<p>Sylvester–Kac type matrices are tridiagonal integral matrices with integral spectra or with eigenvalues presenting some kind of closed form. In general, the entries of the two non-zero subdiagonals are assumed to be strictly positive. There has been a particular interest on the quadratic spectra or some kind of products involving the entries of the subdiagonals. In this article we develop a new combinatorial approach based on a lower Pascal’s triangle matrix, which turns out to be a much more general approach to investigate the Sylvester–Kac matrices. As a result, infinitely many Sylvester–Kac type matrices can be produced. Several new examples with integral spectra are provided as well.</p>

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General Sylvester–Kac matrices with plain eigenvalues

  • Zhibin Du,
  • Carlos M. da Fonseca

摘要

Sylvester–Kac type matrices are tridiagonal integral matrices with integral spectra or with eigenvalues presenting some kind of closed form. In general, the entries of the two non-zero subdiagonals are assumed to be strictly positive. There has been a particular interest on the quadratic spectra or some kind of products involving the entries of the subdiagonals. In this article we develop a new combinatorial approach based on a lower Pascal’s triangle matrix, which turns out to be a much more general approach to investigate the Sylvester–Kac matrices. As a result, infinitely many Sylvester–Kac type matrices can be produced. Several new examples with integral spectra are provided as well.