Fernando Tohmé

A memetic algorithm based on a NSGAII scheme for the flexible job-shop scheduling problem

The Flexible Job-Shop Scheduling Problem is concerned with the determination of a sequence of jobs, consisting of many operations, on different machines, satisfying several parallel goals. We introduce a Memetic Algorithm, based on the NSGAII (Non-Dominated Sorting Genetic Algorithm II) acting on two chromosomes, to solve this problem. The algorithm adds, to the genetic stage, a local search procedure (Simulated Annealing). We have assessed its efficiency by running the algorithm on multiple objective instances of the problem. We draw statistics from those runs, which indicate that this Memetic Algorithm yields good and low-cost solutions.

Single-Crossing, Strategic Voting and the Median Choice Rule

This paper studies the strategic foundation of the Representative Voter Theorem (Rothstein in: Pub Choice 72:193–212, 1991), also called the “second version” of the Median Voter Theorem. As a by-product, it also considers the existence of strategy-proof social choice functions over the domain of single-crossing preferences. The main result shows that single-crossing constitutes a domain restriction over the real line that allows not only majority voting equilibria, but also non-manipulable choice rules. In particular, this is true for the median rule, which is found to be group strategic-proof over the full set of alternatives and over every nonempty subset. In addition, the paper also examines the relation between single-crossing and order-restriction. And it uses this relation together with the strategy-proofness of the median rule to prove that the outcome predicted by the Representative Voter Theorem can be implemented in dominant strategies through a simple mechanism. This mechanism is a two-stage voting procedure in which, first, individuals select a representative among themselves, and then the winner chooses a policy to be implemented by the planner.

Land-Rich Economies, Education and Economic Development

We analyze the emergence of large-scale education systems in a framework where growth is associated with changes in the con guration of the economy. We model the incentives that the economic elite could have (collectively) to accept taxation destined to nance the education of credit-constrained workers. Contrary to previous work, in our model this incentive does not necessarily arise from a complementarity between physical and human capital in manufacturing. Instead, we emphasize the demand for human-capital-intensive services by highincome groups. Our model seems capable to account for salient features of the development of Latin America in the 19th century, where, in particular, land-rich countries such as Argentina established an extensive public education system and developed a sophisticated service sector before starting signi cant manufacturing activities.

Judgement aggregation in multi-agent argumentation

Given a set of conflicting arguments, there can exist multiple plausible opinions about which arguments should be accepted, rejected or deemed undecided. We study the problem of how multiple such judgements can be aggregated. We define the problem by adapting various classical social-choice-theoretic properties for the argumentation domain. We show that while argument-wise plurality voting satisfies many properties, it fails to guarantee the collective rationality of the outcome. We then present more general results, proving multiple impossibility results on the existence of any good aggregation operator. After characterizing the sufficient and necessary conditions for satisfying collective rationality, we study whether restricting the domain of argument-wise plurality voting to classical semantics allows us to escape the impossibility result. We close by mentioning a couple of graph-theoretical restrictions under which the argument-wise plurality rule does produce collectively rational outcomes. In addition to identifying fundamental barriers to collective argument evaluation, our results contribute to research at the intersection of the argumentation and computational social choice fields.

Two approaches to the problems of self-attacking arguments and general odd-length cycles of attack

Fil: Bodanza, Gustavo Adrian. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca; Argentina. Universidad Nacional del Sur; Argentina

Negotiation and Defeasible Decision Making

In economically meaningful interactions negotiations are particularly important because they allow agents to improve their information about the environment and even to change accordingly their own characteristics. In each step of a negotiation an agent has to emit a message. This message conveys information about her preferences and endowments. Given that the information she uses to decide which message to emit comes from beliefs generated in previous stages of the negotiation, she has to cope with the uncertainty associated with them. The assessment of the states of the world also evolves during the negotiation. In this paper we analyze the intertwined dynamics of beliefs and decision, in order to determine conditions on the agents that allow them to reach agreements. The framework for decision making we consider here is based on defeasible evaluation of possibilities: an argument for a choice defeats another one if it is based on a computation that better uses all the available information.

Abduction in economics: a conceptual framework and its model

We discuss in this paper the scope of abduction in Economics. The literature on this type of inference shows that it can be interpreted in different ways, according to the role and nature of its outcome. We present a formal model that allows to capture these various meanings in different economic contexts.

Comparison of Multiobjective Evolutionary Algorithms for Operations Scheduling under Machine Availability Constraints

Many of the problems that arise in production systems can be handled with multiobjective techniques. One of those problems is that of scheduling operations subject to constraints on the availability of machines and buffer capacity. In this paper we analyze different Evolutionary multiobjective Algorithms (MOEAs) for this kind of problems. We consider an experimental framework in which we schedule production operations for four real world Job-Shop contexts using three algorithms, NSGAII, SPEA2, and IBEA. Using two performance indexes, Hypervolume and R2, we found that SPEA2 and IBEA are the most efficient for the tasks at hand. On the other hand IBEA seems to be a better choice of tool since it yields more solutions in the approximate Pareto frontier.

Abducing the crisis

Macroeconomic crises are events marked by “broken promises” that shatter the expectations that many agents had entertained about their economic prospects and wealth positions. Crises lead to reappraisals of the views of the world upon which agents had based their expectations, plans and decisions, and to a reconsideration of theories and models on the part of analysts. A crisis triggers widespread efforts of abduction in search of new hypothesis and explanations. In this paper we will explore, in particular, the abductions that analysts may apply after a crisis and see how they reveal the prevalence of “wrong” abductions at the onset of the crisis. In order to carry out this exercise, we study the general role of abduction in economic analysis, both theoretical and practical. Economic theory generally proceeds by constructing models, that is, mental schemes based on mental experiments. They are often written in mathematical language but, apart from their formal expression, they use metaphors, analogies and pieces of intuition to motivate their assumptions and to give support to their conclusions. We try to capture all these elements in a formal scheme and apply the ensuing model of abduction to the analysis of macroeconomic crises.

The foundations of DeLP: defeating relations, games and truth values

In this paper we examine the mechanism of DeLP (Defeasible Logic Programming). We first study the definition of the defeating relation in a formal setting that allows us to uncover some hidden assumptions, and suggest an alternative definition. Then we introduce a game-theoretic characterization of the system. We obtain a new set of truth values arising from games in which arguments for and against a given literal are played out. We study how additional constraints define protocols of admissible attacks. The DeLP protocol ensures the finiteness of the games, and therefore the existence of winning strategies for the corresponding games. The defeating relation among arguments determines the strategies that will win and consequently the truth values of queries. We find that the DeLP protocol also excludes the warranting of a literal and its negation.