  In this paper, we study the Bose-Einstein condensation of a scalar field with
an attractive self-interaction, with or without gravitational interactions. We
confirm through full dynamical simulation that the condensation timescale due
to self-interaction is inversely proportional to the square of the number
density $n$ and the self-coupling constant $g$ : $\tau \propto n^{-2} g^{-2}$.
We also investigate the condensation timescale when self-interaction and
gravity are both important by solving the Gross-Pitaevskii-Poisson equations,
and find that the condensation time scales according to an additive model for
the cross section. We discuss the relevance of our results to theoretical
models of boson star formation by condensation.
