== !PyLith Development Plans ==
Software development plans for !PyLith

=== Version 1.7 (by June workshop) ===
==== GENERAL ====
  * Output of solution at arbitrary points via interpolation of solution. done
  * Add 2-D plane strain version of the Drucker-Prager elastoplastic rheology. done
  * Add 2-D plane strain version of the power-law viscoelastic rheology. done
  * Elastic pre-step option for time-dependent problems. Remove assumed elastic pre-step at time step 0. done
  * Add --initialize_only property to Problem easy (0%)[[br]]
     Permit users to stop simulation before time stepping in order to diagnose parameter settings.

==== QUASI-STATIC ====
  * Static Green's functions for fault slip. done
==== DYNAMIC ====
  * None
==== COMPUTATIONAL SCIENCE ====
  * Switch to new Sieve implementation. expert (0%) [[br]]
     C implementation better integrated with !PETSc. Smaller memory usage. Facilitates multiphysics and higher order discretizations.

=== Version 1.8 (Fall or Winter 2012) ===
==== GENERAL ====
  * Refactor initial fault tractions easy (5%) [[br]]
     Create Nucleation object with spatial and temporal perturbation of tractions from initial value.

==== QUASI-STATIC ====
  * Create strain hardening/softening 2-D and 3-D Drucker-Prager elastoplastic models.
==== DYNAMIC ====
  * Compute stable time step for explicit time integration easy (5%)
  * Attenuation via generalized Maxwell model (bulk and shear relaxation) intermediate (50%)
==== COMPUTATIONAL SCIENCE ====
  * Accelerate FE integrations using !GPUs difficult (25%) [[br]]
     Will provide significant speedup to simulations run by many users because most are running on desktop machines that have GPUs.

=== Candidate Features for Version 2.0 (Spring 2013) ===
==== MAJOR FEATURES ====
  * Multiphysics
     # Incompressible elasticity via a pressure field expert
     # Elasticity + heat flow expert
     # Elasticity + fluid flow expert
  * Earthquake cycle modeling
     # Same mesh for dynamic and quasi-static parts difficult
         # Dynamic -> quasi-static
         # Quasi-static -> dynamic
         # Complete cycle

  # Different meshes for dynamic and quasi-static parts expert[[br]]
        Requires interpolation of fields between different meshes/discretizations and may require extrapolation of solutions when quasi-static problems span a larger domain than the dynamic problems.

  * Use interpolated meshes (cells, faces, edges, vertices) to permit higher order basis functions expert
==== MINOR FEATURES ====
  * Moment tensor point sources difficult [[br]]
     Moment tensor point sources provide a mesh independent deformation source that is better suited for Green's function calculations than slip on a fault surface via cohesive cells.

  * Time-step based on strain rate intermediate
  * Pressure field for incompressible elasticity problems expert
  * Use KD tree search algorithm to allow output of time histories at an arbitrary location difficult
  * Combined prescribed slip / spontaneous rupture fault condition difficult [[br]]
     Use fault constitutive model to control slip on fault except during episodes of prescribed slip. Need some way to describe when to turn on/off prescribed slip.

  * Use threading to accelerate integrations on multi-core machines. difficult