def METHOD_NAME(C, mag):
    """
    Returns magnitude dependent inter-event standard deviation (tau)
    (equation 14)
    """
    tau = C["tau1"] + (C["tau2"] - C["tau1"]) * ((mag - 6.5) / 0.5)
    tau[mag < 6.5] = C["tau1"]
    tau[mag >= 7.] = C["tau2"]
    return tau