This equation directory contains the descriptions for the various supported
equation systems of the ateles solver.

The general structure for the equation system in the solver is given by
atl_equation_module, which is supported by a set of routines acting on this
data structure given in atl_eqn_helpers_module.
All the modules are supposed to have the atl_eqn_ prefix to easily identify
equation specific things.

Each specific equation system should get its own descriptive module and in
addition some supporting helpers module.
The variables of the different equation systems are defined in
atl_eqn_*_var_module.

Routines to calculate derived quantities of the different equation systems are
defined in atl_eqn_*_derive_module.
