       Re: Problems integrating InterpolatingFunction

• To: mathgroup at smc.vnet.net
• Subject: [mg116070] Re: Problems integrating InterpolatingFunction
• From: DrMajorBob <btreat1 at austin.rr.com>
• Date: Tue, 1 Feb 2011 06:51:34 -0500 (EST)

```You wrote Y as its own integral, which causes \$RecursionLimit errors.

You probably meant something like

Clear[x, y]
x[t_] = x[t] /.
NDSolve[{x''[t] == -x[t]^3 + x[t], x' == 0, x == 1.42},
x[t], {t, 0, 100}] // First
y[t_] = Derivative[-1][y][t]

Bobby

On Mon, 31 Jan 2011 02:23:31 -0600, Roland Franzius
<roland.franzius at uos.de> wrote:

> Am 30.01.2011 01:43, schrieb Sergio Miguel Terrazas Porras:
>> Hello group,
>>
>> I use NDSolve for a nonlinear differential equation, and I get an
>> InterpolatingFunction, as expected.
>>
>> I can plot it, evaluate it, etc.
>>
>> The problem I have is that now I need to integrate 1/(the square of the
>> InterpolatingFunction), and I get nothing but the input back.
>>
>> Any ideas?
>>
>>
>> Sergio Terrazas
>>
>
> Yoy can integrate InterpolatingFunction explitely using Derivative of
> negative order
>
> eg the critical soltion to the equations of motion of an anharmonic
> pendulum
>
> X[t_] = x[t] /.
>     NDSolve[{x''[t] == -x[t]^3 + x[t], x' == 0, x == 1.42},
>      x[t], {t, 0, 100}] // First
>
> Y[t_]=Derivative[-1][Y][t]
>

--
DrMajorBob at yahoo.com

```

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