Distance Integral Complete Multipartite Graphs with s = 5; 6
YANG Ruo-song, WANG Li-gong
2016, 31(2):
111-117.
doi:10.13371/j.cnki.chin.q.j.m.2016.02.001
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Let D(G) =(dij)n×n denote the distance matrix of a connected graph G with order n, where dij is equal to the distance between vertices viand vjin G. A graph is called distance integral if all eigenvalues of its distance matrix are integers. In 2014, Yang and Wang gave a sufficient and necessary condition for complete r-partite graphs Kp1,p2,···,pr=Ka1·p1,a2·p2,···,as···ps to be distance integral and obtained such distance integral graphs with s = 1, 2, 3, 4. However distance integral complete multipartite graphs Ka1·p1,a2·p2,···,as·ps with s > 4 have not been found. In this paper, we find and construct some infinite classes of these distance integral graphs Ka1·p1,a2·p2,···,as·ps with s = 5, 6. The problem of the existence of such distance integral graphs Ka1·p1,a2·p2,···,as·ps with arbitrarily large number s remains open.