Calling sequence of calc_vol

The calling sequence for calc_vol is:

result = calc_vol(z,$\Omega_M$, $\Omega_\Lambda$,H0=x,w=y)

where x is a value for the hubble constant and y is a value for w ( $-1 \leq y \leq 0$). For ``normal'' physics, use w = -1 (see section IIIA above). z can be a scalar or an array. If it is scalar, result is a scalar comoving volume element. If z is an array, result is an array with the comoving volume element for each z value in the array. The parameters $\Omega_M$, $\Omega_\Lambda$ must be specified, whereas H₀ and w can be omitted. H₀ has to be given in terms of $km/(Mpc\,\, s)$. If omitted, H₀ is internally set to 50. If w is omitted, it is internally set to -1.
Note that the function calc_vol needs much more runtime than the other routines because three values for d_M have to be calculated for each point $dV/(dz d\Omega)$ (see section VIF below for more information on this).