On 10.01.2012 04:57, Jed Brown wrote: > On Mon, Jan 9, 2012 at 22:47, Mohamad M. Nasr-Azadani > <mmnasr at gmail.com <mailto:mmnasr at gmail.com>> wrote: > > It might be a naive question, but I am wondering how > KSPSetNullSpace() works when it is passed to a linear system ksp > context? > Say, for instance, we have the simple case of Poisson equation > solved in a square domain and Neumann boundary condition applied > to all boundaries. > Does it take the integral of the solution and set it to zero as an > extra constraint? > > > It just projects out whatever you provide as a null space, so the > Krylov method effectively runs in the remaining subspace. In examples listed on this page:
http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetNullSpace.html You set nullspace without any particular information: ierr = MatNullSpaceCreate(PETSC_COMM_WORLD, PETSC_TRUE, 0, PETSC_NULL, &nullsp); ierr = KSPSetNullSpace(ksp, nullsp); What does it project and how works in this case? Regards, Alexander -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120110/40186b64/attachment.htm>
