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MathGroup Archive 2004

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Problem with order of evaluation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49940] Problem with order of evaluation
  • From: Max Ulbrich <ulbrich at biochem.mpg.de>
  • Date: Sat, 7 Aug 2004 03:51:33 -0400 (EDT)
  • Organization: GWDG, Goettingen
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

I want to find a minimum in dependence of an initial 
condition of a differential eqaution. I can define a 
function f[y]:

L=3.*^-9;
g[y_]=NDSolve[{p''[x]==-1.*^9(43418E^(-38p[x])-43418E^(38p[x])),p[0]==-0.13,p'[0]==y},p[x],{x,0,L}]
f[y_]:=((p[x]/.g[y]/.x->L)[[1]])^2

which evaluates properly:

f[0.22*^8]

However, Mathematica doesn't evaluate it properly when I try 
  NMimimize, FindRoot or whatever:

<<NumericalMath`NMinimize`
NMinimize[f[y],{y,0.1*^8,0.3*^8}]


How do I have to define f[y] that this works?
Thanks a lot,

Max


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