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This paper presents a stylized model of interaction among boundedly rational heterogeneous agents in a multi-asset financial market to examine how agents’ impatience, extrapolation, and switching behaviors can affect cross-section market stability. Besides extrapolation and performance based switching between fundamental and extrapolative trading documented in single asset market, we show that a high degree of ‘impatience’ of agents who are ready to switch to more profitable trading strategy in the short run provides a further cross-section destabilizing mechanism. Though the ‘fundamental’ steady-state values, which reflect the standard present-value of the dividends, represent an unbiased equilibrium market outcome in the long run (to a certain extent), the price deviation from the fundamental price in one asset can spill-over to other assets, resulting in cross-section instability. Based on a (Neimark–Sacker) bifurcation analysis, we provide explicit conditions on how agents’ impatience, extrapolation, and switching can destabilize the market and result in a variety of short and long-run patterns for the cross-section asset price dynamics.

Policymakers around the world impose some form of capital gains taxes to foster the stability of financial markets. Unfortunately, there is no clarity on the effects of capital gains taxes. Based on a stylized behavioral asset-pricing model highlighting the trading activity of extrapolating speculators, we show that policymakers may involuntary destabilize financial markets by imposing capital gains taxes. Most importantly, we find that the imposition of capital gains taxes may trigger endogenous cyclical asset price dynamics occurring around inflated price levels. A number of robustness checks in which we allow for interactions between speculators who use extrapolative and regressive expectation rules confirm our main results.

Starting from the Ladrón‐de Guevara et al.’s framework, we develop a model with an additional sector for the production of leisure services. By introducing consumption of leisure services as a time‐consuming activity, our model general-izes the standard time allocation problem whereby total available time can be allocated between work, education, free time and leisure activities. We analytically characterize the balanced growth paths of the model, particularly in terms of time allocation and growth. Our comparative analysis of different service economies assumed at equilibrium includes the case of an industrial economy without a service sector and the potential multiple equilibria of such an economy.

We develop a model in which investors can participate in stock, bond and housing markets. Investors’ market entry decisions are subject to herding effects and depend on the markets’ price trends and on their mispricings. The dynamics of our model is governed by a four-dimensional nonlinear map and its unique inner steady state is characterized by standard present-value relations between dividends, rents and the bond rate. Amongst other things, we show that endogenous stock and housing market dynamics emerge, countercyclical to each other, if investors react strongly to the markets’ price trends. Such a cross feedback reflects investors’ tendency to transfer their enthusiasm from one speculative market to another.

This special issue on “Nonlinear Economic Dynamics” contains a selection of papers presented at the 9th International Conference on Nonlinear Economic Dynamics (NED2015), that took place on June 25-27, 2015, at Chuo University, Tokyo, Japan. The goal of this special issue is to provide the reader with an overview of new directions in the global analysis of economic dynamics and to show applications of concepts from the qualitative theory of nonlinear dynamical systems in the fields of economics, finance, environment, and strategic interaction in social decisions. The wide spectrum of applications and the mathematical methods employed in the dynamic analysis are intended to offer a broad view on the different research streams that contribute to the blossoming literature on Nonlinear Economic Dynamics.

We combine a standard stock-flow housing market model, incorporating explicit relationships between house prices, the housing stock, and the rent level, with a parsimonious expectation formation scheme of housing market investors, reflecting an evolving mix of extrapolative and regressive expectation rules. The model results in a two-dimensional discrete-time nonlinear dynamical system. Based on realistic parameters, the model is able to generate endogenous boom-bust housing market dynamics with lasting periods of overvaluation and overbuilding. We thus exploit our model to investigate how real forces, in particular supply conditions, interact with expectations-driven housing market fluctuations.

We provide a full analytical treatment of a multi-asset market model in which speculators have the choice between two risky and one safe asset. As it turns out, the dynamics of our model is driven by a four-dimensional nonlinear map and may undergo a transcritical, flip or Neimark–Sacker bifurcation. While the first bifurcation is associated with an undervaluation of the risky assets, the latter two may trigger (complex) endogenous dynamics. To facilitate our analysis, we first study a simpler two-dimensional setup of our model in which speculators can only switch between one risky and one safe asset.

This chapter surveys the state-of-art of heterogeneous agent models (HAMs) in finance using a jointly theoretical and empirical analysis, combined with numerical analysis from the latest development in computational finance. It provides supporting evidence on the explanatory power of HAMs to various stylized facts and market anomalies through model calibration, estimation, and economic mechanisms analysis. It presents HAMs with the mainstream finance a unified framework in continuous time to study the impact of historical price information on price dynamics, profitability and optimality of fundamental and momentum trading. It demonstrates how HAMs can help to understand stock price co-movements and evolutionary CAPM. It also introduces a new HAMs perspective on house price dynamics and an integrate approach to study dynamics of limit order markets. The survey provides further insights into the complexity and efficiency of financial markets and policy implications.

In this paper, starting from the Uzawa-Lucas endogenous growth framework with production of physical and human capital, we develop and investigate a model with an additional sector for the production of leisure services. In turn, our three-sector model builds on and extends Ladron-de Guevara et al. [1999] - where the utility function depends only on consumption of physical goods and on ‘pure’ leisure - by introducing consumption of leisure services. As the latter is a time- consuming activity, the model also generalizes the standard time allocation problem, in that total available time can be allocated among work, education, purely free time and leisure activities in our framework. We characterize analytically the Balanced Growth Paths of this general model, particularly in terms of time allocation and growth. We carry out a comparative analysis across different Service Economies that are supposed to be at their equilibrium, including an ‘Industrial Economy’ without service sector, as well across possibly multiple equilibria of the same economy. Part of the analysis is based on an intuitive yet rigorous framework for determining and representing Balanced Growth Paths in the space of time allocation decisions.

The conditional CAPM with time-varying betas has been widely used to explain the cross-section of asset returns. However, most of the literature on time-varying beta is motivated by econometric estimation using various latent risk factors rather than explicit modelling of the stochastic behaviour of betas through agents' behaviour, such as momentum trading. Misspecification of beta risk and the lack of any theoretical guidance on how to specify risk factors based on the representative agent economy appear empirically challenging. In this paper, we set up a dynamic equilibrium model of a financial market with boundedly rational and heterogeneous agents within the mean-variance framework of repeated one-period optimisation and develop an explicit dynamic behaviour CAPM relation between the expected equilibrium returns and time-varying betas. By incorporating the two most commonly used types of investors, fundamentalists and chartists, into the model, we show that there is a systematic change in the market portfolio, risk-return relationships, and time varying betas when investors change their behaviour, such as the chartists acting as momentum traders. In particular, we demonstrate the stochastic nature of time-varying betas. We also show that the commonly used rolling window estimates of time-varying betas may not be consistent with the ex-ante betas implied by the equilibrium model. The results provide a number of insights into an understanding of time-varying beta. © 2011 Springer-Verlag.

A stylized model of business fluctuations is developed, where investment and debt accumulation are responsible for the endogenous dynamics of income. Despite the simplicity of the model, the resulting nonlinear, two-dimensional discrete-time dynamical system displays a wide range of possible dynamic outcomes. If a key parameter, representing the propensity to invest, shifts exogenously from low to high values, a transition across qualitatively different long-run scenarios is observed, associated to different levels of economic activity. Moreover, coexistence of attractors and path-dependence characterize the dynamics for an intermediate range of such a parameter. The impact of exogenous disturbances on such situations results in aperiodic time series subject to unpredictable booms and slumps.

We develop a three-dimensional nonlinear dynamic model in which the stock markets of two countries are linked through the foreign exchange market. Connections are due to the trading activity of heterogeneous speculators. Using analytical and numerical tools, we seek to explore how the coupling of the markets may affect the emergence ofbull and bearmarket dynamics. The dimension of the model can be reduced by restricting investors' trading activity, which enables the dynamic analysis to be performed stepwise, from low-dimensional cases up to the full three-dimensional model. In our paper we focus mainly on the dynamics of the one- and two- dimensional cases, with numerical experiments and some analytical results, and also show that the main features persist in the three-dimensional model.

In this paper we study a particular case of “multiple” externalities associated to the production of a good/activity, whose external effects can change from positive to negative depending on the level of output (intersecting externalities). To analyze their impact on the public policy we propose a very simple two-agent partial equilibrium model in the technological context of externalities. In a static framework, the centralized solution always implies an optimal policy, which may consist of taxation or subsidization depending on the individual optimum and on the technology parameters. In a dynamic model with local knowledge of the efficiency function and instantaneous output adjustments, such an optimal policy can be structurally stable or unstable. In the latter case, under small changes of the parameters the policy may switch from low taxation/subsidization to high taxation/subsidization or vice versa, or even jump discontinuously from taxation to subsidization or vice versa. Furthermore, the decentralized solution based upon “tradable rights” can be economically equivalent to the centralized solution in the form of taxation policy but the two solutions may be not politically equivalent.

In this paper a nonlinear discrete-time business cycle model of Kaldor-type is considered, to illustrate particular global bifurcations which determine the appearance or disappearance of attracting and repelling closed invariant curves. Such bifurcations sequences, which involve homoclinic tangencies and transversal intersection of the stable and unstable manifolds of saddle cycles, may increase the complexity of the basins of attraction of multiple, coexisting attractors. Particularly, for the business cycle model examined here, such dynamic phenomena explain the co-existence of two stable steady states and an attracting closed curve, with an intricate basin structure, for wide ranges of the parameters.

We combine a standard stock-flow housing market model, incorporating explicit relationships between house prices, the housing stock, and the rent level, with a parsimonious expectation formation scheme of housing market investors, reflecting an evolving mix of extrapolative and regressive expectation rules. The model results in a two-dimensional discrete-time nonlinear dynamical system. Based on realistic parameters, the model is able to generate endogenous boom-bust housing market dynamics with lasting periods of overvaluation and overbuilding. We thus exploit our model to investigate how real forces, in particular supply conditions, interact with expectations-driven housing market fluctuations.

Empirical evidence has suggested that, facing different trading strategies and complicated decision, the proportions of agents relying on particular strategies may stay at constant level or vary over time. This paper presents a simple "dynamic market fraction" model of two groups of traders, fundamentalists and trend followers, under a market maker scenario. Market mood and evolutionary adaption are characterized by fixed and adaptive switching fraction among two groups, respectively. Using local stability and bifurcation analysis, as well as numerical simulation, the role played by the key parameters in the market behaviour is examined. Particular attention is paid to the impact of the market fraction, determined by the fixed proportions of confident fundamentalists and trend followers, and by the proportion of adaptively rational agents, who adopt different strategies over time depending on realized profits. © 2005 Elsevier Ltd. All rights reserved.

We develop a model in which boundedly rational agents apply technical and fundamental analysis to identify trading signals in two different speculative markets. Whether an agent trades and, if so, in which market with which strategy depends on profit considerations. As it turns out, an ongoing evolutionary competition between the trading strategies causes complex price dynamics which closely resembles the behavior of actual speculative prices. Moreover, we find that if the agents have to pay a transaction tax in one market, price variability decreases in this market but increases in the other market. However, the imposition of a uniform tax on all transactions stabilizes both markets. Our results suggest that if regulators of a market introduce a transaction tax, other markets are likely to follow.

In this paper we describe some sequences of global bifurcations involving attracting and repelling closed invariant curves of two-dimensional maps that have a fixed point which may lose stability both via a supercritical Neimark bifurcation and a supercritical pitchfork or flip bifurcation. These bifurcations, characterized by the creation of heteroclinic and homoclinic connections or homoclinic tangles, are first described through qualitative phase diagrams and then by several numerical examples. Similar bifurcation phenomena can also be observed when the parameters in a two-dimensional parameter plane cross through many overlapping Arnold's tongues.

This paper analyses the dynamics of a model of a share market consisting of two groups of traders: fundamentalists, who base their trading decisions on the expectation of a return to the fundamental value of the asset, and chartists, who base their trading decisions on an analysis of past price trends. The model is reduced to a two-dimensional map whose global dynamic behaviour is analysed in detail. The dynamics are affected by parameters measuring the strength of fundamentalist demand and the speed with which chartists adjust their estimate of the trend to past price changes. The parameter space is characterized according to the local stability/instability of the equilibrium point as well as the non-invertibility of the map. The method of critical curves of non-invertible maps is used to understand and describe the range of global bifurcations that can occur. It is also shown how the knowledge of deterministic dynamics uncovered here can aid in understanding the behaviour of stochastic versions of the model.

This book reflects the state of the art on nonlinear economic dynamics, financial market modelling and quantitative finance. It contains eighteen papers with topics ranging from disequilibrium macroeconomics, monetary dynamics, monopoly, financial market and limit order market models with boundedly rational heterogeneous agents to estimation, time series modelling and empirical analysis, and from risk management of interest-rate products, futures price volatility and American option pricing with stochastic volatility to evaluation of risk and derivatives of electricity market. The book illustrates some of the most recent research tools in these areas and will be of interest to economists working in economic dynamics and financial market modelling, to mathematicians who are interested in applying complexity theory to economics and finance, and to market practitioners and researchers in quantitative finance interested in limit order, futures and electricity market modelling, derivative pricing and risk management.

In this paper a discrete-time economic model is considered where the savings are proportional to income and the investment demand depends on the diAerence between the current income and its exogenously assumed equilibrium level, through a nonlinear S-shaped increasing function. The model can be ultimately reduced to a two-dimensional discrete dynamical system in income and capital, whose time evolution is ‘‘driven’’ by a family of two-dimensional maps of triangular type. These particular two-dimensional maps have the peculiarity that one of their components (the one driving the income evolution in the model at study) appears to be uncoupled from the other, i.e., an independent one-dimensional map. The structure of such maps allows one to completely understand the forward dynamics, i.e., the asymptotic dynamic behavior, starting from the properties of the associated one-dimensional map (a bimodal one in our model). The equilibrium points of the map are determined, and the influence of the main parameters (such as the propensity to save and the firms’ speed of adjustment to the excess demand) on the local stability of the equilibria is studied. More important, the paper analyzes how changes in the parameters’ values modify both the asymptotic dynamics of the system and the structure of the basins of the diAerent and often coexisting attractors in the phase-plane. Finally, a particular ‘‘global’’ (homoclinic) bifurcation is illustrated, occurring for suAciently high values of the firms’ adjustment parameter and causing the switching from a situation of bi-stability (coexistence of two stable equilibria, or attracting sets of diAerent nature) to a regime characterized by wide chaotic oscillations of

In this paper we consider a discrete time, finite horizon problem of optimization of the financing/dividend decisions concerning a multiperiod investment project. We assume that for each subperiod of a given time interval the cash movement generated by the project, the borrowing rate and the rate of return on firm’s liquidity are stochastic variables with a known distribution. Adopting an accounting point of view, we assume as objective function the expected amount of retained earnings at the end of the time horizon. Our aim is to obtain the optimal financing/dividend policy for the project in question, i.e. the optimal levels of debt and equity capital for each period and the optimal dividend payment scheme, under various financial constraints.

We develop a novel financial market model in which the stock markets of two countries are linked via and with the foreign exchange market. To be precise, there are domestic and foreign speculators in each of the two stock markets which rely either on linear technical or linear fundamental trading strategies to determine their orders. Since foreign stock market speculators require foreign currency to conduct their trades, all three markets are connected. Our setup entails a natural nonlinearity which may cause persistent endogenous price dynamics. Moreover, we analytically show that market interactions can destabilize the model's fundamental steady state.

Heterogeneity and evolutionary behaviour of investors are two of the most important characteristics of financial markets. This paper incorporates the adaptive behaviour of agents with heterogeneous beliefs and establishes an evolutionary capital asset pricing model (ECAPM) within the mean-variance framework. We show that the rational behaviour of agents switching to better-performing trading strategies can cause large deviations of the market price from the fundamental value of one asset to spill over to other assets. Also, this spill-over effect is associated with high trading volumes and persistent volatility characterized by significantly decaying autocorrelations of, and positive correlation between, price volatility and trading volume. © 2012 Springer-Verlag Berlin Heidelberg.

This paper investigates the impact of speculative behavior on house price dynamics. Speculative demand for housing is modeled using a heterogeneous agent approach, whereas ‘real’ demand and housing supply are represented in a standard way. Together, real and speculative forces determine excess demand in each period and house price adjustments. Three alternative models are proposed, capturing in different ways the interplay between fundamental trading rules and extrapolative trading rules, resulting in a 2D, a 3D, and a 4D nonlinear discrete-time dynamical system, respectively. While the destabilizing effect of speculative behavior on the model’s steady state is proven in general, the three specific cases illustrate a variety of situations that can bring about endogenous dynamics, with lasting and significant price swings around the ‘fundamental’ price, as we have seen in many real markets.

We develop a simple model of a speculative housing market in which the demand for houses is influenced by expectations about future housing prices. Guided by empirical evidence, agents rely on extrapolative and regressive forecasting rules to form their expectations. The relative importance of these competing views evolves over time, subject to market circumstances. As it turns out, the dynamics of our model is driven by a two-dimensional nonlinear map which may display irregular boom and bust housing price cycles, as repeatedly observed in many actual markets. Complex interactions between real and speculative forces play a key role in such dynamic developments.

It is believed that diversity is good for our society, but is it good for financial markets? In particular, does the diversity with respect to beliefs among investors reduce the market risk of risky assets? The current paper aims to answer this question.Within the standard mean-variance framework, we introduce heterogeneous beliefs not only in risk preferences and expected payoffs but also in variances/covariances. By aggregating heterogeneous beliefs into a market consensus belief, we obtain capital asset pricing model-like equilibrium price and return relationships under heterogeneous beliefs.We show that the market aggregate behaviour is in principle a weighted average of heterogeneous individual behaviours. The impact of heterogeneity on the market equilibrium price and risk premium is examined in general. In particular, we give a positive answer to the question in the title by considering some special structure in heterogeneous beliefs. In addition, we provide an explanation of Miller's long-standing hypothesis on the relation between a stock's risk and the divergence of opinions. © 2011 Taylor & Francis.

This article surveys boundedly rational heterogeneous agent (BRHA) models of financial markets. We give particular emphasis to the role of the market clearing mechanism used, the utility function of the investors, the interaction of price and wealth dynamics, and calibration of this class of models. Due to agents' behavioural features and market noise, the BRHA class of models are both non-linear and stochastic. We show that BRHA models produce both a locally stable fundamental equilibrium corresponding to that of the standard paradigm, as well as instability with a consequent rich range of possible complex behaviours that are analysed by both simulation and deterministic bifurcation analysis. A calibrated model is able to reproduce quite well the stylised facts of financial markets. The BRHA framework seems able to better accommodate market features such as fat tails, volatility clustering, large excursions from the fundamental and bubbles than the standard financial market paradigm.

International audience; We enrich the classical cobweb framework by allowing producers to enter different markets. The market entry decision is repeated every period and depends on the markets' historical profit differentials. As a result, the number of producers in a market and thus also a market's total supply vary over time. Analytical and numerical investigations of our four-dimensional nonlinear model indicate that interacting cobweb markets may contribute to the strong cyclical price motion observed in many commodity markets. We furthermore find that endogenous dynamics may either set in via a Flip or a Neimark-Sacker bifurcation. Interestingly, the latter scenario is prevalent if producers are sufficiently risk averse.

In a previous paper Tramontana et al. (2009), we developed a three-dimensional discrete-time dynamic model in which two stock markets of two countries, say H(ome) and A(broad), are linked via and with the foreign exchange market. The latter is modelled in the sense of Day and Huang (1990), i.e. it is characterized by a nonlinear interplay between technical traders (or chartists) and fundamental traders (or fundamentalists). In the absence of connections, the foreign exchange market is driven by the iteration of a one-dimensional cubic map, which has the potential to produce a regime of alternating and unpredictable bubbles and crashes for sufficiently large values of a key parameter, which captures the speculative behavior of chartists. Such a dynamic feature, first observed and explained by Day and Huang (1990) in their stylized model of financial market dynamics, can be understood with the help of bifurcation analysis: an initial situation of bi-stability (two coexisting, attracting non-fundamental steady states around an unstable fundamental equilibrium) evolves into coexistence of cycles or chaotic intervals within two disjoint bull and bear regions, which eventually merge via a homoclinic bifurcation. By introducing connections between markets (i.e. by allowing stock market traders to be active abroad), the endogenous fluctuations originating in one of the markets spread throughout the whole three-dimensional system. It therefore becomes interesting to investigate how the coupling of the markets affects the bull and bear dynamics of the model. With regard to this, in Tramontana et al. (2009) we already performed a thorough analytical and numerical study of two simplified lower-dimensional cases, where connections are either totally absent (each market evolves according to an independent one-dimensional map) or occur in one direction (a two-dimensional system evolves independently of the third dynamic equation). Also a short analysis of the stability of the equilibria of the three-dimensional model was there started, arguing that the global (homoclinic) bifurcations may still be a characteristic of the dynamics. This investigation is precisely the object of the present paper. We shall analyze the dynamic behavior of the complete three-dimensional model, following the approach adopted in Tramontana et al. (2009), based mainly on the numerical and graphical detection of the relevant global bifurcations. Although analytical conditions for such global bifurcation, mainly homoclinic bifurcations, are difficult to be formalized, their existence and occurrence can be numerically detected. As it is standard in the qualitative study of dynamic behaviors, the transverse crossing between stable and unstable sets of unstable cycles, leading to homoclinic trajectories, give numerical tools which may be considered as proofs in a given numerical example.

We develop a discrete-time model in which the stock markets of two countries are linked via and with the foreign exchange market. The foreign exchange market is characterized by nonlinear interactions between technical and fundamental traders. Such interactions may generate complex dynamics and recurrent switching between “bull” and “bear” market phases via a well-known pitchfork and period-doubling bifurcation path, when technical traders become more aggressive. The two stock markets are populated by fundamentalists, and prices tend to evolve towards stable steady states, driven by linear laws of motion. A connection between such markets is established by allowing investors to trade abroad, and the resulting three-dimensional dynamical system is analyzed. One goal of our paper is to explore potential spill-over effects between foreign exchange and stock markets. A second, related goal is to study how the bifurcation sequence which characterizes the market with heterogeneous speculators is modified in the presence of interactions with other markets.

The Sharpe-Lintner-Mossin (Sharpe 1964; Lintner 1965; Mossin 1966) Capital Asset Pricing Model (CAPM) plays a central role in modern finance theory. It is founded on the paradigm of homogeneous beliefs and a rational representative agent. However, froma theoretical perspective this paradigmhas been criticized on a number of grounds, in particular concerning its extreme assumptions about homogeneous beliefs, information about the economic environment, and the computational ability on the part of the rational representative economic agent. The impact of heterogeneous beliefs among investors on the market equilibrium price has been an important focus in the CAPM literature. A number of models with investorswho have heterogeneous beliefs have been previously studied. 1 A common finding in this strand of research is that heterogeneous beliefs can affect aggregate market returns. However, the question remains as to how exactly does heterogeneity affect themarket risk of risky assets? In much of this earlier work, the heterogeneous beliefs reflect either differences of opinion among the investors2 or differences in information upon which investors are trying to learn by using some Bayesian updating rule.3 Heterogeneity has been investigated in the context of either CAPM-like mean-variancemodels (for instance, Lintner 1969; Miller 1977;Williams 1977; and Mayshar 1982) or Arrow-Debreu contingent claims models (as in Varian 1985;Abel 1989; 2002; and Calvet et al. 2004). © 2010 Springer-Verlag Berlin Heidelberg.

Publisher Summary Although there might be agreement that the standard paradigm does not fully explain what is causing the evolution of speculative asset prices, there may be less agreement on where to start to build an improved paradigm. By and large, the view that has been adopted in the boundedly rational heterogeneous agent literature is to retain expected utility maximization as the goal of each agent but to allow the agents to have different risk preferences and different expectations, rather than the single homogeneous rational expectation, about future possible returns. The expectations differ since agents are assumed to have different information and beliefs. Thus the asset price modeling framework is based on the fact that trading is driven more by differences in expectations than by the random arrival of news events. Within this framework, a simple market of one risky asset and one risk-free asset, with agents having different expectations, is considered with two different types of utility functions and two different market-clearing mechanisms. The framework provides the basic elements and structure of the various models. The basic building blocks of this framework are portfolio optimization, agents' utility functions, the market-clearing mechanism, and expectations feedback.

This paper explores the steady-state properties and the dynamic behavior of a generalization of the classical cobweb model. Under fairly general demand and cost functions, producers form naive expectations about future prices and select their output so as to maximize expected profits. Unlike the traditional setup, producers have the choice between two markets, and tend to enter that which was more profitable in the recent past. Such a switching process implies time-varying aggregated supply schedules, thus representing a further source of nonlinearity for the dynamics of prices. Analytical investigations and the numerical simulation of a particular case with linear demand and supply indicate that such interactions may destabilize otherwise stable markets and generate complex dynamics.

This chapter surveys the boundedly rational heterogeneous agent (BRHA) models of financial markets, to the development of which the authors and several co-authors have contributed in various papers. We give particular emphasis to role of the market clearing mechanism used, the utility function of the investors, the interaction of price and wealth dynamics, portfolio implications, the impact of stochastic elements on the markets dynamics, and calibration of this class of models. Due to agents’ behavioural features and market noise, the BRHA models are both nonlinear and stochastic. We show that the BRHA models produce both a locally stable fundamental equilibrium corresponding to that of standard paradigm, as well as instability with a consequent rich range of possible complex behaviours characterised both indirectly by simulation and directly by stochastic bifurcations. A calibrated model is able to reproduce quite well the stylized facts of financial markets. The BRHA framework is thus able to accommodate market features that seem not easily reconcilable for the standard financial market paradigm, such as fat tail, volatility clustering, large excursions from the fundamental and bubbles.

In the fi rst part of our paper we proposed a three-dimensional nonlinear dynamic model of interacting stock and foreign exchange markets, jointly driven by the speculative activity of heterogeneous investors. We focused, in particular, on the typical 'bull and bear' scenario that emerges from simpli ed one- and two-dimensional settings. The goal of this part of the paper is to provide a global analysis of the dynamics of the full model. As it turns out, the results we obtained in the fi rst part may serve as a road map to develop an initial understanding of the much more complicated three-dimensional model.

We develop a three-dimensional nonlinear dynamic model in which the stock markets of two countries are linked through the foreign exchange market. Connections are due to the trading activity of heterogeneous speculators. Using analytical and numerical tools, we seek to explore how the coupling of the markets may affect the emergence of 'bull and bear' market dynamics. The dimension of the model can be reduced by restricting investors' trading activity, which enables the dynamic analysis to be performed stepwise, from low-dimensional cases up to the full three-dimensional model. In Part I of our paper, we focus on the one and two-dimensional case.

Following the framework of a one risky - one riskless asset model developed by Brock and Hommes (1998), this paper considers a discrete-time model of a financial market where heterogeneous groups of agents allocate their wealth amongst multiple risky assets and a riskless asset. Agents follow different expectation formation schemes for both first and second moments of the distribution of returns. Instead of using a Walrasian auctioneer scenario as the market clearing mechanism, a market maker scenario is used. In particular, the paper focuses on the case of two risky assets and two agent types, fundamentalists and trend chasers. Conditions for the stability of the "fundamental" equilibrium are established in terms of the key parameters, in particular the extrapolation rate of the trend chasers and the weight of the two groups in the market. Numerical explorations are performed in order to analyze the combined effect of the interaction between heterogeneous traders and the diversification among multiple risky assets. Particular attention is paid to the effect of the correlation between the risky assets. It turns out that investors' anticipated correlation and portfolio diversification do not always have a stabilizing role, but rather may act as a further source of complexity in the financial market.

Within the standard mean-variance framework, this paper provides a procedure to aggregate the heterogeneous beliefs in not only risk preferences and expected payoffs but also variances/covariances into a market consensus belief. Consequently, an asset equilibrium price under heterogeneous beliefs is derived. We show that the market aggregate behavior is in principle a weighted average of heterogeneous individual behaviors. The CAPM-like equilibrium price and return relationships under heterogeneous beliefs are obtained. The impact of diversity of heterogeneous beliefs on the market aggregate risk preference, asset volatility, equilibrium price and optimal demands of investors is examined. As a special case, our result provides a simple explanation for the empirical relation between cross-sectional volatility and expected returns.

The aim of this paper is to show, within the mean-variance framework, how the market belief can be constructed as the result of the aggregation of heterogeneous beliefs and how the market equilibrium prices of risky assets can thus be determined. The heterogeneous beliefs are defined in terms of not only the means but also variances and covariances. By constructing the mean and variance of the market belief, we analyze the impact of the heterogeneous beliefs on the market equilibrium asset pricing relation. In particular, we extend the standard CAPM under homogenous beliefs to the one under the heterogeneous beliefs.

We reconsider the derivation of the traditional capital asset pricing model (CAPM) in the discrete time setting for a portfolio of one riskless asset and many risky assets. In contrast to the standard setting, it is assumed that agents are heterogeneous in their conditional means and covariances of the risky returns, and that their beliefs about future returns - based on statistical properties of past returns - induce expectations feedback. A Walrasian auctioneer scenario is used for the determination of the market clearing price. In this framework we first construct a consensus belief to represent the aggregate market beliefs about means and variances/covariances of returns, and derive a heterogeneous CAPM which relates aggregate excess return on risky assets with aggregate excess return on the market portfolio via aggregate beta coefficients. We then use this result to establish a dynamic {\em market fraction\/} model in which agents are grouped according to their beliefs. In particular, we focus on three classical heterogeneous agents types - fundamentalists, trend followers and noise traders - and investigate how some of the key agent characteristics affect the time varying behaviour of market returns and beta coefficients

This paper deals with a simple model of financial fluctuations, where a crucial role is played by the dynamic interaction between aggregate current and intertemporal financial ratios. The model results in a 4D discrete-time dynamical system—capable of generating complex dynamics—which is analyzed by means of both analytical tools, such as local stability analysis and bifurcation theory, and numerical simulations. The behavior of the model is studied for different parameter regimes. We show that its dynamic behavior is very sensitive to the parameters that represent (1) the speed of adjustment of the desired current financial ratio towards a safe level of the intertemporal one and (2) the intensity with which aggregate current financial decisions affect future financial constraints. In particular, different parameter regimes are identified, giving rise to two different “routes” to complexity, one leading to chaotic dynamics, the other to a coexistence of attractors and path-dependence.

Following the framework of a one risky - one riskless asset model developed by Brock and Hommes (1998), this paper considers a discrete-time model of a financial market where heterogeneous groups of agents allocate their wealth amongst multiple risky assets and a riskless asset. Agents follow different expectation formation schemes for both first and second moments of the distribution of returns. Instead of using a Walrasian auctioneer scenario as the market clearing mechanism, a market maker scenario is used. In particular, the paper focuses on the case of two risky assets and two agent types, fundamentalists and trend chasers. Conditions for the stability of the “fundamental” equilibrium are established in terms of the key parameters, in particular the extrapolation rate of the trend chasers and the weight of the two groups in the market. Numerical explorations are performed in order to analyze the combined effect of the interaction between heterogeneous traders and the diversification among multiple risky assets. Particular attention is paid to the effect of the correlation between the risky assets. It turns out that investors’ anticipated correlation and portfolio diversification do not always have a stabilizing role, but rather may act as a further source of complexity in the financial market.

A discrete time model of a financial market is developed, in which heterogeneous interacting groups of agents allocate their wealth between two risky assets and a riskless asset. In each period each group formulates its demand for the risky assets and the risk-free asset according to myopic mean-variance maximizazion. The market consists of two types of agents: fundamentalists, who hold an estimate of the fundamental values of the risky assets and whose demand for each asset is a function of the deviation of the current price from the fundamental, and chartists, a group basing their trading decisions on an analysis of past returns. The time evolution of the prices is modelled by assuming the existence of a market maker, who sets excess demand of each asset to zero at the end of each trading period by taking an offsetting long or short position, and who announces the next period prices as functions of the excess demand for each asset and with a view to long-run market stability. The model is reduced to a seven-dimensional nonlinear discrete-time dynamical system, that describes the time evolution of prices and agents' beliefs about expected returns, variances and correlation. The unique steady state of the model is determined and the local asymptotic stability of the equilibrium is analysed, as a function of the key parameters that characterize agents' behaviour. In particular it is shown that when chartists update their expectations sufficiently fast, then the stability of the equilibrium is lost through a supercritical Neimark-Hopf bifurcation, and self-sustained price fluctuations along an attracting limit cycle appear in one or both markets. Global analysis is also performed, by using numerical techniques, in order to understand the role played by the chartists' behaviour in the transition to a regime characterized by irregular oscillatory motion and coexistence of attractors. It is also shown how changes occurring in one market may affect the price dynamics of the alternative risky asset, as a consequence of the dynamic updating of agents' portfolios. © 2005 Taylor & Francis Group Ltd.