       Re: Why is Mathematica assuming k==l and how do I make it

• To: mathgroup at smc.vnet.net
• Subject: [mg92613] Re: [mg92588] Why is Mathematica assuming k==l and how do I make it
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Wed, 8 Oct 2008 06:25:34 -0400 (EDT)

```Integrate[Cos[k alpha] Cos[l alpha], {alpha, -Pi, Pi},
Assumptions -> {l == k, Element[{l, k}, Integers]}]

Pi

Integrate[Cos[k alpha] Cos[l alpha], {alpha, -Pi, Pi},
Assumptions -> {l != k, Element[{l, k}, Integers]}]

0

Assuming[{l == k, Element[{k, l}, Integers]},
Integrate[Cos[k alpha] Cos[l alpha], {alpha, -Pi, Pi}]]

Pi

Assuming[{l != k, Element[{k, l}, Integers]},
Integrate[Cos[k alpha] Cos[l alpha], {alpha, -Pi, Pi}]]

0

Bob Hanlon

---- Aaron Fude <aaronfude at gmail.com> 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

--

Bob Hanlon

```

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