> System solved in 3664 iterations... 42.683 s
The preconditioner is simply not up to the task it has been assigned. This
number of iterations is problematic.
Have you tried -pc_type asm -sub_pc_type lu If that works well you can
try -pc_type asm -sub_pc_type ilu and see if that still works.
If the matrix is indeed symmetric positive definite you will want to use
-ksp_type cg
Barry
On Apr 26, 2011, at 1:37 AM, Alejandro Marcos Arag?n wrote:
> Hi all,
>
> I'm using the standard configuration of the KSP solver, but the time it takes
> to solve a large system of equations is increasing (because of the increasing
> number of iterations?). These are my timing lines and the log from the KSP
> solver in two consecutive solves:
>
> [1] Solving system... 0.154203 s
>
> KSP Object:
> type: gmres
> GMRES: restart=30, using Classical (unmodified) Gram-Schmidt
> Orthogonalization with no iterative refinement
> GMRES: happy breakdown tolerance 1e-30
> maximum iterations=10000
> tolerances: relative=1e-05, absolute=1e-50, divergence=10000
> left preconditioning
> using nonzero initial guess
> using PRECONDITIONED norm type for convergence test
> PC Object:
> type: bjacobi
> block Jacobi: number of blocks = 3
> Local solve is same for all blocks, in the following KSP and PC objects:
> KSP Object:(sub_)
> type: preonly
> 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:(sub_)
> type: ilu
> ILU: out-of-place factorization
> 0 levels of fill
> tolerance for zero pivot 1e-12
> using diagonal shift to prevent zero pivot
> matrix ordering: natural
> factor fill ratio given 1, needed 1
> Factored matrix follows:
> Matrix Object:
> type=seqaij, rows=2020, cols=2020
> package used to perform factorization: petsc
> total: nonzeros=119396, allocated nonzeros=163620
> using I-node routines: found 676 nodes, limit used is 5
> linear system matrix = precond matrix:
> Matrix Object:
> type=seqaij, rows=2020, cols=2020
> total: nonzeros=119396, allocated nonzeros=163620
> using I-node routines: found 676 nodes, limit used is 5
> linear system matrix = precond matrix:
> Matrix Object:
> type=mpiaij, rows=6058, cols=6058
> total: nonzeros=365026, allocated nonzeros=509941
> using I-node (on process 0) routines: found 676 nodes, limit used is 5
>
>
> [1] System solved in 51 iterations... 0.543215 s
> ...
> ...
> ...
>
> [1] Solving system... 0.302414 s
>
> KSP Object:
> type: gmres
> GMRES: restart=30, using Classical (unmodified) Gram-Schmidt
> Orthogonalization with no iterative refinement
> GMRES: happy breakdown tolerance 1e-30
> maximum iterations=10000
> tolerances: relative=1e-05, absolute=1e-50, divergence=10000
> left preconditioning
> using nonzero initial guess
> using PRECONDITIONED norm type for convergence test
> PC Object:
> type: bjacobi
> block Jacobi: number of blocks = 3
> Local solve is same for all blocks, in the following KSP and PC objects:
> KSP Object:(sub_)
> type: preonly
> 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:(sub_)
> type: ilu
> ILU: out-of-place factorization
> 0 levels of fill
> tolerance for zero pivot 1e-12
> using diagonal shift to prevent zero pivot
> matrix ordering: natural
> factor fill ratio given 1, needed 1
> Factored matrix follows:
> Matrix Object:
> type=seqaij, rows=2020, cols=2020
> package used to perform factorization: petsc
> total: nonzeros=119396, allocated nonzeros=163620
> using I-node routines: found 676 nodes, limit used is 5
> linear system matrix = precond matrix:
> Matrix Object:
> type=seqaij, rows=2020, cols=2020
> total: nonzeros=119396, allocated nonzeros=163620
> using I-node routines: found 676 nodes, limit used is 5
> linear system matrix = precond matrix:
> Matrix Object:
> type=mpiaij, rows=6058, cols=6058
> total: nonzeros=365026, allocated nonzeros=509941
> using I-node (on process 0) routines: found 676 nodes, limit used is 5
>
> [1] System solved in 3664 iterations... 42.683 s
>
>
>
> As you can see, the second iteration takes more than 40 seconds to solve.
> Could some explain why this is happening and why he number of iterations is
> increasing dramatically between solves? Thank you all,
>
> Alejandro M. Arag?n, Ph.D.
