def dens_in_meanmatterdens(vo,ro,H=70.,Om=0.3):
    """
    NAME:

       dens_in_meanmatterdens

    PURPOSE:

       convert density to units of the mean matter density

    INPUT:

       vo - velocity unit in km/s

       ro - length unit in kpc

       H= (default: 70) Hubble constant in km/s/Mpc

       Om= (default: 0.3) Omega matter
       
    OUTPUT:

       conversion from units where vo=1. at ro=1. to units of the mean matter density

    HISTORY:

       2014-01-28 - Written - Bovy (IAS)

    """
    return dens_in_criticaldens(vo,ro,H=H)/Om
NAME:

       dens_in_meanmatterdens

    PURPOSE:

       convert density to units of the mean matter density

    INPUT:

       vo - velocity unit in km/s

       ro - length unit in kpc

       H= (default: 70) Hubble constant in km/s/Mpc

       Om= (default: 0.3) Omega matter
       
    OUTPUT:

       conversion from units where vo=1. at ro=1. to units of the mean matter density

    HISTORY:

       2014-01-28 - Written - Bovy (IAS)