The Harary index of a graph G on n vertices was defined by Plavšić et al. (1993) as H(G) = 1/2 sum_(i = 1)^n sum_(j = 1)^n (R D)_(i j), where (R D)_(i j) = {D_(i j)^(-1) | if i!=j 0 | if i = j auto right match is the reciprocal of the graph distance matrix D (Plavšić et al. 1993; Devillers and Balaban, p. 80, 2000).

graph distance matrix | topological index