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 <mailto: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
