Nobuaki Obata

collaborators

3 papers

math.CO2025

Quadratic Embedding Constants of Corona Graphs

Ferdi, Edy Tri Baskoro, Nobuaki Obata +1

The quadratic embedding constant (QEC) of a connected graph is defined to be the maximum of the quadratic function associated with its distance matrix on a certain unit sphere of c…

math.CO2025

Quadratic Embedding Constants of Strongly Regular Graphs

Nobuaki Obata

We obtain an explicit formula for the quadratic embedding constant (QEC) of a strongly regular graph $srg (n, k, λ, μ)$ with $μ \geq 1$ . By using QEC we give a necessary and suff…

math.CO2024

Partial Chebyshev Polynomials and Fan Graphs

Wojciech Młotkowski, Nobuaki Obata

Motivated by the product formula of the Chebyshev polynomials of the second kind $U_{n} (x)$ , we newly introduce the partial Chebyshev polynomials $U_{n}^{e} (x)$ and $U^{\mathr…