Suming InterpolatingFunction Objects

*To*: mathgroup at smc.vnet.net*Subject*: [mg120233] Suming InterpolatingFunction Objects*From*: Gabriel Landi <gtlandi at gmail.com>*Date*: Thu, 14 Jul 2011 05:22:34 -0400 (EDT)

Hello everyone. I encountered the following problem, which I am not sure is a bug or simply a annoying detail. I will use as an example a piece of code from the mathematica tutorials. Say I solve a system of ODEs s = NDSolve[{x'[t] == -y[t] - x[t]^2, y'[t] == 2 x[t] - y[t]^3, x[0] == y[0] == 1}, {x, y}, {t, 20}] My quantity of interest could be x[t] + y[t]. I can plot it: Plot[x[t] + y[t] /. s, {t, 0, 20}] But say I wish to store it as a single object. So I do (this is the kinky part): sum = FunctionInterpolation[x[t] + y[t] /. s, {t, 0, 20}] Now, when I plot the result, it comes out completely different. It looks like something changed with the interpolation order or something. Plot[sum[t], {t, 0, 20}] What do you guys think? Best regards, Gabriel

**Follow-Ups**:**Re: Suming InterpolatingFunction Objects***From:*DrMajorBob <btreat1@austin.rr.com>

**Re: Suming InterpolatingFunction Objects***From:*DrMajorBob <btreat1@austin.rr.com>

**Re: Suming InterpolatingFunction Objects***From:*DrMajorBob <btreat1@austin.rr.com>

**Re: Suming InterpolatingFunction Objects***From:*Oliver Ruebenkoenig <ruebenko@wolfram.com>