Mathematica question : Stepsize control

• To: mathgroup at smc.vnet.net
• Subject: [mg83357] Mathematica question : Stepsize control
• From: "Yannick Bartocci" <yannick.bartocci at gmail.com>
• Date: Sun, 18 Nov 2007 04:48:07 -0500 (EST)

```Hy,
I would like to ask a question on your forum bout some Mathematica code I
cannot solve.

Here is a Riccati type equation I want to solve numerically :

tend = 0.5*10^4;
ktest = 10^(-8);
h[t_, k_] = k + 10^(-6)*Cos[[Pi]/(2*tend)*t];
equ = {f'[t]+(f[t])^2+h[t,ktest] == 0, f[1] == 0.1};
{ndsol, steps} = Reap[NDSolve[equ, f, {t, 1, tend}, MaxSteps -> \[Infinity],
StepMonitor :> Sow[{t, f[t]}]]]

this code gives diverging solution for f[t], but note that if
tend = 10^2
the solution is not diverging, which is what I want to reproduce for tend =
0.5*10^4 or larger.

Actually the system I want to solve uses a more complicated h[t,ktest] as
Interpolating function input which is slowly varying in the beginning but
rapidly oscillating in the end. Initially it behaves like the system
described above and gives NDSolve message ::ndsz.

This clearly is a problem of stepsize control but which has to be adapted on
the fast or slow behavior of the input function h[t,ktest].

Can anybody help me to find out how to control stepsize for this problem?
The mathod in NDSolve is by default Automatic.

Thank you very much,

Yan

```

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