[petsc-users] Null space/Near null space

[Lawrence Mitchell]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 22/07/15 23:57, Barry Smith wrote:
> 
> 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.

FWIW, the HYPRE manual suggests yes:

If the block size is set (PETSc already does this) and nodal systems
coarsening is requested (PETSc has an option for this) then one can
provide the near null modes with HYPRE_BoomerAMGSetInterpVectors,
passing an array of Vecs (PETSc does not do this last step).

Lawrence
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iQEcBAEBAgAGBQJVsKjjAAoJECOc1kQ8PEYvWhQIALEe6KAnENO8yveClQQAUImw
xMkHXkuHiYtnbPZhQH8YeuVEx71pkmimXc0wRk532ee0FjfQZypuKybKrpFtVSvT
HsvpFJwE0n3HxwaVdIYYtG8c0c/Lj3326u1oFxCN5trbcUAY5VUSb41fYPGrLc6q
UQmWwMYgqPBdsGOykdOkVGGvJFbcc2CdR99Of3sEu+C0ub53/8T2Cav4yxAG32rn
+7lxX+a74nN+M6lRCGI8D9HiKLwKtxUKhO8W3+QeTA+y0Hf4ytZ/4AkiPScU7j0n
KwQ5vBdIt9hK8Qc8RU28gAn7uS0Ih4CgsrTtKP4Fdd5ksMEWTRZBQAimd2Yd5Cw=
=bHru
-----END PGP SIGNATURE-----