  We have used a simple spectrum distribution which was derived from a
hydrodynamical equation\cite{Csorgo} to fit the data of the STAR group. It is
found that it can fit the $v_2$ of STAR group very well. We have found that
$v_2$ is sensitive to both the effective temperature of particles and the
expanding velocity. We have suggested a new variable ${\bf z}$ to be used in
the flow analysis. This new variable will measure the correlation of particles
momentum components. We have also shown that one of the $x$ or $y$ direction in
the reaction plane is the direction which has the largest variance.
