Im a first year student of physics. Because of coronavirus we have got online lessons, but my mechanic's lecturer doesn't like us, he didn't explain anything, just give us a problems to solve.  I've got Landau-Lifshitz's book, but I even don't have enough caculus, to understand everything there.  (there is the first and last equation, without derivation, I dont have even partial derivative in lessons [ofc., I learned it in my own, its not too bad, but Landau is still difficult]).  Can you recommend me anything, that can help?

I'm taking a course on  and  Dynamics, and I would like to find a good book/resource with lots of practice questions and answers on either or both topics.  So far at my university library, I have found many books on both subjects, but not ones with good practice questions and answers. I have Schuam's outline of Lagrangian Dynamics, but didn't really find a lot of practice questions.  Any suggestions would be greatly appreciated!


What is "Other" and how do I prevent it from being bloated? I'm having to back up and format my hard drive every year due this happening.  As you can see, I have very little of everything else.  I mainly use some IDE's and web browsers and that's pretty much it. I'm using Catalina at the moment.

Every few days I get notices on my MacBook that it's running or run out of hard drive space. Curiously, restarting the computer will enable me to recover gigabytes of space (this past time, it was able to recover about 2.2GB). However, I can't identify anything in my personal activity that consumed that space.  It's possible that it's a rogue iTunes podcast or a huge software update that my Mac is automatically downloading - would either of these reclaim the space upon a restart?  One possibility that I can think of is that FileVault has some sort of disk leak, allocating but not freeing files. Does this make sense? Is there a tool that I can run to determine where this space is going? Assuming it is FileVault, should I try to disable it? What's the best way to turn of FileVault on a nearly full computer?


I upgraded last weekend, and my monitor (since long having run fine on 2560x1080_60.00) couldn´t get any higher 1920x1080. I tried adding a new resolution using xrandr but failed every time again.  A work around was returning to another kernel. Grub has available:  Found linux image: /boot/vmlinuz-4.13.0-16-generic Found initrd image: /boot/initrd.img-4.13.0-16-generic Found linux image: /boot/vmlinuz-4.10.0-37-generic Found initrd image: /boot/initrd.img-4.10.0-37-generic Found linux image: /boot/vmlinuz-4.4.0-97-generic Found initrd image: /boot/initrd.img-4.4.0-97-generic   And returning to linux image: /boot/vmlinuz-4.4.0-97-generic helped me to get the higher resolution back into the settings menu. With the newer kernel, it returned errors when trying to add modeline using xrandr.  I saw multiple questions on this, none of them (other than switching back to an older kernel) helped solve the problem.  Thanks and regards, Bill

Old title - "change resolution to 1280x1024 using xrandr gives: X Error of failed request: BadValue (integer parameter out of range for operation)"  I have installed a fresh Ubuntu 17.10 and have a monitor with 5:4 resolution. settings has no resolution higher than 1024x768. But I need the resolution 1280x1024 (5:4).  I use the default motherboard graphics card:  # lspci|grep VGA 00:02.0 VGA compatible controller: Intel Corporation 4 Series Chipset Integrated Graphics Controller (rev 03)   Also xrandr gives the following:  $ xrandr Screen 0: minimum 320 x 200, current 1024 x 768, maximum 8192 x 8192 XWAYLAND0 connected 1024x768+0+0 (normal left inverted right x axis y axis) 0mm x 0mm    1024x768      59.92*+   I tried to add the 1280x1024 resolution using xrandr. so first created the resolution information using gtf:  $ gtf 1280 1024 60    # 1280x1024 @ 60.00 Hz (GTF) hsync: 63.60 kHz; pclk: 108.88 MHz   Modeline "1280x1024_60.00"  108.88  1280 1360 1496 1712  1024 1025 1028 1060  -HSync +Vsync   Then added to resolutions:  xrandr --newmode "1280x1024_60.00"  108.88  1280 1360 1496 1712  1024 1025 1028 1060  -HSync +Vsync   then again did the command: xrandr --addmode XWAYLAND0 1280x1024_60.00  Then nothing changed. When I tried to change it using xrandr --output XWAYLAND0 --mode 1280x1024_60.00 --rate 60 But an error occurred:  $ xrandr --output XWAYLAND0 --mode 1280x1024  --rate 60 X Error of failed request:  BadValue (integer parameter out of range for operation)   Major opcode of failed request:  140 (RANDR)   Minor opcode of failed request:  7 (RRSetScreenSize)   Value in failed request:  0x0   Serial number of failed request:  21   Current serial number in output stream:  22   I don't know what did I do wrong. Or how to change resolution to the correct one: 1280x1024


In my aplication i have a fragment were i have any checkbox. When i chek start a TextToSpech. I have created a similar version without fragment and it work fine. But when i implemented it in a fragment it doesn't works. Her is my code:  public class OneFragment extends Fragment implements TextToSpeech.OnInitListener, CompoundButton.OnCheckedChangeListener { private TextToSpeech tts;  ListView listView; ArrayAdapter<Model> adapter; List<Model> list = new ArrayList<Model>();  public OneFragment() { }  @Override public void onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);  }  @Override public View onCreateView(LayoutInflater inflater, ViewGroup container,                          Bundle savedInstanceState) {      View returnView = inflater.inflate(R.layout.fragment_one, container, false);     listView = (ListView) returnView.findViewById(R.id.listView);     adapter = new MyAdapter(getActivity(), getModel());     listView.setAdapter(adapter);     final CheckBox chk = (CheckBox)returnView.findViewById(R.id.checkBox);     chk.setOnCheckedChangeListener(OneFragment.this);      return returnView; }  @Override public void setUserVisibleHint(boolean isVisibleToUser) {     super.setUserVisibleHint(isVisibleToUser);     if (isVisibleToUser) {         tts = new TextToSpeech(getActivity(), this);     } }  private List<Model> getModel() {     list.add(new Model("Linux", "S"));     list.add(new Model("Linux", "S"));     list.add(new Model("Linux", "S"));     list.add(new Model("Linux", "S"));     list.add(new Model("Linux", "S"));      return list; }  @Override public void onInit(int status) {     if (status == TextToSpeech.SUCCESS) {          int result = tts.setLanguage(Locale.ITALIAN);          if (result == TextToSpeech.LANG_MISSING_DATA                 || result == TextToSpeech.LANG_NOT_SUPPORTED) {             Log.e("TTS", "This Language is not supported");         } else {              startSpeak();         }      } else {         Log.e("TTS", "Initilization Failed!");     } }  private void startSpeak() {     tts.speak("Ciao", TextToSpeech.QUEUE_FLUSH, null); }  @Override public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {     CheckBox chk = (CheckBox)getActivity().findViewById(R.id.checkBox);       for (Model i: list ) {         if (chk.isChecked()) {             this.startSpeak();         }     } } }   This is the partial LogCat result:  java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.CheckBox.setOnCheckedChangeListener(android.widget.CompoundButton$OnCheckedChangeListener)' on a null object reference   How should i do?

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


When I drag a window on my Windows 10 laptop I get this blue rectangle that appears that follows my mouse around and lets me snap the window to a portion of the screen.    I suspect that it may have to do with the fact that my laptop has a touchscreen and that it's supposed to make it easier to dock windows, but I don't really know.  Does anybody know how to get rid of this?

In a fresh install of Windows 10 Pro. When I drag a window a snap target position image is displayed. See image.    This is very frustrating as the image is often displayed under the place where I want to place the window. The affect being that the window is therefore snapped and not placed where I intended it to be.  How do I disable this?  To be clear I don't want to disable snapping altogether just the annoying destination image underlay  UPDATE  I do not have the option to "Allow the system to suggest companion windows when using Snap"


I received a .crt certificate to install on my new galaxy tab 10.1. How do I install it?  I see that I can "install from USB storage" but couldn't figure out where this storage is.

I want to connect to my University's wireless using my Nexus One. When I go to "Add Wi-Fi network" in Wireless Settings I fill in the Network SSID and select 802.1x Enterprise for the security and fill everything out.  The problem is that our university's wireless uses Thawte Premium Server CA certificate for certification.  When I click the drop down list for CA certificate I get nothing in the list (just N/A)  Now I have the certificate (Thawte Premium Server CA.pem) and have moved it to my SD card, but it doesn't look like Android automatically detects it.  Where should I put the certificate so that the Android wireless manager recognizes it. In other words, how can I import a CA certificate so that Android recognizes that it is on the phone and displays it in the CA Certificate drop down list.  Thanks for any help,  Tomek  P.S. My phone is not rooted  EDIT: After doing some research it looks like you are able to install certificates by going to your phone's settings > Location & Security > Install from SD card  Unfortunately it looks like the only accepted file extension is .p12. It does not look like there is a way to import .cer or .pem files (which are the only two files that come with the Thawte certificates) at this moment.  It does look like you can use a converter to convert your .cer or .pem files to .p12, however a key file is needed.    I do not know where to get this key file for the Thawte certificates.


I need to find out how to use a class that I add as a selector in jquery after I add the class. So essentially when I change a daterange with the ID #ds_i it adds a class to a button and when that button is pressed I will get a pop up. The code I have so far is as follows.      $("#ds_i").on('change', function(){           $( "#save-button" ).addClass( "sweet-date-pop" );     });      $(".sweet-date-pop").click(function(e,params) {     var localParams = params || {};      if (!localParams.send) {       e.preventDefault();     }      swal({         title: "This job is in progress.",         text: "Are you sure you would like to change the dates?",         type: "warning",         showCancelButton: true,         confirmButtonClass: "btn-warning",         confirmButtonText: "Yes,change dates!",         closeOnConfirm: false,         closeOnCancel: false     }, function(isConfirm){         if (isConfirm) {             $(e.currentTarget).trigger(e.type, {'send': true});         } else {             swal("Cancelled", "Nothing Was Changed", "error");         }         });     });

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.


I understand that correlation coefficient can only capture the linear dependence. I have just read a book saying that:     “As a normalized covariance, the correlation coefficient captures only one particular aspect of dependence: The strength of linear dependence between the underlying random variables.”    I really do not understand: Why does normalized covariance lead the correlation coefficient to only captures the linear dependency structures? So, is that mean, without normalization, we can measure non-linear dependency?!

I'm trying to understand better the difference between  covariance and correlation, besides the fact that the correlation coefficient is a dimensional and has values between $-1$ and $1$.   One unclear point is the following: the correlation coefficient can highlight only a linear relation between two variables, but does  covariance only work for linear relations too? Supposing that the relation is not linear, is the covariance not zero? Is it bigger than in the case in which the relation is linear?   Cauchy inequality says $$|\sigma_{xy}|<\sigma_{x} \sigma_{y}$$  Which seems to say that the covariance is maximum when there is a perfect linear relation.    So I do not get what does happen if the relation is not linear, and, if covariance is not a suitable parameter in that cas I don't get the reason for that, since simply looking at the definition:  $$\sigma_{xy}=\frac{\sum(x-\bar{x})(y-\bar{y})}{N}$$  it looks like that this should be non zero for any kind of relation (like parabolic).  So can this be a difference between the use of covariance and correlation coefficient? (The first is useful for any kind of relation, the second one only for linear ones).


In quantum computers the following two effects should be seen:  If an operator acts on an arbitrary qubit $Q_n$ of a quantum system $S$ consisting of several qubits than we get a new quantum system $S'$ where the amplitudes of all qubits have changed.  If an operator acts on one qubit of a quantum system $T$ consisting of two entangled QuBits than both qubits are affected.   So which one of these is the reason for the exponential speed-up expected from quantum computers?

What feature of a quantum algorithm makes it better than its classical counterpart?  Are quantum computers faster than classical ones in all respects?


I need to evaluate the following:  $$\int_0^1 \dfrac{x}{1+x^3}dx$$  I've managed to get it down to this:  $$-\int_0^1 \dfrac{1}{x+1}dx + \int_0^1 \dfrac{x-1}{x^2-x+1}dx$$  but now I can't integrate the 2nd integral :(   Any hints/tips?  Thanks

I'm new here!  The problem: integrate from zero to infinity x over the quantity x cubed plus one dx. I checked on wolfram alpha and the answer is that the indefinite integral is this:  $$\int \frac{x}{1+x^3} dx = \frac{1}{6}\left(\log(x^2-x+1)-2 \log(x+1)+2 \sqrt{3} \arctan((2 x-1)/\sqrt{3})\right)+\text{constant}$$  and the definite integral is this:  $$\int_0^\infty \frac{x}{1+x^3} dx = \frac{2 \pi}{3 \sqrt{3}}\approx 1.2092$$  I am trying to figure out all the steps in between. I see that there are logs, which are equivalent to the ln variant that i am more familiar with, which means it was integrating $1/x$ at some point; I also see an inverse tangent in there.  I started with long division to simplify and I got (which could be wrong because I am very tired right now) $x/(x^3+1) = x^2+ 1/(x^3+1)$ which seems to be a step in the right direction. Wolfram Alpha thinks I definitely did that step wrong. The two equations do not evaluate as equal.  Then I cheated and took the wolfram alpha factorization of $(x^3+1) = (x+1)(x^2-x+1)$...I probably should have known that but didn't offhand. Now it is looking like $x^2$ plus the partial fraction decomposition $1/(x^3+1) = A/(x+1)+(Bx+C)/(x^2-x+1)$. Am I heading in the right direction with this? At this point do I just plug in and crunch?


Consider the function  $$\frac{t}{e^t - 1} = \sum_{i=0}^{\infty}\frac{B_i}{i!}t^i$$  This has been one of the famous generating functions for the bernoulli numbers. What about the function associated with  $$\sum_{i=0}^{\infty}B_it^i$$  What function could this be?

I know the exponential generating function for the Bernoulli polynomial $B_n(x)$:$$\frac{te^{tx}}{e^t-1}=\sum_{n=0}^\infty B_n(x)\frac{t^n}{n!}.$$ But is there an ordinary generating function? i.e a function $f$ such that $$f(t,x)=\sum_{n=0}^\infty B_n(x)t^n$$ valid for some open interval of $x$ and some open interval of $t$.


I think its a problem probably because of this CleanMyMac 3 app that says i have got only 100mb from my 8gb and when I click on "Free Up" I get more than 3gb free RAM only to fill it again after a while. The only thing feels slow on my system is when I enable the Transparency effects the minimizing and dragging the apps windows seems utterly slow (lagging).   I tried to install fresh copy of Yosemite and it was smoother and the lag was gone but I have to use this system so restored it. That's why I think some apps are causing this issue?    As you can see only 100MB of RAM is free!    My Mac specs:    EtreCheck report as advised:

I thought Mavericks was suppose to utilize RAM memory better, thus run smoother.  Running ML on Mac mini 2012, with 16GB RAM...always running smoothly even with over a dozen apps running.  Now, after installing Mavericks, my Mac is SLOW, eating up RAM like crazy! Looking over usage, of the 16GB of installed memory...on average it uses 10-14 GB RAM when barely running a few apps!!!   There is this kernel_task that is always running with over 1GB of RAM and most apps are not taking that much RAM, so what is using up all my RAM?! File cache? It shows very high in that new description, with about 1/3 of my total RAM


If you are spinning an object using a mass-less string with constant speed in a vertical circle, and when the object is at an angle with the vertical, what happens to the component of weight in the tangential direction?  $$mg \cos\theta + T = \frac{mv^2}{R}$$ $$mg \sin\theta =\ ?$$  or am I completely wrong in assuming no tangential acceleration?

A lot of my problems have objects moving in circular paths with tangential and normal components of acceleration.  If the tangential component is non-zero though, the speed is changing so the radius of its path would also be changing.  So how can its path be considered circular? The size of of its radius of curvature of constantly changing.


Why is the correct spelling of "referrer" with double "r"? Comparison with for example "referee" or "laborer" would lead one to conclude "referer" is the correct spelling. Is there some rule that applies to this situation or is it an exception?

As for the British English it's always taught - compel, compelled, compelling  Some of the books/dictionaries say that in American English you say compel, compeled, compeling instead, you simply don't double that l.  Moreover, Merriam Webster (11th Collegiate) doesn't mention "compeled" at all. With counsel - both options are listed.  Interestingly,  doesn't indicate much usage of "compeled". On the  hand, "counseled" is more popular than "counselled" in AmE  How is it really in American English?


I currently have this div:
     TEST
     I have tried using

 like this:

         TEST

   ^ Doesn't work    I've also tried using

 like this:

         TEST

   ^ Doesn't work    I've also tried using   (even though it is not recommended...
         TEST
    ^ It works!!!    The only problem is that  is terrible to use as it is outdated! So how can I do this without using

How can I horizontally center a
 within another
 using CSS?

Foo foo


I wanna use a external database sqlite in my android app.   I have copied a database in assets folder in my java android project (database.db.zip) but i can't use this database with normal guides on web.  i have create this class  public class MyDatabase extends SQLiteAssetHelper {  private static final String DATABASE_NAME = "parole.db"; private static final int DATABASE_VERSION = 1;  public MyDatabase(Context context) {     super(context, DATABASE_NAME, null, DATABASE_VERSION); }   }  i how i can use this for reading my database ?

If your application requires a database and it comes with built in data, what is the best way to ship that application? Should I:   Precreate the SQLite database and include it in the .apk? Include the SQL commands with the application and have it create the database and insert the data on first use?   The drawbacks I see are:   Possible SQLite version mismatches might cause problems and I currently don't know where the database should go and how to access it. It may take a really long time to create and populate the database on the device.   Any suggestions? Pointers to the documentation regarding any issues would be greatly appreciated.


I have a dual boot system Windows 7 64-bit and Ubuntu 14.04 LTS 64-bit freshly installed today and running. GRUB 2 is in charge of partition selection upon booting but I was wondering if there is a way to tell ubuntu which partition to boot into upon performing a reboot rather than having to wait for GRUB to load.

I have a dual boot system with Ubuntu 11.04 and Windows 7.  My GRUB bootloader defaults to Ubuntu. I mainly use Ubuntu, but I occasionally need to bootup Windows to do a few things.  If I need to do something in Windows I can "shutdown" Ubuntu and select Windows 7 in the bootloader. However, it would be more efficient if I could do this in one click from Ubuntu.   Is it possible to press a key in Ubuntu which means "Shut down, and then boot into Windows"? (or for that matter Shut down and boot into any non-default bootup)


I have a bigger table in my document, including several urls. I made them active with the \url{...}-command, and now I wanted to make them multi-line-cells by using the \specialcell{..\\..}-command, which is defined as  \newcommand{\specialcell}[2][c]{%   \begin{tabular}[#1]{@{}c@{}}#2\end{tabular}}   But this combination (\specialcell{\url{a\\b}}) does not result in a multi-line url, but instead in the url a\\b. Is there another way to get a multi-line url in a table cell?

How can I break hyperref URLs in a tabular environment. Consider the following example:   \documentclass{article}  \usepackage[colorlinks=true,linkcolor=black,anchorcolor=black,citecolor=black,menucolor=black,runcolor=black,urlcolor=black,bookmarks=true]{hyperref} \usepackage{breakurl}  \begin{document}  \url{http://www.avery/long/url?zz/very/very/long/this/should/break/very/long/long.html}  \begin{tabular}{l l}    A long url & \url{http://www.avery/long/url?zz/very/very/long/this/should/break/very/long/long.html}  \end{tabular}   \end{document}   The first one breaks, the second one doesn't. The output looks like:    I am using pdflatex.


I'm not sure if it's true, but if it is, it can help me with another exercise:  Prove that if $\lambda$ is an eigenvalue of $A^2$ such as $A\in M_{n\times n}^F$, ($F=\mathbb{C} $ or $F=\mathbb{R}$), then $\sqrt {\lambda}$ is an eigenvalue of $A$.  I managed to prove to second direction but it's not really helpfull in that case.  Thanks all.

$A$ is an $n\times n$ matrix of complex numbers. Prove that if $\lambda$ is an eigenvalue of $A^2,$ then $\sqrt{\lambda}$ or $-\sqrt{\lambda}$ is an eigenvalue of $A.$    If $\lambda$ is an eigenvalue of $A^2,$ we have $\lambda\alpha=A^2\alpha$ for some $\alpha.$ Then how can we find a $\beta$ s.t. $\sqrt{\lambda}\beta=A\beta?$


Using Ubuntu 16.04, I gave all the permission of my home folder to an unknown username and now I am unable to write to the files under my home folder including Documents, Downloads etc...  How do I give back permission to the current user account?

I would like the user to have full rights on this folder (as well as all sub-directories and files in it):  ~/.blabla   currently owned by root.  I have found numerous posts (in this forum and elsewhere) on how to do this for files but I can't find a way to do it for whole folders.


I have a Samsung Galaxy S4 mini running Android 4.2.2. The problem I face is when I want to make a regular call, Android asks whether to make the call using VoIP or normal. If I chose normal, it first goes to Skype. I have to disconnect that. Then, if I call the same number again, it does a normal voice call.  I have the Skype app installed on my phone. Please advice me how to fix this problem.

My samsung s4 has suddenly started calling through Skype instead of the local network. I have not set any defaults. I have also uninstalled skype, it still goes through skype, then stops then I have to call again then it goes thtough the network. How can resolve this? please help


In my bash script I have a variable that I am trying to pass to a pattern to search for using awk. However what I expected to happen is not working. I have the following text file (text.txt):  ----------- Task:           a  (some info)   .... ------------ Task:           b   (some info)   .... ------------ Task:           c  (some info)   .... ------------   My script has the following:   letter=a awk -v var="$letter" '/Task .* \var/' RS='-+' text.txt   When I do this however I get nothing but if I do the following:  awk '/Task .* a/' RS='-+' text.txt   I get what I expect:   Task:           a  (some info)   ....   NOTE: I need to pass it as a variable because I have a loop that is constantly changing the variable and that's what I am trying to look for. I'd rather use awk since that what I am most familiar with but I am not opposed to hearing other suggestions such as sed or grep.

Having the following in one of my shell functions:  function _process () {   awk -v l="$line" '   BEGIN {p=0}   /'"$1"'/ {p=1}   END{ if(p) print l >> "outfile.txt" }   ' }   , so when called as _process $arg, $arg gets passed as $1, and used as a search pattern. It works this way, because shell expands $1 in place of awk pattern! Also l can be used inside awk program, being declared with -v l="$line". All fine.  Is it possible in same manner give pattern to search as a variable?  Following will not work,  awk -v l="$line" -v search="$pattern" '   BEGIN {p=0}   /search/ {p=1}   END{ if(p) print l >> "outfile.txt" }   '   ,as awk will not interpret /search/ as a variable, but instead literally.


$f(T) = \int_{0}^{1}e^{-iT\lambda(s)}ds$, where $\lambda(s)$ increases monotonously. I want to prove it satisfies $|f(T)|^{2}$ has a proper upper bound that decreases with $T$ for $T \gg 1$. For example, $\lambda(s) = s$ then $|f(T)| \le 2/T$. This question comes from numerical analysis of my research. It's the expression of error analysis in adiabatic evolution. More specifically, the digital error has expression : $\sum_{k=1}^{L}e^{-iT\sum_{j<k}\lambda_{j}}/L$, where $\lambda_{j}$ equals $\lambda_{j} = \lambda(j/L)$. From numerical result I am sure it has an upper bound decays with $T$. However, I don't know how to prove that. I wonder if there is related formulas in complex analysis and fourier series.

$f(T) = \int_{0}^{1}e^{-iT\lambda(s)}ds$, where $\lambda(s)$ increases monotonously. I want to show that  $|f(T)|$ has an upper bound that decreases with $T$ for $T \gg 1$. For example, if $\lambda(s) = s$ then $|f(T)| \le 2/T$. This question comes from numerical analysis of my research. It's the expression of error analysis in adiabatic evolution. More specifically, the digital error has expression : $\sum_{k=1}^{L}e^{-iT\sum_{j<k}\lambda_{j}}/L$, where $\lambda_{j}$ equals $\lambda_{j} = \lambda(j/L)$. From numerical result I am sure it has an upper which bound decays with $T$. However, I don't know how to prove that. I wonder if there is related formulas in complex analysis and fourier series.


inching.   moving slowly/small degree of progress.  As in “Elon is inching his way towards Mars”.   “Metering closer to his goal” sounds … totally off. So how do I avoid using arguably antiquated measurements (which has ) without sounding totally crazy? Are there equivalent expressions using metric units, or do we need a work-around, or ...?

Related to , are there any metric alternatives to these idioms:        He inches closer to her.   a. meters? - too far   b. centimeters? - too weird   c. scoots? - don't use units     By then, she was miles away from him.   a. far away? - again, don't use units   b. kilometers away? - maybe   c. light-years away? - probably better, preserving the hyperbole     This is an amazing foot-long sandwich.   a. half-a-meter-long? - not accurate   b. dong-long? - even less accurate. It rhymes, though   c. about-a-third-of-a-meter-long? - pretty accurate, but not very marketable     I went the whole nine yards.   a. the whole 8.23 meters? - ...No   b. all the way? - again, don't use units   An ounce of common sense is worth a pound of theory.   a. A gram/a tonne? - preserve the weight comparison, but even more hyperbolic   b. A little/a lot? - again, don't use units        Any suggestions? I mean, I've never seen any idioms using obsolete units like ,  or , but I'm sure there were some when they were in common usage.


I came across a question that was horribly written and lacked any research. Then I noticed I had written it. How would I down vote my own question?

Once in a blue moon, I've wanted the ability to downvote my own answer to some question.  ()  Obviously upvoting one's own posts is out of the question.  But down is different.  Voting my own answer down can help me improve the site by pushing my answer lower in the ranking than another answer with a better or more situation-appropriate alternative.  It's not something I'd do often, but I would use this feature if it were available.  If implemented, I'd expect this feature to operate just like downvotes on other user's posts.  That is:   I get a few seconds to undo the downvote;  I get to remove the downvote after an edit to the post;  I lose a point for placing the downvote (CW excepted); I lose two points for receiving the downvote (CW excepted).   If you're noticing that I'd lose 3 points for downvoting my own non-CW post, congratulations! You can add!  I can think of a couple of potential downsides to this change.  The first one may be a dealbreaker; the second is probably not that big a deal.   Strategic downvoting of oneself: since you can undo the vote after an edit, and you can always edit your own posts, someone could downvote themselves soon after posting (especially on a FGITW answer) to garner extra sympathy upvotes. Badge collecting: the Peer Pressure badge just got easier, because if you have a -2 score on an answer, just downvote and delete for an instant badge.


Can a player in football be given a red card during substitution because of entering the field long before the player being substituted exits? I'm curious to know this because in most of the matches that I've watched, the new player only enters after the substituted player exits

In football, a yellow card can be given to a player when he/she is losing time on purpose.  Typically, a team wining the match will make changes on the last minutes to lose some extra time: the player will make sure to be far away from the bench, so that the distance to cover will be quite big. Also, he will walk all the way, making the other team feel very nervous for it.  For this, 30 seconds are summed to the extra time to be added to the end of the match. However, in many cases this change takes way more than this.  I was wondering: would it be possible for a player that is being replaced already having a yellow card to get another one for being so slow during the replacement? Would the replacement then be cancelled? Has it ever happened?


I am lost why execution plan is different if I run query with option recompile to compare to same query (with clean proc cache) without option recompile. The result is one row. The script is:  Create two tables:  CREATE TABLE H (id INT PRIMARY KEY CLUSTERED IDENTITY(1,1), header CHAR(100)) CREATE TABLE D (id INT PRIMARY KEY CLUSTERED IDENTITY(1,1), idH INT, detail CHAR(100)) CREATE INDEX IX_idH ON dbo.D(idH)   Fulfill:  DECLARE @i int = 1 WHILE @i <= 10 BEGIN     INSERT INTO H (header) VALUES ('nonononono')     SET @i = @i + 1     PRINT @i END SELECT * FROM H GO  DECLARE @i int = 1 DECLARE @ii int = 1 WHILE @i <= 7 BEGIN     WHILE @ii <= POWER (10,(@i - 1))     BEGIN         INSERT INTO D (idH, detail) VALUES (@i, 'nonononono')         SET @ii = @ii + 1     END     SET @i = @i + 1     SET @ii = 1 END   The statement:  DBCC FREESESSIONCACHE  DECLARE @hid INT = 1  SELECT * FROM H h JOIN D d ON d.idH = h.id WHERE h.id = @hid OPTION (RECOMPILE)   With OPTION (RECOMPILE) it uses the key lookup for the D table, without it uses scan for D table. I do not understand why. MS SQL version 13.0.4411.0. And simple (7 rows) and actual statistics.

This is on SQL 2005 SP2, but I suspect this is something that applies to all query hints in general.   I've got an adhoc sql statement that gets a different query plan solely because of  OPTION(recompile). The batch statement is never (in practice) being reused as it is using non-parameterized dynamic sql generation where the statement changes with dates / other parameters. I've confirmed this is the case by checking the cached plan_handle, always a different ID as values in batch change.   When I do dbcc freeproccache I expect that the query plan I get for the statement would be exactly the same as one with "option (recompile)" query hint added. But its not, its quite different actually (much much faster).   Does anyone know why addition of a query hint would cause the engine to pick a different query plan?   The statement is something like this  dbcc freeproccache go sp_executesql '  declare @begindate datetime declare @enddate datetime select @begindate='1/1/2011' select @enddate='2/1/2011' select count(*) from tableA where tableA.datecolumn between @begindate and @enddate  and exists(  select A union all select B union all select C )'   all I have to do is change the statement to use recompile query hint and I get different (much better) query plan.  dbcc freeproccache go sp_executesql '  declare @begindate datetime declare @enddate datetime select @begindate='1/1/2011' select @enddate='2/1/2011' select count(*) from tableA where tableA.datecolumn between @begindate and @enddate  and exists( select A union all select B union all select C ) OPTION (RECOMPILE)'   As code is passing in the date values I can't use a plan guide to override the default behavior, looks like code change will be required. But I wish I knew where to look on why recompile would force a different plan to be used.


I have a very weird question today. I am building a huge application with jQuery, Ajax and PHP.  Basically I'm loading the contents of a div with PHP once the page loads.
     Test1     Test2     Test3
   When someone clicks on these, an alert should come up, like this:  $("#click1").on("click", function(){     alert(1); });   However if the client clicks on  Click   a jQuery function is triggered like the following:  $("#click_here").on("click", function(){     fillDiv(); });   fillDiv() function is basically calls and ajax function and fills the div with the result, the PHP page returns.  This is basically the exact same as the top div. Php returns the followig:          Test1         Test2         Test3   And the fillDiv() function places this into the samplediv. I've checked the HTML of the 2 result is the Exact same!  Problem:  When the items are loaded back from the Ajax function, with thee exact same html, IF I click on any of the Test1, Test2, Test3 links, I got back nothing actually. No alert, nothing. Not even an error message.  What could be the issue, which I didn't encounter?

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.


Is there a way by which update to ALL rows of a Mysql table could be denied or avoided?  Background:  I have a table 'Orders' having 'OrderID' (Type VARCHAR) and 'VendorID' (Type Integer) as two of the columns. If I run the below query on this table, it simply resets VendorID in all the rows:  SET `VendorID` = 0 WHERE `OrderID` = 0;   OrderID should not be 0 but because of some bug in the system, it escaped all the checks and created havoc. Had OrderID been of Integer type, this query would not have done anything. But since OrderID has alphabets, it could not be set as Integer type.  Can Mysql be configured in such a way that it rejects Updates to all rows? Would result of this query change if underlying database is not Mysql?  My environment:  nginx/1.4.6 Codeigniter (2.x) / Mysql (5.5) / InnoDB table type  Please suggest how this issue could be avoided in future, thanks.

points out the following security problem with MySQL:  USERS id | email            | password_reset_token 1  | one@example.com  | QTlXww)uV!Hdg3U6aGwKV2FPvAqzVgPx 2  | two@example.com  | CZor5t7WbX#LTeqiG3v@6f3@z#)BfK*n   Here we have nice, random tokens that a user must prove they have in order to reset their account. But the user manages to submit a reset token of 0, so we run this query:  SELECT * FROM `users` WHERE `email` = 'one@example.com' AND `password_reset_token` = 0   MySQL converts the token VARCHAR to an INT in order to make the comparison. It considers a VARCHAR that does not start with a number to equal 0. Therefore, an attacker can match any non-numeric string and take over the account.  Even if the reset token starts some numbers, the situation is not much better. MySQL ignores all characters but the initial numbers when making this comparison, so it considers 12blahblah3blah4 to be equal to 12, which makes guessing exponentially easier.  Can I configure MySQL not to do this kind of typecasting? If, for example, it cast INT to VARCHAR instead of vice versa, this attack would not work.  Note  If the query is run with '0' instead of 0, this doesn't work. The article discusses this vulnerability in terms of Ruby on Rails' acceptance of XML, where a type=integer property convinced Rails to send an actual integer in the query.  That bug has been patched in Rails; it now converts all request parameters to strings, so it would never build a query with an integer. But I still think MySQL should be configurable to prevent this.


I'm attempting to download a serial ftp software from the Ubuntu Software Center. However, for example, for "Serial Port Terminal" software, I'm seeing this message, "Available from the "universe" source" and the button "Use This Source" is grayed out.

How do I get to the Universe Repository in supported versions of Ubuntu?


I don't know the proper term, but I'm a new blender user and I was trying to create a light and the shadows from it are very clipped, but only on Eevee. Works fine on cycles.

I already subdividied the surface, but still getting this raw shadows in between of the spheres.   What can I do?


Fixed point iteration is $p_n={p_{n-1}\over{2}}+{1\over p_{n-1}}$ $n=1,2,...$. As it is fixed point iteration $p_n=g(p_{n-1})$. Hence, $g(x)={x\over 2}+{1\over{x}}$.Can someone give me a head start and that could start this problem. I tried induction but got some really complicated expressions which I cannot simplify. I tried proving $\sqrt{2}<p_n<p_{n-1}$ by induction when $p_0$ is not $\sqrt{2}$. Maybe I am doing something wrong in my induction method.

Suppose that $S_0$ and A are positive numbers, let $$S_{n+1} = \frac{1}{2}\left(S_n +\frac{A}{S_n}\right)$$ with $n \geq 0 $.      (a)Show that $S_{n+1} \geq \sqrt{A} $ if $n \geq 0$       (b)Show that $S_{n+1} \leq S_n $ , if $n \geq 1$      (c) Show that $s= \lim\limits_{n \rightarrow \infty} S_n$ exists      (d) find s   (a) Show that $S_{n+1} \geq \sqrt{A} $ if $n \geq 0$  Given $$P_n:  S_{n+1} = \frac{1}{2}\left(S_n +\frac{A}{S_n}\right) \geq \sqrt{A}$$  $$P_0: S_{1} = \frac{1}{2}\left(S_0 +\frac{A}{S_0}\right) \geq \sqrt{A}  $$  We assume that $P_n$ is true  $$P_{n+1}: S_{n+2}= \frac{1}{2}\left(S_{n+1} +\frac{A}{S_{n+1}}\right)$$ by assumption $$S_{n+2}= \frac{1}{2}\left(S_{n+1}\left(1 +\frac{A}{(S_{n+1})^2}\right)\right) \geq \frac{1}{2}\left(\sqrt{A}\left(1 +\frac{A}{(\sqrt{A})^2}\right)\right)$$ $$ S_{n+2}= \frac{1}{2}\left(S_{n+1} +\frac{A}{S_{n+1}}\right) \geq \sqrt{A}  $$  It follows that $S_{n+1} \geq \sqrt{A} $    (b) Show that $S_{n+1} \leq S_n $ , if $n \geq 1$  $$S_{n+1} \leq S_n$$ $$\frac{1}{2}\left(S_n +\frac{A}{S_n}\right) \leq S_n $$ Dividing by $S_n$ $$\frac{1}{2}\left(1 +\frac{A}{S_n^2}\right) \leq 1 $$ $$\frac{A}{2S_n^2} \leq \frac{1}{2}$$ $$A \leq S_n^2$$ $$S_n \geq \sqrt{A}$$ As  $S_{n+1} \leq S_n$ yields a true statement, it follows $S_{n+1} \leq S_n$ is true.    (c) Show that $s= \lim\limits_{n \rightarrow \infty} S_n$ exists  Since $S_{n+1} \leq S_n$, the sequence is non-increasing,   using the non-increasing theorem stating that      if $\{S_n\}$ is non-increasing then $$\lim\limits_{n \rightarrow > \infty} S_n = \inf\{S_n\} $$     (d) find s    Is the argumentation in (a) and (b) appropriate? Also, I have to admit I m getting less confident in my argumentation (c) and (d). How to proceed in (c) and (d)?  Much appreciated for your input or help.


I'm trying to install node.js version 12 on my Ubuntu 19.10 laptop by following the instructions .  When I execute the curl command I get an error about a locked directory:  $ curl -sL https://deb.nodesource.com/setup_12.x | bash -  ## Installing the NodeSource Node.js 12.x repo...   ## Populating apt-get cache...  + apt-get update Reading package lists... Done E: Could not open lock file /var/lib/apt/lists/lock - open (13: Permission denied) E: Unable to lock directory /var/lib/apt/lists/ W: Problem unlinking the file /var/cache/apt/pkgcache.bin - RemoveCaches (13: Permission denied) W: Problem unlinking the file /var/cache/apt/srcpkgcache.bin - RemoveCaches (13: Permission denied) Error executing command, exiting   I've looked to see if there's an apt-get task and rebooted my machine, but no joy.    Does anyone have a suggestion on how to get past this?

I get this error when trying to use apt-get:  E: Could not get lock /var/lib/dpkg/lock - open (11 Resource temporarily unavailable) E: Unable to lock the administration directory (/var/lib/dpkg/) is another process using it?     How can I fix this?


If a black hole with an event horizon of 1 cm were placed in the Sun core what would be the Suns' lifespan as a visible star? I want to get a visualisation of how much mass per second would be absorbed inside that BH.Should the cross section area be calculated,the growth of the event horizon with time which increases the cross section area of the inward flow? When we get the surface area of the event horizon should that be divided by the area of a helium or hydrogen atom to get how much atoms in parallel transpass the event horizon. After that we should calculate how much atoms in series transpass the e.h. and as we know their speed being almost 300.000kmps and the length of a single atom we can figure out their number per second transpassing the cross section area with the surface of the He or H atom? Or it is much more complicated?

So lately i heard of this theory that planet 9 might be a Primordial Black Hole (PBH) with 5 - 10 times the mass of Earth. I was thinking to myself, what would happen, if such a PBH (if it even exists) were to fall into our sun? Would it slowly consume the sun, even tough its mass is just a fraction of the star? Would the sun eventually become a black hole itself?  PS: Sorry for any typos or any wrong wording (I´m not a native english speaker)  PPS: I´m not a physicist or anything, i´m just interested in the universe and how it works.


Im assigned to collateral, ad design, web banners, etc.  It gets frustrating when the image im gonna put a text on top of has a wide range of color. And sometimes, it gets frustrating to choose what color of the text should be.  Is there a secret to this?

I've come here seeking for a bit of design help or advice on how I could possibly improve the following:  Like the title says, I'm having a website banner with multiple text displayed on different images as backgrounds. Now, since most of the images are dark, I've set the font color as white. But even then, some of the text is not very readable on a couple of images like:    Since I'm working with CSS, I've tried different options such as:  Adding Text Shadows:    CSS:  text-shadow: 3px 3px 0px #000;  Also tried, creating a semi-transparent box around the text:      I feel the box one looks out of place.  I've created a  for anyone who knows CSS. If not, please feel free to advice me based on your imagination alone.  PS: You could also advice on using a different font if that would help it stand out better.


Does it work once a week or does it continually trim the system?  I have seen answers for this but they refer to Ubuntu 14.04 but not to Ubuntu 15.04

I know that the Linux kernel supports TRIM as of version 2.6.33, so there should be TRIM support in ubuntu.  Is TRIM enabled by default or do I need to change some settings or install additional software for it to work? If so, how?


I'm trying to write a List class, but have a problem:     E:\junior_req\test_project\Node.cpp|6|multiple definition of `Node::print()'|   My code:   Node.h:  class Node {     Node* next;     int value; public:     Node() {next = nullptr; value = 0;}     Node(int t) {this->value = t; next = nullptr;}     Node(const Node& t) {this->next = t.next; value = t.value;}     ~Node() {}      int getValue() {return value;}     Node* getNext() {return next;}      void setValue(int t) {value = t;}     void setNext(Node* t) {next = t;}      Node& operator=(Node t);      void print(); };   Node.cpp  #include "Node.h" #include <iostream> using namespace std; void Node::print() {     cout << this->getValue() << endl;     if(this->getNext() != nullptr) this->getNext()->print(); }   List.h and List.cpp classes are same, but there are no errors.   Main.cpp:  #include <iostream> #include "List.h" #ifndef NODE_H #define NODE_H using namespace std; int main() {     cout << "Hello world!" << endl;     List l;     l.add(1);     Node* one;     l.add(one);     one->print();     return 0; } #endif // NODE_H   #pragma once doesn't help  What is wrong with my code?

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


Tom and Luke are playing a chess tournament against each other. Each game results in either a win for Tom, a win for Luke, or a tie. A tie is worth 1 point, a win is worth 2 points, and a loss is worth 0 points. Someone wins the overall tournament when his score exceeds the other player's score by 3 or more points. The probability that Tom wins a game is 0.25. The probability that Luke wins a game is 0.15. The probability that they tie is 0.6 What is the probability that Tom eventually wins?

Have been working on this problem for a while. No clue how to approach! Player A and Player B are playing a game with 3 possible results: win, tie and lose. Player A’s probabilities for each outcome are:  Win: 0.3  Tie: 0.2  Lose: 0.5   A win gives 2 points, tie gives each 1 point, and loss gives 0 points. The first of the two players to win 3 or more points than the other will win the match. What is the probability that Player A will eventually win? Thanks!


I am using drush in my localhost. I am new to drupal and i want to execute some commands in drush for a live site. can anyone know how to use drush for a live site...?

I don´t know how to use drush nor the command line, so I´ve started to read some tutorials, and watch some videos. I´ve installed the drush windows installer, because I have windows.  The thing is that all examples I´ve read so far, start with localhost. What if I have my devel installation in a shared hosting or a VPS, in the cloud? How to access that?  Using my ftp program, I access it using hostname ftp.mysite.com the username and the password to that account. How may I do that with the command line?  Thanks!


I don't think it was ever clearly explained how Ultron came to be in Avengers: Age of Ultron, Stark and Banner were dumbfounded. I was thinking there would be a reveal that it wasn't actually Tony Stark's fault (to redeem him somewhat, but maybe it will come now after his death, to redeem his legacy) and Thanos actually had something to do with it since Ultron came from various sources, and because he gave the mind stone to Loki, and I would guess, probably wouldn't have done so without maintaining some control over it somehow (though this doesn't seem apparent later, though maybe Vision could have broken that connection, which could have influenced Thor to help create Vision after seeing things about the Infinity Stones). Thor comes to the conclusion that someone is pulling strings from behind the curtain at the end of Age of Ultron, which sounds like Thanos to me. The movie ends with Thanos saying he'll have to do things himself, which sounds like to me Ultron was supposed to be doing his bidding (i.e. destroy Earth so he could get the Infinity Stones from it more easily), for some reason. Were there any other possible hints that Thanos was somehow at least partially responsible for the creation of Ultron?

In the Age of Ultron mid-credit scene, Thanos puts on some sort of a glove and says "Fine, I'll do it myself." Which seems to imply his plan to get it done by others has failed. Did Thanos mastermind the events in the movie in any manner?


I am trying to create a class with various data which are read in from several files. The usual way is probably to define a constructor (__init__) and read data inside this routine, e.g.,  from SomeOtherMod import reader   # some data reader  class Myclass:      def __init__( self ):         self.N = reader.readN()         self.data = reader.readdata()         self.foo = self.data.foo()         self.bar = self.data.bar()         ...    # more data to read and associated properties follow      def othefunc( self ):         ...    # use self.N, self.data, ...   But it also seems that I can write the same thing in a header part of the class without using __init__, e.g.,  class Myclass:      N = reader.readN()     data = reader.readdata()     foo = data.foo()     bar = data.bar()     ...      def otherfunc( self ):         ...   which looks more terse than the first code. So I am wondering whether this second code is a valid way for defining various fields of a Python class? Is it considered bad practice to do so, or is there any difference between the first and second approaches? I would appreciate any suggestions because I'm still new to Python. Thanks much!

Is there any meaningful distinction between:  class A(object):     foo = 5   # some default value   vs.  class B(object):     def __init__(self, foo=5):         self.foo = foo   If you're creating a lot of instances, is there any difference in performance or space requirements for the two styles? When you read the code, do you consider the meaning of the two styles to be significantly different?


Is it possible to do this? I don’t care about reformatting, as this laptop has nothing important on it.

I would love to triple-boot Windows XP Pro, Ubuntu 12.10, and Backtrack 5 R3, but is this safe for my harddrive/other OSs on the computer?


I am playing on a Creative world in MCBE, and mess around with everything. I got the idea to obtain a Looting 32 sword using commands, but it errors out and says that the max level is 3. I tried using these methods, but all have failed: /give @s diamond_sword 1 0 {ench:[{id:21,lvl:32}]} /enchant @s looting 32  Is there any way to obtain a high level enchantment using commands, without editing the game code?

I'm on Bedrock Edition (Windows 10, same as PE) and was wondering if there was any way to go above max on enchanting. For example, if I type /enchant ExamplePlayerName sharpness 10 it would just say the enchantment max was 5. Is there any way I can bypass this?


I just experimented a bit in linux and ended up getting very many files in one and the same folder. Now when I try to do      rm -f folder/*.png   I get      -bash: /bin/rm: Argument list too long   Is there some easy way to get past this?     Own work:  I suppose I could make an ugly script which loops through rm on the result of something like     ls /folder/ | head -100 | grep ".*\.png"   But really, there must be an easier Gnu way to do it?

One of my friends wanted to have more logs in the /var/log/ directory, and after some time of using the system, he tried to access the folder and list it, but instead he got the following error:  bash: /bin/rm: Argument list too long   Does anyone know how many files can be added to this rm list?


Ι got a feeling that $$\sum_{x=1}^{\infty}\Big\lvert\sum_{k=0}^{\infty} \frac{x^{2k}}{(k+1)!}(-1)^{k} \Big\rvert \geq \sum_{n=1}^{\infty} \frac{1}{n} $$  because $$\sum_{x=1}^{\infty} \Big\lvert x-\frac{x^2}{3!}+\frac{x^4}{5!}... \Big\rvert \geq 1+\frac{1}{2}+\frac{1}{3}...$$ i feel that somehow terms will get canceled but i cant prove it!!   **this came up as a part of problem i was solving . I got no idea if the above inequallity is true **

It is stated as a problem in Spivak's Calculus and I can't wrap my head around it.


With htaccess I'm trying to make my sites urls clean.  I use very basic urls like: www.mysite.com/pagename.php ("pagename" is variable).   I want www.mysite.com/pagename to display the content of /pagename.php So this is in my htaccess-file now:  Options +FollowSymlinks RewriteEngine On RewriteCond %{REQUEST_FILENAME} !-d RewriteCond %{REQUEST_FILENAME} !-f RewriteRule ^([^\.]+)$ $1.php [NC,L]   But I also want my old urls (/pagename.php), when called, to be rewritten to www.mysite.com/pagename    How to do this? I can't figure it out (get loops all the time)...  Thanks in advance!

This is a  about Apache's mod_rewrite.   Changing a request URL or redirecting users to a different URL than the one they originally requested is done using mod_rewrite. This includes such things as:   Changing HTTP to HTTPS (or the other way around) Changing a request to a page which no longer exist to a new replacement. Modifying a URL format (such as ?id=3433 to /id/3433 ) Presenting a different page based on the browser, based on the referrer, based on anything possible under the moon and sun. Anything you want to mess around with URL   Everything You Ever Wanted to Know about Mod_Rewrite Rules but Were Afraid to Ask!  How can I become an expert at writing mod_rewrite rules?   What is the fundamental format and structure of mod_rewrite rules? What form/flavor of regular expressions do I need to have a solid grasp of? What are the most common mistakes/pitfalls when writing rewrite rules? What is a good method for testing and verifying mod_rewrite rules? Are there SEO or performance implications of mod_rewrite rules I should be aware of? Are there common situations where mod_rewrite might seem like the right tool for the job but isn't? What are some common examples?   A place to test your rules  The  web site is a great place to play around with your rules and test them. It even shows the debug output so you can see what matched and what did not.


I try to upgrade my Ubuntu 12.04 to 13.04 (or upper why not). I read in release notes that I should first upgrade to 12.10 before 13.04.  But when I use the update-manager -d command, the program purposes to install only the release 14.04. How can I chose the target version ?  (I tried to upgrade to 14.04 but I had an error message:  W:Impossible de récupérer http://extras.ubuntu.com/ubuntu/dists/trusty/main/source/Sources  404  Not Found , W:Impossible de récupérer http://extras.ubuntu.com/ubuntu/dists/trusty/main/binary-i386/Packages  404  Not Found , E:Le téléchargement de quelques fichiers d'index a échoué, ils ont été ignorés, ou les anciens ont été utilisés à la place.)

I start the software upgrade application, press check and Ubuntu 12.04 software upgrade does not show 12.10 upgrade on top.  The only way to upgrade seems via CD???? Upgrading to 12.04 worked that way but not to 12.10.  Thanks


If my bike currently has 24 inch wheels, will 26 inch wheels fit?   I have a cruiser with 24 inch wheels an I want to put 26 inch wheels on it, I am not sure they will they fit.

Jamis Aurora Elite comes with disk brakes on 700c wheels. I am wondering is it possible to put 26 inch wheels on?  Since it has disk brakes, I can't see any issues with fitting the brakes. Only problem might be the ground clearance to the pedals.  The 26 inch wheels are good for touring with load, 700c wheels ideal for daily commute. I am looking for a bike which will fit both needs.


The question is     If $f$ and $g$ are measurable and well-defined a.e., show $f+g$ is measurable.   I can show that the case when $f+g$ are well-defined everywhere.   Let $\Omega_{f+g>a}=\{x\in \Omega:f(x)+g(x)>a\}$, then $\Omega_{f+g>a}=\Omega_{f>a-g}$.   There is a theorem in my text book saying that if $f$ is measurable then $\Omega_{f+a}$ is measurable for any real number $a$.  Another theorem states that if both $f,g$ are measurable, then $\Omega_{f>g}$ is measurable.  As a result $\Omega_{f>a-g}$ is measurable, hence $\Omega_{f+g>a}$ is measurable, then $f+g$ is measurable.  Can anyone help with the case when $f,g$ are well-defined a.e. respectively? Thank you!

Suppose $f$ and $g$ are Lebesgue measurable, we want to show $f+g$ is measurable. So, the hint is to consider the continuous functions $F : \mathbb{R}^2 \to \mathbb{R} $ given by $h(x) = F(f ,g ) $. If we can show $F$ Is measurable, then Taking $F = f +g $ would solve our problem.  In other words, I want to show that the set $R = \{ (f,g) : F(f,g) > a $ } is lebesgue measurable.. But this set is just a rectangle in the plane. And since $F$ is continuous, then $R$ must be open, and hence a union of open rectangles which are measurable and hence $R$ must be measurable. Is this a correct approach to the problem? Can someone help me to make this formal? thanks


I found some inconsistencies of notations in my calculus textbook: for example, whenever it uses $\sqrt4$, it assumes that $\sqrt4 = 2$ instead of $\pm2$. But whenever it solves an equation such as $x^2 = 4$, it gives me the answer that $x = \pm2$. I think that square root and square are inverse operations. What I mean is that: if $x^2 = y$ then $\sqrt{y} = x$. Here one of the appropriate solutions would be either $x = \pm2$ and $y = 4$ or $x = 2$ and $y = 4$.

It is perhaps a bit embarrassing that while doing higher-level math, I have forgot some more fundamental concepts. I would like to ask whether the square root of a number includes both the positive and the negative square roots.  I know that for an equation $x^2 = 9$, the solution is $x = \pm 3$. But if simply given $\sqrt{9}$, does one assume that to mean only the positive root? And when simply talking about the square root of a number in general, would one be referring to both roots or just the positive one, when neither is specified?


I was dual-booting Windows 8 and Ubuntu and after installing Windows 8.1 preview two days back, I am no longer getting the option to boot into Ubuntu in the start screen.  Please help! My thesis is due in a few weeks. And all my work is in the ubuntu.  Best

I installed Windows 7, which ate Ubuntu's boot file. When starting up the computer, it now goes straight to Windows, without giving me the option of booting Ubuntu.   How can I get Ubuntu back?


I need to use rand(uniform distribution) function in matlab to generate a gaussian/normal distribution. What is the best way to do this?

In order to simulate a normal distribution from a set of uniform variables, there are several techniques:    The Box-Muller algorithm, in which one samples two independent uniform variates on $(0,1)$ and transforms them into two independent standard normal distributions via: $$ Z_0 = \sqrt{-2\text{ln}U_1}\text{cos}(2\pi U_0)\\ Z_1 = \sqrt{-2\text{ln}U_1}\text{sin}(2\pi U_0) $$ the CDF method, where one can equate the normal cdf $(F(Z))$ to a Uniform variate: $$ F(Z) = U $$ and derive  $$Z = F^{-1}(U)$$      My question is: which is computationally more efficient? I would think   its the latter method - but most of the papers I read use Box-Muller -   why?   Additional information:  The inverse of the normal CDF is know and given by:  $$F^{-1}(Z)\; =\; \sqrt2\;\operatorname{erf}^{-1}(2Z - 1), \quad Z\in(0,1).$$   Hence:  $$ Z = F^{-1}(U)\; =\; \sqrt2\;\operatorname{erf}^{-1}(2U - 1), \quad U\in(0,1).$$


Is there an app to increase/change default fontsize for all applications in mac ? It is really painful for me to read default fonts or to increase fontsize in every app I open, and even worse, the fontsize in many menus(as well as Finder match results) can not be modified!

Is it possible to change the systems font? (finder, alerts, menus etc)


I need to set main font of my document using Times New Roman font. But I just found one solution that is to compile document using xelatex. But my document built since first typing using pdflatex, so when I switch the enggine to xelatex there are so many error I found. And I cannot fix that error immediately. So I need to find solution to set a font to Times New Roman in pdfLatex.

I know that I can put \usepackage{times} in the preamble in order to use the Times font instead of Computer Modern for my document.  But this only affects the text; the math is still typeset using Computer Modern.  How can I make Latex use Times also for the math?


I was lately studying about the Lagrange and Hamiltonian Mechanics. This gave me a perspective of looking at classical mechanics different from that of Newton's. I would like to know if there are other accepted formalism of the same which are not quite useful compared to others (because otherwise if would have been famous and taught in colleges)?

Lagrangian and Hamiltonian formulations are the bedrock of particle and field theories, produce the same equations of motion, and are related through a Legendre transform.  Are there more such mathematical objects that are equivalent, or are these two in some way unique?  If so, why are there two equivalent systems,  rather than a single (or more)?


I need to convert a Particle System to a mesh object, so I can export it to Unity 3D. How could I do this?

I place leaves on my trees with emitter particle systems. Then, to make a forest, I place those trees with another emitter (or hair) particle system.   Problem is particles of particles don't work, I only get the trunks without leaves in my forest.  Following this question : , which solution takes ages (I use about 500 000 leaves per tree), I tried to write a python script, but comes to the same problem. Searching on google, I found Brecht saying it comes from the naming of object (leave.001, leave.002 .... leave.500000) which after 1000 iterations becomes pretty slow and after 10000 extremely slow (so naming 2000 object is much slower than twice the time of naming 1000 of them). Anyway, that step is useless, blender needs one big mesh with all leaves to allow instancing it, not 500000 objects with one linked mesh.  So question is how can I convert all the particles to one unique object in one step (or at least avoid it to take 28 hours every time) ?


I have solved the differential equation $\frac{dy}{dt} = \frac{at+by+m}{ct+dy+n}$ where each of the alphabets $a,b,c,d,m,$ and $n$ is some constant and $ad=bc$ by the following method. Multiplying the RHS of the differential equation by $\frac{d}{d}$, one obtains $\frac{dy}{dt} = \frac{adt+bdy+md}{cdt+d^{2}y+nd}$ Because $ad = bc$, the equation is re-expressed as $\frac{dy}{dt} = \frac{b(ct+dy)+md}{d(ct+dy)+nd}$ Let $x = ct + dy$ One obtains $\frac{dy}{dt} = \left( \frac{1}{d} \right)\left(\frac{dx}{dt} -c\right)$ The differential equation is re-expressed as $\frac{dx}{dt} = \frac{(b+c)x+(md+cn)}{x+n}$ Rearranging the above equation, one obtains $\left(\frac{x+n}{(b+c)x+(md+cn)}\right)\frac{dx}{dt} = 1$ Multiplying the LHS of the above equation by $\frac{\left(\frac{1}{b+c}\right)}{\left(\frac{1}{b+c}\right)}$, one obtains $\left(\frac{1}{b+c}\right)\left(\frac{x+n}{x+\left(\frac{md+cn}{b+c}\right)}\right)\frac{dx}{dt} = 1$ Let $h$ denotes $\left(\frac{md+cn}{b+c}\right)$ $\left(\frac{1}{b+c}\right)\left(\frac{x+n}{x+h}\right)\frac{dx}{dt} = 1$ Integrating both sides of the above differential equation with respect to $t$, $\left(\frac{1}{b+c}\right)\int \left(\frac{x+n}{x+h}\right)\frac{dx}{dt} dt = \int dt$ One obtains, $x + (n-h)$ln$|x+h| + K = (b+c)t$ where $K$ is an arbitrary constant. Substituting $x$ as $ct + dy$ and $h$ as $\left(\frac{md+cn}{b+c}\right)$, $(ct + dy) + (n-\left(\frac{md+cn}{b+c}\right))$ln$|(ct + dy)+\left(\frac{md+cn}{b+c}\right)| + K = (b+c)t$ The above equation is my solution to the differential equation. However, when applying the solution to the differential equation $\frac{dy}{dt} = \frac{-t -2y -3}{2t+4y-1}$ each of the terms with $\left(\frac{md+cn}{b+c}\right)$ is undefined. Is the reason for the case is because my solution to the differential equation is incorrect? The differential equations are obtained from the book Differential Equations and Their Applications: An Introduction to Applied Mathematics, 4th Edition by Martin Braun on the section 1.4.

How would you solve the next ODE?  $$\frac{dy}{dt} = \frac{at + by + m} { ct + dy + n},$$  where $a, b, c, d, m, n$ are constants and $ad = bc$.  Corrected.


In Excel I am trying to apply conditional formatting to an entire table column (it should be automatically applied, when new rows are added into the table)  However, the conditional formatting rules don't seem to work in that way:   Each time I create such rule, the column reference gets translated into an absolute cell reference, which is wrong, because it doesn't scale as the table grows.   =DeptSales[Sales Amount] gets translated to =$D$2:$D$34   For some reason even when editing the rule, I am unable to use the column reference, an error gets displayed.   =WENN(ISTLEER(D2:D34);FALSCH;ZÄHLENWENN(Name_in_system;D2:D34)=0) works, =WENN(ISTLEER(DeptSales[Sales Amount]);FALSCH;ZÄHLENWENN(Name_in_system;DeptSales[Sales Amount])=0) results in an error (shown below)  *- Name_in_System is a list and it is not the cause of the error  How to reference the entire column in a conditional formatting rule?

Often, I create a sheet with conditional formatting, and set the cell ranges so that the conditional formatting rules are only applied once to a range of cells, e.g.   Make $A$1:$A$30 red and Make $B$1:$B$30 blue.   After inserting/deleting a number of rows and/or columns the conditional formatting rule set becomes very fragmented, with the same rules repeated for a different ranges. e.g.   Make $A$1:$A$2 red  Make $A$3:$A$4 red  Make $A$5:$A$9 red Make $A$10:$A$20 red  Make $A$21:$A$30 red ... Make $B$1:$B$2 blue  Make $B$3:$B$4 blue Make $B$5:$B$9 blue Make $B$10:$B$20 blue  Make $B$21:$B$30 blue ....   Is there a good practice way of preventing this, or am I doomed to cleaning up the rule sets manually when they get too messy?


Background: A friend once brought up the integral $\displaystyle\int_0^\infty\frac{1}{1+x^4}\,dx$ and asked me if I can solve it. Now, I converted it into a beta function and solved it using Euler's reflection property (Evaluated to $\frac{\pi}{2\sqrt2}$). But my friend and I are in high school and he didn't know the use of beta function  or most of the techniques that I had used there. He then challenged me to solve it using elementary high school metheds. My Efforts: I thought that since I already knew the value it was going to evaluate  to, I could brute-force my way to find this. I thought to use the sandwich theorem and take the bounds such that they evaluate to $\frac{\pi}{2\sqrt2}$. For the upper bound, I thought that since I want $\pi$ in it I could use the derivative of $\arctan(x)$ since it is also similar to function we are trying to integrate. $$\int_0^\infty \frac{1}{\sqrt2} \frac{1}{(x^2 + 1)}\,dx \geq\int_0^\infty \frac{1}{x^4+1}  $$ Now, the problem here is that I can't exactly prove that this inequality is true. I can definitely say that after a point $x\approx 1.3$ , $\displaystyle \frac{1}{\sqrt2}\frac{1}{1+x^2} > \frac{1}{1+x^4}$. But then from this I can't really comment on the inequality of the above integrals. Also I can't find a suitable lower bound for this. My Question:  Can we prove this inequality mentioned above, also what would be a suitable lower bound for this? Otherwise are there any better bounds I can use here (all knowing what the integral is going to converge to already) ? Or should I accept defeat as there is "no way" to solve this using elementary high school methods?  Any input appreciated..

I have to compute this integral $$\int_{0}^{\infty} \frac{dt}{1+t^4}$$ to solve a problem in a homework. I have tried in many ways, but I'm stuck. A search in the web reveals me that it can be do it by methods of complex analysis. But I have not taken this course yet. Thanks for any help.


We have a 10,000 base of vehicle mounted moving devices which report their GPS position on a time based schedule. All that data is currently being stored in our database for several business related purposes. We think It could also provide us a base for building our own maps, but we really don't know how could this be achieved.   There must be some way to aggregate individual data points (coordinates) into line segments, thus making streets.

Given a trajectory as a sequence of GPS points I would like to create a smooth linestring representing a path where a car drove. The data is stored in postgresql: the input trajectory in a table, where each row represents an individual GPS point, the output in a table, where each row represents the whole smooth tragectory. All points are stored in WGS84.  My approach for this would be the following:   implement everything in C++ retrieve the whole trajectory from the DB, convert it to UTM32N (as this is where the trajectories are coming from), flatten the points with the help of GDAL library compute a some sort of approximate spline linearize the approximate spline transform it back to WGS84 send the data back to Postgres   What would be the best tools/libraries to use for approximate splines and linearization?   Java/C++/Postgis solutions are preferable, as currently we are using only these subsystems.  I suppose this is a very common task people need to do in gis environment, however I haven't found close matches to similar questions on gis stackexchange.  An alternative would be to:   collect all points into linestring ST_LineToCurve  apply Bezier smoothening to the curve ST_CurveToLine


I'm a Sri Lankan student who came to study in Spain, but I"m here not with student visa, but Schengan visa ( a mistake happen in first place). my visa expires at 12th of Dec, but I have to Stay until end of January in Spain. since this is type C , spain embassy said I can not change it to type D being in a European country. Could you please tell me the options I have to get visa ( it's ok even to get the type C again ) from Dec to January without me going back to Sri Lanka and apply again. ( Sri Lanka doesnt have a spain embassy so I have to go to India , if I happen to go)

My daughter applied at the Italian Consulate in Philadelphia, and they gave her two entries for 20 days (we thought it was for 20 days each entry). She was in Italy 12 days, then went to England for 1 week and flew to Venice to take a 10-day cruise. She couldn't make it because they said she has only 8 remaining days, but she still has a land tour already paid this week.  What can she do? Can she extend the Schengen visa for 12 more days? Right now, she is in Madrid, but next week she has to fly from Barcelona to Paris to start with the tour. What would happen if she decides to take the tour with the expired visa? She is a US permanent resident.


I am a beginner in Quantum Mechanics so i am pretty new to the EPR paradox although i have heard about it a long time ago but finally studying in detail. And came across a doubt: Why the hidden characteristics in any particle as predicted by Einstein can not exist? If anyone can provide an  elaborated explanation !

I bet the automatic response to my question would be "Bell's theorem" and of course I am not disputing Bell's proof. I am however uncertain of one of his assumptions.  The so called "no conspiracy" assumption states that we somehow posses this magical thing called free will which makes us able to break free from the causal chain of events that make us measure the $y$-axis instead of the $x$-axis and so on in experiments. Obviously this makes little sense once reviewed under the light of logic. What this naturally implies is that, if a theory is fully deterministic, it is instantly super-deterministic.  Simon Kochen and John Conway published a theorem in 2009, , which simply-put states: either everything is deterministic (super-deterministic) or every particle has free will.  Among the few who accept this to the fullest extent is Gerard 't Hooft. He has proposed that what we call sub-atomic particles are really just templates and that there is a realm beneath the quantum where the true fabric of reality is "hidden". By accepting determinism he escapes Bell's theorem (due to not having to accept the "no conspiracy" assumption) and can construct a local, deterministic and realist hypothesis of reality. In Gerard 't Hooft's model there is cellular automata somewhere near the Planck scale which gives rise to the "emergent quantum mechanics".  This means that there exist no superpositions in objective reality, the cat is always either dead or alive, no collapse of wave functions, no branching universes, non-locality or retro-causality.  The big question for me is basically: Why do people have such a hard time accepting determinism? Some will object and say "oh but it's SUPER-determinism", but that makes no sense whatsoever, either everything is determined (determinism) or only somethings are (quasi-determinism). By accepting it we escape Bell's theorem. Bell himself was well aware of this and mentioned it a few times in interviews in the 80's.  I know some are concerned that if we accept complete determinism we can no longer do science because it's all a HUGE CONSPIRACY. Gerard 't Hooft has answered critics who bring up this here: , section 6.  Additionally, another author who has taken a deeper look into the worries of "conspiracies" in QM interpretations is Peter J. Lewis in his paper  (also ).  So to all of you who dismiss local hidden variables I ask: Why?


I have been given a request to re-size and up the resolution on a handful of images to be printed 40 in. x 30 in. to be hung on the walls in a new facility conference room where clients will see them. A lot of the images I've been given are pretty lo-res (10 in x 8 in, 96 dpi), so obviously when I try to re-size them to 40 in x 30 in, the quality decreases significantly.  So my question really is, do you think I need to get a photographer to go out and shoot new images (these are the only images they have on file), or do you think just upping the resolution in Photoshop on the images I've been given will do the trick?  If we need to re-shoot, what file size/format should as ask to receive from the photographer? And if I can just re-size what resolution do you think it should be in order fpr the images to look clear for viewing?

(This question is meant to be a resource to direct others to given that this is a common question.)  Given the task of creating an image that will be printed at a certain size, what pixel dimensions and resolution should I be setting my file at?


I was wandering whether time really "exists" or is it just a mathematical parameter used to describe how things change.

It seems to me that there is no such thing as time. There  is only movement in the universe and we compare our own movement to a different object to have a sense of time. It can be a clock or a atomic vibration.  Does this view of time work within the current framework of phsics?  Do physicists have an explanation/proof about time's existence?


Let $X,d$ be a metric space .Let $f:X\to \mathbb R$ be a continuous function.Define $G(f)=\{(x,f(x)):x\in X\}$.  Prove that $G(f)$ is homeomorphic to $X$.  My try:  Since $f$ is continuous then $G(f)$ is a closed set. To define a homeomorphism we need a  mapping $g:G(f)\to X$ .Can $g$ be defined as $g((x,f(x))=x$?i.e the projection map.  To check $g$ is a homeomorphism:  Let $U$ be closed in $X$.to show $g^{-1}(U)$ is closed in $G(f)$.Now $g^{-1}(U)=U\times f(U)$ how to show it is closed in $G(f)$??  Next to show that $g$ is a closed map.How to proceed here?  It will be great if someone could check if it is so.

Let $f: X \to Y$ be a function. The graph of $f$ is defined to be the set $G = \{(x, f(x)) : x \in X\}$. Prove that if $f$ is continuous then $G$ is homeomorphic to $X$.     an anyone suggest  me the process of solving this problem, thanks.


It's common knowledge that the universe has three spatial dimensions, and one temporal. But how can we be so sure? Physics tells us that vector forces act independently along different dimensions, so without a source of force along the fourth dimension, or with a component in the fourth dimension, nothing would ever pass out of our little slit of 3D space in a possibly 4D world. Moreover, some materials exhibit different levels of friction, or any other measure of directional "resistance," (using the term as an abstraction for every barrier to motion, physical, fluid and so on) differently along different directions. We could just be stuck on our little 3D slice of 4D universe.  How can we possibly know the world is indeed three-dimensional, especially considering models of two-dimensional motion work so well in our three-dimensional world when motion along the third dimension is heavily restricted?  Note: The question  is somewhat similar in that it asks if spatial dimensions exist at all, but is not a duplicate. I did my research.

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


I am trying to increase (or set to a default number) the amount of characters a textarea can have. I know there is a maxlength attribute for HTML5 but I am using an older version of HTML so this is not an option.  Is there any way to do this? What is the default maximum length of characters allowed in a textarea?

How to restrict the maximum number of characters that can be entered into an HTML <textarea>? I'm looking for a cross-browser solution.


I am building a classification model (let's say logistic regression) using 2 different data sets. The data sets do not come from the same population. Let's say data sets comes from different space-time coordinates (Asia in Fall vs North America in Winter). I have been told that simply mixing the data sets into one and applying a classification model is not right (closest thing I understood was concerns around bias). Are there any techniques or models that I may use to analyze these 2 data sets as one? Note that the variables/features all align (including the target variable, which is binary).

I am building a classification model (let's say logistic regression) using 2 different data sets. The data sets do not come from the same population. Let's say the data sets comes from different space-time coordinates (Asia in Fall vs North America in Winter). I have been told that simply mixing the data sets into one and applying a classification model is not right (closest thing I understood was concerns around bias). Are there any techniques or models that I may use to analyze these 2 data sets as one? Note that the variables/features all align (including the target variable, which is binary).


I was pouring water into a cup.  As the cup filled up, the height between the water in the cup and the spout decreased to about 3cm.  I was able to pour slowly such that the diameter of the falling water column was smaller than the diameter of a drop of water. Furthermore, when the water column contacted the cup's water, there was no splashing.  There were distinct bands that appeared in the water column, like the water column was varying in size.  How would you explain this phenomenon? Is it due to the slow pouring, so that the surface tension just manages to hold neighboring water droplets together?  Or is it that upon contact of the falling water with the water in the mug, waves are produced, which travel back up the water column, and upon equilibrium, appear as standing waves?

as we know, there are some perturbations on a falling jet which are always present and according to their wave number and the radius of the jet, they can grow and decay over time. so, imagine a jet which has those sort of long wavelength waves traveling downward on it, we put an obstacle on the path of the jet and then we would see this :    so, what exactly happens to those waves by the presence of an obstacle?   why have those waves been too larger in amplitude and too short in wavelength in presence of an obstacle?  This photo has taked by sayyedali.m.(  Qom)in Shahid qodosi high school


A week ago I contacted a potential supervisor with shared interests. He answered back on the same day, positively reflecting his will to cooperate and support my application. I replied to him on the second day with a draft of the aimed project. It has been a week since that email and there has been no answer or reply. Should I assume that he is no longer interested?! Or should I wait a bit longer?!

I recently joined a research group as a postdoc. I wrote the professor an email to ask quick but important questions including asking him when when he wanted me to start. It's been over a week and I haven't received get an answer. Other emails I've sent previously have also gone unanswered for long periods as well.   With that background, my question is: do professors sometimes (intentionally or otherwise) not respond to emails in a timely manner?


I only raise this question now as similar just happened to me, but I've witnessed this behaviour several times:   Somebody asks a question Person A answers Person B provides the same answer and links some time later Sometimes Person B receives upvotes from friends/etc. as soon as they answer Person C answers adding something constructive Person B Again copies the new information into their own answer   Sometimes Person B answers first but with no information or something far far wide of the mark, and then waits until somebody posts the correct answer to update their own. I've seen this happen before where Person B has had an outright wrong answer then 20 mins after person A answers, they delete their original answer and post Person A's answer again.  This doesn't seem like behaviour that should be tolerated, is it? Is there some way to flag this? (I'm asking in general, not because I plan to flag the newbie who just did this to me)

I am sure this scenario is familiar to all of you.  You click an unanswered question and after reading the question, you want to help and answer. After you answered, you remain the first and only answerer with a solution.  After 15-20 seconds from your answer posting time, another answer comes up, suggesting exactly the solution you have suggested, but with more text (not necessarily more detail).  After a minute, more answers pop up with, again, exactly the same solution you have suggested.  After an hour, your answer gets no votes, but the other answers each get at least 1 up-vote, and the one posted right after yours not only has the most votes, but is also accepted.  What would be an elegant solution to stop this? I am sure I am not the only one who is annoyed by this situation.  After speaking to others about this situation, one of them happened to mention in passing about hovering the mouse over the time of the posting to see the accuracy of the time posted, which I did not know about.


I have two groups that are particularly unequal 111 vs 29 persons in each group and i would like to know if the Mann-Whitney U test works fine in this case also. I know from previous discussions that when the two groups are not similar 1:2 ratio this works fine. But what about an almost 1:4 allocation?

I have two groups of independent samples whose means I want to compare. The data comes from a distinctly non-normal distribution. (Unimodal, but heavily right skewed).    Let's say that one group (Group A) has 14,000 observations and that another group (Group B) has 700 observations. Thus each group has a decent amount of observations (we are not talking about 2000 versus 5 here).   I am of the opinion that this strong unbalance in the group sizes will not make the Mann-Whitney-Wilcoxon Test any less applicable, however a colleague is suggesting that we randomly sample 700 observations from Group A so that our group sizes are perfectly balanced. He feels that the unbalance of the groups is making the test fail to find the "correct" result. (Where correct result means "result he wants," i.e. that the two groups are statistically significantly different).   As I said, I think that having highly unequal groups does not cause the Mann-Whitney-Wilcoxon Test to somehow stop working.   As far as I understand it, I do believe that the size of the smaller group will have implications for the power of our test, but even there, I am thinking that we probably have at least a decently sufficient sample size for Group B.   Will this highly unbalanced data somehow invalidate my analysis?


These are a defining and a non-defining relative clause :-     (A)  He deleted the picture that upset me.       (B)  He deleted the    picture, which upset me.   Could you please explain the difference in meaning of these sentences?

What is the difference between the words which and that?  For example I have the following sentences:   “I have a car which is blue.” “I have a car that is blue.”   Are there any rules specifying usage of which and that?


What is the value of this series? $$ \sum_{k=1}^\infty \frac{1}{k^k} = 1 + \frac{1}{2^2} + \frac{1}{3^3} + \frac{1}{4^4} + \cdots $$  I found the answer to be equal to $1.29$ by converting the sum to an integral.

Earlier today, I was talking with my friend about some "cool" infinite series and the value they converge to like the Basel problem, Madhava-Leibniz formula for $\pi/4, \log 2$ and similar alternating series etc.  One series that popped into our discussion was $\sum\limits_{n=1}^{\infty} \frac{1}{n^n}$.  Proving the convergence of this series is trivial but finding the value to which converges has defied me so far. Mathematica says this series converges to $\approx 1.29129$.  I tried Googling about this series and found very little information about this series (which is actually surprising since the series looks cool enough to arise in some context).  We were joking that it should have something to do with $\pi,e,\phi,\gamma$ or at the least it must be a transcendental number :-).  My questions are:   What does this series converge to? Does this series arise in any context and are there interesting trivia to be known about this series?   I am actually slightly puzzled that I have not been able to find much about this series on the Internet. (At least my Google search did not yield any interesting results).


Let $M_{32}$ be vector space with inner product of $AB$ given by $\text{tr}(B^TA)$.  The question is to find a non-zero matrix B orthogonal to $$A=\left[\begin{matrix} 1 & 2 \\ 3 & 4 \\ 5 & 6 \end{matrix}\right]$$    Any hints as to how I can start this?

The question is to find in the space $\mathrm{Mat}_{3\times 2}(\mathbb{\mathbb{R}})$ a non-zero matrix that is orthogonal to $$ A= \begin{pmatrix} 1 & 2\\       3 & 4\\       5 & 6\\ \end{pmatrix}.$$  The inner product is $\langle A, B \rangle = tr(A B^T) = tr(B^T A)$.  Any hints or clues on how to start this?


Per my reading of  hotness score of successive questions from same site is penalised by 2%. Taking into account that there could be no more than 5 questions from the same site this means that maximum possible penalty is 8%. I am looking for an explanation of how this is supposed to make a meaningful impact, because at the first glance, it looks too small for that. To have a better idea of what possible impact it could have I sampled score of several questions in some snapshot of hot list. Hotness score values I observed were 46.422, 17.269, 10.194, 7.485, 5.825, 4.658, 3.891 for questions ##1, 16, 31, 46, 61, 76, 91 respectively (for that sample I simply picked top question from each page of the hot list configured with ). Distribution of the scores in above sample suggests that even maximum of 8% would "push" the penalised questions less than 10-15 places down in the list, how is this supposed to make a difference (particularly since questions from the list are anyway randomly shuffled before getting displayed in the sidebar)?  Alright, that limit of 5 is relatively recent thing - but closer look at sample distribution of scores suggests that even without it, even if system allowed 10-20 questions from same site like it did before, the effect of penalty would be negligible. Max penalty in this case would be 20-40% - meaning that question would still have solid chance to stay in the list and get shuffled to sidebar - and this is the most penalised case, for other questions from same site the difference would be even less than that. I really don't understand how this parameter is intended to work.

This feature request is a follow-up to  As was pointed out in the above question, currently this adjustment fails to make any reasonable impact (neither positive nor negative).  hotness score of successive questions from same site is penalised by 2%. Taking into account that there could be no more than 5 questions from the same site this means that maximum possible penalty is 8%... it looks too small... closer look at sample distribution of scores suggests that... even if system allowed 10-20 questions from same site like it did before, the effect of penalty would be negligible...  The answer there explains how it used to work  and how it was eventually broken many years ago.  it was established really long time ago... Back then, the UI displaying hot questions was totally different - there was rather small scrollable dropdown... This whole thing broke badly right after hot questions moved to sidebar because there was no scrolling involved anymore and soon after that randomizing buried it completely because order in the list didn't matter anymore...   Assuming that the above analysis is correct, I think we’d better do something about this confusing and useless tweak.  Specifically, I propose to increase the value of this parameter to make it resemble the initially intended effect. I think it has to change to at least 10% instead of current 2%, or maybe even to 20-30% (in latter case penalising would probably better change to geometric progression instead of current arithmetic).  Alternatively — given the fact that, over many years, the system has proven to work just fine without it — we could just remove this parameter and simplify things to make it easier to understand and manage how the system works. This thing was essentially disabled for over six years and the sky didn't fall. I think this means it is safe to completely get rid of it.


It seems that "reopen" should be changed to "leave open" in Close Votes queue tips box:    since there's no option as "Reopen" but "Leave open" has.

The Public Platform team is continuing to work towards  and we’re here today to announce a new onboarding experience for the review queues. In the  (), we learned that each queues’ instructions could be easily misinterpreted and additional information was difficult to find. Without proper guidance or context, new reviewers would contribute inconsistent reviews and risk having their review privileges suspended. With this release, our goals were to 1) better highlight the review privilege and 2) provide upfront instruction and guidance for successful reviewing. New privilege announcements Community moderation is a significant aspect of Stack Overflow and the Stack Exchange sites. We want users to be aware and familiar with this newly earned privilege, but also celebrate the opportunity to contribute to the community in a unique way.  Many users were discovering the review queues by chance. Once the privilege is earned, a new review queue icon with a red alert would appear in the top-right part of the navigation. We are adding a popover to bring more attention to this easy-to-miss icon. We will also be adding notices for when users earn access to other, higher reputation queues. Additionally, new reviewers will also receive an email notification about the newly earned privilege. They will only get the email if they earn the privilege and don't perform a review within 24 hours (anyone who doesn't want to receive email notifications like this can visit their  and turn off "Tips and Reminders"). We are also showing a popover to users who earned access to review queues in the past, but have never done a review or haven't reviewed in the last 30 days. This popover is only appearing for the next 90 days. The goal is to engage users who may not have interacted with the queues since we made  and . Welcome banner  If a reviewer clicks “Learn more” on the on-page popover or goes to the review queue home page (/review), they’ll be greeted with an onboarding message with general information about the review queues. Informational modals  Queue-specific modals will appear upon page load as you visit each queue. They summarize and highlight important aspects and tips about reviewing in a particular queue. This information can be revisited at any time by clicking “Learn more” under the page header. Feedback As always, please leave your feedback and any bugs you may discover related to this release below this post. We will be monitoring this post for the next few weeks (May 4, 2021). After May 4th, please report any further issues as new questions.


We are running a search engine and are seeing a huge amount of fake search queries coming in over the last days from thousands of IP addresses. There is no real pattern in terms of queries text or IP range. It seems that there is a bot network trying to bring our down. Currently we're seeing about 30 fake queries per second and it's increasing.  We tried to set up cloudflare, but it did not really help. We could try to block out bad traffic with Captchas, but this could decrease usability for our real users.  Does anybody have an idea how we could handle this? We're running on AWS with Route53.

This is a  about DoS and DDoS mitigation.   I found a massive traffic spike on a website that I host today; I am getting thousands of connections a second and I see I'm using all 100Mbps of my available bandwidth.  Nobody can access my site because all the requests time out, and I can't even log into the server because SSH times out too!  This has happened a couple times before, and each time it's lasted a couple hours and gone away on its own.  Occasionally, my website has another distinct but related problem: my server's load average (which is usually around .25) rockets up to 20 or more and nobody can access my site just the same as the other case.  It also goes away after a few hours.  Restarting my server doesn't help; what can I do to make my site accessible again, and what is happening?  Relatedly, I found once that for a day or two, every time I started my service, it got a connection from a particular IP address and then crashed.  As soon as I started it up again, this happened again and it crashed again.  How is that similar, and what can I do about it?


I found there is a similar question . Forgive me since I don't quite like the answer given there—the font, the format, etc.  What I want is something like the one given . I think it's of the same kind as Michael Hopkins's (one can search YouTube to see Michael Hopkins's slides).  I'm very grateful if anyone can tell how to make that kind of , or better, give a template for the slides as an answer. I even don't know if it is made by LaTeX; so if it is produced by some other thing, please tell me what it is, then I can learn how to use it.  (I also want to know how to make the beautiful pictures like the sphere, torus, higher genus surfaces etc. with various colours and submanifolds etc.)

Is there an easy way to draw a contour image of torus below with tikz? Or for that matter with any other graphics package.


i need to pass this id  <a href="edit.php?id=<?php echo $row['user_id']; ?>">  in here <?php if (isset($_POST['id'])) {      $id = $_POST['id'];  } else {      echo "user not find";      die();  }   its echo "user not find". why?

What's the difference when using GET or POST method? Which one is more secure? What are (dis)advantages of each of them?  ()


Last night I was working on installing vsftpd on my Ubuntu 12.10 server. I shutdown last night and when I booted up this morning I seemed to have lost the abilities to sudo anything. It just says, "** is not in the sudoers file. This incident will be reported." Now I wasn't messing with any sudo files, just /etc/vsftpd.confg and /etc/shells. So how did I seemingly lose sudo ability? I'm rather new to Linux in general, but I'm picking it up quick.

I clean-installed Ubuntu 11.10 today, and then installed VirtualBox.  This required me to add myself to the vboxusers group, and since 11.10 seems to no longer have a graphical app to add users to a group, I ran the following command:  sudo usermod -G vboxusers stephane   This is a problem.  I now see what I should have run instead is:  sudo usermod -aG vboxusers stephane   The end result is I'm no longer in the groups I should be in.  Including whatever group is required to run "sudo".  When I run any command as sudo now, I get the following:  $ sudo ls [sudo] password for stephane:  stephane is not in the sudoers file.  This incident will be reported.   Is there a way to fix this, or do I need to re-install from scratch again?