comb

来自「Calc Software Package for Number Calc」· 代码 · 共 66 行

NAME
    comb - combinatorial number

SYNOPSIS
    comb(x, y)

TYPES
    x		integer
    y		integer

    return	integer

DESCRIPTION
    Return the combinatorial number C(x,y) which is defined as:

	       x!
	    ---------
	    y!*(x-y)!

    This function computes the number of combinations in which y things
    may be chosen from x items ignoring the order in which they are chosen.

EXAMPLE
    ; print comb(7,3), comb(7,4), comb(7,5), comb(3,0), comb(0,0)
    35 35 21 1 1

    ; print comb(2^31+1,2^31-1)
    2305843010287435776

LIMITS
    x >= y >= 0
    y < 2^24
    x-y < 2^24

LINK LIBRARY
    void zcomb(ZVALUE x, ZVALUE y, ZVALUE *res)

SEE ALSO
    fact, perm, randperm

## Copyright (C) 1999-2006  Landon Curt Noll
##
## Calc is open software; you can redistribute it and/or modify it under
## the terms of the version 2.1 of the GNU Lesser General Public License
## as published by the Free Software Foundation.
##
## Calc is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
## or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU Lesser General
## Public License for more details.
##
## A copy of version 2.1 of the GNU Lesser General Public License is
## distributed with calc under the filename COPYING-LGPL.  You should have
## received a copy with calc; if not, write to Free Software Foundation, Inc.
## 59 Temple Place, Suite 330, Boston, MA  02111-1307, USA.
##
## @(#) $Revision: 29.4 $
## @(#) $Id: comb,v 29.4 2006/06/25 22:16:55 chongo Exp $
## @(#) $Source: /usr/local/src/cmd/calc/help/RCS/comb,v $
##
## Under source code control:	1994/10/20 04:03:02
## File existed as early as:	1994
##
## chongo <was here> /\oo/\	http://www.isthe.com/chongo/
## Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/