Criss-cross algorithm: Difference between revisions

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Computational complexity: Worst and average cases: put details about Simplex in footnote
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However, like the simplex algorithm of Dantzig, the criss-cross algorithm is ''not'' a polynomial-time algorithm for linear programming. Terlaky's criss-cross algorithm visits all the&nbsp;2<sup>''D''</sup>&nbsp;corners of a (perturbed) cube in dimension&nbsp;''D'', according to a paper of Roos; Roos's paper modifies the [[Victor Klee|Klee]]–Minty construction of a [[unit cube|cube]] on which the simplex algorithm takes&nbsp;2<sup>''D''</sup>&nbsp;steps).<ref name="FukudaTerlaky"/><ref name="Roos"/><ref name="KleeMinty">{{cite book|title=Inequalities&nbsp;III (Proceedings of the Third Symposium on Inequalities held at the University of California, Los Angeles, Calif., September&nbsp;1–9,&nbsp;1969, dedicated to the memory of Theodore&nbsp;S. Motzkin)|editor-first=Oved|editor-last=Shisha|publisher=Academic Press|___location=New York-London|year=1972|MR=332165|last1=Klee|first1=Victor|authorlink1=Victor Klee|last2=Minty|first2= George&nbsp;J.|authorlink2=George J. Minty|chapter=How good is the simplex algorithm?|pages=159–175|ref=harv}}</ref> Like the simplex algorithm, the criss-cross algorithm visits all&nbsp;8 corners of the three-dimensional cube in the worst case.
 
When it is initialized at a random corner of the cube, the criss-cross algorithm visits only&nbsp;''D'' additional corners, however, according to a&nbsp;1994 paper by Fukuda and Namiki.<ref name="FukudaNamiki" >{{harvtxt|Fukuda|Namiki|1994|p=367}}</ref><ref name="FTNamiki" >{{harvtxt|Fukuda|Terlaky|1997|p=385}}</ref> Trivially, the simplex algorithm takes on average&nbsp;''D'' steps for a cube. <ref>More generally, for the simplex algorithm, the expected number of steps is proportional to&nbsp;''D'' for linear-programming problems that are randomly drawn from the [[Euclidean metric|Euclidean]] [[unit&nbsp;sphere]], as proved by Borgwardt and by [[Stephen Smale|Smale]].</ref><ref name="Borgwardt"/> Like the simplex algorithm, the criss-cross algorithm visits exactly&nbsp;3 additional corners of the three-dimensional cube on&nbsp;average.
 
==Variants==