[petsc-users] Problem with PCFIELDSPLIT

Jorti, Zakariae zjorti at lanl.gov
Wed Jul 7 12:51:09 CDT 2021


I am trying to build a PCFIELDSPLIT preconditioner for a matrix

J =  [A00  A01]

       [A10  A11]

that has the following shape:

M_{user}^{-1} = [I   -ksp(A00) A01] [ksp(A00)           0] [I                        0]

                          [0                        I]  [0               ksp(T)] [-A10 ksp(A00)  I ]

where T is a user-defined Schur complement approximation that replaces the true Schur complement S:= A11 - A10 ksp(A00) A01.

I am trying to do something similar to this example (lines 41--45 and 116--121): https://www.mcs.anl.gov/petsc/petsc-current/src/snes/tutorials/ex70.c.html

The problem I have is that I manage to replace S with T on a separate single linear system but not for the linear systems generated by my time-dependent PDE. Even if I set the preconditioner M_{user}^{-1} correctly, the T matrix gets replaced by S in the preconditioner once I call TSSolve.

Do you have any suggestions how to fix this knowing that the matrix J does not change over time?

Many thanks.

Best regards,

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