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Apr
21
revised BC for transport equation using NDSolve
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Apr
21
comment Solving coupled differential equations with an eigenvalue
As mentioned above, ϕ[Ei] == 0 and ϕ'[Ei] == 0 give two equations, use either of them inside FindRoot or RootSearch will give you a result.
Apr
21
revised solve ODE with divergencies
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Apr
21
revised solve ODE with divergencies
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Apr
21
revised solve ODE with divergencies
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Apr
21
comment Analogue for Maple's dchange - change of variables in differential expressions
After playing with it a bit, I feel that writing one-element list is a little inconvenient. It'll be good if syntax like dChange[D[u[x, t], t] == D[u[x, t], {x, 2}], x == ξ s[t], x, ξ, u[x, t]] is supported. Not sure what's the standard way to implement this, though. (Something like {internalold, internalfun} = If[Head@# =!= List, {#}, #] & /@ {oldVars, functions} ?)
Apr
20
comment RegionPlot3D exponentiation issue [Mathematica 10]
No, it's not empty, if you look carefully, you'll see one point at the origin, and it's the only point inside the region.
Apr
20
revised Analogue for Maple's dchange - change of variables in differential expressions
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Apr
20
comment Analogue for Maple's dchange - change of variables in differential expressions
Your design for the syntax is undoubtedly more Mathematica-like and more reasonable. (I admit that when writing the question I haven't deliberated on the syntax design. )
Apr
18
awarded  Nice Question
Apr
18
revised Analogue for Maple's dchange - change of variables in differential expressions
grammar mistakes fixed
Apr
18
revised Analogue for Maple's dchange - change of variables in differential expressions
add examples for expected behavior.
Apr
18
revised Analogue for Maple's dchange - change of variables in differential expressions
added 4 characters in body
Apr
18
comment Analogue for Maple's dchange - change of variables in differential expressions
@m0nhawk Well, as I mentioned above, that's just one of the related questions that are not general enough.
Apr
18
asked Analogue for Maple's dchange - change of variables in differential expressions
Apr
18
comment Integro differential eq boundary difficulties
I suggest you to add the $LaTeX$ or screenshot of your original PDE to your question. BTW, a simple mistake is exp should be Exp.
Apr
18
comment NDSolve to solve a PDF
"Numerically, using the method of lines (the default in this case), condition 1 is not integrated." Yeah, actually this has been (vaguely) mentioned in the possible issue of DiracDelta: Numerical routines will typically miss the contributions from measures at single points.
Apr
18
comment Solving coupled differential equations with an eigenvalue
What approach do you want to take for finding Ei? b[Ei] actually returns 2 InterpolatingFunction while you only have 1 unknown! If you replace the {ϕ, A} inside ParametricNDSolve with ϕ or A, you'll get a solution, whether the solution is correct or not is another story. BTW, you may want to try this package: library.wolfram.com/infocenter/Demos/4482
Apr
18
comment Nest-Recursion leads to overflow - Numerical calculation of Lyapunov exponents
It's just an issue of error accumulation. Use a higher precision e.g. 32 will help. To understand why the overflow happened when you set the precision to 16, you can use NestList instead of Nest and remove ;{First[#], Rest[#]} &@Partition[yt, n] from the code and check the result, you'll see the Precision become lower and lower through the numeric calculation. BTW, you don't need Outer for JacobianMatrix, JacobianMatrix[funs_List, vars_List] := D[funs, {vars}] is enough.
Apr
16
reviewed Approve Is Sow/Reap compatible with Composition?