Using equality in the Krein conditions to prove nonexistence of certain distance-regular graphs |
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Authors: | Kris Coolsaet Aleksandar Jurii |
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Institution: | aDepartment of Applied Mathematics and Computer Science, Ghent University, 9000 Gent, Belgium;bFaculty of Computer and Information Science and IMFM University of Ljubljana, 1000 Ljubljana, Slovenia |
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Abstract: | We prove the nonexistence of a distance-regular graph with intersection array {74,54,15;1,9,60} and of distance-regular graphs with intersection arrays{4r3+8r2+6r+1,2r(r+1)(2r+1),2r2+2r+1;1,2r(r+1),(2r+1)(2r2+2r+1)} | with r an integer and r 1. Both cases serve to illustrate a technique which can help in determining structural properties for distance-regular graphs and association schemes with a sufficient number of vanishing Krein parameters.
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Keywords: | Krein parameters Association scheme Distance-regular graph Strongly regular graph Triple intersection numbers |
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