Time variation of the Equation of State for Dark Energy
  The time variation of the equation of state ($w_Q$) for the dark energy is
analyzed by the current values of parameters $\Omega_Q $, $w_Q $ and their time
derivatives. In the future, detailed feature of the dark energy could be
observed, so we have considered the second derivatives of $w_Q$ for two types
of potential: One is an inverse power-law type ($V=M^{4+\alpha}/Q^{\alpha}$)
and the other is an exponential one ($V=M^4\exp{(\beta M/Q)}$). The first
derivative $dw_Q/da$ and the second derivative $d^2 w_Q/da^2$ for both
potentials are derived. The first derivative is estimated by the observed two
parameters $\Delta=w_Q+1$ and $\Omega_Q$, with the assuming for $Q_0$. In the
limit $\Delta \rightarrow 0$, the first derivative is null and, under the
tracker approximation, the second derivative also becomes null. For the inverse
power potential $V=M^{4+\alpha}/Q^{\alpha}$, the observed first and second
derivatives are used to determine the potential parameter $M$ and $\alpha$. For
the potential of $V=M^4\exp{(\beta M/Q)}$, the second derivative is estimated
by the observed parameters $\Delta$, $\Omega_Q$ and $dw_Q/da$.
