[petsc-users] Help for MatNullSpaceCreateRigidBody

[Jordi Manyer Fuertes via petsc-users]

Dear PETSc users/developpers,

I am currently trying to use the method `MatNullSpaceCreateRigidBody` 
together with `PCGAMG` to efficiently precondition an elasticity solver 
in 2D/3D.

I have managed to make it work in serial (or with 1 MPI rank) with 
h-independent number of iterations (which is great), but the solver 
diverges in parallel.

I assume it has to do with the coordinate vector I am building the 
null-space with not being correctly setup. The documentation is not that 
clear on which nodes exactly have to be set in each partition. Does it 
require nodes corresponding to owned dofs, or all dofs in each partition 
(owned+ghost)? What ghost layout should the `Vec` have?

Any other tips about what I might be doing wrong?

Thanks,

Jordi