[petsc-users] question on extracting a column from a matrix

[RenZhengYong]

Hi, Hong and Barry,
Thanks a lot.
Have a nice day.

Zhengyong

On Tue, May 31, 2011 at 9:48 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   With petsc-dev
> http://www.mcs.anl.gov/petsc/petsc-as/developers/index.html there are very
> easy ways to solve the Schur complement systems using PCFIELDSPLIT see
> http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-dev/docs/manualpages/PC/PCFIELDSPLIT.html
>
>
>   Barry
>
>
> On May 31, 2011, at 2:41 PM, Hong Zhang wrote:
>
> > This is virtually SCHUR complement. You may take a look at
> > petsc-dev/src/ksp/ksp/examples/tests/ex11.c and
> > petsc-dev/src/ksp/ksp/examples/tests/makefile: runex11
> >
> > Hong
> >
> > On Tue, May 31, 2011 at 8:29 AM, RenZhengYong <renzhengyong at gmail.com>
> wrote:
> >> I have a linear system of equation like
> >>  [A  B]  [E]= [C]
> >>  [F  G]  [S]= [D],
> >> where size of matrix A is NxN, B is NxNs, F is Ns_N, G is Ns_Ns; size of
> >> vector E is N, S is Ns, C is N and D is N.
> >> Instead of solving them together, I prefer to solve it by:
> >> (1) AX=B, AY=C;
> >> (2) QS=P, Q= G-FX, P=D-FY,
> >> due to the dense property of G.
> >>
> >> In step (1), I need to extract a new "vec" Bi from "mat" B, according to
> the
> >> way of PETSc telling me. My question is that could I do it as follows,
> >> for a given sparse matrix B, first get transpose of B by
> "MatTranspose(B,
> >> MatReuse, B_t); then, form a new "vec" Bi by "MatGetRow(...)"?
> >> If answer is yes, is it expensive?
> >>
> >>
> >>
> >>
> >> --
> >> Zhengyong Ren
> >> AUG Group, Institute of Geophysics
> >> Department of Geosciences, ETH Zurich
> >> NO H 47 Sonneggstrasse 5
> >> CH-8092, Zürich, Switzerland
> >> Tel: +41 44 633 37561
> >> e-mail: zhengyong.ren at aug.ig.erdw.ethz.ch
> >> Gmail: renzhengyong at gmail.com
> >>
>
>


-- 
Zhengyong Ren
AUG Group, Institute of Geophysics
Department of Geosciences, ETH Zurich
NO H 47 Sonneggstrasse 5
CH-8092, Zürich, Switzerland
Tel: +41 44 633 37561
e-mail: zhengyong.ren at aug.ig.erdw.ethz.ch
Gmail: renzhengyong at gmail.com
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