  In this paper, we contrast an empirical pulse function of gamma-ray bursts
with a theoretical model in order to provide a physical explanation to the
parameters of the KRL function and directly relate parameters in both models.
We find the ratio of the rise index r to the decay index d, derived when fitted
by the KRL function, increases quickly first and then remains nearly invariant
with the relative width of local pulses when the width exceeds 2. The rise and
decay times of pulses are found to be related to the Lorentz factor by a power
law, where the power law index associated with the rise time is less than that
of the decay time, and both are close to -2. In addition, the mean asymmetry
shows a slight trend of decreasing with Lorentz factors. In plots of decay
indices versus asymmetry, there is a descending phase and after this phase
there is a rising portion. We find that these long bursts of the KRL sample are
mainly associated with those light curves arising from co-moving pulses with
the relative width being larger than 0.1. We show that the effect of the
co-moving pulse shape on the KRL function parameters of the resulting pulses is
considerable and can be distinguished by the decay index d when the relative
co-moving pulse width is less than 2.
