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Re: Problems integrating InterpolatingFunction


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?
>
> Thanks in advance.
>
> 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] == 0, x[0] == 1.42},
     x[t], {t, 0, 100}] // First

Y[t_]=Derivative[-1][Y][t]

-- 

Roland Franzius


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