行政院國家科學委員會專題研究計畫 成果報告
正則擬多邊形的研究
計畫類別: 個別型計畫
計畫編號: NSC92-2115-M-009-017-
執行期間: 92 年 08 月 01 日至 93 年 07 月 31 日
執行單位: 國立交通大學應用數學系
計畫主持人: 翁志文
報告類型: 精簡報告
處理方式: 本計畫可公開查詢
中 華 民 國 93 年 9 月 1 日
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×Z` Γ Îà5 D ≥ 3 k ÝÑJa9\ Í 8ø¢ó a1> 0, c2> 1. θ1 Γ ÏÞÝ©Ç Â 3hi&ÆÿÕ θ1≤ k − a1− c2 c2− 1 .&ÆJ|ì (i)–(iii) ÎÝ: (i) îPr Wñ; (ii) Γ Ey θ1 Î Q-94P; (iii) Γ ÎEÁ% Tõ% 9Í Paul Terwilliger )®Þs y European Journal of Combinatorics.
n"Þ a9\; ûÒÑJ%; Q-94P; EÁ %; õ%
Abstract Let Γ denote a near polygon distance-regular graph with diameter d ≥ 3, valency k and intersection numbers a1 > 0, c2 > 1. Let θ1 denote the second largest eigenvalue of Γ. We show
θ1≤
k − a1− c2 c2− 1
.
We show the following (i)–(iii) are equivalent. (i) Equality is attained above; (ii) Γ is Q-polynomial with respect to θ1; (iii) Γ is a dual polar graph or a Hamming graph.
Keywords: near polygon, distance-regular graph, Q-polynomial, dual polar graph, Hamming graph. Þ`ãêÝ
Γ Î×Íà5 D C8ø¢ó ai, bi, ci (0 ≤ i ≤ D)ÝûÒÑJ% ' Γ îtç(àa) ÝFó KÎ a1+ 2 &Æê'AEàa ` ×F xÝûÒ ∂(`, x) y D `Ä°×D3× ` îÝF y ∂(`, x) = ∂(y, x) J&ÆÌ Γ Î×ÍÑJa 9\ A Γ E ∂(`, x) = D `ôb|îP² J Γ ÌÎ×ÑJa 2D \ A Γ E ∂(`, x) = D ` Xb ` îÝF y K ∂(`, x) = ∂(y, x) J Ì Γ Î×ÑJa 2D + 1 \ [2] ÿÕnyÑJ a 2D \Ý¥ D ≤ 3 a1 = 0 c2 = 1 T c3= c22− c2+ 1 [1, p206] ¼9ÝJ b×Í2]ÝD¡Îý0ÝÍi| Xî«®Þ ^ ¬TEÑJa 2D + 1 \ô ÿÕv« ëD¡ &Æݬ^Xî®Þ ¬ÿÕ×Í E?½ÝÑJa9\ôÊàÝP 9Í PrWñ` &Æ|X9Í% Þ û&ÆÝ]° |ÑiÑJ 2D \ qA [1]Ý Proposition 4.4.6(i), &Æb|ìÌ Hoffman boundÝP: θD≥ − k a1+ 1 , ÍrWñ uv°u Γ Î×ÑJa 2D \ h θD Î Γ ÝtÝ©Ç ãy9Í&Æ ÝÝ8«P ËïA¢)!8¿à @s× ° è Þ¼?h]'Äæ °WÝ hi4ÿÕ×Ì¡ hô Euro-pean Journal of Combinatorics#å ¬EÑJa9 \ Γ ÝÑib×°Äæè
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[1 ] A.E. Brouwer, A.M. Cohen, A. Neu-maier, Distance-Regular Graphs, Springer-Verlag, 1989
[2 ] A. E. Brouwer, H.A. Wilbrink, The structure of near polygons with quads, Geom. Dedicata 14:145-176, 1983