(algorithm)
Definition: Choose m of n elements, where m ≤ n.
See also permutation, subset.
Note: A combination is a subset with exactly m elements.
There are n!/(n-m)!m! combinations of n (distinguishable) elements taken m at a time. Why? To begin, there are n! permutations. Permutations that only differ in the order of the n-m elements not taken are the same combination, so divide by (n-m)!. The order of the m elements taken doesn't matter either, so divide by m!, too.
Author: PEB
If you have suggestions, corrections, or comments, please get in touch with Paul E. Black.
Entry modified 26 November 2007.
HTML page formatted Tue Dec 6 16:16:32 2011.
Cite this as:
Paul E. Black, "combination", in
Dictionary of Algorithms and Data
Structures [online], Paul E. Black, ed.,
U.S. National Institute of
Standards and Technology. 26 November 2007. (accessed TODAY)
Available from: http://www.nist.gov/dads/HTML/combination.html
