Guillermo Pineda-Villavicencio1,2, Mirka Miller2,3
1Department of Computer Science, University of Oriente, Santiago de Cuba, Cuba
2School of Information Technology and Mathematical Sciences University of Ballarat, Ballarat, Australia
3Department of Mathematics, University of West Bohemia,Pilsen, Cacch Republic
Abstract:

It is well known that apart from the Petersen graph, there are no Moore graphs of degree 3. As a cubic graph must have an even number of vertices, there are no graphs of maximum degree 3 and \(\delta\) vertices less than the Moore bound, where \(\delta\) is odd. Additionally, it is known that there exist only three graphs of maximum degree 3 and 2 vertices less than the Moore bound. In this paper, we consider graphs of maximum degree 3, diameter \( D \geq 2 \), and 4 vertices less than the Moore bound, denoted as \((3, D, 4)\)-graphs. We obtain all non-isomorphic \((3, D, 4)\)-graphs for \( D = 2 \). Furthermore, for any diameter \( D \), we consider the girth of \((3, D, 4)\)-graphs. By a counting argument, it is easy to see that the girth is at least \( 2D – 2 \). The main contribution of this paper is that we prove that the girth of a \((3, D, 4)\)-graph is at least \( 2D – 1 \). Finally, for \( D > 4 \), we conjecture that the girth of a \((3, D, 4)\)-graph is \( 2D \).

Claude Levesque1
1Départment de Mathématiques et de Statistique Université Laval, Québec, Canada G1IK 7P4
Abstract:

A fast direct method for obtaining the incidence matrix of a finite projective plane of order \( n \) via \( n-1 \) mutually orthogonal \( n \times n \) Latin squares is described. Conversely, \( n-1 \) mutually orthogonal \( n \times n \) Latin squares are directly exhibited from the incidence matrix of a projective plane of order \( n \). A projective plane of order \( n \) can also be described via a digraph complete set of Latin squares, and a new procedure for doing this will also be described.

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