
on Computational Economics 
By:  Mishra, SK 
Abstract:  Keane’s bump function is considered as a standard benchmark for nonlinear constrained optimization. It is highly multimodal and its optimum is located at the nonlinear constrained boundary. The true minimum of this function is, perhaps, unknown. We intend in this paper to optimize Keane’s function of different dimensions (2 to 100) by the Repulsive Particle Swarm and Differential Evolution methods. The DE optimization program has gone a long way to obtain the optimum results. However, the Repulsive Particle Swarm optimization has faltered. We have also conjectured that the values of the decision variables diminish with the increasing index values and they form two distinct clusters with almost equal number of members. These regularities indicate whether the function could attain a minimum or (at least) has reached close to the minimum. We have used this conjecture to incorporate ordering of variable values before evalution of the function and its optimization at every trial. As a result, the performance of DE as well as the RPS has improved significantly. Our results are comparable with the best results available in the literature on optimization of Keane function. Our two findings are notable: (i) Keane’s envisaged min(f) = 0.835 for 50dimensional problem is realizable; (ii) LiuLewis’ min(f) = 0.84421 for 200dimensional problem is grossly suboptimal.Computer programs (written by us in Fortran) are available on request. 
Keywords:  Nonlinear; constrained; global optimization; repulsive particle swarm; differential evolution; Fortran; computer program; Hybrid; Genetic algorithms 
JEL:  C61 C88 
Date:  2007–05–01 
URL:  http://d.repec.org/n?u=RePEc:pra:mprapa:3098&r=cmp 
By:  Manson Nwafor; Adeola Adenikinju; Kanayo Ogujiuba 
Abstract:  The study examines the effects that trade liberalization will have on poverty in Nigeria. Previous studies have been limited by static and partial equilibrium analysis. We use a Dynamic Computable General Equilibrium Model to analyze this issue. The more favorably affected sectors are capital intensive; therefore, capital income improves over time while land and labor income reduce. This has positive implications for urban households and negative implications for rural households due to the dependence of the latter on mostly land and labor income. As a result, urban poverty decreases in the short and long run while rural poverty increases in both periods. Policies to improve the agricultural sector will thus have to be implemented before or concurrently with trade liberalization in order for it to have a propoor effect. In this way, the rural areas which obtain most of their income from this sector will respond more positively to trade liberalization. 
Keywords:  CGE Model, Trade liberalisation, Nigeria, Poverty, Dynamic, ECOWAS, Import tariffs 
JEL:  D58 F13 I32 C68 
Date:  2007 
URL:  http://d.repec.org/n?u=RePEc:lvl:mpiacr:200716&r=cmp 
By:  Yuval Emek; Michal Feldman 
Abstract:  We study an economic setting in which a principal motivates a team of strategic agents to exert costly effort toward the success of a joint project. The action taken by each agent is hidden and affects the (binary) outcome of the agent's individual task stochastically. A Boolean function, called technology, maps the individual tasks' outcomes into the outcome of the whole project. The principal induces a Nash equilibrium on the agents' actions through payments that are conditioned on the project's outcome (rather than the agents' actual actions) and the main challenge is that of determining the Nash equilibrium that maximizes the principal's net utility, referred to as the optimal contract. Babaioff, Feldman and Nisan [1] suggest and study a basic combinatorial agency model for this setting. Here, we concentrate mainly on two extreme cases: the AND and OR technologies. Our analysis of the OR technology resolves an open question and disproves a conjecture raised in [1]. In particular, we show that while the AND case admits a polynomialtime algorithm, computing the optimal contract in the OR case is NPhard. On the positive side, we devise an FPTAS for the OR case, which also sheds some light on optimal contract approximation of general technologies. 
Date:  2007–05 
URL:  http://d.repec.org/n?u=RePEc:huj:dispap:dp452&r=cmp 
By:  Bissey, MarieEdith; Ortona, Guido 
Abstract:  This paper illustrates ALEX4.1, the 2007 version of the program of simulation of electoral systems developed at ALEX, the Laboratory for Experimental and Simulative Economics of the Università del Piemonte Orientale at Alessandria, Italy. The main features of the program have been described with reference to a previous version in Bissey, Carini and Ortona, 2004; the paper may be freely downloaded from the site of the journal where it has been published, or in its working paper version from the site http://polis.unipmn.it/. The organization of this paper is, consequently, rather unusual. The next section presents only the very basic traits of the simulation program, as most details and theoretical considerations may be read in the quoted (and easytofind) reference. Sections 3 and 4 are the most important: they illustrate the novelties of ALEX4.1 with respect to previous versions. Section 5 is very short, as it contains only the instructions for downloading the program, and some caveats regarding its use. The core of the paper is a large appendix that contains the readme file of the package ALEX4.1. Actually, this paper should be considered a handbook for the use of ALEX4.1. 
Date:  2007–05 
URL:  http://d.repec.org/n?u=RePEc:uca:ucapdv:82&r=cmp 