二項分佈式輸出使用Python的CDF/PMF

Question

我正在處理創建二項函數的請求，需要四個輸入，最後一個是真/假。如果爲true，則返回cdf，默認爲true。如果false返回pmf。這是我到目前爲止。有人會告訴我如何完成代碼？

def binomial_distribution(x,n,p,cum): 
    """ 
    Computes the probability of having x successes out of n trials. 
    Each trial has a probability of success p 
    """ 
    nCx = combination(n,x) 
    q = 1-p 
    return nCx*(p**x)*(q**(n-x)) 

Answer 1

這是需要的代碼。注意事項如下：

def factorial(n): 
    if n == 0: return 1 
    factrl = n 
    while n > 2: 
     n -= 1 
     factrl = factrl * n 
    return factrl 

def combination(n, x): 
    return factorial(n)/(factorial(x)*factorial(n-x)) 

def binomial_distribution(x,n,p,cum = True): 
    """ 
    Computes the probability of having x successes out of n trials. 
    Each trial has a probability of success p 
    """ 
    nCx = combination(n,x) 
    q = 1-p 

    #What helps is a conditional return statement as below 
    if cum: return bin_cdf(x, n, p) 
    else: return nCx*(p**x)*(q**(n-x)) 

def bin_cdf(x, n, p): 
    cumul = 0.0 
    while x > 0: 
     print(x) 
     cumul += binomial_distribution(x, n, p, False) #Sums using formula 
     #This kind of recursion is not only possible but encouraged 
     x -= 1 
    return cumul 

結果已經驗證使用第三方計算器。另請注意，它不處理錯誤。好節目，也測試，如果輸入的數值也是有效的（例如是n總是比x和p更大的範圍內[0,1]適當的概率值）