def dens(gamma, pres, eint):
    """
    Given the pressure and the specific internal energy, return
    the density

    Parameters
    ----------
    gamma : float
        The ratio of specific heats
    pres : float
        The pressure
    eint : float
        The specific internal energy

    Returns
    -------
    out : float
       The density

    """
    return pres/(eint*(gamma - 1.0))