== !PyLith Development Plans, Mar 2015 ==

Priorities for !PyLith software development, such as new features and enhancements. This a draft for community comment (Mar 6, 2015).

This plan attempts to balance meeting short-term objectives of delivering high priority, new features and meeting long-term objectives of extending the code to solve a broader range of scientific problems.

Current development has slowed because Brad Aagaard (who is not funded by CIG) is unable to devote much time to !PyLith development as a result of a substantial increase of other obligations.

=== Version 2.2 (Jun 2015) ===

  # Improve fault formulation for spontaneous rupture {{intermediate.png}} [10%]
     * Removes inner solve associated with updating Lagrange multipliers. This will significantly accelerate the nonlinear solve.
  # Add viscoelastic Drucker-Prager bulk rheology

=== Version 2.3 (late 2015) ===

  # Higher order basis functions {{expert.png}} [0%]
     * Allow user to select order of basis functions independent of the mesh (which defines the geometry). This permits higher resolution for a given mesh.
  # Reorganize top-level code to conform to layout needed for multiphysics  [[Image(difficult.png, 25px)]] 0%
     * Setup modular approach for specifying governing equations and computing residuals and Jacobians.
  # Reorganize top-level code to allow different startup cases {{intermediate.png}} [0%]
     * Elastic prestep
     * User-specified initial solution
     * Checkpoint via special spatial database?
  # Multilevel nonlinear solve
  # Radial basis functions for spatial databases {{intermediate.png}} [0%]

=== Version 3.0 (Spring 2016) ===

  # Multiphysics
     * Incompressible elasticity via a pressure field  [[Image(difficult.png, 25px)]]
     * Elasticity + heat flow   [[Image(difficult.png, 25px)]]
     * Elasticity + fluid flow   [[Image(difficult.png, 25px)]]
  # GUI interface for specifying parameters
  # Switch to using PETSc time-stepping (TS) algorithms. {{intermediate.png}} [0%]
     * Replace simple Python-based time-stepping implementations with PETSc time-stepping algorithms that provide support for higher order discretization in time and real adaptive time stepping.
  # Begin implementation of data assimilation capabilities via adjoint equation.

=== Version 3.1 (Fall 2016) ===

  # Earthquake cycle modeling  [[Image(difficult.png, 25px)]]
     * Same mesh for dynamic and quasi-static parts (dynamic -> quasi-static, quasi-static -> dynamic, complete cycle)
  # Create strain hardening/softening 2-D and 3-D Drucker-Prager elastoplastic models. {{intermediate.png}}
  # Moment tensor point sources via equivalent body forces  [[Image(difficult.png, 25px)]] 5%
     * 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. 

=== Features for Future Releases ===

==== Major features ====
  # Earthquake Cycle Modeling
      * Different meshes for dynamic and quasi-static parts {{expert.png}}
        * 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.
  # Data assimilation
      * Use flexibility of multiphysics implementation to support inclusion of data assimilation {{expert.png}}

====Minor features ====
  # Use KD tree search algorithm to allow output of time histories at an arbitrary location   [[Image(difficult.png, 25px)]]
  # Combined prescribed slip / spontaneous rupture fault condition  [[Image(difficult.png, 25px)]]
      * 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. [[Image(difficult.png, 25px)]]