English

Enumeration of Latin squares with conjugate symmetry

Combinatorics 2021-12-09 v1

Abstract

A Latin square has six conjugate Latin squares obtained by uniformly permuting its (row, column, symbol) triples. We say that a Latin square has conjugate symmetry if at least two of its six conjugates are equal. We enumerate Latin squares with conjugate symmetry and classify them according to several common notions of equivalence. We also do similar enumerations under additional hypotheses, such as assuming the Latin square is reduced, diagonal, idempotent or unipotent. Our data corrected an error in earlier literature and suggested several patterns that we then found proofs for, including (1) The number of isomorphism classes of semisymmetric idempotent Latin squares of order nn equals the number of isomorphism classes of semisymmetric unipotent Latin squares of order n+1n+1, and (2) Suppose AA and BB are totally symmetric Latin squares of order n≢0mod3n\not\equiv0\bmod3. If AA and BB are paratopic then AA and BB are isomorphic.

Keywords

Cite

@article{arxiv.2104.07902,
  title  = {Enumeration of Latin squares with conjugate symmetry},
  author = {Brendan D. McKay and Ian M. Wanless},
  journal= {arXiv preprint arXiv:2104.07902},
  year   = {2021}
}