Approximate linear programming for networks: Average cost bounds

This paper uses approximate linear programming (ALP) to compute average cost bounds for queueing network control problems. Like most approximate dynamic programming (ADP) methods, ALP approximates the differential cost by a linear form. New types of approximating functions are identified that offer more accuracy than previous ALP studies or other performance bound methods. The structure of the infinite constraint set is exploited to reduce it to a more manageable set. When needed, constraint sampling and truncation methods are also developed. Numerical experiments show that the LPs using quadratic approximating functions can be easily solved on examples with up to 17 buffers. Using additional functions reduced the error to 1–5% at the cost of larger LPs. These ALPs were solved for systems with up to 6–11 buffers, depending on the functions used. The method computes bounds much faster than value iteration. It also gives some insights into policies. The ALPs do not scale to very large problems, but they offer more accurate bounds than other methods and the simplicity of just solving an LP.