  Large systems of coupled oscillators subjected to a periodic external drive
occur in many situations in physics and biology. Here the simple, paradigmatic
case of equal-strength, all-to-all sine-coupling of phase oscillators subject
to a sinusoidal external drive is considered. The stationary states and their
stability are determined. Using the stability information and numerical
experiments, parameter space phase diagrams showing when different types of
system behavior apply are constructed, and the bifurcations marking transitions
between different types of behavior are delineated. The analysis is supported
by results of direct numerical simulation of an ensemble of oscillators.
