[CIG-SHORT] Convergence problem with Neumann BCs

[Matthew Knepley]

On Wed, Oct 30, 2013 at 5:43 PM, Eric Lindsey <elindsey at ucsd.edu> wrote:

> Hi,
>
> I'd like to apply background stresses to a simple elastic 2D plane strain
> model in pylith, then add fault slip or other quasistatic deformation;
> later I'll modify the material properties etc. Of course the stresses also
> cause some deformation in the volume that I'd like to ignore. So I'm
> imposing the slip at the second time step, with the hopes of subtracting
> out the deformation from the first time step. (Is this the right way to do
> this?)
>
> However, I noticed that the effects from the boundary conditions continue
> to increase, and then oscillate, and don't stabilize until I let it run to
> the 8th step or so (ideally I'd only use 2 time steps, I think). I think
> the problem is with the solver's convergence; I see the message
>
> ...
> 499 KSP Residual norm 9.952574507238e-04
> 500 KSP Residual norm 9.952555275971e-04
> Linear solve did not converge due to DIVERGED_ITS iterations 500
>
> I've taken most of the configuration straight from
> examples/2d/greensfns/strikeslip, and just modified the boundary conditions
> from Dirichlet to Neumann. Config file is attached; any advice would be
> great.
>

This is a really bad solver. I am sure Brad and Charles can comment on the
model setup, but this will not solve
anything fast. I see that other examples have this basic setup. We
definitely did not use it in the online tutorials.
My solver configuration files are in share/solver in the repository. Did
you checkout from Git?

  Thanks,

      Matt


> Thanks,
> Eric
>
>
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