On Tue, Sep 16, 2008 at 11:56 AM, zhifeng sheng <z.sheng at ewi.tudelft.nl> wrote: > Hi, > > how is the nullspace be implemented in the solver? by using Lagrange > multiplier?
You have to have an explicit basis for the null space in order for PETSc to use it. Matt > best regards > Zhifeng > > 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 >>> >> > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
