def mach_from_pr(p_c, p_e, gamma):
    """Find the exit Mach number from the pressure ratio.

    Arguments:
        p_c (scalar): Nozzle stagnation chamber pressure [units: pascal].
        p_e (scalar): Nozzle exit static pressure [units: pascal].
        gamma (scalar): Exhaust gas ratio of specific heats [units: dimensionless].

    Returns:
        scalar: Exit Mach number [units: dimensionless].
    """
    return (2 / (gamma - 1) * ((p_e / p_c) ** ((1 - gamma) / gamma) - 1)
        ) ** 0.5
