English

Another proof of Harer-Zagier formula

Combinatorics 2015-03-20 v1

Abstract

For a regular 2n2n-gon there are (2n1)!!(2n-1)!! ways to match and glue the 2n2n sides. The Harer-Zagier bivariate generating function enumerates the gluings by nn and the genus gg of the attendant surface and leads to a recurrence equation for the counts of gluings with parameters nn and gg. This formula was originally obtained by using the multidimensional Gaussian integrals. Soon after Jackson and later Zagier found alternative proofs that used the symmetric group characters. In this note we give a different, characters-based, proof. Its core is computing and marginally inverting Fourier transform of the underlying probability measure on S2nS_{2n}. Aside from Murnaghan-Nakayama rule for one-hook diagrams, the counting techniques we use are of elementary, combinatorial nature.

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Cite

@article{arxiv.1503.05598,
  title  = {Another proof of Harer-Zagier formula},
  author = {Boris Pittel},
  journal= {arXiv preprint arXiv:1503.05598},
  year   = {2015}
}

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13 pages