On Fri, Jun 28, 2024 at 4:05 AM Blauth, Sebastian < sebastian.bla...@itwm.fraunhofer.de> wrote:
> Hello everyone, > > > > I have a question regarding the naming convention using PETSc’s > PCFieldsplit. I have been following > https://urldefense.us/v3/__https://lists.mcs.anl.gov/pipermail/petsc-users/2019-January/037262.html__;!!G_uCfscf7eWS!bGTaf64ibyuvBn-Qy-UQpxjLdOqFq44f6kBHzEDsXKc0htzQNw1MabtoK463uwb95Pupw_BcLMNwOHdcKldy$ > > to create a DMShell with FEniCS in order to customize PCFieldsplit for my > application. > > I am using the following options, which work nicely for me: > > > > -ksp_type fgmres > > -pc_type fieldsplit > > -pc_fieldsplit_0_fields 0, 1 > > -pc_fieldsplit_1_fields 2 > > -pc_fieldsplit_type additive > > -fieldsplit_0_ksp_type fgmres > > -fieldsplit_0_pc_type fieldsplit > > -fieldsplit_0_pc_fieldsplit_type schur > > -fieldsplit_0_pc_fieldsplit_schur_fact_type full > > -fieldsplit_0_pc_fieldsplit_schur_precondition selfp > > -fieldsplit_0_fieldsplit_u_ksp_type preonly > > -fieldsplit_0_fieldsplit_u_pc_type lu > > -fieldsplit_0_fieldsplit_p_ksp_type cg > > -fieldsplit_0_fieldsplit_p_ksp_rtol 1e-14 > > -fieldsplit_0_fieldsplit_p_ksp_atol 1e-30 > > -fieldsplit_0_fieldsplit_p_pc_type icc > > -fieldsplit_0_ksp_rtol 1e-14 > > -fieldsplit_0_ksp_atol 1e-30 > > -fieldsplit_0_ksp_monitor_true_residual > > -fieldsplit_c_ksp_type preonly > > -fieldsplit_c_pc_type lu > > -ksp_view > By default, we use the field names, but you can prevent this by specifying the fields by hand, so -fieldsplit_0_pc_fieldsplit_0_fields 0 -fieldsplit_0_pc_fieldsplit_1_fields 1 should remove the 'u' and 'p' fieldnames. It is somewhat hacky, but I think easier to remember than some extra option. Thanks, Matt > Note that this is just an academic example (sorry for the low solver > tolerances) to test the approach, consisting of a Stokes equation and some > concentration equation (which is not even coupled to Stokes, just for > testing). > > Completely analogous to > https://urldefense.us/v3/__https://lists.mcs.anl.gov/pipermail/petsc-users/2019-January/037262.html__;!!G_uCfscf7eWS!bGTaf64ibyuvBn-Qy-UQpxjLdOqFq44f6kBHzEDsXKc0htzQNw1MabtoK463uwb95Pupw_BcLMNwOHdcKldy$ > , > I translate my IS’s to a PETSc Section, which is then supplied to a DMShell > and assigned to a KSP. I am not so familiar with the code or how / why this > works, but it seems to do so perfectly. I name my sections with petsc4py > using > > > > section.setFieldName(0, "u") > > section.setFieldName(1, "p") > > section.setFieldName(2, "c") > > > > However, this is also reflected in the way I can access the fieldsplit > options from the command line. My question is: Is there any way of not > using the FieldNames specified in python but use the index of the field as > defined with “-pc_fieldsplit_0_fields 0, 1” and “-pc_fieldsplit_1_fields > 2”, i.e., instead of the prefix “fieldsplit_0_fieldsplit_u” I want to write > “fieldsplit_0_fieldsplit_0”, instead of “fieldsplit_0_fieldsplit_p” I want > to use “fieldsplit_0_fieldsplit_1”, and instead of “fieldsplit_c” I want to > use “fieldsplit_1”. Just changing the names of the fields to > > > > section.setFieldName(0, "0") > > section.setFieldName(1, "1") > > section.setFieldName(2, "2") > > > > does obviously not work as expected, as it works for velocity and > pressure, but not for the concentration – the prefix there is then > “fieldsplit_2” and not “fieldsplit_1”. In the docs, I have found > https://urldefense.us/v3/__https://petsc.org/main/manualpages/PC/PCFieldSplitSetFields/__;!!G_uCfscf7eWS!bGTaf64ibyuvBn-Qy-UQpxjLdOqFq44f6kBHzEDsXKc0htzQNw1MabtoK463uwb95Pupw_BcLMNwOD6iRa_k$ > which seems > to suggest that the fieldname can potentially be supplied, but I don’t see > how to do so from the command line. Also, for the sake of completeness, I > attach the output of the solve with “-ksp_view” below. > > > > Thanks a lot in advance and best regards, > > Sebastian > > > > > > The output of ksp_view is the following: > > KSP Object: 1 MPI processes > > type: fgmres > > restart=30, using Classical (unmodified) Gram-Schmidt > Orthogonalization with no iterative refinement > > happy breakdown tolerance 1e-30 > > maximum iterations=10000, initial guess is zero > > tolerances: relative=1e-05, absolute=1e-11, divergence=10000. > > right preconditioning > > using UNPRECONDITIONED norm type for convergence test > > PC Object: 1 MPI processes > > type: fieldsplit > > FieldSplit with ADDITIVE composition: total splits = 2 > > Solver info for each split is in the following KSP objects: > > Split number 0 Defined by IS > > KSP Object: (fieldsplit_0_) 1 MPI processes > > type: fgmres > > restart=30, using Classical (unmodified) Gram-Schmidt > Orthogonalization with no iterative refinement > > happy breakdown tolerance 1e-30 > > maximum iterations=10000, initial guess is zero > > tolerances: relative=1e-14, absolute=1e-30, divergence=10000. > > right preconditioning > > using UNPRECONDITIONED norm type for convergence test > > PC Object: (fieldsplit_0_) 1 MPI processes > > type: fieldsplit > > FieldSplit with Schur preconditioner, factorization FULL > > Preconditioner for the Schur complement formed from Sp, an assembled > approximation to S, which uses A00's diagonal's inverse > > Split info: > > Split number 0 Defined by IS > > Split number 1 Defined by IS > > KSP solver for A00 block > > KSP Object: (fieldsplit_0_fieldsplit_u_) 1 MPI processes > > type: preonly > > maximum iterations=10000, initial guess is zero > > tolerances: relative=1e-05, absolute=1e-50, divergence=10000. > > left preconditioning > > using NONE norm type for convergence test > > PC Object: (fieldsplit_0_fieldsplit_u_) 1 MPI processes > > type: lu > > out-of-place factorization > > tolerance for zero pivot 2.22045e-14 > > matrix ordering: nd > > factor fill ratio given 5., needed 3.92639 > > Factored matrix follows: > > Mat Object: 1 MPI processes > > type: seqaij > > rows=4290, cols=4290 > > package used to perform factorization: petsc > > total: nonzeros=375944, allocated nonzeros=375944 > > using I-node routines: found 2548 nodes, limit used is > 5 > > linear system matrix = precond matrix: > > Mat Object: (fieldsplit_0_fieldsplit_u_) 1 MPI processes > > type: seqaij > > rows=4290, cols=4290 > > total: nonzeros=95748, allocated nonzeros=95748 > > total number of mallocs used during MatSetValues calls=0 > > using I-node routines: found 3287 nodes, limit used is 5 > > KSP solver for S = A11 - A10 inv(A00) A01 > > KSP Object: (fieldsplit_0_fieldsplit_p_) 1 MPI processes > > type: cg > > maximum iterations=10000, initial guess is zero > > tolerances: relative=1e-14, absolute=1e-30, divergence=10000. > > left preconditioning > > using PRECONDITIONED norm type for convergence test > > PC Object: (fieldsplit_0_fieldsplit_p_) 1 MPI processes > > type: icc > > out-of-place factorization > > 0 levels of fill > > tolerance for zero pivot 2.22045e-14 > > using Manteuffel shift [POSITIVE_DEFINITE] > > matrix ordering: natural > > factor fill ratio given 1., needed 1. > > Factored matrix follows: > > Mat Object: 1 MPI processes > > type: seqsbaij > > rows=561, cols=561 > > package used to perform factorization: petsc > > total: nonzeros=5120, allocated nonzeros=5120 > > block size is 1 > > linear system matrix followed by preconditioner matrix: > > Mat Object: (fieldsplit_0_fieldsplit_p_) 1 MPI processes > > type: schurcomplement > > rows=561, cols=561 > > Schur complement A11 - A10 inv(A00) A01 > > A11 > > Mat Object: (fieldsplit_0_fieldsplit_p_) 1 MPI processes > > type: seqaij > > rows=561, cols=561 > > total: nonzeros=3729, allocated nonzeros=3729 > > total number of mallocs used during MatSetValues calls=0 > > not using I-node routines > > A10 > > Mat Object: 1 MPI processes > > type: seqaij > > rows=561, cols=4290 > > total: nonzeros=19938, allocated nonzeros=19938 > > total number of mallocs used during MatSetValues calls=0 > > not using I-node routines > > KSP of A00 > > KSP Object: (fieldsplit_0_fieldsplit_u_) 1 MPI processes > > type: preonly > > maximum iterations=10000, initial guess is zero > > tolerances: relative=1e-05, absolute=1e-50, > divergence=10000. > > left preconditioning > > using NONE norm type for convergence test > > PC Object: (fieldsplit_0_fieldsplit_u_) 1 MPI processes > > type: lu > > out-of-place factorization > > tolerance for zero pivot 2.22045e-14 > > matrix ordering: nd > > factor fill ratio given 5., needed 3.92639 > > Factored matrix follows: > > Mat Object: 1 MPI processes > > type: seqaij > > rows=4290, cols=4290 > > package used to perform factorization: petsc > > total: nonzeros=375944, allocated nonzeros=375944 > > using I-node routines: found 2548 nodes, limit > used is 5 > > linear system matrix = precond matrix: > > Mat Object: (fieldsplit_0_fieldsplit_u_) 1 MPI processes > > type: seqaij > > rows=4290, cols=4290 > > total: nonzeros=95748, allocated nonzeros=95748 > > total number of mallocs used during MatSetValues > calls=0 > > using I-node routines: found 3287 nodes, limit used > is 5 > > A01 > > Mat Object: 1 MPI processes > > type: seqaij > > rows=4290, cols=561 > > total: nonzeros=19938, allocated nonzeros=19938 > > total number of mallocs used during MatSetValues calls=0 > > using I-node routines: found 3287 nodes, limit used is > 5 > > Mat Object: 1 MPI processes > > type: seqaij > > rows=561, cols=561 > > total: nonzeros=9679, allocated nonzeros=9679 > > total number of mallocs used during MatSetValues calls=0 > > not using I-node routines > > linear system matrix = precond matrix: > > Mat Object: (fieldsplit_0_) 1 MPI processes > > type: seqaij > > rows=4851, cols=4851 > > total: nonzeros=139353, allocated nonzeros=139353 > > total number of mallocs used during MatSetValues calls=0 > > using I-node routines: found 3830 nodes, limit used is 5 > > Split number 1 Defined by IS > > KSP Object: (fieldsplit_c_) 1 MPI processes > > type: preonly > > maximum iterations=10000, initial guess is zero > > tolerances: relative=1e-05, absolute=1e-50, divergence=10000. > > left preconditioning > > using NONE norm type for convergence test > > PC Object: (fieldsplit_c_) 1 MPI processes > > type: lu > > out-of-place factorization > > tolerance for zero pivot 2.22045e-14 > > matrix ordering: nd > > factor fill ratio given 5., needed 4.24323 > > Factored matrix follows: > > Mat Object: 1 MPI processes > > type: seqaij > > rows=561, cols=561 > > package used to perform factorization: petsc > > total: nonzeros=15823, allocated nonzeros=15823 > > not using I-node routines > > linear system matrix = precond matrix: > > Mat Object: (fieldsplit_c_) 1 MPI processes > > type: seqaij > > rows=561, cols=561 > > total: nonzeros=3729, allocated nonzeros=3729 > > total number of mallocs used during MatSetValues calls=0 > > not using I-node routines > > linear system matrix = precond matrix: > > Mat Object: 1 MPI processes > > type: seqaij > > rows=5412, cols=5412 > > total: nonzeros=190416, allocated nonzeros=190416 > > total number of mallocs used during MatSetValues calls=0 > > using I-node routines: found 3833 nodes, limit used is 5 > > > > -- > > Dr. Sebastian Blauth > > Fraunhofer-Institut für > > Techno- und Wirtschaftsmathematik ITWM > > Abteilung Transportvorgänge > > Fraunhofer-Platz 1, 67663 Kaiserslautern > > Telefon: +49 631 31600-4968 > > sebastian.bla...@itwm.fraunhofer.de > > https://urldefense.us/v3/__https://www.itwm.fraunhofer.de__;!!G_uCfscf7eWS!bGTaf64ibyuvBn-Qy-UQpxjLdOqFq44f6kBHzEDsXKc0htzQNw1MabtoK463uwb95Pupw_BcLMNwOFn7-WhZ$ > > > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener 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