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i am trying to evaluate the following

[tex]

A=\sum_{m=-N}^{N} \cos(\frac{mk\pi}{N+1})\cos(\frac{mj\pi}{N+1})[/tex]

to give you an idea of the sort of answer i am after i present to you the following

[tex]

\sum_{m=-N}^{N} \sin(\frac{mk\pi}{N+1})\sin(\frac{mj\pi}{N+1})=(N+1)\delta_{k,j}[/tex]

hopefully there are some knowledgable people that can shed some light on the matter

thanks.

i come up with the following

A=2N+1 if k=j=0

A=N if k=j, k not equal to 0

A=1 if (k+j) is even

A=-1 if (k+j) is odd

but i am not sure how to get this into one nice function so to speak like the example i gave above

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# Sum evaluation help

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