[petsc-users] RK substeps

[Matthew Knepley]

On Fri, Nov 11, 2011 at 3:52 PM, Juha Jäykkä <juhaj at iki.fi> wrote:

> > What exactly are you using TAO to do?
>
> I have a large scale minimisation problem related to the problem I am using
> PETSc to solve. The PETSc code is independent, so I could have two PETSc's
> around and use the older one for TAO, but that seems like a lot of hassle
> without significant benefit.
>
> I know the SNES module could be used as a substitute for TAO. At the
> moment, I
> solve min(\int f(x)), where TAO needs the gradients of f(x); I could also
> solve discrete grad(f(x))=0 with SNES, but as I then need compute the
> Jacobian
> (=Hessian of f(x)), too, this has seemed to be too memory intensive to be
> useful. I am not aware of a way around this.


There are plenty of ways to use SNES without a Mat. You can use -snes_mf,
which
uses a FD approximation to the action of the matrix. You can use -snes_type
qn
which uses a quasi-Newton approximation, or even -snes_type nrichardson,
which
just uses successive substitutions with your residual function.

  Thanks,

      Matt


>
> -Juha

-- 
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
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