正态分布概率计算

[python]代码库

def st_norm(u):
     '''标准正态分布'''
     import math
     x=abs(u)/math.sqrt(2)
     T=(0.0705230784,0.0422820123,0.0092705272,
        0.0001520143,0.0002765672,0.0000430638)
     E=1-pow((1+sum([a*pow(x,(i+1))
                     for i,a in enumerate(T)])),-16)
     p=0.5-0.5*E if u<0 else 0.5+0.5*E
     return(p)
 
def norm(a,sigma,x):
     '''一般正态分布'''
     u=(x-a)/sigma
     return(st_norm(u))
 
while 1:
     '''输入一个数时默认为标准正态分布
     输入三个数(空格隔开)时分别为期望、方差、x
     输入 stop 停止'''
     S=input('please input the parameters:\n')
     if S=='stop':break
     try:
         L=[float(s) for s in S.split()]
     except:
         print('Input error!')
         continue
     if len(L)==1:
         print('f(x)=%.5f'%st_norm(L[0]))
     elif len(L)==3:
         print('f(x)=%.5f'%norm(L[0],L[1],L[2]))
     else:
         print('Input error!')