Dear PETSc user's,
I am trying to solve a poroelasticity problem with an additional
temperature equation. The problem is a 3 fields problem involving a
displacement field (u), a pressure field (p) and a temperature field (t).
I have seen similar examples in
http://www.mcs.anl.gov/papers/P2017-0112.pdf
or in Matt's talk
http://www.caam.rice.edu/~mk51/presentations/SIAMCSE13.pdf
I would like to reproduce them, but I am encountering troubles whem trying
to do so.
Here is how I proceed:
I have a monolithic matrix A stemming .
I build 3 index sets for u,p, and t in A.
Then I set up the KSP context :
call KSPCreate(PETSC_COMM_WORLD,ksp,ierr)
call KSPSetOperators(ksp,A,A,ierr)
call KSPGetPC(ksp, pc, ierr)
call PCSetType(pc, PCFIELDSPLIT, ierr)
call PCFieldSplitSetIS(pc,'u',is_u, ierr)
call PCFieldSplitSetIS(pc,'p',is_p, ierr)
call PCFieldSplitSetIS(pc,'t',is_t, ierr)
call PCSetFromOptions(pc,ierr)
call KSPSetFromOptions(ksp,ierr)
call KSPSolve(ksp,b,x,ierr)
I run the code with the following options
-ksp_view
-log_view
-ksp_rtol 1.0e-5
-ksp_type fgmres
-pc_type fieldsplit
-pc_fieldsplit_type additive
-pc_fieldsplit_0_fields 0,1
-pc_fieldsplit_1_fields 2
-pc_fieldsplit_0_pc_type lu
-pc_fieldsplit_0_ksp_type preonly
-pc_fieldsplit_1_pc_type lu
-pc_fieldsplit_1_ksp_type preonly
I would like to group u and p fields in a "0" block and then temperature
remains in "1" block.
(I start with direct solves in each blocks to check the block decomposition
but I intend to do use iterative methods later, and more precisely to use a
Schur fieldsplit preconditionner for the "0" block)
The output follows :
KSP Object: 1 MPI processes
type: fgmres
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.
right preconditioning
using UNPRECONDITIONED norm type for convergence test
PC Object: 1 MPI processes
type: fieldsplit
FieldSplit with ADDITIVE composition: total splits = 3
Solver info for each split is in the following KSP objects:
Split number 0 Defined by IS
KSP Object: (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 DEFAULT norm type for convergence test
PC Object: (fieldsplit_u_) 1 MPI processes
type: ilu
PC has not been set up so information may be incomplete
ILU: out-of-place factorization
0 levels of fill
tolerance for zero pivot 2.22045e-14
matrix ordering: natural
linear system matrix = precond matrix:
Mat Object: (fieldsplit_u_) 1 MPI processes
type: seqaij
rows=60, cols=60
total: nonzeros=3600, allocated nonzeros=3600
total number of mallocs used during MatSetValues calls =0
using I-node routines: found 12 nodes, limit used is 5
Split number 1 Defined by IS
KSP Object: (fieldsplit_p_) 1 MPI processes
type: preonly
maximum iterations=10000, initial guess is zero
tolerances: relative=1e-05, absolute=1e-50, divergence=10000.
left preconditioning
using DEFAULT norm type for convergence test
PC Object: (fieldsplit_p_) 1 MPI processes
type: ilu
PC has not been set up so information may be incomplete
ILU: out-of-place factorization
0 levels of fill
tolerance for zero pivot 2.22045e-14
matrix ordering: natural
linear system matrix = precond matrix:
Mat Object: (fieldsplit_p_) 1 MPI processes
type: seqaij
rows=8, cols=8
total: nonzeros=64, allocated nonzeros=64
total number of mallocs used during MatSetValues calls =0
using I-node routines: found 2 nodes, limit used is 5
Split number 2 Defined by IS
KSP Object: (fieldsplit_t_) 1 MPI processes
type: preonly
maximum iterations=10000, initial guess is zero
tolerances: relative=1e-05, absolute=1e-50, divergence=10000.
left preconditioning
using DEFAULT norm type for convergence test
PC Object: (fieldsplit_t_) 1 MPI processes
type: ilu
PC has not been set up so information may be incomplete
ILU: out-of-place factorization
0 levels of fill
tolerance for zero pivot 2.22045e-14
matrix ordering: natural
linear system matrix = precond matrix:
Mat Object: (fieldsplit_t_) 1 MPI processes
type: seqaij
rows=8, cols=8
total: nonzeros=64, allocated nonzeros=64
total number of mallocs used during MatSetValues calls =0
using I-node routines: found 2 nodes, limit used is 5
linear system matrix = precond matrix:
Mat Object: 1 MPI processes
type: seqaij
rows=76, cols=76
total: nonzeros=5776, allocated nonzeros=5776
total number of mallocs used during MatSetValues calls =0
using I-node routines: found 16 nodes, limit used is 5
The preconditionner has 3 splits, whereas I would like to group (u,p)
together and see 2 splits
I suspect that
-pc_fieldsplit_0_fields 0,1
-pc_fieldsplit_1_fields 2
are not the appropriate options.
Am I correct ?
What is the right way for grouping two fields defined by index sets ?
Any help would be greatly appreciated !
Natacha
