[petsc-dev] misleading that ROSW uses SNES

[Barry Smith]

On Oct 16, 2012, at 12:00 AM, Matthew Knepley <knepley at gmail.com> wrote:

> On Tue, Oct 16, 2012 at 3:52 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
> On Oct 15, 2012, at 11:48 PM, Matthew Knepley <knepley at gmail.com> wrote:
> 
> > On Tue, Oct 16, 2012 at 3:24 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >    It is seriously misleading that TSType rosw uses SNES as the solver since it is only using SNESKSP and the algorithm really is built around only linear solves.  Are you sure that using SNES is the right model for this family of algorithms? Convince me.
> >
> >    I realize one person among us thinks we should use SNES for both linear and nonlinear solves, but he is wrong :-)
> >
> > Let me try a Venn Diagram:
> >  _________________________________
> > /                                _____________   \
> > |                               /                        \  |
> > |  Nonlinear problems | Linear problems |  |
> > |                               \ _____________/  |
> > \_________________________________/
> >
> > Also, there is no overhead using SNES, so I would say Do Not Multiply Entities Beyond The Necessary.
> 
>    I am not concerned about overhead. I am concerned about things looking like they are doing one thing but that are actually doing something else. In this case, there is actually a nonlinear problem hanging around but the rosw algorithms avoid solving it, which is ok but I find the fact that it prints SNES is then misleading because given a nonlinear problem and SNES one would think it is actually solving a nonlinear problem with SNES, when it is not.
> 
> It is solving a nonlinear problem, just a really easy one :)

   Yes but it is not solving THE nonlinear problem in question. It is a solving a nonlinear problem (that happens to be linear) defined by the Jacobian.  Note: I am objecting to how rosw uses SNESKSP, I am not objecting to SNESKSP.

   Barry

> I guess you could setup the SNES to
> turn on the KSP monitor instead.
> 
>    Matt
>  
> >
> >   Matt
> >
> >    Matt
> >
> >
> >   Barry
> >
> >
> >
> >
> > --
> > 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