[CIG-SHORT] petsc convergence

[Matthew Knepley]

On Thu, Mar 28, 2013 at 11:53 AM, <surendra at caltech.edu> wrote:

> Hi Matt,
>
> I have a 2D plane strain simulation of a plate that isn't converging.  I
> thought you might know what could be happening.
>
> Attached are 'false' and 'log' files.  Petsc setting are pasted below.  I
> ran it on Mac OSX pylith version 1.8.0 binary.
>
> I usually run dynamic friction problem that do not require (explicit)
> petsc but this time I need to run a quasi-static problem with implicit.
>  Any suggestions on what I could try?
>
> Thanks,
> Surendra
>
> --
>
> [pylithapp.petsc]
>
> # Preconditioner settings.
> pc_type = asm
> sub_pc_factor_shift_type = nonzero
>
> # Convergence parameters.
> ksp_rtol = 1.0e-8
> ksp_atol = 1.0e-12
> ksp_max_it = 300
> ksp_gmres_restart = 50
>
> # Linear solver monitoring options.
> ksp_monitor = false
> ksp_view = false
> ksp_converged_reason = true
>
> # Nonlinear solver monitoring options.
> snes_rtol = 1.0e-8
> snes_atol = 1.0e-12
> snes_max_it = 100
> snes_monitor = false
>

This puts the monitor information in the file 'false' which is weird. Just
leave it true.

ASM is a terrible preconditioner. Use the AMG options we showed in the
tutorial and
you will get good convergence.

  Thanks,

     Matt


> snes_view = false
> snes_converged_reason = true
>
> # PETSc summary -- useful for performance information.
> #log_summary = true
>
> # Uncomment to launch gdb when starting PyLith.
> # start_in_debugger = true
>
>
>
>
>


-- 
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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