[petsc-users] Block size

[Natacha BEREUX]

Dear PETSc users,

I am a bit confused  about blocksizes in MPI matrices.

I define a MPI matrix A with a certain blocksize, let say bs = 3.
As far as I understand, the sparse pattern of the matrix A is made of
square blocks of size 3x3, regardless of the actual values of the terms of
A.
Am I right ?

The matrix A is distributed among several processors: does the local number
of rows of A on each processor have to be a multiple of bs   ?

I want to use a multigrid preconditionner to  solve the linear system of
matrix A : A x = b
Is it mandatory to define the right hand side b as a vector with the same
blocksize bs=3 ?

Thank you very much of your help,
Best regards,
Natacha
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