[petsc-users] Help for MatNullSpaceCreateRigidBody

[Jeremy Theler (External)]

just in case it helps, here's one way I have to create the near nullspace:

https://github.com/seamplex/feenox/blob/main/src/pdes/mechanical/init.c#L468

--
jeremy
________________________________
From: petsc-users <petsc-users-bounces at mcs.anl.gov> on behalf of Jordi Manyer Fuertes via petsc-users <petsc-users at mcs.anl.gov>
Sent: Tuesday, December 5, 2023 9:57 AM
To: Matthew Knepley <knepley at gmail.com>; bsmith at petsc.dev <bsmith at petsc.dev>
Cc: petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>
Subject: Re: [petsc-users] Help for MatNullSpaceCreateRigidBody


[External Sender]

Thanks for the prompt response. Both answers look like what I'm doing.

After playing a bit more with solver, I managed to make it run in parallel with different boundary conditions (full dirichlet bcs, vs mixed newmann + dirichlet). This raises two questions:

- How relevant are boundary conditions (eliminating dirichlet rows/cols vs weak newmann bcs) to the solver? Should I modify something when changing boundary conditions?

- Also, the solver did well with the old bcs when run in a single processor (but not in parallel). This seems odd, since parallel and serial behavior should be consistent (or not?). Could it be fault of the PCGAMG? I believe the default local solver is ILU, shoud I be changing it to LU or something else for these kind of problems?

Thank you both again,

Jordi

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