usage: int = quadndg('Fun',xlow,xhigh)
or
int = quadndg('Fun',xlow,xhigh,tol)
This function is similar to QUAD or QUAD8 for n-dimensional integration,
but it uses a Gaussian quadrature integration scheme.
int -- value of the integral
Fun -- Fun(x) (function to be integrated) in this case treat
all the different values of x as different variables
as opposed to different instances of the same variable
x -- n length vector of coordinates
xlow -- n length vector of lower limits of integration
xhigh -- n length vector of upper limits of integration
tol -- tolerance parameter (optional)
Note that if there are discontinuities the region of integration
should be broken up into separate pieces. And if there are singularities,
a more appropriate integration quadrature should be used
(such as the Gauss-Chebyshev for a specific type of singularity).
