The Unified Equation of State for Dark Matter and Dark Energy

We assume that dark matter and dark energy satisfy the unified equation of state: $p=B(z)\rho$, with $p=p_{dE}$, $\rho ={\rho }_{dm}+{\rho }_{dE}$, where the pressure of dark matter $p_{dm}=0$ has been taken into account. A special function $B=-\frac{A}{(1+z{)}^{\alpha }}$ is presented, which can well describe the evolution of the universe. In this model, the universe will end up with a Big Rip. By further simple analysis, we know other choices of the function $B$ can also describe the universe but lead to a different doomsday.