The Python question I am working on requests to create a binomial function, takes four input, last one was true/false. if true returns cdf, and true by default. if false returns pmf. this is what I got so far. Would someone advise me on how to complete the code?
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))
Here is the code required. Things to note are commented below:
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
The results have been verified using a third party calculator. Please also note it does not handle errors. Good programs also test if the values input are also valid (eg that n
is always bigger than x
and p
is an appropriate probability value in the range [0,1]
)
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