@username in comments doesn't autocomplete for some users When I want to address a specific users in the comment section for a question I use @username, sometimes after typing first letters of the username it shows up an autocomplete box but sometimes it doesn't show it up for another user.  I don't know the reason of these different behaviors! and whatever the reason is I think shouldn't be related to auto-complete feature because I just think this is a bug
How do comment @replies work? How do the comment replies (aka &quot;pinging users&quot;) work?  Who can I send an @reply to? How do I respond to a specific user when entering my comment? Will they be notified? What do people mean when they talk about &quot;pinging&quot; another user?  Related:
Prove $f=1+x+x^2+x^3+\cdots+x^n$ has no multiple roots. Prove $f=1+x+x^2+x^3+\cdots+x^n$ has no multiple roots.  My attempt:  Consider the polynomial $g=(x-1)(1+x+x^2+x^3+\cdots+x^n)$  As $f\mid g, g$ all the roots of $f$ are roots of $g$.  This means I have to prove the statement:  If $c$ is a multiple root of $f \Longrightarrow c$ is multiple a root of $g$.  Equivalently:  If $c$ is not a multiple root of $g \Longrightarrow c$ is not a multiple root of $f$.  I'll try to prove this last statement:  Suppose $\exists c$ such that $c$ is a multiple root of $g$, then   $$g(c)=0 \implies g'(c)=0$$  $$ g=(x-1)(1+x+\cdots+x^n) \implies  g'=nx^n $$ $$ g'(c)=nc^n=0 \implies c=0 $$ But  $$ g(0)\neq 0 $$ And we've found the contradiction: $\not \exists c: g(c)=g'(c)=0$. Then $f$ has no multiple roots.  Is this correct?   Also: Assuming this is correct, is it possible to prove $\sum_{k=0}^n \frac {x^n}{n!} $ has no multiple roots in a similar manner? LIGO flawed by the identical expansion of laser wavelength and arms in presence of a gravitational wave? , Laser Interferometer Gravitational-Wave Observatory, is a large-scale physics experiment aiming to directly detect gravitational waves. The device measures the phase shift laser beams.  If I understand this well, the measurement assumes that a suitable gravitational wave reduces and prolongs one of the tubes and the extension will take effect in the phase-shifting laser beams.  But I think if there's a gravitational wave that passes through it, it will affect everything, even the laser beam. This means that when the wave lengthens or shortens the tube, it also lengthens or shortens the wavelength of the laser beam.  In my opinion, therefore, this device does not work. Or am I wrong? Why is there no chat in the footer on Stack Overflow like on other sites? Can it be assumed a evaluation order of the function parameters when calling it in C ? According to the following program, it seems that there is not a particular order when I executed it.   #include &lt;stdio.h&gt;  int main() {    int a[] = {1, 2, 3};    int * pa;      pa = &amp;a[0];    printf("a[0] = %d\ta[1] = %d\ta[2] = %d\n",*(pa), *(pa++),*(++pa));    /* Result: a[0] = 3  a[1] = 2    a[2] = 2 */     pa = &amp;a[0];    printf("a[0] = %d\ta[1] = %d\ta[2] = %d\n",*(pa++),*(pa),*(++pa));    /* Result: a[0] = 2  a[1] = 2     a[2] = 2 */     pa = &amp;a[0];    printf("a[0] = %d\ta[1] = %d\ta[2] = %d\n",*(pa++),*(++pa), *(pa));    /* a[0] = 2  a[1] = 2 a[2] = 1 */  } Assume you have some objects which have several fields they can be compared by:  public class Person {      private String firstName;     private String lastName;     private String age;      /* Constructors */      /* Methods */  }   So in this example, when you ask if:  a.compareTo(b) &gt; 0   you might be asking if a's last name comes before b's, or if a is older than b, etc...  What is the cleanest way to enable multiple comparison between these kinds of objects without adding unnecessary clutter or overhead?   java.lang.Comparable interface allows comparison by one field only Adding numerous compare methods (i.e. compareByFirstName(), compareByAge(), etc...) is cluttered in my opinion.   So what is the best way to go about this? How to parseInt a string with leading 0 Use of a semicolon before and comma after "however" Several years ago, a previous boss told me to use a semicolon and comma with the word "however".  I've always questioned this and would like to know if the following random sentences are using the correct method.        Our plane was delayed overnight; however, the airlines reimbursed us for lodging.   It looks as though he's upset; however, she told me he always has that look on his face.   I want to find him a nice gift; however, I am a broke until payday.      Normally I would use a less "wordy" sentence in casual writing, but hopefully the example will suffice.  For example, on number 3 I would usually type:      I want to get him a nice gift, but I'm broke until payday. I am new to Force.com and trying to learn some concepts.  Currently I am using Single Email Message to send my emails, but I need to change that to mass email, but I don't quite understand how to do that.   I have also created a Visualforce email template, which I would like to use, but it doesn't seem to work.   It would be great if someone could help me out.  //email_disease_map contains pairs of email address and disease ID for (Id id : email_disease_map.keySet())   {     Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();     String[] defaultAddresses = new String[] {'id@test.com'};      List&lt;String&gt; toAddresses = new List &lt;String&gt; (email_disease_map.get(id));      if (!toAddresses.isEmpty())       {         //set addresses for email to be sent         mail.setToAddresses(defaultAddresses);         mail.setCcAddresses(toAddresses);         mail.setTemplateId(Notification);         //set up remaining email         mail.setReplyTo('test@mail.com');          mail.setSenderDisplayName('Ms Test');          Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });       }  } Cannot select text in Safari address bar How are NFL matchups determined for each season? During the 2012 NFL Season, the Pittsburgh Steelers and Baltimore Ravens play each other in weeks 11 and 13, two weeks (in both NFL schedule and time) apart. To me, that seems too close for comfort.   I do know that teams play other teams in their division twice. How does the NFL schedule procedure work? I have a mathematical problem with the following formula. The goal is to transform this equation to have a seperated real and imaginary part. I have already done this with several other equasions, but for this particualar one I don't know where to start.  I dont expect you to do the complete work of transforming for me, it would already be very nice if you could give me a hind on how you would start.  Thank you in advance!  C||RLC      This is my current progress:    My question is:  How can I get rid of the imaginary part jωC2*R?  When the denominator is completely real I can just split up the formula and have an imaginary and a real part. Count where any 3 columns have values (not null) What happens when I run the command cat /proc/cpuinfo? What happens when I write cat /proc/cpuinfo. Is that a named pipe (or something else) to the OS which reads the CPU info on the fly and generate that text each time I call it? Can you help me with my software dependency issue? This is a  about Compile Dependencies and Package Management.    I have a question regarding compiling ports/software or installing RPMs on my *nix server.  When I try to do this I receive lots of messages about missing dependencies.  Can the Server Fault community please help? PythonTEX not working on current Overleaf compiler Is there a way to make PythonTEX compile as of today in Overleaf V2 ?  \documentclass[]{article} \usepackage[utf8]{inputenc} \usepackage{pythontex}  \begin{document} \begin{pyverbatim} def calc_ellipticity(theta, delta):     theta = np.deg2rad(theta)     psi = np.arcsin(np.sin(2*theta) * np.sin(delta))/2     return np.tan(psi) \end{pyverbatim} \end{document}   Compiling gives : ? PythonTEX ? Why does "touch -a" also set the ctime? Is it touch(1) from coreutils-8.4-37.el6.x86_64 or my brain which is broken?  $ touch abc $ LANG=C stat abc   File: `abc'   Size: 0               Blocks: 0          IO Block: 4096   regular empty file Device: fd04h/64772d    Inode: 10485773    Links: 1 Access: (0664/-rw-rw-r--)  Uid: (3060399/ nodakai)   Gid: (  418/   quant) Access: 2016-10-14 18:42:06.189751847 +0800 Modify: 2016-10-14 18:42:06.189751847 +0800 Change: 2016-10-14 18:42:06.189751847 +0800 $ touch -a abc $ LANG=C stat abc   File: `abc'   Size: 0               Blocks: 0          IO Block: 4096   regular empty file Device: fd04h/64772d    Inode: 10485773    Links: 1 Access: (0664/-rw-rw-r--)  Uid: (3060399/ nodakai)   Gid: (  418/   quant) Access: 2016-10-14 18:42:17.374235446 +0800 Modify: 2016-10-14 18:42:06.189751847 +0800 Change: 2016-10-14 18:42:17.374235446 +0800 $ touch --help | grep 'access time'   -a                     change only the access time   As you see, it was not only atime but also ctime which was updated by touch -a !?!?  The filesystem is ext4 over LVM if that makes any differences. How to open pdf file in Windows Phone 8? I have a character playing a multiclass Barbarian/Monk. Does the resistance from rage combine with Deflect Missiles to negate the damage and make the reaction attack? Why would layout_width="wrap_content" take up the entire width of the screen? Difference in output between SAS's proc genmod and R's glm I'm trying to replicate a model fitted in SAS in R but the fit I'm getting gives me slightly different coefficients and standard errors.  Data:  testdata &lt;- data.frame(matrix(c("f","Test", 1.75,   16, 0,  16, 0,  1,  1, "m",    "Test", 1.75,   15, 1,  16, 6.25,   1,  0, "f",    "Test", 2.75,   4,  12, 16, 75, 1,  1, "m",    "Test", 2.75,   9,  6,  15, 40, 1,  0, "f",    "WHO",  1.75,   15, 1,  16, 6.25,   0,  1, "m",    "WHO",  1.75,   14, 2,  16, 12.5,   0,  0, "f",    "WHO",  2.75,   2,  13, 15, 86.6667,    0,  1, "m",    "WHO",  2.75,   3,  13, 16, 81.25,  0,  0 ), ncol=9, byrow=TRUE)) names(testdata) &lt;- c("sex", "vaccine", "dose", "not_p", "para", "n", "pct",                       "vacnum", "sexno")   SAS:  proc genmod data=model_data; class sex; model para/n  = dose sex vacnum    /dist=bin    link=logit   type3; run;  Analysis Of Maximum Likelihood Parameter Estimates  Parameter   DF Estimate Std Error Wald 95% Conf Lim Wald Chi-Square Pr &gt; ChiSq  Intercept   1 -9.4020   1.6220    -12.5810  -6.2230  33.60           &lt;.0001  dose        1  3.9208   0.6460      2.6546   5.1870  36.83           &lt;.0001  sex f       1  0.5574   0.5184     -0.4587   1.5735   1.16           0.2823  sex m       0  0.0000   0.0000      0.0000   0.0000    .              .  vacnum      1 -1.3221   0.5483     -2.3967  -0.2475   5.81           0.0159  Scale       0  1.0000   0.0000      1.0000   1.0000        R:  testdata$sexno &lt;- as.factor(testdata$sexno)     a &lt;- contr.treatment(2, base = 1, contrasts = TRUE)  contrasts(testdata$sexno) &lt;- a  fitreduced &lt;- glm(para/n ~ dose + as.factor(sex) + vacnum,                    family=quasibinomial(link="logit"), data=testdata)  coef(summary(fitreduced))                    Estimate Std. Error   t value    Pr(&gt;|t|) (Intercept)     -9.4013750  1.7613982 -5.337450 0.005935450 dose             3.9173794  0.7001133  5.595351 0.005007179 as.factor(sex)1  0.5704671  0.5568436  1.024466 0.363525300 vacnum          -1.3336100  0.5887552 -2.265135 0.086189704   I believe I have the right contrasts to give me a type III SS but there is a small discrepency in values, have a missed something here?