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

[Barry Smith]

   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
>>