L. Schoppmann’s research while affiliated with Stevens Institute of Technology and other places

This paper considers a probabilistic graph in which the points are perfectly reliable but the edges operate independently of one another, all with some known probability p. The graph G is in an operating state if the surviving edges induce a spanning connected subgraph of G. The all-terminal reliability R(G,p) of G is the probability that G is in an operating state. A graph transformation, called “the swing surgery,” is introduced, and it is shown that this surgery has important properties. First, if H is the graph obtained by deleting m independent edges from the complete graph, then for any other graph G with the same number of points and edges as H, R(H,p) > R(G,p) for all 0 < p < 1. Moreover, the swing surgery yields a simple topological proof of the well-known result that H has more spanning trees than does G. Another important consequence is that given any graph G there exists a threshold graph T with the same number of points and edges as G such that R(T,p) ≤ R(G,p) for all 0 < p < 1.