Function Calc_vol

Calc_vol.pro calculates the derivative of the comoving volume element $dV/(dz d\Omega)$, where $\Omega$ is the solid angle, for given z, $\Omega_M$, $\Omega_\Lambda$ and w. For some basic reference about the w parameter, see [3,4]. However you can also use the function without using this parameter (see IIIB below ). The function checks if the passed parameters would result in a bouncing universe which means that the universe has a turning point in its past, that is, it collapsed from infinite size to a finite radius and is now reexpanding. If the functions detects parameters which describe such a bouncing universe, it returns a large negative number (see sections IIIC and V below).