Showing DF Times S-squared / sigma-squared is a chi-square
How is MSE divided by $\sigma^2$ always a chi-square distribution?
Are Stack Overflow people *still* nice? The title is a reference to . We had the good fortune, to start this experiment with a really positive culture and have managed to hang onto it through vast growth and several fairly bitter internal arguments. But that does not guarantee we'll keep it forever. Lately I've had a unscientific feeling that Stack Overflow has been a bit rougher on newbie mistakes. The actual composition of this question was triggered by the comment thread on  (now with pending delete votes, so it is in danger of being 10k only). The  currently has 3 reputation points and has been a member for all of two days. The question bear the obvious (to me, at least) hallmarks of being written by a non-native English speaker with a shaky grasp of the tongue, and it is a rather simplistic question that could be answered fairly easily by Google. Question body:  Sir, I am mc student, I have knowledge in c,c++,J2EE. I want to ask you should I command in Linux with J2EE. Is it worth?  Instead of trying to improve the question, to discern exactly what the OP meant, or explaining how the question should be improved we get this comment thread instead (without wanting to call out these posters in particular, this was just the thread that got be off my duff):  2 Can you elaborate? – Dave McClelland 21 hours ago 1 Absolutely yes! If it can run on your Blu-Ray player, imagine the possibilities it can do on Linux. – The Elite Gentleman 21 hours ago 1 Basically, it's as worth as running Java on any other platform. – Alexander Gessler 21 hours ago 1 @The Elite Gentleman, You can try run it on your sim-card too) – Stas Kurilin 21 hours ago 1 @STas Kurilin, really? What heapspace size must I give? sarcastic laugh – The Elite Gentleman 21 hours ago 1 @The Elite Gentleman I don't know. But there are some) See for details oracle.com/technetwork/java/javacard/overview/… – Stas Kurilin 21 hours ago @The Elite Gentleman, you're absolutely right given a full fledged desktop machine with Linux, Java would run so fast his program could go back in time and rescue whales from extinction. – Quaternion 21 hours ago @Stas Kurlin, if you have a program that runs on a sim-card isn't it hard to get output? I've always found processorless environments problematic. – Quaternion 21 hours ago @Quaternion - It was a joke) I've newer wrote such programs. But, I think there should be some processor. – Stas Kurilin 20 hours ago @Stas Kurlin, I was joking too, but I have to apologize after reading that page you liked to. You can run Java off a smart card... that's crazy and cool. +1 on account of good learning for the day. – Quaternion 20 hours ago @Quaternion Thanks. I heard about this stuff several weeks ago. Java at a sim card is a really cool argument) – Stas Kurilin 20 hours ago @Quaternion, lol, without having to worry about Segmentation Faults along the way. – The Elite Gentleman 19 hours ago  I've been leaving comments on threads like this from time to time, asking them to be a little more forgiving, but that is a drop in the bucket. Nothing flag-worthy here, but not a &quot;nice&quot; as things once were. There is very little effort to understand what the question may really be, nor why to explain why the question has been closed, what other resources exist, or how that decision could be reversed. With a brand new user who probably has a hard time with English. Ouch. Do we need an official re-iteration of &quot;Be nice.&quot;? Is there something else we can do to encourage our big city to keep the small-town feel we grew up with? arcpy.env.overwriteOutput = True not working for one dataset $1+a$ and $1-a$ in a ring are invertible if $a$ is nilpotent Modifying agsm.bst package bibliography output I would like to change the URL output from:  URL: the html link  into:  [Online]URL: [Accessed on]  I am using:  \usepackage[comma]{natbib} \bibliographystyle{agsm} Many sysv init scripts used a corresponding file in /etc/default to allow the administrator to configure it. Upstart jobs can be modified using .override files. How do I override or configure systemd units, now that systemd is the default in Ubuntu? Given a number, how do I discover in what table and column it could be found within? I don't care if it's fast, it just needs to work. Can I watch the progress of a `sync` operation? How to separate iMessages with shared Apple ID? My son and wife both have iPod Touches and I have an iPhone. We all used the same Apple ID and turned on iMessage. Both my son and wife were getting texts from my friends and my work on their iPods, I think because my cell phone number was linked to the Apple ID.  If I just turn off iMessage on my iPhone, will that solve the issue? A set of elements in a reduced unity ring Let $(A,+,\cdot)$ be a unity ring with the property that if $x \in A$ and $x^2=0$ then $x=0$. Consider the set $M=\{a\in A | a^3=a\}$. Prove that:      a) $2a\in Z(A)$, $\forall a\in M$, where $Z(A)$ denotes the centre of the ring $A$;   b) $ab=ba$, $\forall a,b\in M$.   My attempts revolved around the fact that an idempotent element in a reduced ring is central. So, since for $a\in M$ we have that $(a^2)^2=a^2$, it follows that $a^2\in Z(A)$, $\forall a\in M$. The next thing I wanted to use in order to solve a) was that $Z(A)$ is a subring of $A$, so if I had proved that $(a+1)^2 \in Z(A)$, $\forall a\in M$, then we would have reached the desired conclusion. However, I couldn't prove this and I honestly doubt that it is true. Another idea that I had was to prove that $M$ is a subring of $A$. Of course, this didn't work out because I cannot even prove that $M$ is closed under addition. Again, I don't know if this is true and it most likely isn't. As for b), I think that a) should be of use, but I don't know how. It is a well-known problem that a ring with $x^3=x$ for any $x$ in that ring is commutative, but since $(M,+,\cdot)$ is almost definitely not a ring, this doesn't help. EDIT: Is there any chance that this question is simply wrong? I tended to believe this before asking it here too, but since nobody has made any progress on it until now I am even more inclined to think so. Central Pennsylvanian English speakers: what are the limitations on the "needs washed" construction? Linear Combination of Random Normal Variables In order to prove that the linear combination of two independent normal distributions(say Z=X+Y) is normal, i am using their MGFs to show that the linear combination also has a similar mgf. This works okay when Z = X+Y. But when Z=X-Y, i run into trouble :  E[$e^{tZ}$] = E[$e^{t(X-Y)}$] = E[$e^{tX}$]E[$e^{-tY}$]  Now i cannot put this as $M_{x}$(t) * $M_{y}$(t) because of the negative sign. While CtrlX works fine in vim under windows, CtrlA selects all (duh).  Is there a way to increment a number with a keystroke under windows? VB6 compiling via console (vb.exe) compatibility issue on 64bit (works on 32bit?) Load external php library in custom module I’ve read a lot of topic on this but i can’t figure why it is not working for me.  I’ve built a custom module. It is working fine since return $output; in my controller class is working : I can see in front-end a page with my custom html.  I’ve written a script outside Drupal in order to test. Basically, i connect to a webervice and retrieve all the datas. It’s working fine.  Now, i want to execute that script inside the controller class.  I need to load an external php library to instantiate an object.  In my test php file (outside Drupal) a simple require_once is working.  require_once('nusoap.php');   But it is not working in my controller class.  So, i’ve activated the library module and do :  $path = libraries_get_path('nusoap') . DRUPAL_ROOT . '/modules/contrib/webservices_tr/webservices_dc/src/Controller/nusoap.php';  require($path);   It’s still not working.   Error message indiquactes :     Error: Class 'Drupal\webservices_dc\nusoap_client' not found   I’m sur the file path is correct because if i do this, i can see the content of the file.  echo file_get_contents(DRUPAL_ROOT . '/modules/contrib/webservices_tr/webservices_dc/src/Controller/nusoap.php'); die();   I’ve also tried this :  in nusoap.php (where there is the class i need to include),    namespace Drupal\webservices_dc;   and in module controller class :  use Drupal\webservices_dc\nusoap_client;   But it is still not working.  Finally, i’ve copied the content of the external php library inside the module controller and it is working.  So i’m nearly sure the issue is related to the loading of that external library.  What is the correct way to load external php library (and wait it is fully loaded) in order to use it in a custom module ? Can't view deleted questions via Android app Given a matrix $A \in R^{n \times n}$ which is normal ($AA^H=A^HA$ where $A^H$ is hermitian of $A$) and nilpotent ($A^k=0$ for some $k$). Now we need to show that $A=0$. (This is essentially exercise 5(b) in sec. 80 on p.162 of Paul R. Halmos' Finite-Dimensional Vector Spaces.) I tried to show in the following way, we know that, $AA^H=A^HA$ pre-multiply by $A^{k-1}\implies A^kA^H=A^{k-1}A^HA$ Now, we have $0 = A^{k-1}A^HA$, since $A$ nilpotent. I am not sure how to proceed from here to show $A=0$. Can someone help me in this problem? By accident, I used rm on a file I didn't want to delete. Is there a way that I can get it back under Linux? I am generating a fairly large index of .txt, .tex, and .pdf files. This process has worked for a long time, and the size of the index is not the issue. I have added logic to insert additional links in the index and now am running into:  TeX capacity exceeded, sorry [save size=80000]  Questions:  What are the typical causes of this kind of problem, and any suggestions on how to determine the cause of this. Can the save size be increased?  Of course any solution that just allows me to increase the save size would be preferable if it works, the first question is only important if the size can't be increased or I run into this problem again. Notes:  Generating smaller indices seems to work just fine, only when I attempt to generate the entire index do I run into problems, so coming up with a MWE will be difficult. Text formatting now allowed in comments (List of proven and disproven abilities) Borel-Cantelli-related exercise: Show that $\sum_{n=1}^{\infty} p_n < 1 \implies \prod_{n=1}^{\infty} (1-p_n) \geq 1- S$. This is supposed to be related to the  (my justification for the independence tag). In Williams' Probability with Martingales, 2BCL is proven and then the following is given as an exercise:  Prove $S \doteq \sum_{n=1}^\infty p_n &lt; \infty \implies \prod_{n=1}^\infty (1-p_n) &gt; 0$ assuming $0 \leq p_n &lt; 1$. Hint: Show that $S &lt; 1 \implies \prod_{n=1}^\infty (1-p_n) \geq 1 - S$.   Proving the hint: I tried to find $\{a_n\}$ s.t. $$\prod_{n=1}^\infty (1-p_n) \geq \prod_{n=1}^\infty e^{a_n} = e^{\sum_{n=1}^\infty a_n} \geq 1 - \sum_{n=1}^\infty a_n \geq 1 - S &gt; 0$$ That is, find $\{a_n\}$ s.t.: 1a. $1 - p_n \geq e^{a_n}$ 1b. $a_n \leq p_n$ I thought of $a_n = \ln(1-p_n)$ (a reason why $p_n &lt; 1$, I guess) Is that right? Edit: Actually, assuming my proof is right, is $S &lt; 1$ used in the proof? If so, where?  From Williams book: