  We describe NumBAT, an open-source software tool for modelling stimulated
Brillouin scattering in waveguides of arbitrary cross-section. It provides
rapid calculation of optical and elastic dispersion relations, field profiles
and gain with an easy-to-use Python front end. Additionally, we provide an open
and extensible set of standard problems and reference materials to facilitate
the bench-marking of NumBAT against subsequent tools. Such a resource is needed
to help settle discrepancies between existing formulations and implementations,
and to facilitate comparison between results in the literature. The resulting
standardised testing framework will allow the community to gain confidence in
new algorithms and will provide a common tool for the comparison of
experimental designs of opto-acoustic waveguides.
