Andrea wrote:
> Hi,
> I need to calculate this probability P!/{n \choose p}, varying both n
> and p, n takes values in this range [512:1024] and p in [2:12].
> So i write this code in python:
>
> def factorial(n):
> result=1
> if n==0: return 1
> for i in xrange(1, abs(n)+1):
> result = i*result
> if n >= 0:
> return result
> else:
> return -result
> def binomial(n, k):
> assert n>0 and isinstance(n, (int, long)) and isinstance(k,
> (int,long))
> if k < 0 or k > n:
> return 0
> if k == 0 or k == n:
> return 1
> return factorial(n) // (factorial(k) * factorial(n-k))
>
> I want to call factorial(2)//binomial(1024,2) for example, in this way
> trivially I obtain 0 as probability, how can I obtain the probability
> forcing this division to output extremely small real numbers????
>
'//' is floor division.
>>> 2/523776
0
>>> 2//523776
0
>>> float(2)/523776
3.8184261974584555e-006
>>> from __future__ import division
>>> 2/523776
3.8184261974584555e-006
>>> 2//523776
0
>>>
Duncan
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