def stag_temperature_ratio(M, gamma):
    """Stagnation temperature / static temperature ratio.

    Arguments:
        M (scalar): Mach number [units: dimensionless].
        gamma (scalar): Heat capacity ratio [units: dimensionless].

    Returns:
        scalar: the stagnation temperature ratio :math:`T_0 / T` [units: dimensionless].
    """
    return 1 + (gamma - 1) / 2 * M**2