I found it. To understand the following, you should know that combinations are
also called "choose". When you write nCr(5;3) a mathematecian would write it
like
this:
/ 5 \
\ 3 /
And read it as "5 choose 3".
This is because nCr(5;3) is the number of ways you can choose 3 items from a
collection of 5. So nCr is also called "choose".
The function "combina" corresponds to a function called "multichoose". That is,
you can choose the same object multiple times. And here is the MathWorld entry
about Multichoose:
http://mathworld.wolfram.com/Multichoose.html
And you can see that the numbers match.
It turns out that there is a short formula for Multichoose:
combina(a;b) == nCr(a+b-1 ; b)
How cool is that? :-)
Cheers,
--
Daniel Carrera | I don't want it perfect,
Join OOoAuthors today! | I want it Tuesday.
http://oooauthors.org |
