[petsc-users] Null space/Near null space

Barry Smith bsmith at mcs.anl.gov
Wed Jul 22 17:57:16 CDT 2015

  If your matrix has a null space you should always be setting MatSetNullSpace. 

  If you know the near null space then you should also always set it (it cannot do any harm) because some preconditioners can take advantage of it. 

  I do not think PETSc currently has code that transfers near null space information to hypre; I do not know if hypre has any algorithms that can take advantage of it. Only some AMG multigrid methods can utilize near null space information.


> On Jul 22, 2015, at 5:50 PM, Young, Matthew, Adam <may at bu.edu> wrote:
> Should I be using MatSetNearNullSpace (as opposed to MatSetNullSpace) with -pc_type hypre -pc_hypre_type boomeramg since BoomerAMG is multigrid?
> --Matt
> --------------------------------------------------------------
> Matthew Young
> Graduate Student
> Boston University Dept. of Astronomy
> --------------------------------------------------------------

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