[CIG-ALL] PyLith 1.6.2 bugfix release

[Brad Aagaard]

Greetings,

I am pleased to announce the release of PyLith 1.6.2, 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 v1.6.1. 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

   - Fixed bug in writing tensor data for Xdmf files. Switched Tensor
     to Tensor6 to account for symmetry.

   - Fixed bug in writing HDF5 files in parallel when one processor
     does not write any information (e.g., faults and boundary
     conditions).

   - Added dimensioning of time dataset in HDF5 files. The units are
     now seconds rather than nondimensional time.

   - Fixed memory allocation error (std::bad_alloc) when a processor
     did not contain cells for a boundary condition or output. This bug
     did not show up on all architectures.

   - Increased robustness of spontaneous rupture (fault friction)
     implementation to broaden the range of conditions it can
     handle. The implementation now properly handles cases with fault
     opening and cases with zero shear or normal tractions.


* Internal changes

   - Fault implementation

     Several changes have been made to the fault implementation, but
     none of these affect the user interface. The runtime performance
     is nearly identical with improved accuracy for spontaneous rupture
     (fault friction) simulations. These changes involved switching to
     using tractions (non-integrated quantities) for the Lagrange
     multipliers in the global coordinate system rather than integrated
     quantities in the fault coordinate system. Additionally, initial
     fault tractions are associated with the fault vertices and their
     interpolation uses the finite-element basis functions.

   - Distribution of mesh among processors

     The data structures used to distribute the mesh among processors
     have been improved. This reduces memory use and runtime for this
     stage of the simulations.


KNOWN ISSUES

   The custom line search used with the PETSc nonlinear solver (SNES)
   has difficulty handling some loading cases. In cases where the
   direction of the line search is nearly orthogonal to the
   residual, the rate of convergence in the SNES iterations is extremely
   slow. In other cases the nonlinear solver gets stuck in a local
   minimum. We plan to improve the line search algorithm in a future
   release in order to resolve this issue and improve the rate of
   convergence in spontaneous rupture simulations.


PyLith Development Team
Brad Aagaard, Matthew Knepley, and Charles Williams