• To: mathgroup at smc.vnet.net
• Subject: [mg91846] Re: About NDSolve
• From: Szabolcs Horvát <szhorvat at gmail.com>
• Date: Wed, 10 Sep 2008 05:07:55 -0400 (EDT)
• Organization: University of Bergen
• References: <ga5kq2\$r9j\$1@smc.vnet.net>

```P_ter wrote:
> Hello,
> Daniel Lichtblau wrote in "Re: phase-space versus controlling parameter surface":
>
> k = .3;
>
> Clear[g];
> g[b_?NumberQ] :=
> g[b] = {x[t], v[t], b} /. First[NDSolve[{x'[t] == v[t] ,
> v'[t] == -x[t]^3 - k*v[t] + b*Cos[t], x[0] == 1, v[0] == 0}, {x,
> v}, {t, 0, 2000}, MaxSteps -> Infinity]]
> pts = Table[
> Evaluate[Table[g[b], {b, 0.2, 0.6, .01}]], {t, 1950, 2000}];
>
> If I use h[s_]:= s^3 and replace x[t]^3 by h[x[t]], NDSolve in pts complains. Why can't I do this?
> Piecewise or Which (e.g.,  Which[x[t] < -1, -1, x[t] > 1, 1, True, x[t]]) on the place of x[t]^3 also gives problems.
> Any suggestions?
> P_ter
>

I tried this, but didn't get any errors.

```

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