Spectra of hyperstars

Artikel i vetenskaplig tidskrift, 2022

The purpose of this paper is to introduce a model to study structures which are widely present in public transportation networks. We show that, through hypergraphs, one can describe these structures and investigate the relation between their spectra. To this aim, we extend the structure of (m, k)-stars on graphs to hypergraphs: the (m, k)-hyperstars on hypergraphs. Also, by giving suitable conditions on the hyperedge weights, we prove the existence of matrix eigenvalues of computable values and multiplicities, where the matrices considered are Laplacian, adjacency and transition matrices. By considering separately the case of generic hypergraphs and uniform hypergraphs, we prove that two kinds of vertex set reductions on hypergraphs with (m, k)-hyperstars are feasible, keeping the same eigenvalues with reduced multiplicity. Finally, some useful eigenvector properties are derived up to a product with a suitable matrix, and we relate these results to Fiedler spectral partitioning on the hypergraph.