  We solve the Gross-Pitaevskii equation to model the behaviour of a
weakly-interacting Bose condensate. Solutions are presented for the eigenstates
in one- and two-dimensional harmonic traps. We include the effect of gravity
and coupling to a second condensate to simulate an output coupler for Bose
condensed atoms, and find that the output pulse shape is in qualitative
agreement with experiment. We also model flow under gravity through a
constriction, demonstrating excitation and separation of eigenmodes in the
condensate.
