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Topic: wrong result when computing a definite integral
Replies: 3   Last Post: Jan 11, 2013 10:24 PM

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Kevin J. McCann

Posts: 145
Registered: 12/7/04
Re: wrong result when computing a definite integral
Posted: Jan 11, 2013 10:22 PM
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Well that is disturbing. If you put parens around the inner (y)
integral, it works correctly. Also, the separate individual integrals
work fine. I cannot figure out why this should be.

Kevin

On 1/10/2013 9:38 PM, Dexter Filmore wrote:
> hi group,
>
> i run into this problem today when giving a bunch of easy integrals to mathematica.
> here's a wolfram alpha link to the problem:
> http://www.wolframalpha.com/input/?i=Integrate%5BExp%5BI+Sqrt%5B3%5Dy%5D%2C%7Bx%2C-2Pi%2C2Pi%7D%2C%7By%2C-Pi%2CPi%7D%5D#
>
> the integrand does not depend on the 'x' variable, the inner integration should only result in a factor of 4Pi, and the correct result is a real number, yet the below integral gives a complex number which is far off from the correct value:
> Integrate[Exp[I Sqrt[3] y], {x, -2 Pi, 2 Pi}, {y, -Pi, Pi}] -> -((4 I (-1 + E^(2 I Sqrt[3] Pi)) Pi)/Sqrt[3])
>
> from some trial and error it seems the result is also incorrect for non-integer factors in the exponential.
>





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