The extended Ritz method for functional optimization: overview and applications to single-person and team optimal decision problems

  • Authors:
  • M. Baglietto;M. Sanguineti;R. Zoppoli

  • Affiliations:
  • Department of Communications, Computer and System Sciences (DIST), University of Genoa, Genova, Italy;Department of Communications, Computer and System Sciences (DIST), University of Genoa, Genova, Italy;Department of Communications, Computer and System Sciences (DIST), University of Genoa, Genova, Italy

  • Venue:
  • Optimization Methods & Software
  • Year:
  • 2009

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Abstract

Functional optimization problems entail minimization of functionals with respect to admissible solutions belonging to infinite-dimensional spaces of functions. The extended Ritz method (ERIM) searches for suboptimal solutions expressed as linear combinations of basis functions with 'free' parameters that are optimized, together with the coefficients of the linear combinations, by solving finite-dimensional nonlinear programming problems and exploiting stochastic approximation techniques. The first part of the paper gives an overview of the ERIM and introduces the concept of polynomially complex optimizing sequences. Their elements are given by the solutions of the nonlinear programming problems obtained using an increasing number of basis functions. Under some conditions, the optimizing sequences epi-converge to the optimal solution and for a given approximation accuracy, the number of free parameters increases moderately (e.g. polynomially) with the number of variables in the admissible solutions. Therefore, the ERIM may avoid the curse of dimensionality, i.e. an exponential growth of the number of parameters. In the second and third parts of the paper, the ERIM and the stochastic approximation algorithms are specialized to the solution of stochastic T-stage single-person and stochastic team decision problems, respectively. Numerical results are given for the optimal management of systems of water reservoirs and for the dynamic routing problem in communication networks. In the reservoirs management application, the ERIM is compared with dynamic programming (DP) using random sampling of the state space. The dynamic routing application considers the presence of several destinations and classes of traffic, which are useful to address quality of service requirements. Here, the ERIM is compared with an algorithm based on the open shortest path first protocol.