On the inverse sum indeg index ( I S I ), spectral radius of I S I matrix and I S I energy

The inverse sum indeg index I S I ( G ) of a graph is equal to the sum over all edges u v ∈ E ( G ) of weights d u d v d u + d v . This paper presents the relation between the inverse sum indeg index and the chromatic number. The bounds for the spectral radius of the inverse sum indeg matrix and the inverse sum indeg energy are obtained. Additionally, the Nordhaus-Gaddum-type results for the inverse sum indeg index, the inverse sum indeg energy and the spectral radius of the inverse sum index matrix are given.