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Feel free to correct the grammar mistakes and unidiomatic expressions in my posts.

Can we improve the quality of posts with tag differential-equations?


Jan
9
comment Workarounds for a possible bug in the linearity of FourierTransform
Seems this hasn't been done yet. Hello, welcome to Mathematica.SE! I suggest the following: 1) As you receive help, try to give it too, by answering questions in your area of expertise. 2) Read the faq! 3) When you see good questions and answers, vote them up by clicking the gray triangles, because the credibility of the system is based on the reputation gained by users sharing their knowledge. Also, please remember to accept the answer, if any, that solves your problem, by clicking the checkmark sign!
Jan
9
comment Computation time depends on the matrix elements!
A better check is {Or @@ PackedArrayQ /@ matrix, And @@ PackedArrayQ /@ matrix2} :)
Jan
9
comment Can I force Mathematica to use machine precision?
The only thing I can think of at the moment is Compile, is it of interest?
Jan
9
comment Inverse Fourier Transform - wolfram alpha vs Mathematica 9.0
It's simply because the InverseFourierTransform of your expression doesn't exist. Try InverseFourierTransform[Exp[ -b v^2], v, w, Assumptions -> #] & /@ {b > 0, b < 0}
Jan
9
comment Possible bug with FourierTransform linearity
Just wrote a "shell" for FourierTransform here, which (I think) is a little more stable than the Distribute approach.
Jan
8
comment Integration of a high oscillatory function
@yashar Just search MachinePrecision and WorkingPrecision, and you'll see lots of posts about how and why precision dramatically influence the result. I used to collect just 4 of them here.
Jan
7
comment Integration of a high oscillatory function
@yashar Yeah, that's expected result. 1000 is a number with infinity precision, while 1000.0 is a number with MachinePrecison. There're many posts about this issue in this site, have a search :)
Jan
7
comment Integration of a high oscillatory function
@yashar See my edit.
Dec
31
comment Issue in NDSolve and unknown error
But the current form of the question is really discouraging… in fact I even failed to download your data under my terribly slow network…
Dec
31
comment How to prevent instability blow up in NDSolve?
@Ruslan If this method would have any chance to work, it should be decreasing rather than increasing n or "DifferenceOrder", sadly it seems that decreasing doesn't work either 囧.
Dec
31
comment Alternatives to FiniteElement as Spatial Discretization Method for NDSolve
If user21 doesn't appear under your question, then @ won't remind him… and I think that behavior is irrelevant to this problem.
Dec
25
comment Alternatives to FiniteElement as Spatial Discretization Method for NDSolve
For the second part of question, in that era, Mathematica just can not handle this type of problem, at least cannot handle it elegantly. A typical answer is this. In fact this is one of the reasons causing my self-learning of FDM and FEM.
Dec
25
comment InverseFourierTransform of simple function takes forever
Seems this hasn't been done: Hello, welcome! I suggest the following: 1) As you receive help, try to give it too, by answering in your area of expertise. 2) Read the faq! 3) When you see good questions and answers, vote them up by clicking the gray triangles, because the credibility of the system is based on the reputation gained by users sharing their knowledge. Also, please remember to accept the answer, if any, that solves your problem, by clicking the checkmark sign!
Dec
23
comment How to make a graph of this function?
Are you sure your expression will produce a graph? With[{m = 5}, InverseFourierTransform[FourierTransform[Total[(NestList[Cos, x, m] t^Range[0, m])/Range[0, m]!], t, w] Sqrt[-I w], w, t]] already gives ComplexInfinity.
Dec
23
comment How to make a graph of this function?
Just to make sure. Do you really want Nest[Cos, x, m] rather than Derivative[m][Cos][x]?
Dec
23
comment Divide all but the maximal element in a list by 10?
Hello, welcome to Mathematica.SE! I suggest the following: 1) As you receive help, try to give it too, by answering questions in your area of expertise. 2) Read the faq! 3) When you see good questions and answers, vote them up by clicking the gray triangles, because the credibility of the system is based on the reputation gained by users sharing their knowledge. Also, please remember to accept the answer, if any, that solves your problem, by clicking the checkmark sign!
Dec
23
comment InverseFourierTransform of simple function takes forever
@Hugh Somewhat inspired by your observation, I found a work-around. See my answer below :D
Dec
22
comment The change of precision doesn't work in ParallelDo. Is it a bug in Parallel?
BTW, please don't use "bugs" tag until the community has confirmed it.
Dec
22
comment The change of precision doesn't work in ParallelDo. Is it a bug in Parallel?
Hello, welcome! I suggest the following: 1) As you receive help, try to give it too, by answering questions in your area of expertise. 2) Read the faq! 3) When you see good questions and answers, vote them up by clicking the gray triangles, because the credibility of the system is based on the reputation gained by users sharing their knowledge. Also, please remember to accept the answer, if any, that solves your problem, by clicking the checkmark sign!
Dec
22
comment InverseFourierTransform of simple function takes forever
@Hugh Just tried your code. The answer seems to be incorrect. (The correct one is given by bbgodfrey in the answer below.)