function s=integrate(u,h);
% s=integrate(u,h) is the integral of the solution computed by adfem. 
% u and h are row vectors containing the integrand and the mesh 
% as computed by adfem. The integral is computed by the trapezoidal rule. 
n=size(h); n=n(2);
uu=(u(1:n)+u(2:n+1))/2; 
s=uu*h';

