I want to generate a dataset in R. I see that most of times a distribution must be given e.g. Normal, Poisson, etc.. I want the dataset to follow normal distribution, and having the following: n observations (rows), k parameters (columns) and some of thems to have high correlations. I want to perform various multicollinearity test on them to see how they react and which one gives the otpimal variable selection model. How can i create a dataset with this features in R?
I'm sorry if this seems a bit too basic, but I guess I'm just looking to confirm understanding here. I get the sense I'd have to do this in two steps, and I've started trying to grok correlation matrices, but it's just starting to seem really involved. I'm looking for a concise explanation (ideally with hints towards a pseudocode solution) of a good, ideally quick way to generate correlated random numbers.   Given two pseudorandom variables height and weight with known means and variances, and a given correlation, I think I'm basically trying to understand what this second step should look like:     height = gaussianPdf(height.mean, height.variance)    weight = gaussianPdf(correlated_mean(height.mean, correlation_coefficient),                          correlated_variance(height.variance,                          correlation_coefficient))    How do I calculate the correlated mean and variance? But I want to confirm that's really the relevant problem here.  Do I need to resort to matrix manipulation? Or do I have something else very wrong in my basic approach to this problem?
Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon? Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon?  If so, can quantum mechanics describe the universe at high energies where there is no spacetime?  Schrodinger equation assumes the presence of time dimension. So how can such equations be valid at extremely high energy?  And is it meaningful to do physics if there is no time dimension?  Would the concepts of Hilbert space, wavefunction collapse etc be useful in that case? How to get exact camera view? I'm currently a beginner when it comes to 3D modelling but doing okay so far. I'm struggling a bit when it comes to the final renders of my scene, specifically on the camera view I want. Sometimes its to zoomed in and sometimes to zoomed out that it's gone out of the environment of the blender. I realized the settings for the camera on blender are for actual cameras / photography and I'm no expert on that too. A tip on how to control them precisely would be nice. Thank you. Number of reflexive relations defined on a set A with n elements Better to buy an older high-level camera or newer entry-level camera? What are the pros and cons of buying an older higher-level camera if the price is about the same as a new entry-level one? Is it possible to change he/she (he or she) in a sentence into one word? For instance: When a student comes in, ask him or her to... What is $\int_0^1\frac{x^7-1}{\log(x)}\mathrm dx$? /A problem from the 2012 MIT Integration Bee is $$ \int_0^1\frac{x^7-1}{\log(x)}\mathrm dx $$ The answer is $\log(8)$. Wolfram Alpha gives an indefinite form in terms of the logarithmic integral function, but times out doing the computation. Is there a way to do it by hand? pygame.event.get() not returning any events when inside a thread Boolean Modifiers not working normally When using a Boolean modifier on an object, the "Operation" choices (Difference, Union, Intersect) are all not working normally. Choosing "Union" makes it do the effect of "Intersect" and "Difference" makes it do what "Intersect" is supposed to do. What's the deal here?   This is happening with following a simple tutorial. It's a simple primitive cube and primitive cylinder. No normals or doubles problems.   My specs are:  Macbook Pro 13" Retina early 2015 512GB i7 with 16gb RAM upgrade OS-X version 10.11.4 Multiple chrome.exe processes in Task Manager I know that each new tab on Google Chrome have its own process, but I have 14 chrome.exe processes running actually as I can see it on the Task Manager, and only two tabs are opened on Google Chrome.    Could it be due to Chrome extensions? What other reason can open more chrome.exe process and how to avoid it? Is there a way to run Python on Android? We are working on an  version and this platform has a nice Python API..  However, there is nothing official about Python on Android, but since  exists, is there a way to let the snake and the robot work together?? Getting No module name exifread error from QGIS Photo2Shape plugin? 90s (or earlier) movie with experimental, invisible, teleporting, time-traveling ship Windows 10 Search not loading, showing blank window It was soft and covered in flies. My guess is fungi.  Location: South Florida. Why is the node editor showing different kinds of nodes? 1.  Why is the wave function complex? I've collected some layman explanations but they are incomplete and unsatisfactory. However in the book by Merzbacher in the initial few pages he provides an explanation that I need some help with: that the de Broglie wavelength and the wavelength of an elastic wave do not show similar properties under a Galilean transformation. He basically says that both are equivalent under a gauge transform and also, separately by Lorentz transforms. This, accompanied with the observation that $\psi$ is not observable, so there is no "reason for it being real". Can someone give me an intuitive prelude by what is a gauge transform and why does it give the same result as a Lorentz tranformation in a non-relativistic setting? And eventually how in this "grand scheme" the complex nature of the wave function becomes evident.. in a way that a dummy like me can understand.  2.   A wavefunction can be thought of as a scalar field (has a scalar value in every point ($r,t$) given by $\psi:\mathbb{R^3}\times \mathbb{R}\rightarrow \mathbb{C}$ and also as a ray in Hilbert space (a vector). How are these two perspectives the same (this is possibly something elementary that I am missing out, or getting confused by definitions and terminology, if that is the case I am desperate for help ;)   3.   One way I have thought about the above question is that the wave function can be equivalently written in $\psi:\mathbb{R^3}\times \mathbb{R}\rightarrow \mathbb{R}^2 $ i.e, Since a wave function is complex, the Schroedinger equation could in principle be written equivalently as coupled differential equations in two real functions which staisfy the Cauchy-Riemann conditions. ie, if $$\psi(x,t) = u(x,t) + i v(x,t)$$ and $u_x=v_t$ ; $u_t = -v_x$ and we get $$\hbar \partial_t u  = -\frac{\hbar^2}{2m} \partial_x^2v + V v$$ $$\hbar \partial_t v  = \frac{\hbar^2}{2m} \partial_x^2u - V u$$ (..in 1-D) If this is correct what are the interpretations of the $u,v$.. and why isn't it useful. (I am assuming that physical problems always have an analytic $\psi(r,t)$). Solidify thickness doesn't correspond to specified scale I'm Having trouble with setting the thickness applied by solidify. The selected block is 15 by 28 cm (single mesh sides) and the thickness of solidify is set to 3mm (pointing inwards). Checking off even thickness makes it even worse. I was using the function in a different object earlier today and it worked just fine. Is there something I'm missing or is this just a bug?   Feel free to treat me like an idiot, I've literally started using blender yesterday :) Double dual mappings Reset the password in Ubuntu / Linux Bash in Windows I have installed Linux Bash on Windows 10 (available from Microsoft), but I've forgotten my password.  I've searched for a solution but I only find suggestions that involve doing something before the system boots, like accessing recovery mode, but that will not work in this case as this Ubuntu is just an application within a Windows system and doesn't have its own boot process.  How can I reset my password? Occasionally, the Unicode character sequence U+200C U+200B (ZWNJ ZWSP) is inserted into comments In     ... the number "5000" does not paste as such but instead as  5 0 U+200C U+200B 0 0   The HTML source looks like this:  perhaps the easiest would be &lt;code&gt;\edef\tmp{\everypar{\widowpenalty\the\widowpenalty\relax}}\tmp\widowpenalty=-50&amp;zwnj;&amp;#8203;00&lt;/code&gt; that may reset   Or (smaller snippet):  \widowpenalty=-50&amp;zwnj;&amp;#8203;00&lt;/code&gt; that   So in the HTML, we have extraneous &amp;zwnj; and &amp;#8203; in between the two middle digits of 5000.  Upon pasting and trying out this code, this first led to a mysterious compiler error. The same issue happened within a (now deleted) comment thread below ; there, these or similar two characters were inserted after the letter "r" within the string \ref ("\ref").  Note that not all browsers wrap the same way. The above screenshot was for Firefox 19.0.2, in which it breaks between \relax}} and \tmp, with 5000 insidiously left intact on the second line but with the two special characters remaining in the middle. So that is why this took me completely by surprise. Other browsers might indeed only break on the invisible Unicode characters, such as Chrome 25:    Or on a smaller screen with the mobile site, multiple line breaks might show, possibly still leaving the Unicode characters unused: