       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

```

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