Re: Problems integrating InterpolatingFunction

*To*: mathgroup at smc.vnet.net*Subject*: [mg116090] Re: Problems integrating InterpolatingFunction*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Tue, 1 Feb 2011 06:55:25 -0500 (EST)

Use FunctionInterpolation s = y /. NDSolve[{y'[x] == y[x] Cos[x + y[x]], y[0] == 1}, y, {x, 0, 30}][[1]]; NIntegrate[1/s[x]^2, {x, 0, 30}] 10325.5 v = FunctionInterpolation[ Evaluate[ Table[ D[ Integrate[1/s[t]^2, {t, 0, x}], {x, k}], {k, 0, 1}]], {x, 0, 30}]; v[30] 10325.5 Plot[v[x], {x, 0, 30}] Bob Hanlon ---- Sergio Miguel Terrazas Porras <sterraza at uacj.mx> wrote: ============= Hi again, the thing is that I need a function as a result of the integration, no a number. I can make a very long table of the results of NIntegrate, then try to fit the elements of Table, etc. I just needed to know if it was possible to obtain a function directly from the indefinite integral. In the documentation there is an example of an indefinte integral of an InterpolatinFuntion. Thanks to all who responded. Sergio ________________________________________ De: Bob Hanlon [hanlonr at cox.net] Enviado el: domingo, 30 de enero de 2011 01:32 a.m. Para: mathgroup at smc.vnet.net Asunto: [mg116049] Re: Problems integrating InterpolatingFunction You must use NIntegrate s = y /. NDSolve[{y'[x] == y[x] Cos[x + y[x]], y[0] == 1}, y, {x, 0, 30}][[1]]; NIntegrate[1/s[x]^2, {x, 0, 30}] 10325.5 Bob Hanlon ---- Sergio Miguel Terrazas Porras <sterraza at uacj.mx> wrote: ========================== 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