Python 阶乘factorial

整数的阶乘（factorial）是所有小于及等于该数的正整数的积，0的阶乘为1。即：n!=1×2×3×...×n。

import numpy as np
import matplotlib as mpl
import matplotlib.pyplot as plt
from scipy.special import gamma
from scipy.special import factorial

mpl.rcParams['axes.unicode_minus'] = False
mpl.rcParams['font.sans-serif'] = 'SimHei'


if __name__ == '__main__':
    N = 5
    x = np.linspace(0, N, 50)
    y = gamma(x+1)
    plt.figure(facecolor='w')
    plt.plot(x, y, 'r-', x, y, 'm*', lw=2)
    z = np.arange(0, N+1)
    print z
    f = factorial(z, exact=True)    # 阶乘
    print f
    plt.plot(z, f, 'go', markersize=8)
    plt.grid(b=True)
    plt.xlim(-0.1,N+0.1)
    plt.ylim(0.5, np.max(y)*1.05)
    plt.xlabel(u'X', fontsize=15)
    plt.ylabel(u'Gamma(X) - 阶乘', fontsize=15)
    plt.title(u'阶乘和Gamma函数', fontsize=16)
    plt.show()