[petsc-users] getting the near nullspace from PCSetCoordinates

[Jeremy Theler]

Hi all

I want to check that the near nullspace I provide to GAMG gives "almost
null vectors" when multiplying each vector in the near nullspace against
the matrix problem.

This way I can check that the unknown ordering I am using is consistent,
for example using by MatNullSpaceCreateRigidBody() or by computing the
nullspace by myself.


The thing is I do not know how I can get the nullspace object after
calling PCSetCoordinates(). It gets a pointer to the PC object, but
MatGetNearNullSpace() needs the matrix object. I assume at some point
the matrix and the PC get linked, but when I ask
MatGetNearNullSpace(matrix) passing the problem matrix after setting
PCSetCoordinates(pc) I get:

error: PETSc error 85-0 'Null Object: Parameter # 1'
in /home/gtheler/libs/petsc-3.7.4/src/mat/interface/matnull.c
MatNullSpaceGetVecs:64


thanks

-- 
Jeremy Theler
www.seamplex.com