On Thu, Feb 8, 2018 at 5:29 AM, Marco Cisternino < [email protected]> 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 > [email protected] > _______________________________ > OPTIMAD Engineering srl > Via Giacinto Collegno 18, Torino, Italia. > +3901119719782 > www.optimad.it > > > ________________________________________ > Da: Matthew Knepley <[email protected]> > 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 < > [email protected]<mailto:[email protected]>> 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 > [email protected]<mailto:[email protected]> > _______________________________ > OPTIMAD Engineering srl > Via Giacinto Collegno 18, Torino, Italia. > +3901119719782<tel:%2B3901119719782> > 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/>
