[petsc-users] testing for and removing a null space using JFNK

[Dave Lee]

Hello PETSc,

I'm attempting to solve a JFNK problem for a system where I only have a
function to compute the residual, but no matrix.

I wanted to know if there exists functionality in PETSc to do the following:

1) approximate a null space from a set of Krylov vectors

2) remove such a null space if it exists

I'm vaguely familiar with the MatNullSpaceCreate/Remove() functionality,
however I don't know the precise form of a null space, so I don't have a
set of vectors I can assemble and pass to this.

Cheers, Dave.
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