摘要
Let S be a primitive non-powerful symmetric loop-free signed digraph on even n vertices with base 3 and minimum number of arcs. In [Lihua YOU, Yuhan WU. Primitive non- powerful symmetric loop-free signed digraphs with given base and minimum number of arcs. Linear Algebra Appl., 2011, 434（5）, 1215-1227], authors conjectured that D is the underlying digraph of S with exp（D）= 3 if and only if D is isomorphic to EDn,3,3, where EDn,3,3 = （V, A） is a digraph with V = {1, 2,..., n}, A = {（1, i）, （i, 1） [ 3 〈： i 〈 n} U {（2i - 1, 2i）, （2i, 2i - 1） [ 2 〈 〈 2} U {（2, 3）, （3, 2）, （2, 4）, （4, 2）}）. In this paper, we show the conjecture is true and completely characterize the underlying digraphs which have base 3 and the minimum number of arcs.
Let S be a primitive non-powerful symmetric loop-free signed digraph on even n vertices with base 3 and minimum number of arcs. In [Lihua YOU, Yuhan WU. Primitive non- powerful symmetric loop-free signed digraphs with given base and minimum number of arcs. Linear Algebra Appl., 2011, 434（5）, 1215-1227], authors conjectured that D is the underlying digraph of S with exp（D）= 3 if and only if D is isomorphic to EDn,3,3, where EDn,3,3 = （V, A） is a digraph with V = {1, 2,..., n}, A = {（1, i）, （i, 1） [ 3 〈： i 〈 n} U {（2i - 1, 2i）, （2i, 2i - 1） [ 2 〈 〈 2} U {（2, 3）, （3, 2）, （2, 4）, （4, 2）}）. In this paper, we show the conjecture is true and completely characterize the underlying digraphs which have base 3 and the minimum number of arcs.
基金
Supported by the National Natural Science Foundation of China(Grant Nos.10901061
11071088)
Programon International Cooperation and Innovation,Department of Education,Guangdong Province(Grant No.2012gjhz0007)
the Zhujiang Technology New Star Foundation of Guangzhou City(Grant No.2011J2200090)
