  A framework for simulating the elastic-wave modes in waveguides, taking into
account the full tensorial nature of the stiffness tensor, is presented and
implemented in the open-source finite element solver, FEniCS. Various
approximations of the elastic wave equation used in the stimulated Brillouin
scattering literature are implemented and their validity and applicability are
discussed. The elastic mode-solver is also coupled with an electromagnetic
counterpart to study the influence of elastic anisotropies on Brillouin gain.
