Skew-symmetric association schemes with two classes and strongly regular graphs of type L 2n-1(4n-1)

• Main Author: Pasechnik, Dmitrii V.
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2013
• Subjects: DRNTU::Science::Mathematics
• Online Access: https://hdl.handle.net/10356/87926; http://hdl.handle.net/10220/9466
• Institution: Nanyang Technological University

A construction of a pair of strongly regular graphs Γn and Γ'n of type L 2n-1 (4n-1) from a pair of skew-symmetric association schemes W, W' of order 4n-1 is presented. Examples of graphs with the same parameters as Γn and Γ'n, i.e., of type L 2n-1 (4n-1), were known only if 4n-1 = p^S, where p is a prime. The first new graph appearing in the series has parameters (v, k, λ) = (225, 98, 45). A 4-vertex condition for relations of a skew-symmetric association scheme (very similar to one for the strongly regular graphs) is introduced and is proved to hold in any case. This has allowed us to check the 4-vertex condition for Γn and Γ'n, thus to prove that Γn and Γ'n are not rank three graphs if n > 2.