The modules defining the physics process and the numerical methods are:
Spatial loops for the gas-dynamics solver.
Create a _algorithm.GasAlgorithm object.
>>> # create a valid solver as the test fixture.
>>> from solvcon.testing import create_trivial_2d_blk
>>> blk = create_trivial_2d_blk()
>>> blk.clgrp.fill(0)
>>> blk.grpnames.append('blank')
>>> class SubSolver(GasSolver):
... pass
>>> svr = SubSolver(blk)
>>> # number of equations.
>>> svr.neq
4
>>> # valid GasAlgorithm.
>>> svr.alg is not None
True