Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Does this integral exist?

  1. May 30, 2010 #1
    1. The problem statement, all variables and given/known data
    2. Relevant equations

    (sin(100*x))^x , integral from 0 to 2pi

    3. The attempt at a solution
    I typed it into the wolfram integration calculator and another i found online, and both say that this is probably a nonelementary integral.
    Any thoughts?

    miss fangula
  2. jcsd
  3. May 30, 2010 #2
    Mathematica also says it doesn't. Even NIntegrate (integrating numerically) returns error messages.
  4. May 30, 2010 #3
    What is the domain of definition of the integrand

    \sin^{x}(100 \, x)
  5. May 30, 2010 #4
    Yes Miss Fangula. You should break it apart and analyze what's going on. Just consider sin(a x). As a increases, it oscillates more. That's a problem for numerical integrators and that is the message Mathematica gives you when a=100. Now what happens when you put a real number as an exponent? For example, what happens when say for example sin(ax)=-0.5 and the exponent is for example 1/2? That's going to be a complex number right? Also, Mathematica will always use the "principal" value for the root and that may not represent the analytic continuation of the function throughout the domain of integration and thus even the numerical answer you get may not be the one you want. So try plotting the function for just some values of a to get some understanding of what it looks like. Also try plotting just the real or imaginary part and keep in mind it's multi-valued in general and also I think it's antiderivative is non-elementary.
  6. Jun 2, 2010 #5
    Thanks for all the replies. I will try the plotting, jackmell. Dickfore, the domain is [0,100]. any thoughts about that?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook