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MathGroup Archive 2004

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options in NDSolve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46217] options in NDSolve
  • From: Guibout <guibout at ifrance.com>
  • Date: Thu, 12 Feb 2004 07:15:45 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

I use NDSolve several times in one of my programs and therefore I want 
to define a variable called method that stores the options I want to 
use. Here is what I did:

option = MidPoint;
Choose[option,
  "MidPoint", method = {Method -> {"FixedStep", Method -> 
LinearlyImplicitMidpoint}, StartingStepSize -> 0.01, MaxSteps -> Infinity},
  "IRK", method = {Method -> ImplicitRungeKutta, MaxSteps -> Infinity},
  "IRK4", method = {Method -> {"ImplicitRungeKutta", DifferenceOrder -> 
4}, StartingStepSize -> 0.01, MaxSteps -> Infinity},
   "ERK", method = {Method -> {"ExplicitRungeKutta", DifferenceOrder -> 
4}, MaxSteps -> Infinity},
  "Standard", method = {MaxSteps -> Infinity, MaxStepSize -> 0.1}];

solution=NDSolve[equations,variables,method];

You can copy and paste this code and you will see that it does not work. 
  Indeed, method does not contain what I expect:
In[3]:= method
Out[3]={MaxSteps->Infinity, MaxStepSize->0.1}

Mathematica seems to combine StartingStepSize->0.01 and FixedStep to 
obtain MaxStepSize->0.1 and drop Method->LinearlyImplicitMidPoint.

Why does mathematica behave like that? Is there another way to do what I 
want to do?
Thanks in advance,
Vincent


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