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nishijima
2008 Feb 14
0
reordering combn(n,p)
...columns only differed by one element.
I assumed that this was a problem known to the Assyrians and
resisted the temptation to write to r-help, and through assiduous
googling finally discovered that this was still a topic of current
research in computer science.
Solution: Limin Xiang and Kazuo Ushijima (2001) "On O(1) Time
Algorithms for
Combinatorial Generation," Computer Journal, 44(4), 292-302.
provides a nice algorithm (in Pascal) which I then translated into
ratfor and plan to incorporate eventually into quantreg. It manages
to do n=500 p = 3 in about 3 secs on my old G5. It pr...