Raju,
If you call MatSetBlockSize(mat,4) then GAMG will keep the 4 variables
together through all the levels.
You might consider using the point block Jacobi smoother with it instead of
the default Jacobi smoother -mg_levels_pc_type pbjacobi
There is also PCPATCH which supports Vanka smoothing (though it is to well
hidden) PCPatchSetConstructType(pc,PC_PATCH_VANKA) -pc_patch_construct_type
vanka
For coupled Navier stokes you might also consider using PCFIELDSPLIT and
GAMG just for the pressure solve inside it.
Barry
> On Sep 22, 2020, at 9:24 PM, Raju Mandhapati via petsc-users
> <petsc-users@mcs.anl.gov> wrote:
>
> Hello,
>
> Does Petsc have an option to solve block matrices using AMG
> solver/preconditioner. My block matrix is coming from solving u,v,w,p
> (coupled Navier stokes) at each cell.
>
> thanks
> Raju.
