To run test_rexi you need to specify the geometry (and relevant
parameters), the name of the setup (defined in sw_setup.py) which will
specify the initial conditions, the time at which you wish to evaluate
the solution and the REXI parameters h and M. You can also specify
whether to run with a direct or block iterative solver.

For example, to run the f plane wave test from Schreiber et. a. 2016, type:

python test_rexi.py --square 1. 128 wave_scenario 0.1 0.2 200

This will set up a square mesh of size 1. with 128 cells in each
direction. u and h will be initialised with functions provided in the
paper and specified in sw_setup.py. The remaining 3 parameters are t,
the time to evaluate the solution, and the REXI parameters h and M.

The default is to use the block iterative solver parameters, or you
can specify --direct_solve.