dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Nov 01, 2012 at 07:49:03AM +0000, Garth N. Wells wrote:
> I've added a demo for solving singular systems using a Krylov solver via PETSc:
>
>    demo/undocumented/singular
>
> This can provide a good alternative to, for example, pinning the
> pressure in a Stokes problem or using a global Lagrange multiplier. In
> contrast to pinning or Lagrange multipliers, it doesn't mess up
> preconditioners or introduce a global row to the matrix.

Very useful. What is exactly the logic of

null_space = Vector(u.vector())
V.dofmap().set(null_space, 1.0)
solver.set_nullspace([null_space])

?

Why does the dofmap need to be involved?

> Does anyone know if Trilinos/AztecOO has similar functionality to
> PETSc for solving singular problems?

No idea.

--
Anders