Lex, I would strongly advice against using AffineConstraints::condense() in an MPI parallel computation. It is inefficient and also likely incorrect if you run it before distribute_sparsity_pattern(). Instead, use distribute_local_to_global during assembly (see step-40 for an example).
-- Timo Heister http://www.math.clemson.edu/~heister/ ________________________________ From: dealii@googlegroups.com <dealii@googlegroups.com> on behalf of Lex Lee <hitlex...@gmail.com> Sent: Wednesday, September 27, 2023 8:15:14 PM To: deal.II User Group <dealii@googlegroups.com> Subject: [deal.II] Difference between 2 Wasy to Initialize System Matrix in MPI World This Message Is From An External Sender: Use caution when opening links or attachments if you do not recognize the sender. Hello all, Previously, I initialized my system matrix in this way (option A) DoFTools::make_flux_sparsity_pattern(dof_handler, dsp, cell_coupling, face_coupling); constraints_newton_update.condense(dsp); SparsityTools::distribute_sparsity_pattern(dsp, hp_index_set, mpi_communicator, hp_relevant_set); system_matrix.reinit(hp_index_set, hp_index_set, dsp, mpi_communicator); However, the generated system matrix is singular. I was stuck by the singular matrix problem for about 2 weeks. Then, I initialized the matrix with option B, which generates a full rank matrix. Although, I don't see the difference between these 2 ways. Can someone explain this to me? Thans in advance. DoFTools::make_flux_sparsity_pattern(dof_handler, dsp, cell_coupling, face_coupling); constraints_newton_update.condense(dsp); sparsity_pattern.copy_from(dsp); system_matrix.reinit(hp_index_set, sparsity_pattern, mpi_communicator); -- 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<mailto:dealii+unsubscr...@googlegroups.com>. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/abecb5ba-e894-47eb-bc0d-1ef5590ba14cn%40googlegroups.com<https://groups.google.com/d/msgid/dealii/abecb5ba-e894-47eb-bc0d-1ef5590ba14cn%40googlegroups.com?utm_medium=email&utm_source=footer>. -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/BN7PR06MB528358C2164AB180FA3660FDA1C1A%40BN7PR06MB5283.namprd06.prod.outlook.com.
