43,946 reputation
165178
bio website uoregon.edu/~noeckel
location
age
visits member for 2 years, 7 months
seen 2 hours ago

6h
comment Operator and VariationalMethods
Also, I think there's probably a mistake in the functional (the laplacian isn't what you want, I bet). I voted to close because the main issue is the simple syntax problem pointed out above.
8h
comment Operator and VariationalMethods
To amplify what @swish already said: g is a symbol that does not represent the expression you want to insert into VariationalD. You want VariationalD[g[x,y,z],f[x,y,z],{x,y,z}], and then the result will be $2 \left| f(x,y,z)\right| \text{Abs}'(f(x,y,z)) \left(g \left| f(x,y,z)\right| ^2+U(x,y,z)\right)$
12h
comment Export MatrixPlot graphics to PDF
I just remembered that I had asked a closely related question myself in 2012, and that this answer also applies there: Color ramp banding in PDFKit when exporting Raster image Inset to PDF.
12h
comment Export MatrixPlot graphics to PDF
@Lou New dictionary item - "jens-sastic (adj.): awkward and painful solution to a problem that shouldn't exist in the first place"
1d
comment Transformation of Derivatives under change of coordinates
Closely related: How to change coordinates of a differential operator? The main thing is to apply the chain rule. This question is simpler than the linked one because the transformation is linear.
2d
comment Selectively updating individual graphics in a dynamic, multiple-plot Show
@RonaldMonson In your updated post, the statement that Show expects Graphics is not correct. Besides Graphics3D, it also accepts Legended@Graphics and Legended@Graphics3D. My point is the Plot can produce the Legended output, too, and I automatically account for that.
2d
comment Selectively updating individual graphics in a dynamic, multiple-plot Show
My advice is that if you can get by without taking apart the output of built-in functions such as Plot, then that's less likely to break in future versions. The introduction of PlotLegends illustrates this. It creates Plot output with Head Legended instead of Graphics. In earlier versions, that didn't happen, so that code relying on the internal structure of Plot output from the old version will not work. My solution doesn't rely on any undocumented internal structures.
2d
comment Customizing display of partial differential equations
@Mr.Wizard Are you saying that there is anything wrong with Format in the context of this question? Note that the question is only about formatting for TraditionalForm.
2d
comment Counting the zeros in a factorial expansion
You only need to apply DigitCount to the factorial.
2d
comment Selectively updating individual graphics in a dynamic, multiple-plot Show
This won't work if you add PlotLegends to one or both of the plots (e.g.).
Aug
25
comment Selectively updating individual graphics in a dynamic, multiple-plot Show
There were indeed errors as @Pickett observed, due to the argument of the Locator containing a constant and not a variable. I posted a version that fixes this and also addresses the Show issue.
Aug
24
comment How to apply Gaussian kernel to smooth density of points on 2D (algorithmically)
I show a more low-level implementation in this answer, so you may want to read that and look up GaussianFilter
Aug
24
comment Customizing display of partial differential equations
I can't resist pointing out that suppress is written with two p...
Aug
24
comment Under what conditions does Mathematica give a natural antiderivative when integrating?
@Anixx I don't think it's a bug in the 1/(x-1) case - it's a situation where the inverse Fourier transform involves a Cauchy principal-value integral (otherwise it's undefined). This seems to be a genuine counterexample to the thesis that all anti-derivatives of Fourier-transformable functions lead to the same unique choice of integration constants for both methods. I.e., the answer to your question is: there are no obvious general necessary and sufficient conditions that I would be able to formulate. But at least it works for many cases, including polynomials.
Aug
24
comment Can we teach Mathematica about functional differentiation?
@chris Sure, Mathematica probably can't do the limit in that case. But that's still better than getting a wrong result for that case, as you would with the accepted answer. Anyway, if you have an integral, are you sure you don't want the variational derivative instead of the functional derivative?
Aug
24
comment Higher order eigenvalue problem
This becomes an eigenvalue problem for the unknown energy $E$ only when you specify the boundary conditions.
Aug
23
comment What are the best tips in Michael Trott's beer/whiskey Wolfram Blog post?
Clearly the best tip: "Drive responsibly on brewery tours!" In terms of Mathematica, I'm afraid it's impossible to answer this.
Aug
22
comment Horizontally compress a picture with varying compression ratio
Do you mean that the part of the image from the left to the horizontal fraction x should be compressed, and that this compressed part of the image should replace the original part of the image? Or do you just want to get the left part of the image by itself? And by compression, you do you mean that you just want a quick display of that process or you actually want a new image with the result? The difference is that the display can be done without any image manipulations (image manipulations are quite slow in Mathematica).
Aug
22
comment On using DiracDelta[t] in OutputResposne in version 10. Different result from version 9
I see this issue too (version 10 on Mac OS X). The result is correct if I replace the delta function by 1000 HeavisideTheta[1/1000-t]. Seems like this would have to be called a bug...
Aug
21
comment ArrayPlot copied to PDF shows blurred mesh
I don't understand why you post this as a solution. Have you actually tried it? Then you must be seeing something in the FullForm of the PDF that I am not.