in reply to Re: Binomial Expansion
in thread Binomial Expansion
You do say right away that is a valid formula for binomial coefficients, but then you say it's hardly a good one?
It is a formula for calculating r-combinations, not binomial coefficients.
The formula for binomial expansion is:
n _ (x+y)^n = \ C(n,j) * x^(n-j) *y^j / ¯ j=0
And btw, it is the definitive formula for calculating r-combinations. It's like saying 4/2 is not the same as 2. While 2 is a better way to write 4/2, not every one recognizes 2 right away, and I feel, for the benefit of the reader of me 'craft', n!/(r!(n-r)! is a better way to go.
As for your function, it is shorter, but a litle mysterious when it comes to the math.
update:9! 9*8*7* 6! 9*8*7 504 nCr(9,3) = --------- = ----------- = ------ = --- = 84 3!*(9-3)! 3*2*1*(6!) 3*2*1 6 which follows from the fact that nCr(n,r) = nCr(n,n-r) n! n! n! _ n! ------- = ----------------- = ------------- = --------- r!(n-r) (n-r)!(n-(n-r))! (n-r)!(n-n+r)! (n-r)!(r)!This however only works for n>r, as long as n and r are both non-negative integers, but shouldn't be a problem in this case.As for things being integer, since the input is an integer, it follows that any integer multiple of that integer, will also be an integer.
I give, I give, theory v. practice, there is a difference.
___crazyinsomniac_______________________________________
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