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MathGroup Archive 2005

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FindRoot/NDSolve problem in VS5

  • To: mathgroup at smc.vnet.net
  • Subject: [mg54822] FindRoot/NDSolve problem in VS5
  • From: "Dr A.H. Harker" <a.harker at ucl.ac.uk>
  • Date: Wed, 2 Mar 2005 22:29:11 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

  Can anybody explain why the following simple illustration of a multiple
shooting solution works under Mathematica V4, but fails under V5.0?

deq = y''[x] - x^2 y[x] == x + x^3;
eqsol[s_] := NDSolve[{deq, y[-1] == 0, y'[-1] == s}, y[x], {x, -1, 1}]
y[x] /. eqsol[1][[1]] /. x -> 1;
ss = FindRoot[((y[x] /. eqsol[s][[1]] ) /. x -> 1) == 0, {s, 0, 10}]
ysol[x_] = y[x] /. eqsol[s /. ss][[1]]

  To add to the confusion, the following is fine in both versions.

ch[k_] = y''[x] - k Sqrt[1 + y'[x]^2] == 0
guess[s_] := NDSolve[{ch[.35], y[0] == 0, y'[0] == s}, y[x], {x, 0, 10}]
ssol = FindRoot[((y[x] /. guess[s][[1]]) /. x -> 10) == 0, {s, -1, -10}]
soln[x_] = y[x] /. guess[s /. ssol][[1]]

 Tony Harker 
 Department of Physics and Astronomy
 University College London
 Gower Street
 LONDON
 WC1E  6BT
 (44)(0)207 679 3404
 a.harker at ucl.ac.uk




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