Y-index of four join operations of graphs

Abstract

For a molecular graph  the -index is defined as the sum of fourth powers of degrees of all vertices of the graph. The Y-index is defined as  and the coindex is defined as  In this paper, we obtain the explicit expressions for index and coindex of four join operations of graphs such as vertex and edge S-join, vertex and edge R-join, vertex and edge Q-join and vertex and edge T-join of two graphs.