[firedrake] NonlinearVariationalSolver

[David Ham]

Hi Anna,

The linear variational solves you are seeing are the projection of your
solution fields into the bilinear function space for output purposes. This
is because direct output of quadratic functions to VTU is not supported.
This won't change the answer, but obviously it will have some impact on the
visualisation of the answer.

Regards,

David

On 19 November 2014 19:45, Anna Kalogirou <a.kalogirou at leeds.ac.uk> wrote:

> Hello,
>
> Can someone of you please check the way I use NonlinearVariationalSolver
> in the code attached? The code runs but the result is a bit odd. In
> addition, in the screen it writes
>
> pyop2:INFO Solving linear variational problem...
>
> and I am suspecting it might be solving the corresponding linear problem
> instead of the nonlinear one.
>
> Thank you very much.
>
> Best, Anna.
>
>
>
> On 11/11/14 12:31, Lawrence Mitchell wrote:
> > Hi Anna,
> >
> > On 10/11/14 20:25, Lawrence Mitchell wrote:
> >> Hi Anna,
> >>
> >> On 10 Nov 2014, at 19:39, Anna Kalogirou <a.kalogirou at leeds.ac.uk>
> >> wrote:
> >>
> >>> Hi Lawrence,
> >>>
> >>> Does it matter that I am solving a linear problem with the
> >>> nonlinear solver? I am just trying to reproduce the linear one that
> >>> works first, before introducing the nonlinear terms. I tried also
> >>> adding the parameter {'snes_type': 'ksponly'} and the code works,
> >>> but the result is not as good.
> >>>
> >>> Do you have any idea what might be happening?
> >>>
> >>> P.S. The linear code can be found attached.
> >>
> >> Thanks, I think I have found the problem, it is not in your code.
> >> The problem appears to be a subtle issue in which we interact with
> >> PETSc, which means that it is not computing the initial residual
> >> correctly.  I will prepare a fix tomorrow and let you know when
> >> things are fixed.
> > I've now fixed the problem.  If you reinstall PyOP2 (I guess with pip,
> > if you followed the website instructions) your nonlinear problem should
> > now run fine.
> >
> > Let us know if you have any problems.
> >
> > Cheers,
> >
> > Lawrence
>
> --
>
>   Dr Anna Kalogirou
>   Research Fellow
>   School of Mathematics
>   University of Leeds
>
>


-- 
Dr David Ham
Departments of Mathematics and Computing
Imperial College London

http://www.imperial.ac.uk/people/david.ham
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