  We present numerical evidence for an extended order parameter and conjugate
field for the dynamic phase transition in a Ginzburg-Landau mean-field model
driven by an oscillating field. The order parameter, previously taken to be the
time-averaged magnetization, comprises the deviations of the Fourier components
of the magnetization from their values at the critical period. The conjugate
field, previously taken to be the time-averaged magnetic field, comprises the
even Fourier components of the field. The scaling exponents beta and delta
associated with the extended order parameter and conjugate field are shown
numerically to be consistent with their values in the equilibrium mean-field
model.
