Re: A NDSolve within a FindMinimum/NMinimize
- To: mathgroup at smc.vnet.net
- Subject: [mg90606] Re: A NDSolve within a FindMinimum/NMinimize
- From: dh <dh at metrohm.ch>
- Date: Tue, 15 Jul 2008 06:49:49 -0400 (EDT)
- References: <g5htfb$j7t$1@smc.vnet.net>
Hi Philipp,
you have 2 bugs here. First, NMinimize first calls the function with a
symbolic argument to see if it can do a symbolic simplification. You may
fix this by wrapping a function with a numerical argument around your code.
Second, NMinimize returns a list of results, even if there is only one
result. To fix this, you simply take the first element of the list. Here
is the corrected code:
f[a_?NumericQ]:=(s=NDSolve[{El'[x]+a Sin[x]
El[x]==0,El[0]==a},El,{x,-1,1}][[1]];(El[1]/.s) a)
NMinimize[f[a],a]
hope this helps, Daniel
philip.ingrey at googlemail.com wrote:
> I'm trying to find the value of a coefficient that minimizes a
> function. Below is a simplified version of the problem:
> Using a Table to print out some results is fine:
>
> Table[{a, s = NDSolve[{El'[x] + a Sin[x] El[x] == 0, El[0] == a}, El,
> {x, -1, 1}]; ((El[1] /. s) a)[[1]]}, {a, -1, 1, 0.1}]
>
> But a NMinimize or FindMinimum gives errors:
>
> NMinimize[s = NDSolve[{El'[x] + a Sin[x] El[x] == 0, El[0] == a}, El,
> {x, -1, 1}]; (El[1] /. s) a, a]
>
> As it seams to try and evaluate the NDSolve then apply a value for a,
> is there a way to solve this?
>
> Thanks in advance,
> Phil I
>
--
Daniel Huber
Metrohm Ltd.
Oberdorfstr. 68
CH-9100 Herisau
Tel. +41 71 353 8585, Fax +41 71 353 8907
E-Mail:<mailto:dh at metrohm.com>
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