The problem is defined on a directed network G = (N,A), where each
arc (i, j) 2 A has a capacity ui,j and a convex cost Ci,j(xi,j), and each
node i 2 N is associated with a number di to specify the node’s supply
or demand, depending on whether di > 0 or di < 0. The objective
is to minimize the total network flow cost.