A fast NCHOOSEK alternative for engineers who like fast NCHOOSEK alternatives

This code recursively generates K-subsets of an N-set.

GETNEXTCOMBINATION returns the next K-subset of an N-set. It implements the "Revolving Door" (NEXKSB) algorithm found in "Combinatorial Algorithms", 2nd Ed., by Albert Nijenhuis and Herbert S. Wilf. It is a recursive alternative to the NCHOOSEK command that is extremely fast (O(1)), at the expense of slightly more user interaction. (You do get something that NCHOOSEK does not give you for
this extra effort: see input "m".) Apart from its efficiency, it is awesome because each new K-subset differs from the last by a single element and the last combination generated differs from the first combination by a single element.