse(dataRow.FirstClientID, out tempInt)                          ? tempInt                          : 0);   not compile because      type of conditional statement cannot be determined since there is no   implicit conversion between null and int   and does  if (dataRow.IsFirstClientIDNull())     firstClientID = null; else if (int.TryParse(dataRow.FirstClientID, out tempInt))     firstClientID = tempInt; else     firstClientID = 0;   work? They seem to do the same thing.

EmployeeNumber = string.IsNullOrEmpty(employeeNumberTextBox.Text)     ? null     : Convert.ToInt32(employeeNumberTextBox.Text),  I often find myself wanting to do things like this (EmployeeNumber is a Nullable<int> as it's a property on a LINQ-to-SQL dbml object where the column allows NULL values).  Unfortunately, the compiler feels that  There is no implicit conversion between 'null' and 'int'  even though both types would be valid in an assignment operation to a nullable int on their own. Using the null coalescing operator is not an option as far as I can see because of the inline conversion that needs to happen on the .Text string if it's not null. As far as I know the only way to do this is to use an if statement and/or assign it in two steps.  In this particular case I find that very frustrating because I wanted to use the object initializer syntax and this assignment would be in the initialization block... Does anyone know a more elegant solution?


Using vnstat, I observed a lot of uploaded data from my computer and I don't know which process sent data out of my computer. Is there a tool to get stats on how much data a process consumed during a period of time? Thank you.  Update: Looks like the process isn't sending data anymore, I installed nethogs to monitor live data transfer and everything seem totally normal.

I think I'm being the victim of a bug here. Sometimes while I'm working (I still don't know why), my network traffic goes up to 200 KB/s and stays that way, even tough I'm not doing anything internet-related.   This sometimes happens to me with the CPU usage. When it does, I just run a top command to find out which process is responsible and then kill it. Problem is: I have no way of knowing which process is responsible for my high network usage. Both the resource monitor and the top command only tell me my total network usage, neither of them tells me process specific network info.  I've found questions here about monitoring total bandwidth usage, but, as I mentioned, that's not what I need. Is there another command I can use to find out which process is getting out of hand?  The command iftop gives results that disagree entirely with the information reported by System Monitor. While the latter claims there's high network traffic, the former claims there's barely 1 KB/s.  I've already tried killing all the obvious ones (Firefox, update-manager, Pidgin, etc) with no luck. So far, restarting the machine is the only way I found of getting rid of the issue.


I am not sure how to start this hw problem.  Here it is:  Let $x$ be a given vector in $\ell^p$ with $1\le p\lt\infty$. Show that $x \in \ell^\infty$ and  $$\lim_{p \to \infty} \|x\|_p = \|x\|_\infty.$$  This seems like it would be obvious, but trying to prove it is different. I am not sure how to even start this one. Thanks.  EDIT: Would the triangle inequality be useful here?

If we are in a sequence space, then the $ l^{p} $-norm of the sequence $ \mathbf{x} = (x_{i})_{i \in \mathbb{N}} $ is $ \displaystyle \left( \sum_{i=1}^{\infty} |x_{i}|^{p} \right)^{1/p} $.  The $ l^{\infty} $-norm of $ \mathbf{x} $ is $ \displaystyle \sup_{i \in \mathbb{N}} |x_{i}| $.  Prove that the limit of the $ l^{p} $-norms is the $ l^{\infty} $-norm.  I saw an answer for $ L^{p} $-spaces, but I need one for $ l^{p} $-spaces. Besides, I didn’t really understand the $ L^{p} $-answer either.  Thanks for your help!


Hope you guys are doing well. I want to ask one question to you guys. Please help me out.  I am using Macbook pro. I have a friend who is using Windows 7 but wants to switch to Ubuntu Operating system. He actually got bored of using windows. Now, I do not have any Ubuntu CD but I do have a USB device.  Can you please tell me guys how I can make my USB bootable and run the ubuntu on a windows computer? I want a complete guide please...  Thanks for your help. I really appreciate it.

I have a working MacBook Pro and a crashed Windows 7 PC. I was running Ubuntu on my PC, but after a recurrent issue now I can't boot either OS. I would like to install only Ubuntu on my PC and will make Windows 7 history for good, but I am a bit puzzled by the instructions for creating a bootable USB options on the website.  If I create a bootable USB on my Mac following the instructions for OS X, would it boot in a PC?


There's a story I read when I was a kid, probably in the 1980-1985 time range, though of course it could have been published any time before that.  Aside from the fact that the protagonist was an Asian-American woman--possibly specifically Vietnamese, though I'm not sure on that point--I only really recall the creepy ending.  The woman had had her mind tampered with by an evil machine intelligence that she'd uncovered evidence of earlier in the story.  (The story is set in the then present day, so the machine intelligence would have been a novelty.)  One by one, several "relays" in her mind close, each compelling her to perform some action.  She returns home and disables whatever component that prevents her microwave oven from operating while the door is open.  (She was very technically adept and nerdy.)  She sits silently for several minutes until the final relay switches off, then puts her head in the microwave and turns it on, to all appearances committing suicide.  She may have been sobbing as she did so.  It was really pretty disturbing.  And as far as I remember, the story ends there, the machine intelligence presumably going on to conquer the world.  Can anyone identify this story?  It sometimes comes to mind when I'm waiting in front of a microwave for something to finish cooking, as it did just prior to my composing this question.

Does anyone know this story? It was a novelette published with another one (I don't remember what it was) in . The premise was that the narrator is an old man whose neighbor, a hacker, dies under mysterious circumstances. A younger woman who is an expert in computer security is hired by the police to investigate what happened, and she has a fling with the narrator. After a while she dies as well, and the narrator realizes that it is an evil force that comes through electric lines is responsible for the killings. The title has interesting formatting in that it ends with a square (much like a command prompt cursor: [_] )


I see other people doing this, occasionally.   They'll add something like the following to the start of their terminal, sort of a welcome screen:    ____  _____    _  _  _____  __  __    _    _    __    _  _  ____    ____  _____    ____  __      __   _  _      __       ___    __    __  __  ____  ___ (  _ \(  _  )  ( \/ )(  _  )(  )(  )  ( \/\/ )  /__\  ( \( )(_  _)  (_  _)(  _  )  (  _ \(  )    /__\ ( \/ )    /__\     / __)  /__\  (  \/  )( ___)(__ )  )(_) ))(_)(    \  /  )(_)(  )(__)(    )    (  /(__)\  )  (   )(      )(   )(_)(    )___/ )(__  /(__)\ \  /    /(__)\   ( (_-. /(__)\  )    (  )__)  (_/ (____/(_____)   (__) (_____)(______)  (__/\__)(__)(__)(_)\_) (__)    (__) (_____)  (__)  (____)(__)(__)(__)   (__)(__)   \___/(__)(__)(_/\/\_)(____) (_)   It happens when the shell starts, and I would like to have it happen for me when the shell starts, too.   I am pretty proficient with vim for text editing, so I think I could figure out a way to do it.   If vim fails, I can use something like the following, but how do I make it come up not garbled when I start my new shell?   Please note that this question is not just about ASCII art, but is also about how to successfully add it to my bash, and about possible escapes required for the bash shell to get it to work properly.

I'm looking for an ASCII art generator (text is preferred, but images will do too) in the  style, but with text instead of trains. Any suggestion?


Blackbody radiation is the radiation given off an object solely as a result of its absolute temperature. The (continuous) spectrum is given solely by the temperature.  How can this be? Why should a slab of Tungsten at 400 K emit the exact same spectrum as a pile of powdered sodium chloride at the same temperature? Why should the emitted radiation be independent of the chemical composition of the object, the electron transition energies, and the mass of the atomic nuclei?  What is the actual, physical process, that gives rise to the emission of blackbody radiation?

By conservation of energy, the solid is left in a lower energy state following emission of a photon.  Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium is a statement of the mean behaviour of the system, not a statement that the internal energy is constant on arbitrarily short timescales.  The energy has to come from somewhere during emission, and go somewhere during absorption.  Energy in a solid can be stored as kinetic and potential energy of electrons and nuclei, either individually or in collective modes such as phonons and plasmons.  In thermal equilibrium energy will be stored more or less in various forms depending on the temperature and material.  However, even if most of the thermal energy in a particular solid at temperature $T$ is stored in the form of phonons, it could be that phonons primarily interact with light indirectly via electrons, e.g. a phonon excites an electron in a phonon-electron interaction, which can interact with light via the EM field.  Given that light is an EM field, it makes sense to me that it is emitted and absorbed by charged particles.  The electron-photon interaction is probably dominant for visible and ultraviolet light, given that metals are opaque, while semiconductors and insulators are transparent to (visible and UV) light with energy lower than their bandgap. However, once you get into energies in the IR and below, or X-rays and above, other mechanisms apparently take over.  For example, on the high-energy end of the spectrum I've heard that gamma rays can interact directly with nuclear degrees of freedom, which is reasonable considering that gamma rays are emitted during a lot of nuclear reactions.  A review of  might give clues to important light-matter interactions over a broad range of wavelengths.  Whether all of the these processes are involved in blackbody emission is a somewhat different question.  What physical processes mediate energy transfer during blackbody emission, and in which energy ranges are the various processes dominant?


In Chapter one of Harry Potter and the Half-Blood Prince, Cornelius visits "The Other Minister" and is asked if the visit has anything to do with this "Serious Black" man, and Fudge states that no, it turned out that he was actually innocent.  ‘Is Serious Black with – er – He Who Must Not Be Named?’ ‘Black? Black?’ said Fudge distractedly, turning his bowler rapidly in his fingers.  ‘Sirius Black, you mean? Merlin's beard, no. Black's dead. Turns out we were – er – mistaken about Black. He was innocent after all. And he wasn't in league with He Who Must Not Be Named either. […]’ – The Half-Blood Prince Chapter 1: The Other Minister  How did he come to that realization and conclusion?

In Prisoner of Azkaban, Professor Dumbledore explains to Harry why he cannot convince the ministry that Sirius is innocent.  Yet, in the beginning of Half-Blood Prince, the Minister of Magic admits to the Muggle Prime Minister that Sirius Black was innocent:     ‘Is Serious Black with – er – He Who Must Not Be Named?’      ‘Black? Black?’ said Fudge distractedly, turning his bowler rapidly in his fingers.  ‘Sirius Black, you mean? Merlin's beard, no. Black's dead. Turns out we were – er – mistaken about Black. He was innocent after all. And he wasn't in league with He Who Must Not Be Named either. […]’      – The Half-Blood Prince Chapter 1: The Other Minister   What has changed that has made them admit his innocence?  Sirius's body disappears in the fight in Order of the Phoenix, so there's no evidence left that he has fought there.  Pettigrew is still in hiding.  There's still only Harry and Hermione's word against Snape's story that would prove Sirius's innocence.


I use Raspberry Pi 3 and program GPIOs using C and Sysfs/WiringPi. If someone provides a static library (.a file) to work with my Raspberry Pi C project, is there a way to list what functions, with what parameters needed, are available inside this static library? For instance, if I get "test.a" without any documentation/explanation of it, I want to find out that this static library has void foo(int param1); char bar(void);

How do I determine whether a function exists within a library, or list out the functions in a compiled library?


I am a first-year Math undergraduate and have been searching online for books in Analysis and have found two which seem to be good for an introduction.  Ross' Elementary Analysis:The Theory Of Calculus. Abbott's Understanding Analysis.  I did a quick skim at the content and it seems that Abbott's Understanding Analysis has more content（breadth) but Ross' seems to go deeper? I am not sure which book to choose (self-study) and any other recommendations/suggestions are welcome and highly appreciated!

Does anybody know of a good book in real analysis for self study for a beginner? What about Analysis 1 by Terence Tao?


When I have an output stream:  a b c d e   How can I double the newlines:   a  b  c  d  e

Mail logs are incredibly difficult to read. How could I output a blank line between each line printed on the command line? For example, say I'm grep-ing the log. That way, multiple wrapped lines aren't being confused.


In UTF-8 it should be possible to use ä and ö. But actually in my code listing I use the package listings I receive by this example \lstset{language=HTML}  % Set your language (you can change the language for each code-block optionally) \begin{lstlisting}[caption=Socket Connection, frame=single]  % Start your code-block  // einbinden der Library mittels CommonJs var net = require('net');  // Socket Client erstellen var client = new net.Socket();  // mit dem Server verbinden IP Port angeben client.connect(<PORT>, '<IP>', function() {     console.log('Connected');     client.write('Hello, server! Love, Client.'); });  // verschiedene Events Listener // dieser wird ausgelöst s der Server Daten zum Client sendet  client.on('data', function(data) {     console.log('Received: ' + data);     client.destroy(); // kill client after server's response });  client.on('close', function() {     console.log('Connection closed'); });  \end{lstlisting}  the error message ! Package inputenc Error: Invalid UTF-8 byte sequence.  And it is denoting to the line with the 'ö' // dieser wird ausgelöst s der Server Daten zum Client sendet Note: Sure I know it isn't HTML but when I say JavaScript it doesn't work In the preamble I say \usepackage[utf8]{inputenc} % Unicode Text

I'm having some problems with listings and UTF-8 in my document. Maybe someone can help me? Some characters work, like é and ó, but á and others appear at the beginning of words...  \documentclass[12pt,a4paper]{scrbook} \KOMAoptions{twoside=false,open=any,chapterprefix=on,parskip=full,fontsize=14pt}  \usepackage[portuguese]{babel} \usepackage[utf8]{inputenc} \usepackage[T1]{fontenc} \usepackage{listingsutf8}  \usepackage{inconsolata} \lstset{     language=bash, %% Troque para PHP, C, Java, etc... bash é o padrão     basicstyle=\ttfamily\small,     numberstyle=\footnotesize,     numbers=left,     backgroundcolor=\color{gray!10},     frame=single,     tabsize=2,     rulecolor=\color{black!30},     title=\lstname,     escapeinside={\%*}{*)},     breaklines=true,     breakatwhitespace=true,     framextopmargin=2pt,     framexbottommargin=2pt,     extendedchars=false,     inputencoding=utf8 }  \begin{document} \begin{lstlisting} <?php  echo 'Olá mundo!'; print 'Olá mundo!'; \end{lstlisting}  \end{document} \end{lstlisting}


How can I show that the sum of n independet poisson random variables is a poisson random variable? I need to conclude that the sum of i.r.v with distribution $Poisson(\lambda_i)$, i=1,...,n, is $Poisson(\sum_1^n \lambda_i)$.

Given the identically distributed and independant random variables $X_1,X_2,\ldots\sim\operatorname{Po}(\lambda)$ and $S_n=X_1+\ldots+X_n$ show with induction that   $$\Pr[S_n=k]=\frac{(n\lambda)^k}{k!}e^{-n\lambda}.$$   So far for $n=1$ via the definition of the density function for Poisson:$$\Pr[S_1=k]=\Pr[X_1=k]=\frac{e^{-\lambda}\lambda^k}{k!}$$ With $n=2$ and independency: $$\Pr[X_1+X_2=k]=\sum\limits_{n=0}^k\Pr[X_1=n]\Pr[X_2=k-n]=\sum\limits_{n=0}^k\frac{\lambda^n}{n!}e^{-\lambda}\frac{\lambda^{k-n}}{(k-n)!}e^{-\lambda}$$$$=\frac{1}{k!}e^{-2\lambda}\sum\limits_{n=0}^k\binom{k}{n}\lambda^n\lambda^{k-n}=\frac{(2\lambda)^k}{k!}e^{-2\lambda}$$ I assume now that with $S_n\sim\operatorname{Po}(\lambda)$ every $X_i\sim\operatorname{Po}(\lambda/n)$ and every Poisson variable can obviously split up, but how can I prove this?


I updated from ubuntu 13.10 to 14.04.   I have a quad core, and one core is pegged at 100% usage because of kworker.  I know that kworker generally is doing things on behalf of the kernel, but I don't know how to determine what the issue is.   Any help would be greatly appreciated.

I recently upgraded to the Kubuntu Natty Beta 1 and I've been having a lot of issues with the process kworker. At moments it uses almost half my CPU. Also, strangely enough it seems to affect my USB ports; whenever I plug in an USB drive, the process kworker goes into hyperdrive, leaving me unable to work.  I have thought about filing a bug but since I haven't even found any reasonable explanation on what kworker is I figured I should find out first.


"Give a man a hammer, and everything he sees will be a nail," is an astute observation of human behavior. What is the name for someone with slight power, for example, the power to vote to close a question on this site, who exercises that power obsessively and gleefully?

Is there any idiom for a person who somehow obtained a (usually small) power to control people and is using it in every possible way to make problems for people around him?


I need to convert date string "Dec 17 00:00:06" to string "2014-12-17 00:00:06" in python. I looked at the datetime.strptime but still can't find a way for this. eg:     Dec 17 00:00:06 to 2014-12-17 00:00:06

I've got a huge list of date-times like this as strings:  Jun 1 2005  1:33PM Aug 28 1999 12:00AM   I'm going to be shoving these back into proper datetime fields in a database so I need to magic them into real datetime objects.   This is going through Django's ORM so I can't use SQL to do the conversion on insert.


I have a sample dir as follows:  /path/to/dir/ - f1.txt - f2.txt - f3.txt   I want to clear or remove all the files under /path/to/dir without actually deleting the directory /path/to/dir itself.  How to do it?  Currently, I am just using the rm -rf /path/to/dir command to remove the directory and the creating the directory again using mkdir /path/to/dir. But this command deletes the directory also.

Is there a command to remove all files and subdirectories in a directory without deleting the directory?  For example if I have directory dontDeleteMe with subdirectories 1, 2, 3 and each subdirectory has a few pictures in it, how can I remove the subdirectories 1, 2, and 3 and all the files in the them, without removing the parent directory dontDeleteMe?


I tried to install NVIDIA driver with software and update application, adding a PPA and install the package nvidia-driver-xxx , using the installer from NVIDIA, but all of these solutions don't work. I tried 390, 435 and 450 versions and I have the same problem. When I use the software and update application, it give me this error:  When I try to use sudo apt install nvidia-driver-xxx (I tried with every version the command ubuntu-drivers devices gave me,) it says this :  When I try the nvidia installer (when I run it in console mode), it says: Unable to load the 'nvidia-drm' kernel module  I try to install a prior version of the nvidia driver 440 because I used a laptop and since driver 440, my second screen is not detected. I have a Lenovo Legion Y530 with a GTX 1060 6GB using Ubuntu 20.04 with Windows in dual boot. When i try sudo ubuntu-drivers autoinstall, it gave me the same error as the second screenshot.

I need to use NVIDIA drivers, and I used the nvidia-smi command to check which NVIDIA I have, but this was the output: Command 'nvidia-smi' not found, but can be installed with:  sudo apt install nvidia-utils-390  # version 390.138-0ubuntu0.19.10.1, or sudo apt install nvidia-utils-440  # version 440.100-0ubuntu0.19.10.1 sudo apt install nvidia-340        # version 340.107-0ubuntu7 sudo apt install nvidia-utils-430  # version 430.50-0ubuntu2 sudo apt install nvidia-utils-435  # version 435.21-0ubuntu2  Any clue which one to install? I am running on Ubuntu Live on a , but let me know if you need any more information about my system


I want to know the limit of the sequence that:  $$a_{1}=a>0,$$ $$a_{n+1}=\ln(1+a_{n})$$  then  $$\lim_{n\to\infty}na_{n}$$  I knew that $$\lim_{n\to\infty}a_{n}=0$$, but I can't get the value of  $$\lim_{n\to\infty}na_{n}$$  This is my first question, and Sorry for my poor English.

Suppose that $a_{n+1}=\log(1+a_n),~a_1>0$. Then find $\lim_{n \rightarrow \infty} n \cdot a_n$.   I can find $\lim_{n \rightarrow \infty}a_n=0$. But I have no idea how to find $\lim_{n \rightarrow \infty} n\cdot a_n$. (In this problem, $\log$ denotes the natural logarithm.) Could you give me key idea about solving this problem?


I have a Bluetooth 3.0 keyboard and the space key,page down and end doesn't work. I think I pressed alt options .All the other keys are working beside these 3 keys.Can someone please help me

This is an attempt to write a canonical QA for this issue, as per the Meta post:   I expect it to be periodically edited with the goal of becoming a comprehensive information resource.  I have a MacBook Pro that has a key(Shift, Return,   Command, P, etc.) that doesn’t respond when pressed or is stuck in the down position.    It's possible that my favorite beverage was spilled (or some other liquid damage).  It's also possible that I have no idea what happened.  It was working yesterday and suddenly today it's no longer working.  Is there any way to bypass or remap the key?  Can I  have the system ignore it completely?  (This question can also apply to external USB keyboards or the Bluetooth keyboards)


City is involved in a very long war along a front which is subject to some kind of warping, such that you can never actually get there—just fire through it. At the end, protagonists suggests that the front is a mirror, and the city is battling itself.

Trying to remember a short story (most likely from the sixties).  It starts with a soldier at the front line fighting an unknown enemy on the other side of the front line.  He then gets withdrawn and you realise that time is passing slower the further he moves from the front. He then spends years in peace away from the front, before being sent back to the front where only a short time (hours or days perhaps) have passed.      I seem to remember their was an inference that they were actually fighting against themselves, with their attacks coming back at themselves, which was perhaps the entire cause of the war, and an interesting critique on war.  I can't remember if this all this was stated explicitly, or just left for the reader to infer.


I'm trying to insert a Cyrillic value in the MySQL table, but there is a problem with encoding.  Php:  <?php  $servername = "localhost"; $username = "a"; $password = "b"; $dbname = "c";  $conn = new mysqli($servername, $username, $password, $dbname);  mysql_query("SET NAMES 'utf8';");  mysql_query("SET CHARACTER SET 'utf8';");  mysql_query("SET SESSION collation_connection = 'utf8_general_ci';");   if ($conn->connect_error) {     die("Connection failed: " . $conn->connect_error); }   $sql = "UPDATE  `c`.`mainp` SET  `search` =  'test тест' WHERE  `mainp`.`id` =1;";  if ($conn->query($sql) === TRUE) {    } $conn->close();  ?>   MySQL:                                       | id |    search   |             | 1  |   test Ð°Ð² |   Note: PHP file is utf-8, database collation utf8_general_ci

I'm setting up a new server and want to support UTF-8 fully in my web application. I have tried this in the past on existing servers and always seem to end up having to fall back to ISO-8859-1.  Where exactly do I need to set the encoding/charsets? I'm aware that I need to configure Apache, MySQL, and PHP to do this — is there some standard checklist I can follow, or perhaps troubleshoot where the mismatches occur?  This is for a new Linux server, running MySQL 5, PHP, 5 and Apache 2.


I just bought a refurbished Thinkpad X220.   When I install Ubuntu I always select the option to erase the hard disk as I dont want any Windows on it. After installing I restart the laptop but Windows come back. I already tried to install it 5 times.  Any idea on how to solve this problem? Thank you very much!

I want to keep Ubuntu but remove Windows.


I have three random variables $X,Y,Z$ that all have a mean of $\mu=10$ and a standard deviation of $\sigma=2$. Now, I would like to say that they are negatively correlated with $\rho_{X,Y}=-1, \rho_{Y,Z}=-1, \rho_{X,Z}=-1$.  My question would be, what is the variance of $X+Y+Z$? Normally, we would say: $Var(X+Y+Z)=Var(X)+Var(X)+Var(Z)+2Cov(X,Y)+2Cov(Y,Z)+2Cov(X,Z)$  However, in our simple example, this leads to $3\cdot2^2+3\cdot2\cdot(-1)\sqrt{2^2\cdot2^2}=-12$ which cannot make sense.  Where is my logical error? I presume because of some transitivity, $\rho_{X,Z}$ cannot be $-1$ if the other two $\rho_i$ are -1 but which principle is behind this?

I was asked this question regarding correlation recently, and although it seems intuitive, I still haven't worked out the answer satisfactorily. I hope you can help me out with this seemingly simple question.  Suppose I have three random variables $A$, $B$, $C$. Is it possible to have these three relationships satisfied? $$ \mathrm{corr}[A,B] = 0.9 $$ $$ \mathrm{corr}[B,C] = 0.8 $$ $$ \mathrm{corr}[A,C] = 0.1 $$ My intuition is that it is not possible, although I can't see right now how I can prove this conclusively.


We are given that, $$a+b+c=0$$ Then, what is the value of: $$P= \dfrac{a^2}{2a^2+bc}+\dfrac{b^2}{2b^2+ca}+\dfrac{c^2}{2c^2+ab}$$

I'm stuck at this algebra problem, it seems to me that's what's provided doesn't even at all.  Provided:  $$a+b+c=0$$  Find the value of:  $$\frac{a^2}{2a^2+bc}+\frac{b^2}{2b^2+ac}+\frac{c^2}{2c^2+ab}$$  Like I'm not sure where to start, and the provided clue doesn't even make sense.  There's no way I can think of to factor this big polynomial into a form like $a\times p+b\times q+c\times r=s$ where $p,q,r,s\in\mathbb{Z}$.  Thanks!


I'm new to this site :)  Anyway, I decided to learn java a couple of days ago and I have a small problem which I don't know how to fix. This is my code: When name = Jim I want it to output "Hello Jim", when it doesnt  = Jim then output "Youre not Jim, youre " + name  import java.util.*; public class app {     public static void main(String[] args) {         String name;         Scanner inputName = new Scanner(System.in);          System.out.println("Enter a name: ");         name = inputName.nextLine();          if (name == "Jim") {             System.out.println("Hello " + name);         } else {             System.out.println("Youre not Jim! You are " + name);         }      } }

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


I was a bit confused by the wording for Martial Arcanist.     Martial Arcanist (Ex): At 5th level, you master the art of combining your militant and mystical training. From this point on, your caster level in a chosen arcane spellcast- ing class is equal to your base attack bonus (unless it would otherwise be higher). For example, a 7th-level fighter/1st-level wizard/5th-level abjurant champion has a base attack bonus of +12 (and thus a caster level of 12th). You can apply this benefit to only one arcane class to which you have added spellcasting levels by your advancement as an abjurant champion.   Does this mean, if I were a sorcerer 1 fighter 5 abj champ 5 that I'd have the spells of an 11th level sorcerer? Or does it mean I just get bonuses relating to caster level (like having more magic missiles)

A  adds +1 caster level, what does this affect?   Damage from spells? (Like fireball) Duration and area of effect? "Amount" of effect (Like number of missiles from magic missile) Spells known by a wizard (ie +1 caster level mean a level 2 wizard gets the spells as if they were level 3?) Anything else?


Assuming that $\overline{K}$ is an algebraic closure of the field $K$, how would one go about proving that $\overline{K}$ must be a splitting field? I am trying to do this by finding a set $\mathcal{P}$ of polynomials such that $\overline{K}$ is a splitting field of $\mathcal{P}$ over $K$.

Consider following two statements from same book of Cohn: Basic Algebra.  Proposition : If $k$ is any field and $\mathcal{F}$ is a set of polynomials over $k$, then any two minimal splitting fields for $\mathcal{F}$ over $k$ are isomorphic. Theorem: If $k$ is any field then $k$ has algebraic closure and any two algebraic closures are isomorphic.  My question is, if we take $\mathcal{F}$ to be set of all the monic irreducible polynomials over $k$, then by 7.3.2, doesn't it imply that any two algebraic closures are isomorphic? Further, just after Theorem 7.3.2, the author gives also the existence of minimal splitting field for $\mathcal{F}$ (it is not visible in link). Then doesn't it imply that algebraic closure of any field exists and is unique up to isomorphism? In other words, I was thinking that Theorem 7.3.2 and existence of minimal splitting field actually gives proof of theorem 11.8.3 above. Why it was differently stated and proved I didn't understand. Are these two theorems really different?


Using the following code, I try to create the markup for a HTML list and then attach an event handler to every list element.    The list is created as expected and everything seems to work fine, the only problem is that it always alerts I am 4, no matter what li I click. So I guess that every event handler overwrites the preceding, by why?  Also I see one big downside of the way I do it, because I have to add every li to the DOM before I can add the event listener, which causes a lot of reflows. I would prefer to add all li elements to the ul and then add the complete list to the DOM. Is it possible to do it this way and add the event handler anyway?  Maybe there is a more better way in general?  MyTest.prototype.createDots = function() {     var self = this;     var dots = document.createElement("ul");      this.element.parentNode.appendChild(dots);      for (var i = 0; i <= 3; i++) {         var dot = document.createElement("li");          dot.innerHTML = "" + i;         dot.setAttribute("id", "dot-" + i);         dots.appendChild(dot);          document.getElementById("dot-" + i).addEventListener("click", function() {             alert("I am " + i)         }, false)          console.log(i);     } }

How would you explain JavaScript closures to someone with a knowledge of the concepts they consist of (for example functions, variables and the like), but does not understand closures themselves?  I have seen  given on Wikipedia, but unfortunately it did not help.


Kourtney Kardashian said "there's people that are dying Kim" in one of the KUWTK episodes- why did she use there is instead of there are?

For example:     There's two options here   or     There are two options here   I hear a lot of people say the first line (or something similar), but isn't that incorrect? Isn't it plural and therefore you should use "there are"?


After upgrading to Firefox 57 Quantum many website have rendering issues, such as empty frames, missing text or fonts, etc. I use Kubuntu 16.04 64 bit.  So far, I've tried:   Restarting Firefox in safe mode Disabling "hardware acceleration"   Wiping out my profile Purging Firefox and reinstalling Running Firefox from a clean user account   But nothing helped so far.  Any tips on how to solve this are much appreciated

I've just upgraded to FF 57 and websites that use their own fonts have stopped displaying text.   I know this is a problem others have had, e.g. , but the solutions there have not worked. Safe mode does not help either, the problem only goes away if I uncheck the custom fonts option in Preferences.  I have custom fonts installed as well (from TexLive and and a couple more) so I'm thinking that might be the cause.   Any ideas on how to troubleshoot this?  Example from Github:


Can't we just simplify f(x) and treat it same as that of g(x)?

If I have, for example, the function $$f(x)=\frac{x^2+x-6}{x-2}$$ there will be a removable discontinuity at $x=2$, yes?  Why does this discontinuity exist at all if the function can be simplified to $f(x)=x+3$?  I suppose the answer is that you can't simplify it because you can't divide by something that could potentially equal $0$.  But what if you start with $f(x)=x+3$? What's stopping you from multiplying it by $1$ in the form $\frac{x-2}{x-2}$? Can multiplying by $1$ really introduce a discontinuity to the function?


I would like to have a signature line for my thesis. I tried to use \hrulefill, but it creates a long line. Is there any way to have a short line?

I'm trying to create a signature and date line in a document.  I need the date line to always be in the same spot on the page no matter what name is under the signature line, such as:  ----------------------   ---------------------- Representative           Date  ----------------------   ---------------------- Program Manager          Date   Here is the code I currently have:  \makebox[2.5in]{\hrulefill} \hspace {1.0in}\makebox[2.5in]{\hrulefill} \\ User Representative \makebox[2.5in][r]{Date} \\  \vspace{.2in} \makebox[2.5in]{\hrulefill} \hspace {1.0in}\makebox[2.5in]{\hrulefill} \\ Program Manager \makebox[2.5in][r]{Date} \   I want to be able to change the names, such as change Program Manager to Joe Foo and have the word 'Date' stay in the exact place.  Any help would be greatly appreciated.  I'm still a newbie at TeX so please forgive my ignorance.


How can I prove that the language $L = \{0^n1^m0^{nm} ∣m,n \ge 0 \}$ is not context-free using the pumping lemma

I have troubles constructing pushdown automata for the following language: $L=\{a^i b^j c^k \mid k=i*j; \quad i,j=0,1,2...\}$ .I am not interested in the automata itself, just the idea of handling the product.


I have the fps issues, when I did play in the last patch it did work fine, but this patch seems to ruin everything! I did play on high graphics and had shadows and anything at high, now I play on low graphics did turn shadows off but still got the problem, I normally have 60 fps when i play but 4-6 times in a game it drops down to 5-6 fps then it last in 2-3 mins and it goes up again to 60 fps.  How to solve this problem?

I've been playing League of Legends for some time now on a desktop, it was fine, my FPS was consistent at around 59-60 FPS. However, since my desktop is currently under repair, I am using a laptop to play League of Legends and sometimes my frame rate drops from 60 FPS to 1-10 FPS randomly. I know that the internet isn't a problem because my ping is consistent at around 10-20. What could be the problem here? I set all my settings to Very Low and turned off shadows and everything, still the same happens. Specs:  Processor: Intel(R) Pentium (R) CPU 2117U @ 1.80GHz RAM: 8GB System OS: x64 bit Windows 8.1 GPU: Nvidia Geforce GTX 780M


I need to run multiple instances of Google Chrome. Each instance must run on different monitor in a multi monitor system (Windows OS) but in full screen without any buttons or menus.  I tried several combination of switches but without luck  --start-fullscreen  --window-position=10,10 -window-size=800,600  --kiosk   --new-window  The Kiosk mode works but If I try to run the next instance it will go again on the  primary screen.  Is there a way to run the Kiosk mode (preffered) or FullScreen mode  of different Windowed Chrome instances in a multimonitor system ?  Probably if nothing works I would need to start each instance programmatically and  send F11 keys to each window. This will work but it is some kind of hacking solution.  I am interested to know if there is some gracefull way to tell to Chrome "run this instance in a window in full screen or kiosk mode."

My goal is to show different web content full screen on multiple monitors automatically after booting from a single computer. The browser I would like to use is Chrome. If Chrome does not support this and Firefox does that would be fine.  The OS I would prefer is Windows, if it turns out that Linux is possible that would be fine.  On Windows it is possible to set the position of the Chrome browser window (--window-position=) and make Chrome start in full screen mode (--kiosk). Using these options combined you can start Chrome full screen on any of the desktops/screens that you have connected to your computer. I have managed to get this working.  However, if I then try to do the same thing a second time to have Chrome full screen on a second screen the second Chrome window will open over the first window, no matter the coordinates I use for the --window-position parameter.  I have tried using Chrome profiles and copying the Chrome directory and starting the second chrome.exe. All these things result in the same behaviour.


Let me explain what I mean by an imaginary case. Let's imagine a 10 V battery in series with two resistors equal in resistance value. The voltage in between those resistors is 5V according to the voltage division rule. I have a component (does not matter what it is) which needs to be powered up by 5 volts. When I try to use that 5V voltage value in between those resistors to power it up, the voltage division rule breaks and I get less than 5 volts across that component. I cannot figure out how to provide it 5 volts to power it up by using voltage division or basic circuit analysis techniques. What is the way to achieve any voltage value across any component we want?

When would you use a voltage regulator vs a resistor voltage divider?  Are there any uses for which a resistor divider is particularly bad?


I want an HTML element (a footer for example) to be absolutely positioned to the bottom of a page but at the same time I don't want it to overlap the content when the viewport is small (vertically resize the browser to see the issue). I want the footer to stay after the content when the viewport is small to avoid overlapping. Is there any CSS-only solution for that?   Here's a fiddle showing the issue:
Content
 footer with absolute position  footer {     width: 400px;     background-color: #ccc;     position: absolute;     bottom: 0; }   Google's homepage has this implemented but I'm unable to understand if it is a CSS-only method or it requires JavaScript. Here's a screenshot of Google's footer with position: absolute;   And here's a screenshot of Google's footer staying after the content and not overlapping:   Any help appreciated. Thanks in advance!

I have a simple 2-column layout with a footer that clears both the right and left div in my markup.  My problem is that I can't get the footer to stay at the bottom of the page in all browsers.  It works if the content pushes the footer down, but that's not always the case.


If I create an element with class in jQuery that element wont include the attached functions.  For example, in below code first of all I am creating 2 different element in html and in (document.ready) I assign the change event this class.  These two elements working properly. However, When click the button, I create a new element which has same class but related event wont work for this element.  Why this happen? and how can I attach all events the new element easily?  Thanks in advance.  My Code:
         <input class="test" value="2" type="text">         <input class="test" value="3" type="text">         <input class="button" value="Click" type="button">

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


When Cooper (the daughter) worked out the equations which allegedly assured the survival of the human race on Earth, she threw her notes from the balcony in the space center: "EUREKA!" Now, her father sent her information to solve the puzzle she was working on. Presumably a quantum theory of gravity (quantum gravity). He got this information ("quantum data") from Tars, who found it inside the tesseract. So somewhere in the future human beings were taught how to construct quantum gravity. But where did they got the means to construct one from? Probably from the physics books in which Cooper's theory is explained. She is a famous scientist (even the temporary cylindrical space station is named after her), so for sure her theory will be published and taught to others. So, in effect, she teaches the theory to future generations. These generations put the theory inside the tesseract and father Cooper sends it back to his daughter. The paradox is clear. Where the hell did the theory come from? Out of nothing? Is there a name for such a paradox? (If it's a paradox at all; the twin paradox refers to a situation that can happen in reality, while at first sight, the situation is not about to occur. The same situation occurs in J.J. Abraham's Star Trek. Spock sends information from the future about a present puzzle in teleportation. The puzzle is solved in the present and will be part of future knowledge.

In  (2014) the human race seemed to be facing pretty poor odds until they discovered a convenient wormhole placed by an unknown entity expressed as "they". Later in the movie, we discover that       "they" are actually the human race in the future, reaching back in  time to save itself.   The end of the movie gets a little wild on the physics end, and I'm happy to take that ending as is - no need for it to make sense - but one very basic detail does bother me:  How could the human race have gone back in time to save itself from circumstances that would have caused us to go extinct without our own help (the convenient wormhole)?


As far as my knowledge goes, the third conditional is used in cases where we're talking about a past condition for example  If she had come home early , she would have got to meet him.  Well the person didn't get home early so she didn't get to see whoever she wanted to see. But what about the cases where it's not certain whether the condition with 'if' clause got fulfilled or not? In the above sentence if it wasn't known whether she came home early or not. What should be used instead of If she had come early? It clearly implies that she didn't come home early .

I have a question regarding conditional sentences, as far I know the “third conditional” is used when we’re talking about a condition from the past that never actually happened after all.  For example:  If she had come home early, she would have gotten to meet him.  In this example, the person did ɴᴏᴛ get home early so she did ɴᴏᴛ get to see whomever she had been wanting to see. But what about the cases where it’s uncertain whether that if clause’s condition had ever ended up getting fulfilled or not? If in the example sentence it had ɴᴏᴛ been known whether she had come home early — maybe she did, maybe she didn’t, but we don’t know — what then would have been used in place of If she had come home early, given how that particular construction would clearly imply that she had ɴᴏᴛ come home early and we want to allow for doubt about that?


In the films it's obvious that whatever the blasters and turbolasers are firing, they aren't lasers. The bolts travel way slower than the speed of light. So slow in fact that people with preternaturally high reflexes are able to block and dodge the shots.  This question  mentions a number of these quandaries but doesn't actually answer them, instead wondering if actual lasers exist in the EU.   So what are they firing? And is there any in-universe reason as to why people don't use projectile firearms as a way of taking down these annoying Jedi who seem able to deflect all their blaster bolts?  I am aware that the out of universe reason is "because it looks cool". Which is fine. Just wondering if anyone's ever tried to explain this discrepancy in canon.

Is there a canon explanation (based on how Star Wars blasters work) for why the blaster bolts are so slow? Intuitively, one would expect them to be like lasers, traveling at the speed of light.


I have a simple regular expression inside a match function like this: text.match(/.{1,20}/g);  Is it possible to replace the 20 with a dynamic variable? Thanks a lot!

I would like to create a String.replaceAll() method in JavaScript and I'm thinking that using a regex would be most terse way to do it.  However, I can't figure out how to pass a variable in to a regex.  I can do this already which will replace all the instances of "B" with "A".  "ABABAB".replace(/B/g, "A");   But I want to do something like this:  String.prototype.replaceAll = function(replaceThis, withThis) {     this.replace(/replaceThis/g, withThis); };   But obviously this will only replace the text "replaceThis"...so how do I pass this variable in to my regex string?


I've had Windows 7 and Ubuntu 16 installed as a dual for some time now running well until I made a stupid move by being curious to see if my new arrived Qubes3.2 would run live from the disc on boot-up.Once I got into system of Qubes I couldn't get out of it, so I shut down the system. Went to reboot again with out Qubes USB into windows 7 or Ubuntu but none were present just Qubes error message, sorry did not write them down. After that I decided to use my Ubuntu 16 USB thought maybe I could restore system so I ran the Boot-Repair " I was unable to see this in the Unetbootin software to download on disc, they may have change the name' so I install via commands. Ran the system this is what the output is:  Now it did bring back the Ubuntu OS in boot-up but not the Windows 7...Any help would be appreciated...

I installed Windows on my computer, followed by an installation of Ubuntu. However, now I'm unable to boot into my Windows install.  What can I do to fix this?


The question  was recently deleted by its poster (a CM, if that matters). And an  of CoC was introduced.   What I want to know is:    has this always been the case that a new revision of a policy was preceded by suppression of the information by limiting access to the earlier revision(s) of the policy? The urge to set things right, or otherwise, might tempt a person (includes legal persons) to suppress the information which is not in that person's interest. However, given that the community has a direct stake in a policy, shouldn't transparency (access to information - necessary for individuals to know the past and to frame convincing arguments in the future if an aforesaid person makes a similar or a more severe mistake) be given priority here?   I can neither find nor can access any reason on the deleted post for its deletion.    I understand that the question was received negatively with votes and most of the addresses to it in the comments and the answers further added to that negative outlook. I also know that some individuals took the criticism as the opportunity  to  channel their disdain towards certain gender groups (I flagged one on my answer a few hours ago) which probably might have overburdened and also put in a very difficult situation the moderators of this meta. But difficulty in moderation doesn't justify the deletion  of the source. Locking down the post for a certain period could have been adequate for "reasons of Moderation".   It can be argued that the deletion would put to rest some of the controversy by restricting access to controversial information so that new or unsuspecting users can focus on what matters to the company (but not necessarily to the community), but given that those who are most vocal on both sides of the spectrum already has consumed the information or has accees to it (10k privilege), how is deletion beneficial to both the community and the company?   Preventing new or unsuspecting users from knowing the mistakes / blunders hardly justifies deletion.  On the contrary, this action could be deemed as a policy to handle a negatively received policy -- damage control to be precise.   So, what good (and for whom) would come out of the aforesaid taken action?   Note: I am not trying to incite anyone to go on a rage towards anyone, including the company. I am aghast by the severity of the action and its possible consequences and trying to seek sense out of it.

I noticed that the  was deleted.   When the  came out, I tried to look for my old answer as well as others for comparison.  Why not just mark the old one superseded by [insert link]?  Note: I don't care about lost rep. There were a lot of useful links in answers and comments there (and some less-than-useful ones too).     Old CoC FAQ may be available  and . Source: (, ).


I have been trying to style some OSMM data using  which include a font with some of their symbology in. I've added the font to my system (ubuntu 14.04 LTS) and when viewed in FontMatrix and other system font tools it looks fine:  But when I come to use it in QGIS the font has no glyphs visible and I end up with ugly rectangles instead of my symbols.  Is there some trick to get QGIS to recognise this font?

I am currently learning how to work with OSMastermap Data with postgreSQL and postGIS. After much tinkering I have finally got OS Translator II working and have the Topographic data converted and in the database, with style applied.   The only issue I have now is I can't seem to get OSMasterMap.ttf to work properly within QGIS. It recognises that the font is present, but it does not apply the font when rendering, it reverts back to normal letters.   When I go to select a font it can be selected from the drop down, but the symbols are not used.    The font is installed on the system, as it can be seen in the font book.    Does anyone know if there is a solution to this problem?


How can I get the Cartesian product (every possible combination of values) from a group of lists?  Input:   somelists = [    [1, 2, 3],    ['a', 'b'],    [4, 5] ]   Desired output:  [(1, 'a', 4), (1, 'a', 5), (1, 'b', 4), (1, 'b', 5), (2, 'a', 4), (2, 'a', 5) ...]


I'm just getting into Real Estate photography, I'm currently using a D3100 that seems to work well for me so far. I have been told I really need to move up to a FX camera body. Ok I understand the sensor size, but really what am would I gain? It is a pretty good chunk of money a good FX body.

I'm trying to decide on a higher-end digital SLR, and I'm down to choosing between an APS-C model and a full-frame model.  I understand that the sensors are of different sizes, and as such have an effect on the perceived magnification of the lens, with the smaller APS-C sensor having an effective focal length greater than what it otherwise would be with a full frame sensor. But why does this matter?     What things should drive my choice between one or the other?   In which situations is one better than the other, and why?


Let H be a subgroup of finite index of an infinite group G. Prove that G has a normal subgroup of finite index which is contained in H.   I am not sure how to start on this problem, and would appreciate any suggestions.

Prove that if H has finite index n then there is a normal subgroup N of G with $N \subset H $ and [G:N]$ \le $n!.  I tried to solve the problem but could not done exactly. Since [G:H]=n , Let A={$a_i H$:i=1,2,..,n}. Consider the left multiplication group action on A .Then kernal of the action is intersection N= $\cap a_iHa_i^{-1}$ i=1,2..,n.  Then N is the largest normal subgroup of G contained in  H. Now it is clear that $[G:a_iHa_i^{-1}]$ =n for all i.{by orbit stabliser theorem}.Now how to find [G:N]? yes I got it. By Caley's theorem G/N is isomorphic to a subgroup of $ S_{A}$ .Therefone [G:N] divides n!.


Is it possible to list all instances of a class? I don't mean definitions, I mean allocated declarations of a class. Reflection is typically used to get a list of classes defined but that is not what I am asking for.  This is for educational purposes. I want to list all instances of a specific class (such as the string class) to learn about that class. Actually, I want to list all instances of the WPF Binding class since that will help me understand how bindings work in WPF. This however is not a WPF question.  Update: I don't think that  answers the question. It says that walking the heap or stack might be possible but there are no details of how to do that. I don't need detailed code but I am asking for more guidance than saying to walk the heap or stack.  I have found the following suggestions:        I am not familiar with any of those but I can learn if it will help here. I will however appreciate reasonable assurance that it is worth the time to pursue something.  Also, I know C++ and I am familiar with Detours (as in my ). If Detours can be used then a hint about what to detour would help.

We need to get all the instances of objects that implement a given interface - can we do that, and if so how?


states the following:     If the target drops to 0 hit points before this spell ends, you can   use a bonus action on a subsequent turn of yours to mark a new   creature.   Does that mean that if the target drops to 0 and combat ends then starts again within the hour, you can mark a new target?

I'm looking to play a ranger. The Hunter's Mark spell says:     If the target drops to 0 hit points before this spell ends. you can use a bonus action on a subsequent turn of yours to mark a new creature.   Does that mean I can keep marking a new enemy each time the last one dies until the hour's up?


I'm looking to replace our SQL Server:     HP Proliant DL360 G4   2x 64-bit Intel Xeon 3.60 GHz, 1M Cache, 800 MHz FSB   4GB RAM DDR2   HP Smart Array 6i   2x 146GB SCSI 15K (RAID 1)   With this:     HP ProLiant SE316M1   2x Intel Xeon L5520 (8M Cache, 2.26 GHz, 5.86 GT/s Intel QPI)   Nehalem   16GB RAM DDR3   HP Smart Array P410 512 MB BBWC Cache   2 x 120GB Intel DC S3500 SSD (RAID 1)   I'm also upgrading from SQL Server 2000 and Windows 2003 to SQL Server 2008 R2 and Windows 2008 R2.  I understand the SE316M1 is basically a DL160 G6.   I know our current setup is so ancient (10-year-old) that almost anything can be a big improvement. And this new setup is not a big deal either (5-year-old and pretty unexpensive). But I want to do something as good as I can with my limited budget, but also very reliable.  My biggest concern is the P410 Smart Array and the SSDs (Intel DC S3500). I understand they're compatible, the S3500 is a decent and reliable SSD, and that the P410 won't be a bottleneck for the SSDs.  But what is the Battery Backed Write Cache (BBWC) Module for? Is it a must? What would I be missing in this setup if I don't have it? I'm reading this: . Would I loose performance whith those Intel SSDs? The server will be protected with a UPS. Sorry, I'm a bit confused here! Thanks!

I'm familiar with what a BBWC (Battery-backed write cache) is intended to do - and previously used them in my servers even with good UPS. There are obvously failures it does not provide protection for. I'm curious to understand whether it actually offers any real benefit in practice.  (NB I'm specifically looking for responses from people who have BBWC and had crashes/failures and whether the BBWC helped recovery or not)  Update  After the feedback here, I'm increasingly skeptical as whether a BBWC adds any value.  To have any confidence about data integrity, the filesystem MUST know when data has been committed to non-volatile storage (not necessarily the disk - a point I'll come back to). It's worth noting that a lot of disks lie about when data has been committed to the disk (). While it seems reasonable to assume that disabling the on-disk cache might make the disks more honest, there's still no guarantee that this is the case either.  Due to the typcally large buffers in a BBWC, a barrier can require significantly more data to be commited to disk therefore causing delays on writes: the general advice is to disable barriers when using a non-volatile write back cache (and to disable on-disk caching). However this would appear to undermine the integrity of the write operation - just because more data is maintained in non-volatile storage does not mean that it will be more consistent. Indeed, arguably without demarcation between logical transactions there seems to be less opportunity to ensure consistency than otherwise.   If the BBWC were to acknowledge barriers at the point the data enters it's non-volatile storage (rather than being committed to disk) then it would appear to satisfy the data integrity requirement without a performance penalty - implying that barriers should still be enabled. However since these devices generally exhibit behaviour consistent with flushing the data to the physical device (significantly slower with barriers) and the widespread advice to disable barriers, they cannot therefore be behaving in this way. WHY NOT?  If the I/O in the OS is modelled as a series of streams then there is some scope to minimise the blocking effect of a write barrier when write caching is managed by the OS - since at this level only the logical transaction (a single stream) needs to be committed. On the other hand, a BBWC with no knowledge of which bits of data make up the transaction would have to commit its entire cache to disk. Whether the kernel/filesystems actually implement this in practice would require a lot more effort than I'm wiling to invest at the moment.  A combination of disks telling fibs about what has been committed and sudden loss of power undoubtedly leads to corruption - and with a Journalling or log structured filesystem which don't do a full fsck after an outage its unlikely that the corruption will be detected let alone an attempt made to repair it.   In terms of the modes of failure, in my experience most sudden power outages occur because of loss of mains power (easily mitigated with a UPS and managed shutdown). People pulling the wrong cable out of rack implies poor datacentre hygene (labelling and cable management). There are some types of sudden power loss event which are not prevented by a UPS - failure in the PSU or VRM a BBWC with barriers would provide data integrity in the event of a failure here, however how common are such events? Very rare judging by the lack of responses here.   Certainly moving the fault tolerance higher in the stack is significantly more expensive the a BBWC - however implementing a server as a cluster has lots of other benefits for performance and availability.  An alternative way to mitigate the impact of sudden power loss would be to implement a SAN - AoE makes this a practical proposition (I don't really see the point in iSCSI) but again there's a higher cost.


In Windows 8 how do I restart explorer without admin privileges?

Windows Explorer is the default shell under Windows (since Windows 95).  Sometimes you need to restart it, so my usual way is to kill it using the Task Manager (Ctrl+Shift+Esc, click on Processes, select explorer.exe, click on End Process).  Is there a way to cleanly shut down / close Windows Explorer without logging out?


I learn that any work needs a source of energy, the work of gravity force  (like keeping the Moon in the orbit by the Earth gravity force) comes from where? Can we find any mass reduction (transform to energy source) during the time?

I would like to know where gravity gets its energy to attract physical bodies?  I know that the law of conservation states that total energy of an isolated system cannot change. So gravity has to be getting its energy from somewhere, or else things like hydropower plants wouldn't be able to turn the power of the falling water into a spinning rotor.  Just to be clear, Lets create an example:  Lets say we have two objects with equal mass close to each other. So gravity does its job and it pulls each other closer, this gets turned into kinetic energy. This is where I'm lost. According to the law of conservation energy can't be created or destroyed and the kinetic energy comes from the gravitational pull so where does the gravitational pull gets its energy.  If that energy isn't being recycled from some where else then that means you have just created energy, therefore breaking the law of conservation.


I would like to hear if this is safe enough for storing passwords in a mysql DB.  <?php     $password=hash('sha512',$_POST['password']);     //and then insert it into and mysql database ?>   Is this safe? If not how could I do it more safe?

It is currently said that MD5 is partially unsafe. Taking this into consideration, I'd like to know which mechanism to use for password protection.  This question,   suggests that hashing multiple times may be a good idea, whereas  suggests using salt.  I'm using PHP. I want a safe and fast password encryption system. Hashing a password a million times may be safer, but also slower. How to achieve a good balance between speed and safety? Also, I'd prefer the result to have a constant number of characters.   The hashing mechanism must be available in PHP It must be safe It can use salt (in this case, are all salts equally good? Is there any way to generate good salts?)   Also, should I store two fields in the database (one using MD5 and another one using SHA, for example)? Would it make it safer or unsafer?  In case I wasn't clear enough, I want to know which hashing function(s) to use and how to pick a good salt in order to have a safe and fast password protection mechanism.  Related questions that don't quite cover my question:


I'm using huawei nova 3i,and right now when I transfer my sim card to other phone, my text messages are not there. But when I put it back to my phone, it's there. What should I do to transfer it from my phone to my sim?

How do I backup and restore SMS Messages?


Let a, b natural numbers such that $ab+1 | a^2 + b^2$ . Prove that $(a^2 + b^2)/(ab+1)$ is a square number. I've tried a few things but it's getting me nowhere and it's annoying. Please help.

Let $a,b$ be positive integers.  When $$k = \frac{a^2 + b^2}{ab+1}$$ is an integer, it is a square.    Proof 1: (Ngô Bảo Châu): Rearrange to get $a^2-akb+b^2-k=0$, as a quadratic in $a$ this has two values: $a$ and $kb - a = (b^2-k)/a$. (The second root is determined in two different ways from the expansion $(x-r_1)(x-r_2) = x^2 - (r_1 + r_2)x + r_1 r_2$.)  Now suppose we have $a,b$ such that $k$ is an integer but not a square, by the investigation about roots we have that the second root is a nonzero integer since $k,b,a$ are integers and $k \not = b^2$, futhermore it is positive which is easily seen from its defining equation.  WLOG assume $a \ge b$ so that the second root is strictly smaller than $a$. This leads to a decent, replacing $a$ with the second root.    Proof 2 (Don Zagier): Apply reduction theory (specifically, Sätze 1 and 2 of Section 13 of my book on quadratic fields) to the quadratic form $x^2 + kxy + y^2$, which is the unique reduced quadratic form in its equivalence class.    Note that Proof 2 is pretty much the same as Proof 1 when written out in explicit detail, but I could not read Zagier's book because I cannot read German.  I would like to know more approaches to this and other alternative proofs of this result if possible! Thanks in advance.  I would also be interested in related problems (especially easier ones of a similar nature) and texts which cover the reduction theory in English.


My child's surname has changed and he has a new passport, but the B2 visa has his old surname. Can we travel with the two passports and the documents that show his surname change?

I had my US visa about 7 month age, and I had to renew my passport for certain circumstances, so there was a mismatch in the name between both the visa and the new passport, you see they had to put my grand grandfather's name which was not on the old passport nor the visa, the name on old passport and visa is: Abdelrahman Samy Ali Mohammed and the new passport is: Abdelrahman Samy Ali Ibrahim Mohammed. My grand grandfather's name is Ibrahim, so the question is that gonna cause me any troubles concerning my entry to the US? is there any document should I consider taking it while i'm traveling?  Thanks,,


Sometimes when going back through e.g. my previous answers to find some information, I know the question I am looking for contains an image, and I know the language tag, but I'm a little hazy on the other parameters.    Is there a search option to restrict results to only those posts that contain an image? Akin to filtering email to show only those with attachments I guess.  I see that with  you can filter by user, votes, answer count or whether a question has an accepted answer, or has been closed or migrated. But not images?

There are some great posts on SO and other SE sites with explanatory images that give a better understanding of the problem or its solution.  Recently I was searching for a particular post I had come across that had an image that easily explained java collections in a simple way.  I found it hard to search for. It would be great if we had a new search operator 'hasImage:1' like the existing 'votes:1' (searches post with minimum number of votes), 'views:1000' (with minimum 1k views), etc.  'hasImage:1' would return posts containing a image, and matching the other search keywords.  How do people feel about this?  EDIT  It can be simpler, just img:1 or image:1 as proposed by other users.


How to Get Random Number Between Given Range in Java if minimum is more than 1? for example if i want to get random number between 6 to 20. currently i am using this code   Random rand = new Random();  int  rnd = rand.nextInt(499) + 1;   it is working well, but if i change 1 to some high number for example 6, it will not work properly, i want to get random number that is between 6 and 20. is it possible using above function ?

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


Am having windows 7 in my laptop, and i have installed ubuntu 16.04 in my virtual box. For my project work i need to use some files in ubuntu virtual os, how can i copy those files to ubuntu from windows?

I want to have a directory which is accessible on both Windows 7 installed on Ubuntu host, and the Ubuntu as well.  So I have installed the Virtualbox additions on both Windows and Ubuntu.  Then in Ubuntu:  sudo mkdir /media/win7share sudo mount -t vboxsf win7share /media/win7share   I get:  /sbin/mount.vboxsf: mounting failed with the error: No such device    What do I need to type in Shared folders in Virtualbox Manager settings? What do I need to set up on Windows?