Greetings,

I am pleased to announce the release of PyLith 1.6.3, a finite-element
code designed to solve dynamic elastic problems and quasi-static
viscoelastic problems in tectonic deformation.

This release fixes several bugs in PyLith v1.6.2. We strongly
recommend all users of previous PyLith releases switch to this latest
release, especially anyone running in parallel or using fault friction.

You can download the source code and binaries from

    http://geodynamics.org/cig/software/packages/short/pylith

Detailed installation instructions for the binary packages are in the
User Manual with detailed building instructions for a few platforms
in the INSTALL file bundled with the PyLith Installer utility.


RELEASE NOTES

* Bug fixes

  - Improved error messages for problems encountered during processing
    of parameters. A backtrace of the object hierarchy is now included
    to pinpoint in which object the error occurred.

  - Added a line search to the inner friction solve in quasi-static
    simulations to increase the robustness of the nonlinear
    solve. Simulations using rate and state friction now converge
    under a much wider range of circumstances.

  - Fixed bug in updating slip state variable in slip-weakening
    friction. This caused slight errors in the cumulative slip. We
    also added a parameter that forces healing to occur in a single
    time step. This is used to confine slip to a single time step in
    quasi-static simulations. See examples/3d/hex8/step13.cfg for an
    example.

  - Tuned parameters in the slip-weakening friction and rate and state
    friction examples (step13.cfg and step14.cfg, respectively) in
    examples/3d/hex8 to give stick-slip behavior.

  - Fixed communication issue associated with writing boundary
    condition information output in parallel. 

  - Changed info in Xdmf file for fields that are not scalars,
    vectors, or tensors so that the each component is extracted,
    facilitating visualization in ParaView. The corresponding HDF5
    file remains the same.

  - Added the ability to specify non-derived units (e.g., degree and
    radian). This is useful in specifying parameters for the
    Drucker-Prager elastoplastic rheologies. If no units are
    specified, radians are assumed.

* Internal changes

  - Rate and state friction with ageing law

    The implementation of rate and state friction with ageing law was
    modified to work better with the iterative solver. We switched to
    the conventional, unregularized formulation but added a minimum
    cutoff for the slip rate. Below this cutoff friction has a linear
    rather than logarithmic dependence on slip rate. As long as this
    cutoff is close to the SNES solver tolerance, the difference in
    behavior is negligible while improving the ability of the solver
    to converge for very small deformations.

KNOWN ISSUES

  The rate and state friction with ageing law has not been tested for
  dynamic rupture simulations. We plan to run the SCEC Dynamic Rupture
  benchmarks for rate and state friction as soon as we add a
  spatial-temporal specification of initial fault tractions, which are
  required for the benchmark problems.

  Running simulations with more than a million cells and large faults
  in parallel can result in severe memory imbalances among
  processors. Some processors around the fault may use 10x more memory
  than processors away from the fault. We expect this problem to
  disappear in v1.7 when we switch to new, more efficient Sieve
  implementation.
