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Substitution of variables to remove singularities.

  1. Feb 10, 2013 #1
    1. The problem statement, all variables and given/known data
    I am given an integral for which I need to substitute variables to remove a singularity so that the integral can be computed in Matlab using the Composite Trapezoidal Method, and then compared to the integral computed in Maple to 16 digit precision. I am stuck on the variable substitution. The integral is:

    [itex] \int_0^1 \frac{e^{-x}}{x^{3/4}}\,dx [/itex]

    3. The attempt at a solution
    I attempted the following substitution:
    [itex] du= \frac {dx}{x^{3/4}} [/itex] so that [itex] u=4x^{1/4} [/itex] which resulted in the integral:
    [itex] \int_0^4 e^{ -{\frac{u^4}{256}}}\,du [/itex]

    Which doesn't seem to work at all. I suspect the error is in the substitution of variables. Any help/input would be fantastic.
     
    Last edited: Feb 10, 2013
  2. jcsd
  3. Feb 10, 2013 #2

    Dick

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    i) what happened to the minus sign in the exponential? ii) x isn't u^4/64. Check that '64'. And iii) when you go to the u integration, you'd better change the x limits to u limits.
     
  4. Feb 10, 2013 #3
    Hey, the missing minus and 64 were typos. I changed x to equal u^4/256 and included the minus sign, and then changed the limits of integration from 0 to 1 to 0 to 4, but still no luck.
     
  5. Feb 10, 2013 #4

    Dick

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    Then it should be ok. How do you mean, 'no luck'?
     
  6. Feb 10, 2013 #5
    The assignment said that removing the singularity would make it doable in Maple but all Maple is returning for me is a series of WhittakerM functions, which I am not familiar with. Perhaps the assignment made it seem to simple and more legwork is required.
     
  7. Feb 10, 2013 #6
    Dick, the remaining issue was in my coding in Maple. Thank you very much for your help, it was great.
     
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