Re: NDSolve with arrays

• To: mathgroup at smc.vnet.net
• Subject: [mg89241] Re: NDSolve with arrays
• Date: Sun, 1 Jun 2008 03:35:30 -0400 (EDT)
• References: <g1m8ev\$ia\$1@smc.vnet.net>

```to be more precise,
play[x_, j_] :=If[ IntegerPart[x^2+j^2]>n, n, IntegerPart[x^2+j^2]>n],
i.e. the index on the rhs of my equation depends both on j and x.
any suggestions?
thanks
svend

On May 29, 2:44 pm, svend <dom... at tphys.uni-heidelberg.de> wrote:
> hi all,
> i want to solve a PDE by discretizing in one variable in an array and solv=
e. the equations are of the following type:
> n = 10;
> x0 = 1;
> x1 = 10;
>
> play[x_] := IntegerPart[x]
>
> eq1 := {D[f[j][x], x] == f[play[x]][x], f[j][x0] == j^2}
>
> eqs = Flatten[Table[eq1, {j, 1, n}]]
> fun = Flatten[Table[f[j], {j, 1, n}]];
> tes = NDSolve[eqs, fun, {x, x0, x1}][[1]];
>
> my problem is that the variable x, in which the equation is differential, =
also appears on the rhs in the "index" of my array. mathematica does not eva=
luate "play[x]" during NDSolve and just tells me that the rhs is not numeric=
al. I tried "_NumericQ" and similar things but nothing seems. I would be ver=
y happy if someone could tell me how to resolve this.
>
> thanks
> svend

```

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