attaches a null space to a matrix, which is often the null space (rigid body modes) of the operator without boundary conditions This null space will be used to provide near null space vectors to a multigrid preconditioner built from this matrix.
Logically Collective on mat
mat - the matrix
nullsp - the null space object
Overwrites any previous near null space that may have been attached
You can remove the null space by calling this routine with an nullsp of NULL