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An integral for thought

  1. Apr 2, 2007 #1
    I am trying to integrate:

    x(z)/(1+x(z)) wrt z.

    I know the function x(z), it basically just made up a linear combination of several decimal powers of z. Mathematica refuses to do an numerical integration and just crashes when it gets a couple of minutes in on my laptop.

    If x(z) was just z then I could obviously use some standard integrals but I think this is more complex than that. Any ideas on how to solve this one? I have attached the exact equation in a mathematica notebook.


    Attached Files:

  2. jcsd
  3. Apr 3, 2007 #2
    Is this complex or real integration? And what are your limits of integration? And it would probably help if you wrote out the entire integral.
  4. Apr 3, 2007 #3


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    Dearly Missed

    Remember that this can effectively be reduced to integrating:
    It is by no means obvious why this should at all be possible; if it were, you would for example be able to solve for the particular choice:
    That would be equivalent to find an anti-derivative to the error function..
  5. Apr 3, 2007 #4


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    I was trying to approve the attachment, but my PC doesn't know what file type *.NB is. What application uses *.NB files?
  6. Apr 3, 2007 #5
  7. Apr 3, 2007 #6
    I posted the original content of the .nb file to the attached pdf. Maybe the forum needs a tutorial on the simple process for Mathematica -> TeX.

    From a mathematica point of view, you natski are not integrating numerically, you are forcing a symbolic result. To integrate numerically, just use the function NIntegrate, like this:

    Code (Text):

    NIntegrate[integrand, {ψ, 0, N[Pi/2]}]

    Then the result is:1.66469

    Attached Files:

    Last edited: Apr 3, 2007
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