stolen from thomas

def g_parameter(time_residual):
    """stolen from thomas"""
    mean = np.mean(time_residual)
    time_residual_prime = (time_residual - np.ones(time_residual.shape) * mean)
    time_residual_prime *= time_residual_prime / (-2 * 1.5 * 1.5)
    time_residual_prime = np.exp(time_residual_prime)
    g = np.sum(time_residual_prime) / len(time_residual)
    return g