Hello DealII's users: I would like to clarify a concept. I try to calculate the error |p(n)-p_h(n)| within L2 norm in the following way:
FE_Q<DIMENSION> fe_velocity(VELOCITY_ORDER); FE_Q<DIMENSION> fe_pressure(PRESSURE_ORDER); FESystem<DIMENSION> fe_total(fe_velocity,DIMENSION, fe_pressure,1); //DIMENSION=2 ComponentSelectFunction<DIMENSION> seleccionp (2,1,3); if(PRESSURE_ORDER==2) integrando_pres=2; else if(PRESSURE_ORDER==2) integrando_pres=1; //L2norm de p: VectorTools::integrate_difference(dof_handler_total, Bvector_solution, mi_Functions::Kim_Moin2d_final<DIMENSION(DIMENSION+1,viscosity,time_step*time_step_value), difference_per_cell_p,QGauss<DIMENSION(integrando_pres),VectorTools::L2_norm,& seleccionp); long double errorpre=difference_per_cell_p.l2_norm(); If I use Q2 for pressure, I will use a Gauss-Legendre quadrature of 2 order (QGauss<DIMENSION(integrando_pres) with integrando_pres=2). And if I use Q1 for pressure, I will use a Gauss-Legendre quadrature of 1 order (QGauss<DIMENSION(integrando_pres) with integrando_pres=1), since with n quadrature points I get an exact integration for polynomials of degree 2n-1. I calculate this error in that way for different refined meshes (a square of 32*32 elements, i.e. with a mesh size of h=1/32, a square of 64*64 elements,i.e. with a mesh size of h=1/64,...). If I calculate the error in that way, I obtain a good behaviour of the error, i.e. pressure error with a mesh size of h=1/32 is bigger than the pressure error with a mesh size of h=1/64. However, if I use QGauss<DIMENSION(3), i.e. with a bigger order in the quadrature, in the VectorTools::integrate_difference() method, I get a pressure error that isn't smaller with a small mesh size, on the contrary: pressure error with a mesh size of h=1/32 is smaller than the pressure error with a mesh size of h=1/64. Could you help me explaining me this behaviour? Is this result possible? Thanks in advance and best regards. Isa _______________________________________________ dealii mailing list http://poisson.dealii.org/mailman/listinfo/dealii
