== !PyLith Development Plans, Feb 2014 ==
Priorities for !PyLith software development, such as new features and enhancements. This a draft for community comment (Feb 20, 2014).

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 2.0 (early March 2014) ===
Status: We have almost everything working. We are in the process of fixing a few bugs related to creating cohesive cells and running in parallel.

  # Replace C++ Sieve implementation of finite-element data structures with C DMPlex implementation.  [[Image(expert.png, 40px)]]  99%
     * DMPlex provides a simpler, more efficient implementation of the finite-element data structures that conforms to the PETSc data management (DM) interface. This provides tighter integration with the rest of PETSc. Additionally, this rewrite of the data structures results in a more efficient memory layout, resulting in better performance.
  # Switch from using Subversion to Git for version control.  [[Image(done.png, 25px)]]
  # Add ability to recursively refine a mesh.  [[Image(done.png, 25px)]]
=== Version 2.1 (by Jun 2014) ===
This is the version that will be available for use at the June 2014 workshop. We are behind schedule for getting multiphysics done by then, and because this is a fixed deadline, we will probably aim to get some additional less ambitious features completed. Allowing different startup cases could slip to version 2.2.

  # 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.
  # Higher order basis functions   [[Image(expert.png, 40px)]] 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     [[Image(intermediate.png, 25px)]]   0%
     * Elastic prestep
     * User-specified initial solution
     * Checkpoint via special spatial database?
  # Radial basis functions for spatial databases    [[Image(intermediate.png, 25px)]]  0%
  # Improved handling of buried fault edges    [[Image(intermediate.png, 25px)]]  25%
=== Version 2.2 (Summer/Fall 2014) ===
  # 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.   [[Image(intermediate.png, 25px)]]   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.
  # Multilevel nonlinear solve
=== Version 2.3 (Spring 2015) ===
  # 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 organization to support inclusion of data assimilation [[Image(expert.png, 40px)]]
==== 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)]]