[petsc-users] Parallel vs. single processor

[Rob Kunz]

Hi:
I have a pressure based CFD code using PETSC for nearly SPD pressure equation.
PETSC default solver + preconditioner (GMRES+BJ for n-proc) is very reliable for me.
However I have a very tough bearing problem with extremely high aspect ratio cells and the 1-processor run works fine (GMRES+ILU0), but for nproc>1 the code does not converge.
Of course I can get the code to return identical 1-proc and 12-proc convergence histories if I choose a point preconditioner like Jacobi, but that kills the convergence of both.
Any recommendations?
Thanks
Rob Kunz
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