[petsc-users] Input and output distributions of vectors for PCShellSetApply 'apply' routine

[Jack Poulson]

Sorry to hit the list so quickly again, but the PCShellSetApply
documentation doesn't say anything about how the 'xin' and 'xout' vectors
will be distributed, or if it's up to the user to determine it.

Given that a distributed Mat implies a right and left vector distribution, I
would assume that the 'xin' should be distributed like the 'left' vector
distribution for a left preconditioner.

Is it up to the application routine to determine the 'xout' vector
distribution? If so, is there a performance penalty for making it something
other than the 'right' vector distribution implied by the matrix registered
with the KSP? If not, what distribution does it need to be?

Jack
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