Institution: | 1. Centre of Mathematics for Applications, University of Oslo, P.O. Box 1053, Blindern, N‐0316 Oslo, Norway and Agder University College , Department of Economics and Business Administration , Serviceboks 422, N‐4604 Kristiansand, Norway;2. Centre of Mathematics for Applications, University of Oslo, P.O. Box 1053, Blindern, N‐0316 Oslo, Norway and Department of System Research , Klaip?da University , H. Manto 84, LT‐5808 Klaip?da, Lithuania |