ztnb_em.py 文件源码

def ztnb_cdf(y, mu, alpha):
    r = 1.0/alpha
    if y <= 0:
        raise Exception('y must be larger than 0.')
    p = mu/(mu+r+0.0)
    F_ztnb = ( 1 - special.btdtr(y+1, r, p) - np.power(1-p, r) ) / (1-np.power(1-p,r))
    return F_ztnb