Does linear regression assume all variables (predictors and response) to be multivariate normal?
What if residuals are normally distributed, but y is not?
I was playing terraria today, and my friend came and deleted the my world.  Is there a way for me to recover my world? Assume $T \in \mathbb{R}^{d\times d}$. Let $\rho(T)$ be the spectral radius of $T$ and $\rho \ge 0$. Prove that  $\rho(T) &lt; \rho$ if and only if there exists a $P \succ 0$ satisfying $T^TPT - \rho^2 P \prec 0$.  I can prove the Necessity: If $P = I$, for any $x \in \mathbb{R}^d$,   \begin{equation} x^T T^T P T x - \rho^2 x^T P x = \| Tx \|^2 - \rho^2 \| x\|^2 &lt; 0 \end{equation} so $T^T PT - \rho^2 P \prec 0$  I get stuck in proving the Sufficiency. An alternative to translation for non-English speakers? How to run ffmpeg from command line in android Why is my StackOverflow with an indent and doesn't have reputation Well everything is in the title. Why is StackOverflow showing up with a indent and why don't I see my rep next to it like on the other websites. How do I figure out what package something is in without resorting to Google? I often find myself wanting to install something, but I'm unsure of what package it's in. This is a very common occurrence for me:  $ make html sphinx-build -b djangohtml -d _build/doctrees   . _build/html make: sphinx-build: Command not found make: *** [html] Error 127  $ sudo apt-get install sphinx E: Unable to locate package sphinx  $ sudo apt-get install sphinx-build E: Unable to locate package sphinx-build   googles  $ sudo apt-get install python-sphinx   Is there a better way? How does a Windows 10 'digital license' activate the OS? I have added a background image to the world settings. However, it has disappeared from my 3D view and only shows when I view the scene from the camera. Does anyone know if there is something I can do to make it reappear? Placement of question mark when terminal quote has no question mark but sentence does Possible Duplicate:          If I'm quoting something someone said and the quote does not have a question mark, but I want to end the sentence with a question mark, would it be     Are you sure she said "Spicy?"   or       Are you sure she said "Spicy"? Is it time to be rid of automatic down votes on certain closed questions? Brace expansion not working in a script Cross-reference packages: which to use, which conflict? In my assignment I have to prove that the following function doesn't have a limit:  $$f(x)=\frac{x}{x-\lfloor{\sin x}\rfloor}$$ when $${x \to 0}$$  In other words, I have to prove that for every $\delta$ such that $0&lt;|x-{x_0}|&lt;\delta,$ $|f(x)-L|&gt;\epsilon$.  In fact, I don't even know how to start. Do I choose my $\delta$? I know that the sin function has certain values that's supposed to help me. How do I use it?  I have to prove this by definition, so I can't use limit arithmetic for example  Thanks. Ownership of .Xauthority transferred to root Somehow, while playing around with LightDM and Webkit Greeter, the ownership of the .Xauthority file in my home dir was given to the root user and I couldn't login because I hadn't the privilegues to lock the file.  I was able to regain ownership of the file and I could login again. (After several hours of reinstalling LightDM and it's greeters)  So now everything's working fine again. But I'd like to know how this happened. Is this a bug in LightDM or Webkit Greeter or something else? How to render text pixel-perfectly with subpixel antialising with Illustrator? Concurrent requests limit exceeded - how to find the problematic code I am a developer for a Salesforce org that serves as a community portal for thousands of users. We have been consulting with a large team of developers for years and everything we have is custom coded. Our pages are built using AngularJS to remotely call Apex code. We are on an Unlimited Edition org and we are nearing 90% of our total allowed code. We have a lot of callouts to external services and many times these callouts can run long.  We are now running into issues where users are seeing the "Unable to Process Request - Concurrent requests limit exceeded" error. The issue is there is so much code written by so many different developers it is hard to identify what/where the problematic code is. Sometimes users see this error when they are trying to perform a callout. Sometimes it's when they are inserting a record and triggers are firing. The long-running code issue can be anywhere in our org. Another issue is error handling has been done very poorly, so if any process does run long, we most likely are not looking for it or logging it.  Other than enhancing the logging on our callouts, I do not know where to even begin to find other problematic code. Every developer before me has written code with no regards to limits, so inefficient code can be anywhere. Is there any way or best practice to being able to analyze such a complex org and find where the problems may be? All I can think of is enhanced logging EVERYWHERE, but that may not be the best approach and would be very time consuming, especially considering how many developers we have constantly writing and pushing new code.  I have tried to replicate the issue in a sandbox however I cannot seem to get it working. I wrote Javascript to remotely call an Apex method that waits for 6 seconds. I called this remotely 11 times at once, causing 11 synchronous transactions running concurrently each longer than 5 seconds. However instead of getting the concurrent limit error, each Apex transaction just errors out with a timeout.  Any help would be greatly appreciated. I am not familiar with the majority of the code/functionality of our org, so I do not know how to really solve this issue considering I don't even know what could be problematic aside from long running callouts. Thanks! Unable to play MP3 or MP4 files in Rhythmbox or Movie Player I am unable to play any MP3 or MP4 files. When I try to open any MP3 or MP4 file, both show an error, a Python 2.7 plug-in is required. Canonical map $R/(I\cap J)\rightarrow R/I\times _{R/(I+J)} R/J$ is an isomorphism Is there a limit to a total number of months a holder of UK multiple entry visitor visa can spend in UK per calendar year? Delay in approval leads to missing out on being awarded an "Explainer" badge