* Dave Angel:
kj wrote:
Before I go off to re-invent a thoroughly invented wheel, I thought
I'd ask around for some existing module for computing binomial
coefficient, hypergeometric coefficients, and other factorial-based
combinatorial indices. I'm looking for something that can handle
fairly large factorials (on the order of 10000!), using floating-point
approximations as needed, and is smart about optimizations,
memoizations, etc.
TIA!
~K
You do realize that a standard. python floating point number cannot
possibly approximate a number like 10000!
I think what kj is looking for, provided she/he is knowledgable about the
subject, is code that does something like
>>> from math import *
>>> log_fac = 0
>>> for i in range( 1, 10000+1 ):
... log_fac += log( i, 10 )
...
>>> print( "10000! = {}e{}".format( 10**(log_fac % 1), int( log_fac ) ) )
10000! = 2.84625968062e35659
>>> _
which turned out to be accurate to 10 digits.
Better use longs.
That would involve incredible overhead. E.g., how many bytes for the number
above? Those bytes translate into arithmetic overhead.
I'd check out the gamma function, which matches factorial for integer
arguments (plus or minus 1).
Or, e.g., logarithms... ;-)
Cheers & hth.,
- Alf
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