Thanks for the quick response. I've tried both orthogonalizing and not, having convergence in both cases and very similar solutions. Likely since b has been almost orthogonal to Null(A) already. /H?kan On Sep 16, 2008, at 6:35 PM, Barry Smith wrote:
> > 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 >> >
