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Homework Help: Contour integral, exp(-z^2)

  1. Mar 20, 2010 #1
    1. The problem statement, all variables and given/known data Integrate exp(-z^2) over the rectangle with vertices at 0, R, R + ia, and ia.



    2. Relevant equations

    int(0, inf)(exp(-x^2)) = sqrt(pi/2)

    3. The attempt at a solution I really don't have much of an idea here - the function is analytic so has no residues... The part from 0 to R is just the real integral, but for the other 3 sides I'm not too sure on how to proceed.
     
  2. jcsd
  3. Mar 20, 2010 #2

    ideasrule

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    Isn't the contour integral equal to 0 if there are no poles?
     
  4. Mar 20, 2010 #3
    This is what I would have thought, but I'm supposed to be using the integral of e^(-z^2) to evaluate the real integral int(0,inf)((e^(-x^2))*cos(2ax)), which is apparently equal to
    sqrt(pi)*exp(-a^2)/2.
     
  5. Mar 20, 2010 #4
  6. Mar 20, 2010 #5

    ideasrule

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    Ah, that makes much more sense.

    If we want to integrate from R+ia to ia, just integrate e^(-z^2)dz=e^-(x+ia)^2 dx from R to 0. Do the same for the other 3 sides. You won't get an analytic answer, but that's OK; just write out the entire contour integral first and you'll see where this is going.
     
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