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Re: InterpolatingFunction in NDSolve
*To*: mathgroup at smc.vnet.net
*Subject*: [mg21647] Re: InterpolatingFunction in NDSolve
*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
*Date*: Fri, 21 Jan 2000 03:59:56 -0500 (EST)
*Organization*: Universitaet Leipzig
*References*: <86196r$la7@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
Hi,
the code
Clear[sss];
Clear[solution];
Clear[sol2];
solution =
NDSolve[{Derivative[1][y][x] == -10*y[x], y[0] == 1}, y, {x, 0, 0.5}]
sss = (y[x] /. solution[[1]])[[0]];
(*interpolating function seems to be ok : can Plot it*)
Plot[sss[t], {t, 0, 0.5}];
Derivs[y_, x_?NumericQ] := If[x < 0.25, sss[x], -sss[x]]
sol2 = NDSolve[{Derivative[1][y][x] == Derivs[y, x], y[0] == 0},
y, {x, 0, 0.5}]
Plot[Evaluate[y[x] /. sol2], {x, 0, 0.5}];
works fine. What is your problem ? Look at my Derivs[] function
and never test a unrestricted pattern against a number.
Hope that helps
Jens
eborzova at my-deja.com wrote:
>
> Hi everybody.
> My question could be simple, but I just can't
> figure it out. I need to use InterpolatingFunction
> inside yet another function (Derivs) that is rhs
> for NDSolve (please refer to the code below). The
> problem is that if my rhs "Derivs" has some sort
> of conditional logic (e.g. "If"), then it stops
> working (see a comment with Return[sss[x]]).
>
> Any help/hints/feedback are greatly appreciated!
>
> Thanks.
> Elena.
> Clear[sss];
> Clear[solution];
> Clear[sol2];
> solution = NDSolve[{Derivative[1][y][x]==-10*y
> [x], y[0] == 1},
> y,{x, 0, 0.5}]
>
> sss = (y[x] /. solution[[1]])[[0]];
>
> (* interpolating function seems to be ok: can
> Plot it *)
> Plot[sss[t], {t, 0, 0.5}];
>
> Derivs[y_, x_] := Block[{},
>
> (* uncomment below to make it work *)
>
> (* Return[sss[x]]; *)
>
> If[x < 0.25, Return[sss[x]], Return[-sss
> [x]]];
>
> Print["Ooops!!!!"];
>
> Abort[];
> ];
>
> sol2 = NDSolve[{Derivative[1][y][x] == Derivs[y,
> x], y[0] == 0},
> y,{x, 0, 0.5}]
>
> Plot[Evaluate[y[x] /. sol2], {x, 0, 0.5}];
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.
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