Thanks for all your input!
How can I set these options in the program instead of as runtime options (in
the .petsc file)? For example, which subroutine shall I call to set
'-pc_factor_nonzeros_along_diagonal", and what is corresponding argument value?
Thanks,Qin
On Wednesday, July 8, 2020, 02:15:11 PM CDT, Barry Smith <bsm...@petsc.dev>
wrote:
There is also -pc_factor_nonzeros_along_diagonal which reorders to move the
zeros off the diagonal before the numerical factorization
But if having 0 leads to a factorization without error then it will produce
the correct answer (this means that zero got filled in during the factorization)
On Jul 8, 2020, at 2:11 PM, Mark Adams <mfad...@lbl.gov> wrote:
On Wed, Jul 8, 2020 at 2:43 PM Qin Lu via petsc-users <petsc-users@mcs.anl.gov>
wrote:
Hello,
I am using the Petsc native direct solver (with KSPPREONLY and PCLU) to solver
a small Linear equation system. The matrix has a couple of diagonal terms with
value 0, which makes the solver fail. Then I set a very small value (e.g.,
1e-10) at these terms and the solver works. Can this cause noticeable errors in
the solution?
Can't say.
Are there any options in Petsc to make the direct solver do row/column pivoting
so that all the diagonal terms are non-zero?
I see:
-pc_factor_pivot_in_blocks <true,false>- allow pivoting within the small blocks
during factorization (may increase stability of factorization.
and
-pc_factor_shift_type <shifttype>- Sets shift type or PETSC_DECIDE for the
default; use '-help' for a list of available types
-pc_factor_shift_amount <shiftamount>- Sets shift amount or PETSC_DECIDE for
the default
Thanks for any suggestions.
Regards,Qin
