randomwalk.py 文件源码

def poisson_from_positiveK(mean):
    # solve x/(1 - exp(-x)) == mean
    def f(x):
        return x/(1. - np.exp(-x))
    def f1(x):
        return (np.expm1(x) - x)/(2.*np.cosh(x) - 2.)

    x = solve_newton(mean, f, f1, mean, n=10)
    return x