[petsc-users] Nested Fieldsplit for custom index sets
Lawrence Mitchell
lawrence.mitchell at imperial.ac.uk
Thu Jul 28 03:35:30 CDT 2016
Dear Artur,
On 28/07/16 02:20, Safin, Artur wrote:
> Barry, Lawrence,
>
>> I think the SubKSPs (and therefore SubPCs) are not set up until you call KSPSetUp(ksp) which your code does not do explicitly and is therefore done in KSPSolve.
>
> I added KSPSetUp(), but unfortunately the issue did not go away.
>
>
>
> I have created a MWE that replicates the issue. The program tries to solve a tridiagonal system, where the first fieldsplit partitions the global matrix
>
> [ P x ]
> [ x T ],
>
> and the nested fieldsplit partitions P into
>
> [ A x ]
> [ x B ].
Two things:
1. Always check the return value from all PETSc calls. This will
normally give you a very useful backtrace when something goes wrong.
That is, annotate all your calls with:
PetscErrorCode ierr;
ierr = SomePetscFunction(...); CHKERRQ(ierr);
If I do this, I see that the call to KSPSetUp fails:
[0]PETSC ERROR: --------------------- Error Message
--------------------------------------------------------------
[0]PETSC ERROR: Petsc has generated inconsistent data
[0]PETSC ERROR: Unhandled case, must have at least two fields, not 1
[0]PETSC ERROR: See
http://www.mcs.anl.gov/petsc/documentation/faq.html for trouble shooting.
[0]PETSC ERROR: Petsc Development GIT revision: v3.7.2-931-g1e46b98
GIT Date: 2016-07-06 16:57:50 -0500
...
[0]PETSC ERROR: #1 PCFieldSplitSetDefaults() line 470 in
/data/lmitche1/src/deps/petsc/src/ksp/pc/impls/fieldsplit/fieldsplit.c
[0]PETSC ERROR: #2 PCSetUp_FieldSplit() line 487 in
/data/lmitche1/src/deps/petsc/src/ksp/pc/impls/fieldsplit/fieldsplit.c
[0]PETSC ERROR: #3 PCSetUp() line 968 in
/data/lmitche1/src/deps/petsc/src/ksp/pc/interface/precon.c
[0]PETSC ERROR: #4 KSPSetUp() line 393 in
/data/lmitche1/src/deps/petsc/src/ksp/ksp/interface/itfunc.c
[0]PETSC ERROR: #5 main() line 65 in /homes/lmitche1/tmp/ex.c
The reason is you need to call KSPSetUp *after* setting the outermost
fieldsplit ISes.
If I move the call to KSPSetUp, then things seem to work. I've
attached the working code.
Cheers,
Lawrence
$ cat options.txt
-pc_type fieldsplit
-pc_fieldsplit_type multiplicative
-fieldsplit_T_ksp_type bcgs
-fieldsplit_P_ksp_type gmres
-fieldsplit_P_pc_type fieldsplit
-fieldsplit_P_pc_fieldsplit_type multiplicative
-fieldsplit_P_fieldsplit_A_ksp_type gmres
-fieldsplit_P_fieldsplit_B_pc_type lu
-fieldsplit_P_fieldsplit_B_ksp_type preonly
-ksp_converged_reason
-ksp_monitor_true_residual
-ksp_view
$ ./ex -options_file options.txt
0 KSP preconditioned resid norm 5.774607007892e+00 true resid norm
1.414213562373e+00 ||r(i)||/||b|| 1.000000000000e+00
1 KSP preconditioned resid norm 1.921795888956e-01 true resid norm
4.802975385197e-02 ||r(i)||/||b|| 3.396216464745e-02
2 KSP preconditioned resid norm 1.436304589027e-12 true resid norm
2.435255920058e-13 ||r(i)||/||b|| 1.721985974998e-13
Linear solve converged due to CONVERGED_RTOL iterations 2
KSP Object: 1 MPI processes
type: gmres
GMRES: restart=30, using Classical (unmodified) Gram-Schmidt
Orthogonalization with no iterative refinement
GMRES: happy breakdown tolerance 1e-30
maximum iterations=10000, initial guess is zero
tolerances: relative=1e-05, absolute=1e-50, divergence=10000.
left preconditioning
using PRECONDITIONED norm type for convergence test
PC Object: 1 MPI processes
type: fieldsplit
FieldSplit with MULTIPLICATIVE composition: total splits = 2
Solver info for each split is in the following KSP objects:
Split number 0 Defined by IS
KSP Object: (fieldsplit_P_) 1 MPI processes
type: gmres
GMRES: restart=30, using Classical (unmodified) Gram-Schmidt
Orthogonalization with no iterative refinement
GMRES: happy breakdown tolerance 1e-30
maximum iterations=10000, initial guess is zero
tolerances: relative=1e-05, absolute=1e-50, divergence=10000.
left preconditioning
using PRECONDITIONED norm type for convergence test
PC Object: (fieldsplit_P_) 1 MPI processes
type: fieldsplit
FieldSplit with MULTIPLICATIVE composition: total splits = 2
Solver info for each split is in the following KSP objects:
Split number 0 Defined by IS
KSP Object: (fieldsplit_P_fieldsplit_A_) 1 MPI processes
type: gmres
GMRES: restart=30, using Classical (unmodified)
Gram-Schmidt Orthogonalization with no iterative refinement
GMRES: happy breakdown tolerance 1e-30
maximum iterations=10000, initial guess is zero
tolerances: relative=1e-05, absolute=1e-50, divergence=10000.
left preconditioning
using PRECONDITIONED norm type for convergence test
PC Object: (fieldsplit_P_fieldsplit_A_) 1 MPI processes
type: ilu
ILU: out-of-place factorization
0 levels of fill
tolerance for zero pivot 2.22045e-14
matrix ordering: natural
factor fill ratio given 1., needed 1.
Factored matrix follows:
Mat Object: 1 MPI processes
type: seqaij
rows=25, cols=25
package used to perform factorization: petsc
total: nonzeros=73, allocated nonzeros=73
total number of mallocs used during MatSetValues
calls =0
not using I-node routines
linear system matrix = precond matrix:
Mat Object: (fieldsplit_P_fieldsplit_A_) 1 MPI processes
type: seqaij
rows=25, cols=25
total: nonzeros=73, allocated nonzeros=73
total number of mallocs used during MatSetValues calls =0
not using I-node routines
Split number 1 Defined by IS
KSP Object: (fieldsplit_P_fieldsplit_B_) 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_P_fieldsplit_B_) 1 MPI processes
type: lu
LU: out-of-place factorization
tolerance for zero pivot 2.22045e-14
matrix ordering: nd
factor fill ratio given 5., needed 1.43836
Factored matrix follows:
Mat Object: 1 MPI processes
type: seqaij
rows=25, cols=25
package used to perform factorization: petsc
total: nonzeros=105, allocated nonzeros=105
total number of mallocs used during MatSetValues
calls =0
not using I-node routines
linear system matrix = precond matrix:
Mat Object: (fieldsplit_P_fieldsplit_B_) 1 MPI processes
type: seqaij
rows=25, cols=25
total: nonzeros=73, allocated nonzeros=73
total number of mallocs used during MatSetValues calls =0
not using I-node routines
linear system matrix = precond matrix:
Mat Object: (fieldsplit_P_) 1 MPI processes
type: seqaij
rows=50, cols=50
total: nonzeros=148, allocated nonzeros=148
total number of mallocs used during MatSetValues calls =0
not using I-node routines
Split number 1 Defined by IS
KSP Object: (fieldsplit_T_) 1 MPI processes
type: bcgs
maximum iterations=10000, initial guess is zero
tolerances: relative=1e-05, absolute=1e-50, divergence=10000.
left preconditioning
using PRECONDITIONED norm type for convergence test
PC Object: (fieldsplit_T_) 1 MPI processes
type: ilu
ILU: out-of-place factorization
0 levels of fill
tolerance for zero pivot 2.22045e-14
matrix ordering: natural
factor fill ratio given 1., needed 1.
Factored matrix follows:
Mat Object: 1 MPI processes
type: seqaij
rows=50, cols=50
package used to perform factorization: petsc
total: nonzeros=148, allocated nonzeros=148
total number of mallocs used during MatSetValues calls =0
not using I-node routines
linear system matrix = precond matrix:
Mat Object: (fieldsplit_T_) 1 MPI processes
type: seqaij
rows=50, cols=50
total: nonzeros=148, allocated nonzeros=148
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=100, cols=100
total: nonzeros=298, allocated nonzeros=500
total number of mallocs used during MatSetValues calls =0
not using I-node routines
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