[petsc-users] Rigid body nullspace for Stokes operator

[Amneet Bhalla]

Hi Folks,

I am trying to solve the momentum equation in a projection preconditioner
using GAMG or Hypre solver. The equation looks like for velocity variable
*v* looks like:


 [image: Screenshot 2024-10-28 at 4.15.17 PM.png]

Here, μ is spatially varying dynamic viscosity and λ is spatially varying
bulk viscosity. I understand that I need to specify rigid body nullspace
modes to the multigrid solver in order to accelerate its convergence.
Looking into this routine MatNullSpaceCreateRigidBody() (
https://urldefense.us/v3/__https://petsc.org/release/manualpages/Mat/MatNullSpaceCreateRigidBody/__;!!G_uCfscf7eWS!eKqgIJjCdMzIU76f7X65AmGxrU_-lC7W02BMWafJ77DNf_IuQk6O1X3qU1x9Ez8NJ20vZEL-mF6T1yNmDnwv0eWa2w$ ), I
see that I need to provide the coordinates of each node. I am using
staggered grid discretization. Do I need to provide coordinates of
staggered grid locations?

Thanks,
-- 
--Amneet
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