Re: NDSolve differences between mathematica 8 and 9
- To: mathgroup at smc.vnet.net
- Subject: [mg129586] Re: NDSolve differences between mathematica 8 and 9
- From: Alexei Boulbitch <Alexei.Boulbitch at iee.lu>
- Date: Sat, 26 Jan 2013 01:41:16 -0500 (EST)
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- Delivered-to: l-mathgroup@wolfram.com
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Hello,
I am using mathematica 9 and having some problems with a particular expression, but when I tried it on mathematica 8 it worked perfectly. My expression is:
NDSolve[{D[T[n,z],n]+i 2 D[T[n,z],{z,2}]+z^2 T[n,z]==0,T[0,z]==1,Derivative[0,1][T][n,5]==0,Derivative[0,1][T][n,0]==0},T,{n,0,5},{z,0,5}]
where i is the imaginary number, and on both I had a new window to work on, with nothing having been done previously on it.
Mathematica 8 gave me this:
{{T-> InterpolatingFunction[{{0.,5.},{0.,5.}},<>]}}
and mathematica 9 gave me this:
NDSolve::ndnum : Encountered non-numerical value for a derivative at n==0.`.>>
Does anyone know what is going on here? I cannot use mathematica 8, as I do not have continual access to that machine.
Thank you for your help.
Hi, Teresa,
It works for me with Mathematica 9:
NDSolve[{D[T[n, z], n] + I 2 D[T[n, z], {z, 2}] + z^2 T[n, z] == 0,
T[0, z] == 1, Derivative[0, 1][T][n, 5] == 0,
Derivative[0, 1][T][n, 0] == 0}, T, {n, 0, 5}, {z, 0, 5}]
{{T -> \!\(\*
TagBox[
RowBox[{"InterpolatingFunction", "[",
RowBox[{
RowBox[{"{",
RowBox[{
RowBox[{"{",
RowBox[{"0.`", ",", "5.`"}], "}"}], ",",
RowBox[{"{",
RowBox[{"0.`", ",", "5.`"}], "}"}]}], "}"}], ",", "\<\"<>\"\>"}],
"]"}],
False,
Editable->False]\)}}
The only difference is that I used "I" instead of "i". Indeed "I" in Mathematica is the imaginary unit, while "i" is a variable, like any other letter, say, "a", "b", "c" and so on. As long as you did not give it any value, it is understood as an undefined (i.e. non-numerical) variable by Mathematica, and that's what Mathematica reports you: " Encountered non-numerical value...".
Have fun, Alexei
Alexei BOULBITCH, Dr., habil.
IEE S.A.
ZAE Weiergewan,
11, rue Edmond Reuter,
L-5326 Contern, LUXEMBOURG
Office phone : +352-2454-2566
Office fax: +352-2454-3566
mobile phone: +49 151 52 40 66 44
e-mail: alexei.boulbitch at iee.lu