On Sep 16, 2008, at 10:10 AM, H?kan Jakobsson wrote:
> Hi,
>
> How does PETSc handle the solution of a singular system Ax=b which
> also happens to be inconsistent? More specifically: is b
> orthogonalized against Null(A) internally by PETSc?
No, you are expected to do this before calling the solver on the
right hand side. Note: if A is not symmetric then I think you want to
apply the Null(A')
MatNullSpaceCreate() and KSPSetNullSpace() are a way you can tell
the iterative solver the null space, otherwise most iterative solvers
will create a giant
solution in the null space direction and not converge.
Barry
>
>
> Thanks
>
> H?kan Jakobsson
>
