1. A method for controling the purchase, manufacture, or transfer of items employing a multi-echelon inventory system, wherein the multi-echelon inventory system comprises multiple flow paths, comprising: receiving inventory data of items associated with multiple flow paths on a computer server from a computerized relational database and/or a computer network; based at least in part on the inventory data, determining at least one sub-problem on the computer server, wherein the at least one sub-problem includes at least one customer and a plurality of suppliers, items or locations interconnected with each other; based at least in part on the sub-problem, using the computer server to determine a data structure associated with each sub-problem; based at least in part on the data structure for each sub-problem, determining a solution to each sub-problem on the computer server; based at least in part on the sub-problem solutions, determining an initial solution for the multi-echelon inventory system on the computer server; and controlling the purchase, manufacture, or transfer of the items in accordance with the initial solution.