Abstract
LetG be a finite abelian group,K a subfield ofC, C[G] regarded as an algebra of matrices.A K G {AεC[G]| all the entries and eigenvalues ofA are inK} is an association algebra overK. In this paper, the association scheme ofA K G is determined and in the caseK=Q(i), the first eigenmatrix of the association scheme computed. As an application, it is proved thatZ 4×Z 4×Z 4 is the only abelian group admitted as a Singer group by some distance-regular digraph of girth 4 on 64 vertices.
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Hou, Xd. On theG-matrices with entries and eigenvalues inQ(i) . Graphs and Combinatorics 8, 53–64 (1992). https://doi.org/10.1007/BF01271708
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DOI: https://doi.org/10.1007/BF01271708