[CIG-SHORT] Rate and State and Initial Traction

[Brad Aagaard]

Romain,

It looks like you are using Schur complement preconditioner settings. 
The jump in the KSP residual at iteration 10 is odd and suggests 
something is not quite right in the linear solve (probably related to 
the preconditioner). Try using the AMG preconditioner. It may not be 
quite as fast but it is more robust. Matt can probably help you tune the 
Schur complement solver conditions some more if necessary.

Your SNES tolerances are quite large. I suggest using tolerances similar 
to those in examples/3d/hex8/step14.cfg.

SOLVER TOLERANCES

ksp_rtol = 1.0e-16
ksp_atol = 1.0e-12

snes_rtol = 1.0e-14
snes_atol = 1.0e-10


AMG PRECONDITIONER SETTINGS

[pylithapp.timedependent.formulation]
split_fields = True
matrix_type = aij

[pylithapp.petsc]
ksp_gmres_restart = 100
fs_pc_type = fieldsplit
fs_pc_fieldsplit_real_diagonal = true
fs_pc_fieldsplit_type = multiplicative
fs_fieldsplit_0_pc_type = ml
fs_fieldsplit_1_pc_type = jacobi
fs_fieldsplit_0_ksp_type = preonly
fs_fieldsplit_1_ksp_type = preonly

Brad


On 08/29/2012 11:42 AM, Romain Jolivet wrote:
> Hello Brad, Matt, Charles and the pylith team,
>
> Following your advice from the other day, I am experimenting  how to create earthquakes on a frictional interface by applying a traction change history. It works fine with the SlipWeakening law in 2D. I'm trying to move on to the RateStateAgeing behavior and I have problems applying the initial traction conditions:
>
> I use a SimpleDB to apply the frictional properties on the fault: one domain is rate-strengthening, the other is rate-weakening with a linear transition between the two domains. If I do not try to turn on any traction_perturbation option, the code runs great, and I have a slow slip all the along the fault at any time.
>
> As I want the rate-weakening domain to be stuck sometimes, I want to turn on traction_perturbation.db_initial. I use a SimpleDB to put a negative traction all along the fault, and a shear traction compatible with the friction coefficients I impose. However, when I run this, I have the following error message from PETSc (I attach the log):
>
>   >> /Users/jolivetinsar/MYBIN/pylith/pylith-1.7.1-darwin-10.6.8/lib/python2.7/site-packages/pylith/problems/Implicit.py:215:step
>   -- implicit(info)
>   -- Solving equations.
>    0 SNES Function norm 2.679589636063e+01
>      0 KSP Residual norm 9.637565795900e-01
>      1 KSP Residual norm 3.564937135471e-08
>      2 KSP Residual norm 4.313963401911e-16
>      3 KSP Residual norm 3.050427683646e-16
>      4 KSP Residual norm 2.490663081181e-16
>      5 KSP Residual norm 2.156976950523e-16
>      6 KSP Residual norm 1.929258577738e-16
>      7 KSP Residual norm 1.761163907914e-16
>      8 KSP Residual norm 1.630520838230e-16
>      9 KSP Residual norm 1.525212509706e-16
>     10 KSP Residual norm 1.833325155789e-11
>     11 KSP Residual norm 7.039784754868e-23
>    Linear solve converged due to CONVERGED_ATOL iterations 11
> [0]PETSC ERROR: --------------------- Error Message ------------------------------------
> [0]PETSC ERROR: Floating point exception!
> [0]PETSC ERROR: Infinite or not-a-number generated in norm!
>
> If anyone has an idea about that error message....
>
> I think it has to do with some slip vector. If I set friction.min_slip_rate=1e-1, this problem does not happen (the nonlinear solver does not converge, but at least, no crash). If I set the normal traction to be positive, it does not crash as well (and it does not converge as well). I join to this message the cfg file I am using for that experiment.
>
> Thank you
> Romain
>
>
>
>
> Romain Jolivet
> Postdoctoral Scholar
> Geological and Planetary Sciences
> California Institute of Technology, Pasadena, CA
> rjolivet at caltech.edu
> +1 (626) 560 6356
>
>
>
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