  The elliptic flow parameter (component), $v_2$, in the Fourier expansion of
event-by-event charged particle multiplicity azimuthal distribution in the
momentum space is studied by taking into account the multiplicity fluctuations.
The correlations between charge multiplicity and impact parameter as well as
between elliptic flow parameter and impact parameter (multiplicity) are
investigated by both the parton and hadron cascade model PACIAE and a multiple
phase transport model AMPT. A discussion is given for the event-wise average
and particle-wise average in the definition of elliptic flow parameter.
