Wilf on packing distinct

There has been significant interest in the topic of finding permutations containing many copies of the same pattern. In this paper, we will be concerned with the other extremity, permutations containing as many different patterns as possible. At the Conference on Permutation Patterns, Otago, New Zealand, 2003, Herb Wilf asked how many distinct patterns could be contained in a permutation of length n. Based on empirical evidence, it seemed this number may approach the theoretical upper bound of 2n.

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For n  2, let PG(n, 2) be the finite projective geometry of dimension n over F2, the field of order 2. The elements or points of PG(n, 2) are the one-dimensional vector subspaces of Fn+1 2 ; the lines of PG(n, 2) are the two-dimensional vector subspaces of Fn+1 2 . Each such one-dimensional subspace {0, x} is represented by the non-zero vector x contained in it. For ease of notation, if {e0, e1, . . . , en} is a basis of Fn+1 2 and x is an element of PG(n, 2), then we denote x by a1 . . .as, where x = ea1 +·...

7p thulanh5 12-09-2011 34 2   Download