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
>