[CIG-SHORT] Linear convergence for nonplanar faults

[Brad Aagaard]

Josimar,

Your solver settings in pylithapp.cfg are obsolete. To use fieldsplit 
and the custom preconditioner, please use the solver settings in 
share/settings/solver_fault_fieldsplit.cfg (shown below). Note that 
instead of 0/1 for the field, we now use names 
(displacement/lagrange_multiplier).

These settings will only work well if there is a fault. Without a fault, 
you can just use ML as the preconditioner. See 
examples/3d/hex8/step02.cfg (just use pc_type = ml).

Regards,
Brad


[pylithapp.problem.formulation]
split_fields = True
matrix_type = aij
use_custom_constraint_pc = True

[pylithapp.petsc]
fs_pc_type = fieldsplit
fs_pc_use_amat =
fs_pc_fieldsplit_type = multiplicative
fs_fieldsplit_displacement_pc_type = ml
fs_fieldsplit_lagrange_multiplier_pc_type = jacobi
fs_fieldsplit_displacement_ksp_type = preonly
fs_fieldsplit_lagrange_multiplier_ksp_type = preonly



On 11/08/2016 11:00 AM, Josimar Alves da Silva wrote:
> Dear Brad, Matt and Charles,
>
> I am running Pylith for a 2D friction model with gravity for a nonplanar
> fault. I am finding that the linear solver does not converge when the
> fault is included on the model. When the fault is not included on the
> model the linear solver takes roughly 500 to 1000 iterations to
> converge. Please refer to the attached "log_no_fault.cfg" file.
>
> The three links below show previous discussions on linear convergence:
>
> http://lists.geodynamics.org/pipermail/cig-short/2012-September/001123.html
>
>
> http://lists.geodynamics.org/pipermail/cig-short/2008-December/000453.html
>
>
> http://lists.geodynamics.org/pipermail/cig-short/2013-March/001320.html
>
>
>
> As pointed out by Charles previously and also discussed on the links
> above, overall, it seems that there are 3 main causes for convergence
> issues: 1) Poor quality mesh; 2) incorrect solver settings; 3) Poor
> setup/initial conditions.
>
>
> For my set up, I am unable to make the linear solver to converge.
>
>
> This is what I have done so far, based on recommendations from previous
> discussions:
>
>
> 1) Make sure that the mesh has condition number and aspect ratios <1.5.
> Please see attached presentation for histograms.
>
> 2) used the solver parameters shown
> on share/settings/solver_fault_fieldsplit.cfg
>
>
> I would like to know if there is anything else that I can do in order to
> make the linear solver to converge. Any other advices to improve my
> simulation would be very much appreciated.
>
>
> You can find attached the pylith .cfg files that I am using and also the
> log files for the case without the fault (log_no_fault.out) and with the
> fault (log_with_fault.out).
>
>
> I run my simulation using:
>
>
> 1) pylith no_fault.cfg > log_nor_fault.out
>
> 2) pylith no_fault.cfg   fault.cfg > log_with_fault.out
>
>
>
> Thank you in advance for you help,
>
> Josimar
>
>
>
>
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