xt_n_choose_k(3)

NAME
xt_n_choose_k() - Compute binomial coefficient N choose K

LIBRARY
#include <xtend/math.h>
-lxtend

SYNOPSIS
#include <stdint.h>
#include "math.h"
unsigned long   xt_n_choose_k(unsigned long n, unsigned long k)

ARGUMENTS
n   Number of items to choose from
k   Number of items chosen

DESCRIPTION
Compute the binomial coefficient N choose K = N! / (K! * (N-K)!). This represents the number of ways to choose K items out of a pool of N, such that we don't care about order. E.g., if choosing 2 letters from the set [A B C D E], [C D] is considered the same [D C]. This implementation avoids overflow by alternating multiply and divide operations (rather than try to compute factorials first, which will fail for relatively small values of N or K).

RETURN VALUES
The number of ways to choose K items from N objects.

EXAMPLES
#include <xtend/math.h>
unsigned long   n = 5, k = 2;
printf("Ways to choose %lu items from %lu = %lun",
        k, n, xt_n_choose_k(n, k));

SEE ALSO
lgamma(3)