Need analytic solution!

by quasar_4
Tags: analytic, solution
quasar_4 is offline
Apr17-08, 10:15 PM
P: 290
Hi everyone. Maple and I have collectively racked our brains and I've tried most of the integration techniques I know. Does anyone know the solution to the integral

[tex]\int[/tex] exp(-a*abs(x))*exp(i*(k0-k)*x)*dx

from -infinity to infinity (not sure how to get the limits over the integral sign here in this text box)???

There might be a good change of variables, but my brain is now too fried to think of it. Or does this baby just not have a nice solution? anyone?
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esbo is offline
Apr17-08, 11:07 PM
P: 84
Not me :O)
uart is offline
Apr17-08, 11:13 PM
Sci Advisor
P: 2,751
What? That's trivial if you just split the integral into two parts, one part from -infinity to zero and the other from 0 to infinity as it lets you get rid of the annoying abs(x).

I got [tex] \frac{1}{a-bi} + \frac{1}{a+bi} = \frac{2a}{a^2+b^2}[/tex]

BTW. [tex]b = k_0 - k[/tex] in my solution.

quasar_4 is offline
Apr18-08, 09:02 AM
P: 290

Need analytic solution!

Haha, yes, I realized that once I got home and felt REALLY dumb for posting the previous msg. I think in fact you can use trig identities and Euler's relation as well to split into a sin and cos part, then the sin drops out (since it's over a symmetric interval) and you can take twice the integral of the cos part from 0-infinity. That hadn't worked at the time, but it turns out I was being brain-dead and forgetting to drop my abs. Duh!! That's what I get for doing homework on 2 hours of sleep...

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