In determining the actual flow used to complete the trade, computer 1 uses a minimum cost flow algorithm such as one described in chapter 9 of said Ahuja reference, where the cost to be minimized is a function of the actual cost to execute the trade and other factors, such as projected settlement costs, flow balancing heuristics, and a randomizing component. [0099] The network 6, 7 of FIG. 6 is a