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

Simultaneous equations with an integral

  1. Jun 11, 2009 #1
    Hello

    I am having a problem solving a set of simultaneous equations in mathematica. One of the equations is an integral, with the unkowns as limits of integration, and the other is a function containing both variables, but no closed form solution can be found for either variable. I am therefore attempting to solve it numerically.

    I have tried both FindRoot and NSolve, and i get the same error for both, namely that algebraic limits cannot be supplied with Nintegrate. Below is a sample of what I'm trying to do (I have replaced the functions with simpler examples to avoid confusion - I am aware that this problem does not need to be solved numerically!!)

    Code (Text):
    f[s_] := 2 s
    NSolve[{NIntegrate[f[s], {s, (a + b)/2, a + 2 b}] == 0, a - 2 b + 2 == 0. {a, b}]
    Apologies if i the above code has errors, I have had to copy it from one machine to another, and may have made a mistake in doing so.

    Any help would be greatly appreciated.

    Mat Davies
     
  2. jcsd
  3. Jun 12, 2009 #2
    I have now solved this problem

    For the record, the messages were only warnings in the above code, but they were errors in my original code. The solution was to use the more stable FindMinimum function

    Thanks

    mat
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook