> > If you use elements of order p, you need to choose a quadrature > > formula with p+1 points in each direction, since your integrand is a > > polynomial of degree 2p and your quadrature formula needs to integrate > > that correctly. > > You mean the integrand is a polynomial of degree 2p using elements of > order p because I am working with a 2D problem, doesn't it?
No. It's because you integrate the square of a function of polynomial degree p in each variable, so the degree is 2p. > > I can't tell what is going wrong, but you should definitely use a > > quadrature formula that has enough points to make sure the integration > > is exact (or that the integration error is of higher order than the > > error in the numerical approximation). > > So, to avoid having the integration error of higher order than the error > in the numerical approximation, the only way is using (PRESSURE_ORDER+1) > in the quadrature formula, isn't it? Yes, or PRESSURE_ORDER+2, etc. W. ------------------------------------------------------------------------- Wolfgang Bangerth email: [email protected] www: http://www.math.tamu.edu/~bangerth/ _______________________________________________ dealii mailing list http://poisson.dealii.org/mailman/listinfo/dealii
