[petsc-dev] fixing inconsistent right hand side

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:

>    Should we add some option to KSP to “fix” the right hand side if it
>    is inconsistent? 

Perhaps.

>    Presumably this can be done if we know the null space of A?

The right and left null spaces may not match.

What is a SNES line search going to do when you come out with a step
that is the minimum norm solution to a singular system with an
inconsistent RHS?  (SNES is not going to converge to a small residual or
the minimum norm solution.)
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