== !PyLith Development Plans, Nov 2016 ==

Priorities for !PyLith software development, such as new features and enhancements. This a draft for community comment (Nov 7, 2016).

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.

=== Version 3.0 (Spring 2017) ===

  # Multiphysics [[Image(expert.png, 40px)]] 30%
     * Implement modular approach for specifying governing equations and computing residuals and Jacobians.  [[Image(expert.png, 40px)]] 
     * Incompressible elasticity via a pressure field [[Image(intermediate.png, 25px)]] 20%
     * Poroelasticity [[Image(difficult.png 25px)]] 5%
  # Higher order basis functions {[[Image(difficult.png 25px)]] 25%
     * Allow user to select order of basis functions independent of the mesh (which defines the geometry). This permits higher resolution for a given mesh.
   # Switch to using PETSc time-stepping (TS) algorithms. [[Image(intermediate.png, 25px)]] 25%
    * 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.
  # Improve fault formulation for spontaneous rupture [[Image(intermediate.png, 25px)]] 10%
     * Removes inner solve associated with updating Lagrange multipliers. This will significantly accelerate the nonlinear solve.
  # Allow full specification of the initial conditions (solution and state variables) [[Image(intermediate.png, 25px)]] 0%
  # Update user manual
     * Convert from !LyX to !LaTeX for ease of maintenance and editing. {{easy.png}} [0%]
     * Reorganize for multiphysics implementation. [[Image(intermediate.png, 25px)]] 5%
     * Reorganize examples. [[Image(intermediate.png, 25px)]] 0%
       * Focus on demonstrating the range of physics and features beginning with simple cases and building towards more complex cases.
       * Include !ParaView Python scripts for plotting results.
       * Consider moving examples to Jupyter notebooks; export to PDF files for "print" documentation.

=== Version 3.1 (late 2017) ===

  # GUI interface for specifying simulation parameters [[Image(difficult.png 25px)]]
  # Add additional multiphysics implementations and rheologies
     * Drucker-Prager bulk rheology with relaxation to yield surface [[Image(intermediate.png, 25px)]]
     * Elasticity + heat flow [[Image(difficult.png 25px)]]
  # Reorganize output for time-dependent Green's functions and adjoints [[Image(intermediate.png, 25px)]]
  # Multilevel nonlinear solve [[Image(expert.png, 40px)]] 
  # Radial basis functions for spatial databases [[Image(intermediate.png, 25px)]]
  # Convert to Python 3 and Pyre 1.0.

=== Version 4.0 (TBD) ===

  # 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. [[Image(intermediate.png, 25px)]]
  # 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 [[Image(expert.png, 40px)]] 
        * 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 [[Image(expert.png, 40px)]] 

==== Minor features ====
  # Begin implementation of data assimilation capabilities via adjoint equation.
  # 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)]]

----
==== difficulty rating system ====

||[[Image(intermediate.png, 25px)]] intermediate 

||[[Image(difficult.png, 25px)]] difficult  

||[[Image(expert.png, 40px)]] expert 

||

''based on the ski trail rating system''