Hi!Everyone:
Glad to join the mailing list.Recently I 've been working on a program
using block jacobi preconditioner for a sequence solve of two linear system
A_1x_1=b_1,A_2x_2=b_2.
Since A1 and A2 have same nonzero pattern and their element values are
quite close, we hope to reuse the preconditoners constructed when solving
A_1x_1=b_1 ,
however after calling KSPSetReusePreconditioner, though the iteration
number of second ksp solve is very small but the time used did not decrease
much, these are my code:
ierr = KSPSetUp(ksp);CHKERRQ(ierr);
ierr = PCBJacobiGetSubKSP(pc, &num_local, &idx_first_local,
&subksp);CHKERRQ(ierr);
for (i=0; i<num_local; i++)
{
ierr = KSPGetPC(subksp[i], &subpc);CHKERRQ(ierr);
if (i==0)
{
ierr =
KSPSetType(subksp[i],"gmres");CHKERRQ(ierr);
ierr = PCSetType(subpc, PCLU);CHKERRQ(ierr);
ierr = PCFactorSetMatSolverType(subpc,
"mkl_pardiso");CHKERRQ(ierr);
ierr = KSPSetOptionsPrefix(subksp[i],
"Blk0_");CHKERRQ(ierr);
ierr =
KSPSetReusePreconditioner(subksp[i],PETSC_TRUE);CHKERRQ(ierr);
ierr =
KSPSetFromOptions(subksp[i]);CHKERRQ(ierr);
}
if (i==1)
{
ierr =
KSPSetType(subksp[i],"gmres");CHKERRQ(ierr);
ierr = PCSetType(subpc, PCHYPRE);CHKERRQ(ierr);
ierr = PCHYPRESetType(pc,
"boomeramg");CHKERRQ(ierr);
ierr =
KSPSetReusePreconditioner(subksp[i],PETSC_TRUE);CHKERRQ(ierr);
ierr = KSPSetOptionsPrefix(subksp[i],
"Blk1_");CHKERRQ(ierr);
}
}//nlocal
}//isbjacobi
//Solve the Linear System
ierr = KSPSetFromOptions(ksp);CHKERRQ(ierr);
//Solve the Linear System
t0 = MPI_Wtime();
ierr = KSPSolve(ksp, b1, x1);CHKERRQ(ierr);
t0 = MPI_Wtime()-t0;
ierr = PetscPrintf(PETSC_COMM_SELF,"First KSP Solve time: %g
s\n",t0);CHKERRQ(ierr);
//Preconditioner Reuse
ierr = KSPSetReusePreconditioner(ksp, PETSC_TRUE);CHKERRQ(ierr);
ierr = KSPSetOperators(ksp,A2,A1);CHKERRQ(ierr);
t0 = MPI_Wtime();
ierr = KSPSolve(ksp,b2,x2);CHKERRQ(ierr);
t0 = MPI_Wtime()-t0;
ierr = PetscPrintf(PETSC_COMM_SELF,"Second KSP Solve time: %g
s\n",t0);CHKERRQ(ierr);
The total block number is 2, and the first block is solved using direct method
and the second block is solved using hypre's boomeramg, so I hope to reuse the
factor of the first block and the set up phase of boomeramg as preconditioner
of the next solve, is there anything wrong with the reuse code?
Best Wishes
WANG Yijia
2021/10/15
