On Mon, May 4, 2015 at 5:57 PM, Reza Yaghmaie <reza.yaghma...@gmail.com> wrote:
> > Dear Matt, > > The initial guess was zero for all cases of SNES solvers. The initial > jacobian was identity for all cases. The system is small and is ran > sequentially. > I have to add that I use FDColoring routine for the jacobian as well. > So, the initial Jacobian was the identity, but we have no idea how close that is to the true Jacobian. You could use the coloring routines (the default) combined with http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESQNSetScaleType.html using Jacobian, which sets the initial guess to the true Jacobian. That would give us an idea whether the initial guess impacted QN covergence. Thanks, Matt > Regards, > Ray > > > > > > On Monday, May 4, 2015, Matthew Knepley <knep...@gmail.com> wrote: > >> On Mon, May 4, 2015 at 5:41 PM, Reza Yaghmaie <reza.yaghma...@gmail.com> >> wrote: >> >>> >>> Dear Matt, >>> >>> Actually the initial jacobian was identity. Regular SNES converges in 48 >>> iterations, GMRES in 19, NCG in 67,... >>> Do you think SNESQN with the basiclineseach was the problem for >>> divergence? >>> If I use SNESQN by default should not it converge with initial identity >>> jacobian? >>> >> >> Do you mean that you used an initial guess of the identity, or that the >> Actual Jacobian was the identity at your >> initial guess? >> >> Matt >> >> >>> Best regards, >>> Reza >>> >>> >>> >>> >>> On Monday, May 4, 2015, Matthew Knepley <knep...@gmail.com> wrote: >>> >>>> On Mon, May 4, 2015 at 2:11 PM, Reza Yaghmaie <reza.yaghma...@gmail.com >>>> > wrote: >>>> >>>>> >>>>> Dear PETSC representatives, >>>>> >>>>> I am solving a nonlinear problem with SNESNGMRES and it converges >>>>> faster with less iterations compared to otehr SNES methods. Any idea why >>>>> that is the case? >>>>> >>>> >>>> It is impossible to tell with this information. >>>> >>>> >>>>> Also SNESQN diverges quickly. I tried to use SNESLINESEARCHBASIC for >>>>> the linesearch option and nothing changes. >>>>> >>>> >>>> This can happen, especially if your matrix is far from the identity. >>>> >>>> >>>>> I presume it is using the default SNESQN method. Btw, there are three >>>>> options for QN, as "SNES_QN_LBFGS, SNES_QN_BROYDEN, SNES_QN_BADBROYEN" >>>>> in teh manual. I tried to associate them with SNES however it seems these >>>>> hyphened names don't work there. What am I missing? >>>>> >>>> >>>> -snes_qn_scale_type <lbfgs,broyden,badbroyden> >>>> >>>> from >>>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESQNSetType.html >>>> >>>> Thanks, >>>> >>>> Matt >>>> >>>> Best regards, >>>>> Ray >>>>> >>>> >>>> >>>> >>>> -- >>>> 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 >>>> >>> >> >> >> -- >> 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 >> > -- 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