Date: Aug 22, 2012 2:25 AM
Author: Chris Arthur
Subject: Re: Problem with NIntegrate

Maybe i'm getting rusty with integration but since this is a triple 
integral with the limits of one variable defined in terms of another,
you should change the order of integration a bit so that the integral
with respect to Z evaluates before R. Maybe that will help.

So it is NIntegrate[....,{\[phi],...,..},{Z,...,...},{R,...,...}]

Chris

maves a écrit :
> Hello, I'm trying to numerically integrate a complicated expression and Mathematica keeps showing plenty of error messages, such as
> "NIntegrate::slwcon:Numerical integration converging too slowly; /.../",
> "NIntegrate::eincr: The global error of the strategy GlobalAdaptive has increased more than 2000 times./../" and so on. If I only want to see the spatial distribution of the solution (contour plots in different planes etc.) , it somehow manages to come to an end, but the problem is that I need to use this solution in NDSolve, so it would take too long for the program to find the root.
>
> One of the problematic integrals is for instance
>
> NIntegrate[
> R (x - R Cos[\[Phi]] )/((x - R Cos[\[Phi]] )^2 + (y -
> R Sin[\[Phi]] )^2 + (0 - Z)^2)^(3/2), {\[Phi], 0, 2 Pi}, {R,
> b, b + c}, {Z, R - (b + c), -R + (b + c)}
>
> Any idea what is "wrong" with the integrand so that I get all these error messages?
>
>
>