  We numerically study the temporal evolution of a black-hole laser
configuration displaying a pair of black and white hole horizons in a flowing
atomic condensate. This configuration is initially prepared starting from a
homogeneous flow via a suitable space-dependent change of the interaction
constant and the evolution is then followed up to long times. Depending on the
values of the system parameters, the system typically either converges to the
lowest energy solution by evaporating away the horizons or displays a
continuous and periodic coherent emission of solitons. By making a physical
comparison with optical laser devices, we identify the latter regime of
continuous emission of solitons as the proper black-hole laser effect. We
include some movies of the temporal evolution of the spatial density and
velocity profiles in the most significant cases.
