[petsc-users] How to create and assemble matrices for DA vectors??

[Алексей Рязанов]

Hello.

When I create vectors using

VecCreate(PETSC_COMM_WORLD,&u);
VecSetSizes(u,PETSC_DECIDE, VecSize);
VecSetFromOptions(u);
VecDuplicate(u,&b);

and matrix using

MatCreate(PETSC_COMM_WORLD,&A);
MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,VecSize,VecSize);
MatSetFromOptions(A);

PETSc distributes their elements in a proper identical way among processors,
so I can use procedures like

MatMult(A,u,b);

and
     KSPSolve(ksp,b,x);
Ofcourse after matrix assembling and initialization of KSP and PC

KSPCreate(PETSC_COMM_WORLD,&ksp);
KSPSetOperators(ksp,A,A,DIFFERENT_NONZERO_PATTERN);

And thats great and works amazingly!




But now I've created DA vectors "u" and "b" and assembled them through the
natural grid indexing.

And I need to solve the same SLE Au=b, where A is a Laplacian.

How should I create and assemble the A matrix according to my DA vector to
use the same functionality?

Thank you!

Alexey Ryazanov
______________________________________
Nuclear Safety Institute of Russian Academy of Sciences
<http://www.ibrae.ac.ru/>
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