Re: Why is Mathematica assuming k==l and how do I make it not to?

*To*: mathgroup at smc.vnet.net*Subject*: [mg92611] Re: Why is Mathematica assuming k==l and how do I make it not to?*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Wed, 8 Oct 2008 06:25:11 -0400 (EDT)*Organization*: Uni Leipzig*References*: <gcffpl$f4g$1@smc.vnet.net>*Reply-to*: kuska at informatik.uni-leipzig.de

Hi, it doe not do that, it compute the integral and get (2*k*Cos[l*Pi]*Sin[k*Pi] - 2*l*Cos[k*Pi]*Sin[l*Pi])/(k^2 - l^2) and Sin[k*Pi] is 0 for any integer k and Sin[l*Pi] is 0 for any integer l. So it get 0 with out an assumption about the relation between k and l and you must treat the case k==l explicit. Regards Jens Aaron Fude wrote: > As in > > Assuming[Element[{k, l}, Integers] , > Integrate[Cos[k alpha] Cos[l alpha], {alpha, -Pi, Pi}]] > > I get 0 whereas the answer is Pi if k=l; > > Thanks! > > Aaron >