# PETSC ERROR when use simulations in Pylith 4.1.3

**URL:** <https://community.geodynamics.org/t/petsc-error-when-use-simulations-in-pylith-4-1-3/3836>\
**Category:** PyLith\
**Created:** [December 23, 2024, 5:14am UTC](https://community.geodynamics.org/t/petsc-error-when-use-simulations-in-pylith-4-1-3/3836 "2024-12-23T05:14:52Z")\
**Posts on this page:** 1\
**Showing post:** 6

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**Author:** ![baagaard](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/baagaard/32/615_2.png) [@baagaard](https://community.geodynamics.org/u/baagaard)\
**Post date:** [January 7, 2025, 4:38pm UTC](https://community.geodynamics.org/t/petsc-error-when-use-simulations-in-pylith-4-1-3/3836/6 "2025-01-07T16:38:46Z")

</div>

## Fault output

For information on specifying faults in PyLith v3 and later, I recommend the PyLith tutorials on YoutTube (for example, [https://www.youtube.com/watch?v=fcHKL8PqFDk&list=PLNTb1ey7FFk7aaP7meQlevDqahYa-7S1h&index=3](https://www.youtube.com/watch?v=fcHKL8PqFDk&list=PLNTb1ey7FFk7aaP7meQlevDqahYa-7S1h&index=3)) and [Horizontal Cross-Section of Strike-Slip Fault (2D) — PyLith 5.0.0dev documentation](https://pylith.readthedocs.io/en/latest/user/examples/strikeslip-2d/index.html).

In PyLith v3 and later, in most cases you do not need to do as much for output. In `examples/strikeslip-2d`, we specify the fields we want output (we can select from slip, traction change, and any solution fields) in [`pylithapp.cfg`](https://github.com/geodynamics/pylith/blob/5ccb0cd3625c21fc843f2016884195f558da31b0/examples/strikeslip-2d/pylithapp.cfg):

```auto
# Output `slip` and the change in tractions on the fault.
observers.observer.data_fields = [slip, traction_change]

```

## Poroelasticity solver error

Changing the material properties may be creating an ill-conditioned system due to the inconsistency between the material properties and the scales used for nondimensionalization. For a well-conditioned system for poroelasticity, the ratio of the nondimensional permeability to viscosity should be about 1. Assuming the stress and length scales are appropriate for your problem, then you would adjust the time scale so that the nondimensional permeability to viscosity ratio is about 1.

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