Re: Integrating an InterpolatingFunction times another function

*To*: mathgroup at smc.vnet.net*Subject*: [mg126070] Re: Integrating an InterpolatingFunction times another function*From*: A Retey <awnl at gmx-topmail.de>*Date*: Sat, 14 Apr 2012 03:13:15 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <jm8q6r$j74$1@smc.vnet.net>

Hi > I have made a sample InterpolatingFunction: > > points = {{0, 0}, {1, 1}, {2, 3}, {3, 4}, {4, 3}, {5, 0}}; > ifun = Interpolation[points] > > The following integral computes fine: > > Integrate[ifun[x], {x, 1, 5}] > > However, this integral will not be evaluated: > > Integrate[x*ifun[x], {x, 1, 5}] > > Why will this integral not be computed? Is there any way that I can > compute this integral? Use NIntegrate. It's probably worth noting that it is a very special feature that integration of just interpolating functions works symbolically, you can even get another interpolating function for the indefinite integral, e.g.: Integrate[ifun[x],x] hth, albert