usage: int = quad2dg('Fun',xlow,xhigh,ylow,yhigh)
or
int = quad2dg('Fun',xlow,xhigh,ylow,yhigh,tol)
This function is similar to QUAD or QUAD8 for 2-dimensional integration,
but it uses a Gaussian quadrature integration scheme.
int -- value of the integral
Fun -- Fun(x,y) (function to be integrated)
xlow -- lower x limit of integration
xhigh -- upper x limit of integration
ylow -- lower y limit of integration
yhigh -- upper y limit 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).
