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MathGroup Archive 2002

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RE: How to change time stepsize for Integration

  • To: mathgroup at smc.vnet.net
  • Subject: [mg33978] RE: [mg33956] How to change time stepsize for Integration
  • From: "DrBob" <majort at cox-internet.com>
  • Date: Thu, 25 Apr 2002 02:59:51 -0400 (EDT)
  • Reply-to: <drbob at bigfoot.com>
  • Sender: owner-wri-mathgroup at wolfram.com

I think the MaxStepSize option will help with that.

Bobby Treat

-----Original Message-----
From: Winston Garira [mailto:uceswga at ucl.ac.uk] 
To: mathgroup at smc.vnet.net
Subject: [mg33978] [mg33956] How to change time stepsize for Integration

Hi!

Can anyone help me on this one:  


Pends[init_, time_, {c_, w_, p_}] := 
    Module[{}, 
      pend = NDSolve[{x''[t] + c x'[t] + (1 + p Cos[w t])Sin[x[t]] == 0,

            x[0] == init[[1]], x'[0] == init[[2]]}, {x}, {t, 0, time}, 
          MaxSteps -> 200000];
      xd[t_] := x[t] /. pend[[1]];
      xdd[t_] := x'[t] /. pend[[1]];];
c = 0.1; w = 0.30; p = 1.1;

Pends[{1.37, 0}, 5000, {c, w, p}];
plt = Plot[{t, xd[t], xdd[t]}, {t, 0, 500}];

I want to reduce the time stepsize
in my numerical integration with mathematica. Each time
I try to get coordinates generated from the command
Plot[ ......, {t, tmin, tmax}]; or
Table[......, {t, tmin, tmax}];

I always notice that in all these case time stepsize = 1.
Is there anyway I can reduce the the timestep to say, 
time stepsize =0.001 in the above numerical integration using
NDsolve.


Thanks in advance

Winston






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