       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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