[petsc-users] Assembling primal Schur matrix in FETI-DP method

[Jed Brown]

On Mon, Nov 21, 2011 at 09:00, Thomas Witkowski <
Thomas.Witkowski at tu-dresden.de> wrote:

> I have to multiple two matrices, one is implicitly defined by a KSP, the
> other one is explicitly assembled. So when using KSPSolve(), it must be
> called for each column of the second matrix? This seems not to be very
> efficient as I thought the matrices are stored row wise? Is there a way to
> get the columns of a SEQAIJ matrix?


In this context, I think it is easier to store the matrix as a collection
of column vectors, but you can also use MATDENSE. This thing isn't sparse
(and it wouldn't do you any good anyway; there are few algorithms that can
solve sparse right hand sides and there isn't much point because the
solutions would still be dense).
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