tailieunhanh - Báo cáo toán học: "Colorings and orientations of matrices and graphs"

Tuyển tập các báo cáo nghiên cứu khoa học về toán học trên tạp chí toán học quốc tế đề tài: Colorings and orientations of matrices and graphs. | Colorings and orientations of matrices and graphs Uwe Schauz Department of Mathematics University Tubingen Germany Submitted Feb 9 2005 Accepted Jul 6 2006 Published Jul 28 2006 Mathematics Subject Classifications 05C15 05C50 15A15 05C20 05C45 05C10 Abstract We introduce colorings and orientations of matrices as generalizations of the graph theoretic terms. The permanent per A of certain copies A of a matrix A can be expressed as a weighted sum over the orientations or the colorings of A . When applied to incidence matrices of graphs these equations include Alon and Tarsi s theorem about Eulerian orientations and the existence of list colorings. In the case of planar graphs we deduce Ellingham and Goddyn s partial solution of the list coloring conjecture and Scheim s equivalency between not vanishing permanents and the four color theorem. The general concept of matrix colorings in the background is also connected to hypergraph colorings and matrix choosability. Introduction The original idea behind this paper was to interpret Ryser s evaluation formula for permanents as a statement about colorings corollary and the text below and to utilize this interpretation in new proofs for Scheim s equation and a strengthened quantitative version of Alon and Tarsi s theorem . Our proofs do not use the graph polynomial neither in combination with the combinatorial nullstellensatz as in Al2 AlTa nor with quantitative relations between the coefficients and the values of polynomial functions as in Sch Lemma 1 . The color formula for n-regular graphs follows unlike in ElGo or Al without use of 2-factorizations. Our methods are new and this could be of interest. However we thought that it should be possible to use Alon and Tarsi s common and powerful methods to prove the main theorems about matrix colorings in section . This led us to the conviction that there is a stronger quantitative version of the combinatorial .

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