[CIG-SHORT] Nonlinear solve diverged_function_count

Bobak Karimi bkarimi at clarion.edu
Mon Feb 29 13:05:09 PST 2016


1.      Is this a 2D or 3D problem, and how large is it?

a.       It is a 2D problem and has around 13,000 cells (dimension wise it’s about 400 km long and 300 km wide)

2.      Is it a single fault or multiple faults?

a.       Multiple faults. One through-going, and several intersecting faults.

3.      What does the convergence for the linear solver look like (slow convergence, large number of iterations, etc.)?

a.       Convergence is pretty slow, iterations around 2,800.

4.      Have you tried using an exact solver for the fault (look in pylith/share/settings)?

a.       We haven’t tried an exact solver.

5.      Is your mesh of high quality?

a.       The mesh quality is high quality.



From: CIG-SHORT [mailto:cig-short-bounces at geodynamics.org] On Behalf Of Charles Williams
Sent: Monday, February 29, 2016 3:00 PM
To: cig-short <cig-short at geodynamics.org>
Subject: Re: [CIG-SHORT] Nonlinear solve diverged_function_count

I guess it might help to know more about your problem and what the current convergences are like.  I see that you have really large values for your maximum iterations.  Have those been necessary?  Here are some questions for you:

1.  Is this a 2D or 3D problem, and how large is it?
2.  Is it a single fault or multiple faults?
3.  What does the convergence for the linear solver look like (slow convergence, large number of iterations, etc.)?
4.  Have you tried using an exact solver for the fault (look in pylith/share/settings)?
5.  Is your mesh of high quality?

That’s all I can think of right now, but let me know if you make any progress on this.

Cheers,
Charles


On 1/03/2016, at 3:14 AM, Bobak Karimi <bkarimi at clarion.edu<mailto:bkarimi at clarion.edu>> wrote:

Hi Charles,

The tight factors for rtol were purposeful to force the controlling tolerance to be the atol. This was what I had gleaned from session iv, step03 in the 2015 pylith tutorial. My PetSc values are below:

# PETSc
# ----------------------------------------------------------------------
# Set the solver options.

[pylithapp.petsc]

# Preconditioner settings.
pc_type = asm
sub_pc_factor_shift_type = nonzero

# Convergence parameters.
ksp_rtol = 1.0e-20
ksp_atol = 1.0e-11
ksp_max_it = 1000000
ksp_gmres_restart = 100

# Linear solver monitoring options.
ksp_monitor = true
ksp_view = true
ksp_converged_reason = true

# Nonlinear solver monitoring options.
snes_rtol = 1.0e-20
snes_atol = 1.0e-9
snes_max_it = 1000000
snes_monitor = true
snes_view = true
snes_converged_reason = true
snes_error_if_not_converged = true

# PETSc summary -- useful for performance information.
log_summary = true

# Uncomment to launch gdb when starting PyLith.
# start_in_debugger = true


# End of file

From: CIG-SHORT [mailto:cig-short-bounces at geodynamics.org] On Behalf Of Charles Williams
Sent: Sunday, February 28, 2016 2:57 PM
To: cig-short <cig-short at geodynamics.org<mailto:cig-short at geodynamics.org>>
Subject: Re: [CIG-SHORT] Nonlinear solve diverged_function_count

Dear Bobby,

It’s hard to say without seeing all of your settings, but those seem like pretty tight values for rtol.  Is there a reason you are setting them so small?

Cheers,
Charles


On 27/02/2016, at 6:36 AM, Bobak Karimi <bkarimi at clarion.edu<mailto:bkarimi at clarion.edu>> wrote:

Hello,

I recently got this error on a simulation I was running, and am not sure how to apply a fix for it:

Nonlinear solve did not converge due to DIVERGED_FUNCTION_COUNT iterations 2743

My KSP and NSES rtol = 1.0e-20
KSP_atol = 1.0e-11
SNES_atol = 1.0e-9

The zero-tolerance on my faults is 1.0e-10.

Any help would be much appreciated,

Thanks!
Bobby

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Charles A. Williams
Scientist
GNS Science
1 Fairway Drive, Avalon
PO Box 30368
Lower Hutt  5040
New Zealand
ph (office): 0064-4570-4566
fax (office): 0064-4570-4600
C.Williams at gns.cri.nz<mailto:C.Williams at gns.cri.nz>

_______________________________________________
CIG-SHORT mailing list
CIG-SHORT at geodynamics.org<mailto:CIG-SHORT at geodynamics.org>
http://lists.geodynamics.org/cgi-bin/mailman/listinfo/cig-short

Charles A. Williams
Scientist
GNS Science
1 Fairway Drive, Avalon
PO Box 30368
Lower Hutt  5040
New Zealand
ph (office): 0064-4570-4566
fax (office): 0064-4570-4600
C.Williams at gns.cri.nz<mailto:C.Williams at gns.cri.nz>

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