Jens
Reputation
1552/1000 score
 Mar 3 comment Linearization of differential equations OK - I added a version where I wrap everything in a function called op. Mar 3 comment Linearization of differential equations I don't understand exactly what you mean by X and T are constants. What is T? Do you mean that you add some constant to the differential equation? By "doesn't work," do you mean you want such constants to be dropped? Mar 3 comment How can I define or use a new coordinate system in Mathematica? @jvriesem That bit of text was unintentional, I believe. So I just removed it to avoid confusion... Mar 1 comment Plotting less of a sphere Or use SphericalRegion -> True, ImageSize -> 400 (with some fixed ImageSize to your liking. Feb 28 comment How to find soccer balls in an image? I don't think this is a well-defined question about a specific Mathematica issue. If there were some code to start with, and a less open-ended collection of images, it might be more encouraging. As is, I would suggest closing the question as too broad. Feb 27 comment Isolating cross terms @Kuba Your'e right about DeleteCases. The Select just reflects my thought process... I want the variables to be happy that they got selected. Feb 26 comment Isolating cross terms @sm_physicist But your desired replacement is mathematically inconsistent. I assumed you wanted correct math. If not, you have to do pattern matching, but then you should be very specific about the rules for each of your variables. Feb 26 comment Why do the eigenvectors for two similar matrixes differ by a large amount @Mr.Wizard Thanks - the view must be nice up there where you are at 130K... maybe I'll find out one day. Feb 25 comment Is there an easy way to transform unit vectors from spherical to Cartesian coordinates? The answer to this question is part of the answer to the following: How to change coordinates of a differential operator?, so I think this is a duplicate. Feb 25 comment How can I define or use a new coordinate system in Mathematica? I think the coordinate systems included in Mathematica are the ones in which the Laplace equation is separable. The "dipolar coordinates" in the paper don't belong to that class. Of course one can define infinitely many other orthogonal coordinate systems (e.g. from the real and imaginary parts of an analytic function), but those aren't "special" enough to be included. It makes sense to me - but it's not too hard to do all the calculations in that linked paper in Mathematica ab initio. Feb 24 comment Why do the eigenvectors for two similar matrixes differ by a large amount That's probably one of the mysteries that only a Wolfram employee can answer definitively... it's worth knowing that such discrepancies exist, but since there is no reason to not expect them, I would simply not depend on any properties of the eigenvectors that are mathematically not required to have any specific value. Feb 24 comment How to make a symbolic vector into a pure function? You have a typo in grad2: f should be func. (+1) Feb 23 comment How can I make an animated demonstration of the Wigner semicircle distribution? The crash bug has been fixed in version 10. But in version 8, don't use this, or the user will lose all their unsaved changes in the crash. Feb 23 comment How can I make an animated demonstration of the Wigner semicircle distribution? To illustrate the workflow I just described, see my answer to How to create animated snowfall? Feb 23 comment How can I make an animated demonstration of the Wigner semicircle distribution? Since it is not clear whether an exported GIF is also desired, or just an embedded movie, I would say this could be a duplicate of Is it possible to insert an animated image into Mathematica notebook?. The workflow would simply be to first create a GIF from within Mathematica, then re-import that using the function makeAnimation in my answer. That function fixes a bug which leads to a hard crash when you right-click on the animation created using Kuba's method (in version 8). Feb 23 comment How can I make an animated demonstration of the Wigner semicircle distribution? Just a warning: Unfortunately, this crashes (in version 8) when you right-click on the animation. See my answer here where I work around this problem in the function makeAnimation. Feb 22 comment citation insertion from bibtex file does not seem to work Feb 21 comment Solving an inhomogeneous partial differential equation I'll let you think about it for yourself - to do it by hand given what I said above, use the superposition principle. Feb 21 comment Solving an inhomogeneous partial differential equation The edit contains boundary conditions, too. So you could use the rest of my answer, too. Feb 21 comment Solving an inhomogeneous partial differential equation I tried my answer linked above on this question with pde = Function[ψ, D[ψ, {r, 2}] - 1/r D[ψ, r] + D[ψ, {x, 2}] == A r^2] and it works fine. I kept my variable names so none of the remaining code in my answer has to be changed. My answer assumes you also have boundary conditions, which isn't the case here. So you only need the part of that answer up to xSolution[x_]....