Re: A Problem with Simplify

*To*: mathgroup at smc.vnet.net*Subject*: [mg87444] Re: A Problem with Simplify*From*: dh <dh at metrohm.ch>*Date*: Fri, 11 Apr 2008 01:40:10 -0400 (EDT)*References*: <ftkb7f$a9m$1@smc.vnet.net>

Hi Kevin, the culprit is Integrate not Simplify. In the manual one finds: "For indefinite integrals, Integrate tries to find results that are correct for almost all values of parameters." I think this to be a trap for the unwary. hope this helps, Daniel Kevin J. McCann wrote: > I have the following rather simple integral of two sines, which should > evaluate to zero if m is not equal to n and to L/2 if they are the same. > > The following is just fine > > Imn = Simplify[Integrate[ > Sin[(m*Pi*x)/L]* > Sin[(n*Pi*x)/L], > {x, 0, L}]] > > > However, if I specify that m and n are integers, I only get the > "general" solution of zero, i.e. when m and n are not equal. > > Imn = Simplify[Integrate[ > Sin[(m*Pi*x)/L]* > Sin[(n*Pi*x)/L], > {x, 0, L}], > Element[m, Integers] && > Element[n, Integers]] > > The workaround is obvious in this case, but shouldn't Mathematica give multiple > answers? Perhaps something similar to what it already does with Integrate? > > Kevin