tailieunhanh - Báo cáo toán học: "A Colorful Involution for the Generating Function for Signed Stirling Numbers of the First Kind"

Tuyển tập các báo cáo nghiên cứu khoa học ngành toán học tạp chí toán học quốc tế đề tài: A Colorful Involution for the Generating Function for Signed Stirling Numbers of the First Kind. | A Colorful Involution for the Generating Function for Signed Stirling Numbers of the First Kind Paul Levande Department of Mathematics David Rittenhouse Lab. 209 South 33rd Street Philadelphia PA 19103-6395 plevande@ Submitted Nov 3 2009 Accepted Dec 13 2009 Published Jan 5 2010 Mathematics Subject Classification 05A05 05A15 05A19 Abstract We show how the generating function for signed Stirling numbers of the first kind can be proved using the involution principle and a natural combinatorial interpretation based on cycle-colored permuations. We seek an involution-based proof of the generating function for signed Stirling numbers of the first kind written here as E 1 kc n k xk 1 n x x 1 x n 1 k where c n k is the number of permutations of n with k cycles. The standard proof uses 2 an algebraic manipulation of the generating function for unsigned Stirling numbers of the first kind. Fix an unordered x-set A for example a set of x letters or colors . For n G Sn let Kn be the set of disjoint cycles of n including any cycles of length one . Let Sn A n f n G Sn f Kn A be the set of cycle-colored permutations of n where f is interpreted as a coloring of the cycles of n using the colors of A. We follow 1 in using colored permutations . Further let Kn i be the unique cycle of n containing i for any 1 i n and K n Kn be the number of cycles of n. Note that E 1 K n E 1 K n x n 1 kc n k xk n f Sn A nèSn k This research was supported by the University of Pennsylvania Graduate Program in Mathematics THE ELECTRONIC JOURNAL OF COMBINATORICS 17 2010 N2 1 For n f G Sn A let R n f i j 1 i j n f Kn i f Kn j be the set of pairs of distinct elements of n in cycles-not necessarily distinct-colored the same way by f . Define a map Ộ on Sn A as follows for n f G Sn A If R n f 0 let ộ n f n f Otherwise let i j G R n f be minimal under the lexicographic ordering of R n f Let n i j n the product of the transposition i j and n in Sn. Note that if Kn i Kn j left-multiplication by i

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