[CIG-SHORT] Pylith's error including `dtStable > 0.0' failed

[Brad Aagaard]

Kejing Huang,

The error you are getting means that the stable time step computed for a 
material is zero or negative. This is a very unusual error. You did not 
include the .cfg files with the material info, so I cannot tell what 
types of materials you are using. If you are using a linear Maxwell 
viscoelastic material, be sure to check your viscosity to make sure it 
gives reasonable Maxwell relaxation times. If you have a powerlaw 
viscoelastic material, then check its parameters as well to make sure 
they are reasonable.

I recommend first trying all linearly elastic materials to rule out 
setup and mesh errors. Once that works and the results look okay, then 
add a viscoelastic material one at a time. I would also work with a 
coarse resolution version of the mesh and then switch to a finer 
resolution once you have these errors fixed.

Regards,
Brad

On 08/17/2018 02:45 AM, hkj at mail.ustc.edu.cn wrote:
> Dear Sir,
> 
> When I running pylith using my own FEM model, the error including" 
> `dtStable > 0.0' failed"  appears very frequently, and I found that this 
> can be avoided by using fewer nodes like
> 
> from
> /pylith postseis.cfg mat_viscoelastic.cfg solver_fieldsplit.cfg --nodes=20/
> to
> /pylith postseis.cfg mat_viscoelastic.cfg solver_fieldsplit.cfg --nodes=10/
> /
> /
> But after I rebuilt my FEM model by using a larger area, this error 
> still occurs even if I use only 1 node,
> I also chose dt from dt = 1*year to dt = 0.001*year , but it didn't work.
> 
> 
> *The .cfg file is attached, and the time formulation part is*
> 
> /```/
> /# ----------------------------------------------------------------------/
> /# problem/
> /# ----------------------------------------------------------------------/
> /[pylithapp.problem.formulation.time_step]/
> /# Define the total time for the simulation and the time step size./
> /total_time = 2*year/
> /dt = 0.001*year/
> /```/
> /
> /
> *And the output error is*
> *
> *
> /``` [OUTPUT]/
> /......./
> /......./
> /......./
> /-- Creating Jacobian matrix./
> / >> 
> /home/khuang/Pylith/lib/python2.7/site-packages/pylith/problems/Implicit.py:163:initialize/
> / -- implicit(info)/
> / -- Initializing solver./
> / >> 
> /home/khuang/Pylith/lib/python2.7/site-packages/pylith/problems/TimeDependent.py:132:run/
> / -- timedependent(info)/
> / -- Solving problem./
> / >> 
> /home/khuang/Pylith/lib/python2.7/site-packages/pylith/problems/TimeDependent.py:138:run/
> / -- timedependent(info)/
> / -- Preparing for prestep with elastic behavior./
> /mpinemesis: 
> ../../../pylith-2.2.1/libsrc/pylith/materials/ElasticMaterial.cc:405: 
> virtual PylithScalar 
> pylith::materials::ElasticMaterial::stableTimeStepImplicit(const 
> pylith::topology::Mesh&, pylith::topology::Field*): Assertion `dtStable 
>  > 0.0' failed./
> /[0]0:Return code = 0, signaled with Aborted/
> /```/
> 
> Can you tell me how to fix this error?
> 
> Sincerely
> Kejing Huang