Let G be a graph and du the degree of its vertex u. The geometric-arithmetic (GA) index of G is defined GA(G)=Sum((2(du.dv)^(1/2))/(du+dv)) and the summation runs over all edges of G. Let G(1,n) be the set of connected simple graphs of order n with minimum degree 1. In this paper, we use linear programming formulation to find graphs on which the geometric-arithmetic index attains minimum and maximum value.
