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

    Parameters
    ----------
    gamma : float
        The ratio of specific heats
    dens : float
        The density
    eint : float
        The specific internal energy

    Returns
    -------
    out : float
       The pressure

     """
    return dens*eint*(gamma - 1.0)