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] == 0, x[0] == 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? >> >> 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] > -- DrMajorBob at yahoo.com