Optimal Graphs for Independence and $k$-Independence Polynomials

Abstract

The independence polynomial $I(G,x)$ of a finite graph $G$ is the generating function for the sequence of the number of independent sets of each cardinality. We investigate whether, given a fixed number of vertices and edges, there exists optimally-least (optimally-greatest) graphs, that are least (respectively, greatest) for all non-negative $x$. Moreover, we broaden our scope to $k$-independence polynomials, which are generating functions for the $k$-clique-free subsets of vertices. For $k\ge 3$, the results can be quite different from the $k=2$ (i.e. independence) case.