Dear Alberto, Now I understand your concern. The boolean flag that is passed as the final parameter to MatrixTools::apply_boundary_values <https://www.dealii.org/8.5.0/doxygen/deal.II/namespaceMatrixTools.html#a9ad0eb7a8662628534586716748d62fb> determines whether column elimination is performed. You've set it to false, so this is not done and the RHS is unaltered. So switching it to true (the default) should preserve the symmetry of the system and make the necessary adjustments to the RHS vector.
J-P On Thursday, April 20, 2017 at 2:19:50 AM UTC+2, Alberto Salvadori wrote: > > Dear Jean-Paul, > > thanks for your reply. > > I see your point. It was my understanding (wrong, I guess) that in > imposing Dirichlet BC deal.II would modify the rows but also the columns, > adjusting the rhs accordingly. In this way, the symmetry of the system > matrix would have been preserved. I see now that this is not happening, in > all cases, is it correct? Then my question is about the solver, can we > still use CG as a solver if the system matrix looses symmetry? Does deal.II > make some further elaboration? > > Thank you again > > Alberto > > > > > > *Alberto Salvadori* Dipartimento di Ingegneria Civile, Architettura, > Territorio, Ambiente e di Matematica (DICATAM) > Universita` di Brescia, via Branze 43, 25123 Brescia > Italy > tel 030 3711239 > fax 030 3711312 > > e-mail: > alberto.salvad...@unibs.it > web-pages: > http://m4lab.unibs.it/faculty.html > http://dicata.ing.unibs.it/salvadori > > On Tue, Apr 18, 2017 at 11:10 AM, Jean-Paul Pelteret <> wrote: > >> Dear Alberto, >> >> The correctness of my answer depends on the numbering assigned to the >> degrees-of-freedom, which is something that you've not mentioned above. But >> from what I can discern the 9th row relates to the pressure test function, >> so K_{8,[0-7]} are the components from the coupling block K_{pu}, K_{88} is >> K_{pp} and K_{89} is K_{pJ}. Since these degree's of freedom are not >> constrained, this row should remain untouched after boundary values are >> applied. So, to me, nothing necessarily appears amiss on row 9 (as you've >> indicated). >> >> Do you agree with this? >> >> Kind regards, >> Jean-Paul >> >> On Tuesday, April 18, 2017 at 12:32:44 PM UTC+2, Alberto Salvadori wrote: >>> >>> Hi, >>> >>> sorry for asking your help again, that I really appreciated. >>> Today's issue is about imposing boundary conditions for a three-fields >>> formulation. >>> >>> In brief, I defined a 4 nodes square element, of type: >>> >>> fe(FE_Q<dim>(poly_degree), dim, // displacement >>> >>> FE_DGPMonomial<dim>(poly_degree - 1), 1, // pressure >>> >>> FE_DGPMonomial<dim>(poly_degree - 1), 1), // dilatation >>> >>> with poly_degree = 1. >>> >>> While debugging on a single element, which has 10 dofs in 2D ( 4x2 >>> displacements + 1 pressure + 1 dilatation), I aim at imposing Dirichlet >>> boundary conditions on displacements, whereas body forces are zero. >>> >>> The cell matrix and the cell_rhs are the following. >>> >>> *Cell matrix = * >>> >>> *{ 0.7037, 0.0278, -0.2037, -0.4722, -0.1481, 0.4722, -0.3519, >>> -0.0278, -1.0000, 0.0000}, * >>> >>> *{ 0.0278, 0.7037, 0.4722, -0.1481, -0.4722, -0.2037, -0.0278, >>> -0.3519, -1.0000, 0.0000}, * >>> >>> *{ -0.2037, 0.4722, 0.7037, -0.0278, -0.3519, 0.0278, -0.1481, >>> -0.4722, 1.0000, 0.0000}, * >>> >>> *{ -0.4722, -0.1481, -0.0278, 0.7037, 0.0278, -0.3519, 0.4722, >>> -0.2037, -1.0000, 0.0000}, * >>> >>> *{ -0.1481, -0.4722, -0.3519, 0.0278, 0.7037, -0.0278, -0.2037, >>> 0.4722, -1.0000, 0.0000}, * >>> >>> *{ 0.4722, -0.2037, 0.0278, -0.3519, -0.0278, 0.7037, -0.4722, >>> -0.1481, 1.0000, 0.0000}, * >>> >>> *{ -0.3519, -0.0278, -0.1481, 0.4722, -0.2037, -0.4722, 0.7037, >>> 0.0278, 1.0000, 0.0000}, * >>> >>> *{ -0.0278, -0.3519, -0.4722, -0.2037, 0.4722, -0.1481, 0.0278, >>> 0.7037, 1.0000, 0.0000}, * >>> >>> *{ -1.0000, -1.0000, 1.0000, -1.0000, -1.0000, 1.0000, 1.0000, >>> 1.0000, 0.0000, -4.0000}, * >>> >>> *{ 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, >>> 0.0000, -4.0000, 6.6667}, * >>> >>> *Cell rhs =0.000e+00 0.000e+00 0.000e+00 0.000e+00 0.000e+00 0.000e+00 >>> 0.000e+00 0.000e+00 0.000e+00 0.000e+00 * >>> >>> They seem to be correct. After calling >>> >>> system_matrix.compress(VectorOperation::add); >>> >>> system_rhs.compress(VectorOperation::add); >>> >>> the system matrix coincides with the cell matrix, the same for the rhs. >>> To impose BCs I followed the scheme of step-18, as follows: >>> >>> std::map<types::global_dof_index,double> boundary_values; >>> >>> >>> ComponentMask displacements_mask = fe.component_mask (displacements); >>> >>> VectorTools::interpolate_boundary_values (dof_handler, >>> >>> 0, >>> >>> >>> IncrementalDirichletBoundaryValues<dim>( TIDM, NRit, GPDofs ), >>> >>> boundary_values, >>> >>> displacements_mask); >>> >>> >>> >>> PETScWrappers::MPI::Vector tmp (locally_owned_dofs,mpi_communicator); >>> >>> MatrixTools::apply_boundary_values (boundary_values, >>> >>> system_matrix, >>> >>> tmp, >>> >>> system_rhs, >>> >>> false); >>> >>> incremental_displacement = tmp; >>> >>> where the class IncrementalDirichletBoundaryValues implements the >>> Dirichlet BC and GPDofs = 4. >>> The boundary values after VectorTools::interpolate_boundary_values turn >>> out to be: >>> >>> *boundary_values = -0.0500, -0.0500, -0.0500, 0.0500, 0.0500, >>> -0.0500, 0.0500, 0.0500, 0.0000, 0.0000, * >>> >>> *tmp = -0.0500, -0.0500, -0.0500, 0.0500, 0.0500, -0.0500, >>> 0.0500, 0.0500, 0.0000, 0.0000, * >>> >>> which are pretty much what I expected. However, after MatrixTools >>> ::apply_boundary_values the system matrix and the rhs are as follows, >>> >>> * System matrix = * >>> >>> *{ 0.7037, 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, >>> 0.0000, 0.0000, 0.0000}, * >>> >>> *{ 0.0000, 0.7037, 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, >>> 0.0000, 0.0000, 0.0000}, * >>> >>> *{ 0.0000, 0.0000, 0.7037, 0.0000, 0.0000, 0.0000, 0.0000, >>> 0.0000, 0.0000, 0.0000}, * >>> >>> *{ 0.0000, 0.0000, 0.0000, 0.7037, 0.0000, 0.0000, 0.0000, >>> 0.0000, 0.0000, 0.0000}, * >>> >>> *{ 0.0000, 0.0000, 0.0000, 0.0000, 0.7037, 0.0000, 0.0000, >>> 0.0000, 0.0000, 0.0000}, * >>> >>> *{ 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, 0.7037, 0.0000, >>> 0.0000, 0.0000, 0.0000}, * >>> >>> *{ 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, 0.7037, >>> 0.0000, 0.0000, 0.0000}, * >>> >>> *{ 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, >>> 0.7037, 0.0000, 0.0000}, * >>> >>> *{ -1.0000, -1.0000, 1.0000, -1.0000, -1.0000, 1.0000, 1.0000, >>> 1.0000, 0.0000, -4.0000}, * >>> >>> *{ 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, >>> 0.0000, -4.0000, 6.6667}, * >>> >>> *System_rhs = -0.0352, -0.0352, -0.0352, 0.0352, 0.0352, -0.0352, >>> 0.0352, 0.0352, 0.0000, 0.0000, * >>> >>> The* System_rhs *seems correct, but the matrix, particularly the 9th >>> row, does not, but I am not sure why. >>> >>> Many thanks in advance, >>> Alberto >>> >> -- >> The deal.II project is located at http://www.dealii.org/ >> For mailing list/forum options, see >> https://groups.google.com/d/forum/dealii?hl=en >> --- >> You received this message because you are subscribed to the Google Groups >> "deal.II User Group" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to dealii+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. >> > > > > Informativa sulla Privacy: http://www.unibs.it/node/8155 > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. 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