Pier Mario Pacini

Growth and Coalition Formation

In this paper we analyse a growth model where agents have different factor endowments and form coalitions to produce output. Economic growth is the result of the accumulation of human capital. The latter in turn is a by-product of the production activity within a coalition. The maximum rate of growth is obtained when the grand coalition forms. However, if endowments are heterogeneous and the rule governing the division of the coalitional output states an equal sharing among the members of a coalition, agents with better endowments may not be willing to coalesce with poorly endowed agents. Indeed richer agents tend to form coalitions among themselves and the poor ones cannot benefit of the positive externalities of coalescing with the richest agents. This determines both a lower output and a lower long-run growth rate.

Coalition Formation with Boundedly Rational Agents

We analyse the process of coalition formation in which agents’ expectations evolve through repeated interactions in a large population setting. The selection of equilibrium outcomes strongly depends on agents’ initial beliefs and individual learning speed; the efficient coalition structure is reached starting from a very limited set of initial beliefs.

Production Partnerships Formation with Heterogeneous Agents: a Simulation in SWARM

This paper analyzes the organization of an economy where agents with heterogeneous endowments of (human and/or physical) capital and labor can join and form partnerships in order to produce an outputs. We suppose that the formation of a partnership is the result of a common willingness of a (sub)set of agents to pool and contribute their resources to a production process that takes place within the partnership that has been formed, without any externality onto or from other partnerships. The members of a partnership agree to divide the output among themselves according to an exogenously given distributive rule.

A Genetic Algorithms Approach: Social Aggregation and Learning with Heterogeneous Agents

We analyze an economy in which increasing returns to scale incentivate social aggregation in a population of heterogeneous boundedly rational agents; however these incentives are limited by the presence of imperfect information on others’ actions. We show by simulations that the equilibrium coalitional structure strongly depends on agents’ initial beliefs and on the characteristics of the individual learning process that is modeled by means of genetic algorithms. The most efficient coalition structure is reached starting from a very limited set of initial beliefs. Furthermore we find that (a) the overall efficiency is an increasing function of agents’ computational abilities; (b) an increase in the speed of the learning process can have ambiguous effects; (c) imitation can play a role only when computational abilities are limited.

An ABM-Evolutionary Approach: Bilateral Exchanges, Bargaining and Walrasian Equilibria

This paper analyzes, via intensive use of simulation techniques, the effects of the introduction of direct exchange relationships through bilateral trades in a simple general equilibrium pure exchange economy. Agents are heterogeneous in their endowments and repeatedly match in random pairs bargaining on how to split the advantages of a trade; possibly they can agree to exchange at the known market clearing prices. Simulations of this evolutionary process show that while walrasian outcomes emerge in the interaction among people with similar outside opportunities, people of different groups converge to accept an equilibrium in which agents with the best outside opportunity extract the greater part of the surplus out of an exchange. On other hand the acceptance of market mediation (i.e. walrasian outcomes) is more probable when either the parties try to exploit too much from the opponent or when there is anonymity in the trading process. The results show evidence that the acceptance of decentralized, personalized contracting (apart from efficiency considerations) increases the probability of amplifying the asymmetries in the initial distribution beyond what is produced by the pure market mechanism.