[petsc-users] Mixed sparse and dense CG

[Jed Brown]

Ross Brodie <ross.c.brodie at icloud.com> writes:

> I have considered using libElemental for the dense part (to make use
> of the grid cyclic layout) and PETSc for the sparse part of the PCG
> matvec product but I am not sure it is wise to mix packages.

The PETSc interface to Elemental can do this.  In principle, you don't
have to deal with the cyclic ordering, but you should assemble the rows
and columns returned by MatGetOwnershipIS().

> On a different note could you clarify the terminology for the
> sequential vector VECSEQ. Does it mean: (i) It is an independent
> uniprocessor object such that the data storage is not distributed and
> if you change an element on one process the change is NOT reflected on
> other processes, 

Yes, and only makes sense on a communicator of size 1 (effectively
PETSC_COMM_SELF).
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