Journal of Economic Interaction and Coordination

This study examines the plausibility of the emergence of sunspot equilibria in an agent-based artificial stock market. Using the agent-based model, we make the sunspots explicit so that we can test, e.g., by means of the Granger causality test, whether purely extrinsic uncertainty can influence price dynamics. In addition, through agent-based simulation, the coordination process, which is mainly driven by genetic programming, becomes observable, which enables us to analyze what agents perceive and whether they believe in sunspots. By manipulating different control variables, three series of experiments are conducted. Generally speaking, the chances of observing “sunspot equilibria” in this agent-based artificial stock market are small. However, the sunspot believers can never be driven out of the market. Nevertheless, they are always outnumbered by fundamental believers, which is evidence that the market as collective behavior is rational. We also find that lengthening the time horizon will make it difficult for sunspot believers to survive.

The use of equations to describe agent-based model dynamics allows access to mathematical theory that is not otherwise available. In particular, equation models can be effective at solving optimization problems—that is, problems concerning how an agent-based model can be most effectively steered into a particular state. In order to illustrate this strategy, we describe a modified version of the well-known SugarScape model and implement taxation. The optimization problem is to determine tax structures that minimize deaths but maximize tax income. Tax rates are dependent upon the amount of sugar available in a particular region; the rates change over time. A system of discrete difference equations is built to capture agent-based model dynamics. The equations are shown to capture the dynamics very well both with and without taxation. A multi-objective optimization technique known as Pareto optimization is then used to solve the problem. Rather than focusing on a cost function in which the two objectives are assigned weights, Pareto optimization is a heuristic method that determines a suite of solutions, each of which is optimal depending on the priorities of the researcher. In this case, Pareto optimization allows analysis of the tradeoff between taxes collected and deaths caused by taxation. The strategies contained here serve as a framework for a broad class of models.

We use three stochastic games for the wealth of economic agents which may be at work in a real economy and we derive their statistical equilibrium distributions. Based on a heuristic argument, we assume that the expected observed wealth distribution is a mixture of these three distributions. We compare the Lorenz curves obtained from this conjecture with the empirical curves for a set of countries.

In this game [Aruka in Avatamsaka game structure and experiment on the web. In: Aruka Y (ed) Evolutionary controversies in economics. Springer, Tokyo, pp 115–132, 2001], selfishness may not be determined even if an agent selfishly adopts the strategy of defection. Individual selfishness can only be realized if the other agent cooperates, therefore gain from defection can never be assured by defection alone. The sanction by defection as a reaction of the rival agent cannot necessarily reduce the selfishness of the rival. In this game, explicit direct reciprocity cannot be guaranteed. Now we introduce different spillovers or payoff matrices, so that each agent may then be faced with a different payoff matrix. A ball in the urn is interpreted as the number of cooperators, and the urn as a payoff matrix. We apply Ewens’ sampling formula to our urn process in this game theoretic environment. In this case, there is a similar result as in the classic case, because there is “self-averaging” for the variances of the number who cooperate. Applying Pitman’s sampling formula to the urn process, the invariance of the random partition vectors under the properties of exchangeability and size-biased permutation does not hold in general. Pitman’s sampling formula depends on the two-parameter Poisson–Dirichlet distribution whose special case is just Ewens’ formula. In the Ewens setting, only one probability α of a new entry matters. On the other hand, there is an additional probability θ of an unknown entry, as will be argued in the Pitman formula. More concretely, we will investigate the effects of different payoff sizes from playing a series of different games for newly emerging agents. As Aoki and Yoshikawa (Non-self-averaging in macroeconomic models: a criticism of modern micro-founded macroeconomics, Economics Discussion Papers 2007-49. http://www.economics-ejournal.org . November 26, 2007) and Aoki (J Econ Interact Coord 3:1–3, 2008) dealt with a product innovation and a process innovation, they criticized Lucas’ representative method and the idea that players face micro shocks drawn from the same unchanged probability distribution. In the light of Aoki and Yoshikawa (Non-self-averaging in macroeconomic models: a criticism of modern micro-founded macroeconomics, Economics Discussion Papers 2007-49. http://www.economics-ejournal.org . November 26, 2007), we show the same argument in our Avatamsaka game with different payoffs. In this setting, innovations occurring in urns may be regarded as increases of the number of cooperators in urns whose payoffs are different.

We investigate the relationship between productivity and unemployment with an ABM approach. In particular, we use the framework of Riccetti et al. (J Econ Interact Coord 10(2):305–332, 2015) to run computer simulations considering different levels of productivity and analyse the corresponding effects on unemployment. The simulation results show the emergence of a fluctuating pattern of the unemployment rate, the public deficit and the inflation rate as functions of productivity. The marked pattern of the unemployment rate in the model is empirically validated by the OECD database. This unexpected oscillating behaviour remains in subsequent simplifications of the baseline model. Thus, our approach allows us to explain the productivity–employment linkage as an emergent macroeconomic property of a complex system. We conclude that economic policies aimed at increasing labour productivity could have unintended side effects on the unemployment rate, the government deficit and the inflation rate, which should be explored and taken into account before the policy is implemented.

In this paper we set up a baseline, but nevertheless advanced and complete model representing detailed goods market dynamics, heterogeneous labor markets, dual and cross-dual wage-price adjustment processes, as well as counter-cyclical government policies. The cyclical movements of output generate, through Okun’s law, employment variations in the heterogeneous labor market. The core of the resulting Keynesian macrodynamics is however given by credit-financed investment behavior and loan-rate setting by credit suppliers. The framework is constructed in such way that simplified, lower dimensional versions of the model can be obtained by setting parameters describing specific feedback effects from one sector to another equal to zero. Starting from such low dimensional sub-dynamics, we show the local stability of the full 7D model through a “cascade of stable matrices” approach if the feedback chains are sufficiently tranquil in their transmission mechanisms. However, local stability is the point of departure for the numerical investigation of local explosiveness and the forces that can bound such a behavior.

A theoretical foundation for the Keynesian multiplier process is derived from a simple model in which economic interactions are coordinated by a decentralized and self-organizing network of adaptive business enterprises. Deviation amplification arises from business failures that interrupt the flow of trading, and does not depend directly on lack of price-flexibility. Numerically the model produces almost the same hump-shaped impulse-response pattern as exhibited by GDP data in the United States.