[petsc-users] GAMG issue

[Jed Brown]

On Wed, Mar 14, 2012 at 11:27, Mark F. Adams <mark.adams at columbia.edu>wrote:

> The matrix is asymmetric. Does this require the setting of an option?
>
>
> Yes:  -pc_gamg_sym_graph
>

Mark, I don't like this name. First, it's imperative in the sense that it's
describing a procedure for fixing something rather than declarative
(stating some property of the problem). Second, there is already a way to
state symmetry, MatSetOption():

  Options Describing Matrix Structure:
+    MAT_SPD - symmetric positive definite
-    MAT_SYMMETRIC - symmetric in terms of both structure and value
.    MAT_HERMITIAN - transpose is the complex conjugation
.    MAT_STRUCTURALLY_SYMMETRIC - symmetric nonzero structure
-    MAT_SYMMETRY_ETERNAL - if you would like the symmetry/Hermitian flag
                            you set to be kept with all future use of the
matrix
                            including after MatAssemblyBegin/End() which
could
                            potentially change the symmetry structure, i.e.
you
                            KNOW the matrix will ALWAYS have the property
you set.


Is there a reason you can't just use this information? If you have multiple
methods for handling nonsymmetric structure, then I would suggest using
PetscOptionsList() or PetscOptionsEnum() to select which to use.
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