tailieunhanh - Báo cáo toán học: "Edge-bandwidth of the triangular grid"

Tuyển tập các báo cáo nghiên cứu khoa học về toán học trên tạp chí toán học quốc tế đề tài: Edge-bandwidth of the triangular grid. | Edge-bandwidth of the triangular grid Reza Akhtar Dept. of Mathematics and Statistics Miami University Oxford OH 45056 USA reza@ Tao Jiang Dept. of Mathematics and Statistics Miami University Oxford OH 45056 USA jiangt@ Dan Pritikin Dept. of Mathematics and Statistics Miami University Oxford OH 45056 USA pritikd@ Submitted May 19 2006 Accepted Aug 16 2007 Published Oct 5 2007 Mathematics Subject Classification 05C78 Abstract In 1995 Hochberg McDiarmid and Saks proved that the vertex-bandwidth of the triangular grid Tn is precisely n 1 more recently Balogh Mubayi and Pluhár posed the problem of determining the edge-bandwidth of Tn. We show that the edge-bandwidth of Tn is bounded above by 3n 1 and below by 3n o n . 1 Introduction A labeling of the vertices of a finite graph G is a bijective map h V G 1 2 . V G . The vertex-bandwidth of h is defined as B G h max h u h v u v eE G and the vertex-bandwidth or simply bandwidth of G is defined as B G min B G h h THE ELECTRONIC JOURNAL OF COMBINATORICS 14 2007 R67 1 in which the minimum is taken over all labelings of V G . The edge-bandwidth of G is defined as B G B L G where L G is the line graph of G. Edge-bandwidth has been studied for several classes of graphs in various sources among them 1 2 5 and 6 . In this article we study the edge-bandwidth of the triangular grid Tn. For any integer n 0 Tn is the graph whose vertices are ordered triples of nonnegative integers summing to n with an edge connecting two triples if they agree in one coordinate and differ by 1 in the other two see Figure 1 for an illustration of T5 the bottom row vertices from left to right being 0 5 0 1 4 0 2 3 0 3 2 0 4 1 0 and 5 0 0 . The vertexbandwidth of Tn was studied by Hochberg McDiarmid and Saks in 4 they proved that B Tn n 1. The problem of determining B0 Tn was posed by Balogh Mubayi and Pluhár in 1 . Our main result is Theorem . 3n o n B0 Tn 3n 1. It is easy to obtain the stated upper bound on .