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New upper bounds for nonbinary codes based on the Terwilliger algebra and semidefinite programming
Authors:Dion Gijswijt  Hajime Tanaka
Institution:a Department of Mathematics, University of Amsterdam, Plantage Muidergracht 24, 1018 TV Amsterdam, The Netherlands
b CWI, Kruislaan 413, 1098 SJ Amsterdam, The Netherlands
c Division of Mathematics, Graduate School of Information Sciences, Tohoku University, Sendai, Japan
Abstract:We give a new upper bound on the maximum size Aq(n,d) of a code of word length n and minimum Hamming distance at least d over the alphabet of q?3 letters. By block-diagonalizing the Terwilliger algebra of the nonbinary Hamming scheme, the bound can be calculated in time polynomial in n using semidefinite programming. For q=3,4,5 this gives several improved upper bounds for concrete values of n and d. This work builds upon previous results of Schrijver A. Schrijver, New code upper bounds from the Terwilliger algebra and semidefinite programming, IEEE Trans. Inform. Theory 51 (2005) 2859-2866] on the Terwilliger algebra of the binary Hamming scheme.
Keywords:Codes  Nonbinary codes  Upper bounds  Delsarte bound  Terwilliger algebra  Block-diagonalization  Semidefinite programming
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