[petsc-users] FieldSplit, multigrid and blocksize

[Lawrence Mitchell]

On 07/12/16 13:43, Karin&NiKo wrote:
> Thanks Barry.
> I must emphasize that my unknowns are not numbered in a regular way :
> I am using a P2-P1 finite element and the middle nodes do not carry a
> pressure DOF. So the global numbering is somewhat like :
> -----------------------------------------------------------------------------------------------------------
> u1x, u1y, u1z, p, u2x, u2y, u2z, p2, u3x, u3y, u3z, u4x, u4y, u4z, p4,
> .....
>  node 1 DOF     |  node 2 DOF       | node 3 DOF  |    node 4 DOF     |
> -----------------------------------------------------------------------------------------------------------
> 
> So my global matrix does not have a block-size of 4. Nevertheless the
> A00 matrix has a block size of 3!
> Is there a way to specify that only on the A00 sub-matrix?

I presume you are defining the splits by providing ISes.  You need to
set the block size on the IS that defines the A00 block appropriately,
then the submatrix will have it.

Lawrence

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