Integral of exponential involving sines and cosines

  • Thread starter Repetit
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  • #1
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Main Question or Discussion Point

Hey!

Can someone help me solve the following integral

[tex]
\int_0^{2\pi} exp[-i(G_x \cos\theta + G_y \sin\theta] d\theta
[/tex]

I've tried splitting the exponential into a product of two exponetials and rewriting the exponentials in terms of sines and cosines. But I always end up getting stuck. Some of my rewritings ended up looking close to a Bessel function but it's just not quite the same. Can someone just give me a hint on where to start?

Im not sure about the limits, they might have to be from [tex]-\pi[/tex] to [tex]\pi[/tex] but I don't believe that should change anything.

Thanks in advance
 

Answers and Replies

  • #2
141
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Probably the answer will look like some combination of Bessel Js.

[tex]
J_{n}(x) = \int_{0}^{2\pi}\frac{d\phi}{2\pi}e^{-ix\sin\phi + in\phi}
[/tex]

There is an expansion:

[tex]
e^{-ix\sin\phi} = \sum_{k=-\infty}^{\infty}J_{k}(x)e^{-ik\phi}
[/tex]

So in principle you can expand each exponentional term into Fourier harmonics and evaluate the angular integral, then resum the resulting expression. There is probably an easier way though....
 

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