I'm sorry Matt but I cannot understand what flexible gmres computes when no null space is created. Could you give me some hints, please? Even in very simple cases... Thanks
Marco Cisternino, PhD marco.cistern...@optimad.it _______________________________ OPTIMAD Engineering srl Via Giacinto Collegno 18, Torino, Italia. +3901119719782 www.optimad.it ________________________________________ Da: Matthew Knepley <knep...@gmail.com> Inviato: mercoledì 7 febbraio 2018 19:38:08 A: Marco Cisternino Cc: petsc-users Oggetto: Re: [petsc-users] Elliptic operator with Neumann conditions On Thu, Feb 8, 2018 at 5:29 AM, Marco Cisternino <marco.cistern...@optimad.it<mailto:marco.cistern...@optimad.it>> wrote: Thanks Matt, I'm using KSPFGMRES and I'm sorry but what do you mean with initial residual? I also force a non-zero initial guess. If your initial residual has a component in the null space of the operator, it is likely to stay there. Matt Thanks again Marco Cisternino, PhD marco.cistern...@optimad.it<mailto:marco.cistern...@optimad.it> _______________________________ OPTIMAD Engineering srl Via Giacinto Collegno 18, Torino, Italia. +3901119719782<tel:%2B3901119719782> www.optimad.it<http://www.optimad.it> ________________________________________ Da: Matthew Knepley <knep...@gmail.com<mailto:knep...@gmail.com>> Inviato: mercoledì 7 febbraio 2018 18:57:56 A: Marco Cisternino Cc: petsc-users Oggetto: Re: [petsc-users] Elliptic operator with Neumann conditions On Thu, Feb 8, 2018 at 4:43 AM, Marco Cisternino <marco.cistern...@optimad.it<mailto:marco.cistern...@optimad.it><mailto:marco.cistern...@optimad.it<mailto:marco.cistern...@optimad.it>>> wrote: Hi everybody, I would like to ask what solution is computed if I try to solve the linear system relative to the problem in subject without creating the null space. I tried with and without the call to MatNullSpaceCreate(m_communicator, PETSC_TRUE, 0, NULL, &nullspace); and I get zero averaged solution with and the same solution plus a constant without. How does PETSc work in the second case? It depends on the Krylov method you use and the initial residual. We do not do anything special. Thanks, Matt Does it check the matrix singularity? And is it able to create the null space with the constant automatically? Thanks. Marco Cisternino, PhD marco.cistern...@optimad.it<mailto:marco.cistern...@optimad.it><mailto:marco.cistern...@optimad.it<mailto:marco.cistern...@optimad.it>> _______________________________ OPTIMAD Engineering srl Via Giacinto Collegno 18, Torino, Italia. +3901119719782<tel:%2B3901119719782><tel:%2B3901119719782> www.optimad.it<http://www.optimad.it><http://www.optimad.it> -- 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 https://www.cse.buffalo.edu/~knepley/<http://www.caam.rice.edu/~mk51/> -- 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 https://www.cse.buffalo.edu/~knepley/<http://www.caam.rice.edu/~mk51/>
