The formula for the order of the gauss quadrature in step 11 takes only the mapping order into account. If you increase the degree of the finite element the order of the quadrature formula must be increased, too. Usually you have to integrate products of finite element functions exactly (ansatz- times testfunction). Therefore the gaussorder should be increased to fe.degree+1. Otherwise you get a singular matrix in most cases. Hopefully this is the source of your problem.
Johannes Markus Bürg wrote: > Martin, > > the problem statement should be OK, because I chose the problem from step-11 > (f=-2, g=1). But I found the solution by myself. I have to choose finite > elements of order 1, then it runs well. At the moment I don't know why, but I > will figure out. > > Thank you for your help, > Markus > > > _______________________________________________ > dealii mailing list http://poisson.dealii.org/mailman/listinfo/dealii _______________________________________________ dealii mailing list http://poisson.dealii.org/mailman/listinfo/dealii
