dolfin team mailing list archive

["Johan Hoffman" <jhoffman@xxxxxxxxxxx>]

> Quoting Johan Hoffman <jhoffman@xxxxxxxxxxx>:
>
>>
>> Me neither is very familiar with the PETSc non-linear solvers. But if
>> what
>> you say is true, then I agree that it seems more reasonable at this
>> point
>> to wrap the linear algebra of PETSc rather than the non-linear solvers.
>>
>> Apart from the difference in speed (10%), is there any additional
>> functionality in the PETSc non-linear solvers that you miss in your
>> Newton
>> solver of 20 lines of code?
>
> The PETSc solvers do have some extra functionality, but this isn't
> difficult to
> implement. On the other hand, they lack some functionality which I will
> eventually need (such as path following techniques), which would be much
> simpler
> to implement using the linear algerbra wrappers only.
>
> A good approach would be to implement our own Newton procedures, and set
> things
> up such that users can use the PETSc nonlinear solvers without too much
> difficulty if they are willing to call PETSc functions directly.
>
> An interesting feature that PETSc does have the is the computation of
> approximate Jacbian matrices. This feature seems to be under development
> still.

Ok. So let us go with our own Newton procedures for now. And then possibly
add a wrapper for computing approximate Jacobian matrices?

/Johan





>
> Garth
>
>>
>> /Johan
>>
>>
>>
>> >>
>> >> /Anders
>> >>
>> >>
>> >> On Fri, Dec 02, 2005 at 05:14:11PM +0100, dolfin@xxxxxxxxxx wrote:
>> >> > Commit from garth (2005-12-02 17:14 CET)
>> >> > -----------------
>> >> >
>> >> > Updates to nls demos.
>> >> >
>> >> > The nonlinear solver demos solve using both the class
>> NonlinearSolver
>> >> (which exploits the PETSc Newton solvers) and a hand programmed
>> Newton
>> >> procedure. The PETSc solvers are typically about 10% faster for the
>> >> tests
>> >> I've done. However, the NonlinearSolver class and the interface to it
>> >> would
>> >> be simpler if I programmed the NewtonSolver, and just relied on the
>> >> existing
>> >> linear algerbra wrappers for PETSc vectors, matrices and linear
>> solvers.
>> >> I
>> >> think that this would be better given that the speed-up using the
>> PETSc
>> >> solver is not so large, we could probably equal it with some with
>> some
>> >> optimisations. Also, we then restrict PETSc to the linear algerbra
>> >> classes,
>> >> limiting the intrusion of PETSc into DOLFIN. Are there reasons to
>> stick
>> >> with
>> >> the PETSc Newton solvers that I might be missing?
>> >> >
>> >> > Garth
>> >> >
>> >> >   dolfin  src/demo/nls/nonlinearpoisson/main.cpp  1.2
>> >> >   dolfin  src/demo/nls/poisson/main.cpp           1.2
>> >> >
>> >> > _______________________________________________
>> >> > DOLFIN-dev mailing list
>> >> > DOLFIN-dev@xxxxxxxxxx
>> >> > http://www.fenics.org/cgi-bin/mailman/listinfo/dolfin-dev
>> >> >
>> >>
>> >> --
>> >> Anders Logg
>> >> Research Assistant Professor
>> >> Toyota Technological Institute at Chicago
>> >> http://www.tti-c.org/logg/
>> >>
>> >> _______________________________________________
>> >> DOLFIN-dev mailing list
>> >> DOLFIN-dev@xxxxxxxxxx
>> >> http://www.fenics.org/cgi-bin/mailman/listinfo/dolfin-dev
>> >>
>> >
>> > _______________________________________________
>> > DOLFIN-dev mailing list
>> > DOLFIN-dev@xxxxxxxxxx
>> > http://www.fenics.org/cgi-bin/mailman/listinfo/dolfin-dev
>> >
>>
>>
>> --
>> Johan Hoffman, PhD
>> Assistant Professor
>> School of Computer Science and Communication
>> Royal Institute of Technology KTH
>> SE-100 44 Stockholm
>> Sweden
>>
>> Email: jhoffman@xxxxxxxxxxx
>> URL: www.nada.kth.se/~jhoffman
>>
>>
>> _______________________________________________
>> DOLFIN-dev mailing list
>> DOLFIN-dev@xxxxxxxxxx
>> http://www.fenics.org/cgi-bin/mailman/listinfo/dolfin-dev
>>
>


-- 
Johan Hoffman, PhD
Assistant Professor
School of Computer Science and Communication
Royal Institute of Technology KTH
SE-100 44 Stockholm
Sweden

Email: jhoffman@xxxxxxxxxxx
URL: www.nada.kth.se/~jhoffman