[petsc-users] lying about nullspaces

[Geoffrey Irving]

Hello,

I have a matrix A and an orthogonal projection operator P onto a
fairly large (but sparse) linear subspace.  I want to solve the system

    PAPx = Pb

If set up a MatNullSpace object with MatNullSpaceSetFunction, with KSP
solve the system I want even if A is nonsingular?

Thanks,
Geoffrey