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Re: A Problem with Simplify
*To*: mathgroup at smc.vnet.net
*Subject*: [mg87490] Re: A Problem with Simplify
*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
*Date*: Fri, 11 Apr 2008 01:48:47 -0400 (EDT)
*References*: <ftkb7f$a9m$1@smc.vnet.net>
Hi,
the problem is Integrate[] and not simplify because
Integrate[Sin[(n*Pi*x)/L]*Sin[(n*Pi*x)/L], {x, 0, L}]
is different from
Integrate[Sin[(m*Pi*x)/L]*Sin[(n*Pi*x)/L], {x, 0, L}]
and Mathematica should integrate twice.
Regards
Jens
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
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