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FindMinimum on Interpolating Function?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg41711] FindMinimum on Interpolating Function?
  • From: "Minas Theodorakis" <minas at edu.physics.uoc.gr>
  • Date: Mon, 2 Jun 2003 04:35:19 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

I have defined these equations:
f[t_] = (a - p*y[t])x[t]
g[t_]=-(b-q*x[t])y[t]

Solving this system, I get two Interpolating functions:
solution[xo_,yo_,T_]:=NDSolve[{x'[t]=f[t],y'[t]=g[t],
       x[0]=xo, y[0]=yo},
    {x,y}, {t,0,T}]

I can plot these functions without a problem:
solution1=solution[8.5, 1.5, 10]
Plot[y[t] /. solution1, {t, 0, 2}]

But I can't use FindMinimum on them!
FindMinimum[y[t]/.solution1, {t, 0, 2}]

I even tried to do a ListPlot with some of their values:
Table[{t, y[t]/.solution1}, {t, 0, 5}]
and they were of the form:
{{t1, {y[t1]}}, {t2, {y[t2]}}, ...}

meaning that the values of the function are enclosed in {}, which I think
creates the problem. Needless to say that ListPlot returned an error.

My main concern is the calculation of the minimum values for the functions.
However any info that points me in the right direction about the nature of
the problem would be grately appreciated.

Minas Theodorakis


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