Heterogeneous Agents Research Articles

Intermittent output tracking control of heterogeneous multi-agent systems over wide-area clustered communication networks

In this paper, an output tracking problem is investigated for a wide-area heterogeneous multi-agent system with multiple leaders through intermittent communication, where the communication network consists of clustered subnetworks distributed in a wide area. Firstly, a hierarchical clustered network model is built to describe the communication network topology of heterogeneous agents communicated by an intermittent communication mechanism. Subsequently, dynamic compensators are designed for the heterogeneous agents to estimate the leaders’ state information and a dynamic state feedback hybrid control strategy is designed for each agent to ensure the output tracking consensus. Furthermore, the proposed hybrid control strategy is extended to a case where the complete state information of the agent itself is also not available. Then, under the proposed hybrid control strategy, the closed-loop tracking error system is modeled by a switched system. Consequently, sufficient conditions are derived for the stability of the closed-loop tracking error system under the proposed hybrid control strategy by using a piecewise Lyapunov function and convex synthesis methods. Finally, two numerical examples are provided to demonstrate the effectiveness of the proposed hybrid control strategy.

Learning about unprecedented events: Agent-based modelling and the stock market impact of COVID-19

We model the learning process of market traders during the unprecedented COVID-19 event. We introduce a behavioural heterogeneous agents’ model with bounded rationality by including a correction mechanism through representativeness (Gennaioli et al., 2015). To inspect the market crash induced by the pandemic, we calibrate the STOXX Europe 600 Index, when stock markets suffered from the greatest single-day percentage drop ever. Once the extreme event materializes, agents tend to be more sensitive to all positive and negative news, subsequently moving on to close-to-rational. We find that the deflation mechanism of less representative news seems to disappear after the extreme event.

Optimal redistributive policy in debt constrained economies

How should governments with a preference for redistribution design tax policies when facing limited borrowing? This paper studies optimal taxation in a small open economy with heterogeneous agents and endogenous debt constraints arising from the government's limited commitment to fiscal policies. The optimal labor tax decreases over time and is nonzero in the limit, and the optimal capital and domestic borrowing taxes are positive in the limit, deviating from the standard Ramsey tax results. The government's redistributive motive directly affects optimal tax levels, whereas binding debt constraints influence optimal tax dynamics. In the numerical analysis, a stronger redistributive preference requires greater initial tax distortions and a higher external debt level in the long run.

Programmable self-organization of heterogeneous microrobot collectives

At the microscale, coupled physical interactions between collectives of agents can be exploited to enable self-organization. Past systems typically consist of identical agents; however, heterogeneous agents can exhibit asymmetric pairwise interactions which can be used to generate more diverse patterns of self-organization. Here, we study the effect of size heterogeneity in microrobot collectives composed of circular, magnetic microdisks on a fluid-air interface. Each microrobot spins or oscillates about its center axis in response to an external oscillating magnetic field, in turn producing local magnetic, hydrodynamic, and capillary forces that enable diverse collective behaviors. We demonstrate through physical experiments and simulations that the heterogeneous collective can exploit the differences in microrobot size to enable programmable self-organization, density, morphology, and interaction with external passive objects. Specifically, we can control the level of self-organization by microrobot size, enable organized aggregation, dispersion, and locomotion, change the overall shape of the collective from circular to ellipse, and cage or expel objects. We characterize the fundamental self-organization behavior across a parameter space of magnetic field frequency, relative disk size, and relative populations; we replicate the behavior through a physical model and a swarming coupled oscillator model to show that the dominant effect stems from asymmetric interactions between the different-sized disks. Our work furthers insights into self-organization in heterogeneous microrobot collectives and moves us closer to the goal of applying such collectives to programmable self-assembly and active matter.

Biocidal activity of multifunctional cuprite-doped anion exchanger – Influence of bacteria type and medium composition

The study presents unconventional, bifunctional, heterogeneous antimicrobial agents – Cu2O-loaded anion exchangers. The synergetic effect of a cuprous oxide deposit and polymeric support with trimethyl ammonium groups was studied against the reference strains of Enterococcus faecalis ATCC 29212 and Pseudomonas aeruginosa ATCC 27853. Biological testing (minimum bactericidal concentration, MBC), time- and dose-dependent bactericidal effect (under different conditions – medium composition and static/dynamic culture) demonstrated promising antimicrobial activity and confirmed its multimode character. The standard values of MBC, for all studied hybrid polymers and bacteria, were similar (64–128 mg/mL). However, depending on the medium conditions, due to the copper release into the bulk solution, bacteria were actively killed even at much lower doses of the hybrid polymer (25 mg/mL) and low Cu(II) concentrations in solution (0.01 mg/L). Simultaneously, confocal microscopic studies confirmed the effective inhibition of bacterial adhesion and biofilm formation on their surface. The studies conducted under different conditions showed also the influence of the structure and physical properties of studied materials on the biocidal efficacy and an antimicrobial action mechanism was proposed that could be significantly affected by electrostatic interactions and copper release to the solution. Although the antibacterial activity was also dependent on various strategies of bacterial cell resistance to heavy metals present in the aqueous medium, the studied hybrid polymers are versatile and efficient biocidal agents against bacteria of both types, Gram-positive and Gram-negative. Therefore, they can be a convenient alternative for point-of-use water disinfection systems providing water quality in medical devices such as dental units, spa equipment, and aesthetic devices used in the cosmetic sector.

Output Bipartite Consensus for Second-Order Heterogeneous Uncertain Agents With State-Dependent Cooperation-Competition Interactions

For state-dependent cooperation-competition networks, the output bipartite consensus problem of heterogeneous uncertain agents is studied in this paper. In our framework, all the agents are described by second-order continuous-time nonlinear systems with different intrinsic dynamics, and the agents' uncertainties are characterized by unknown parameters in the intrinsic term. Then, the edge evolution rules with hysteresis coefficients are proposed via the classification strategy. To solve this problem, the distributed Lyapunov-based redesign method with the potential function term is first applied to such second-order heterogeneous uncertain multi-agent system. Through the three-step correlation design, the explicit expressions of the distributed controllers and the unknown parameter estimators are obtained, and it is shown that the state-dependent cooperation-competition network is always connected and maintains structural balance for all time if an initial structurally balanced and connected network topology is provided. On this basis, it follows from the total Lyapunov function that output bipartite consensus can be achieved asymptotically for the heterogeneous uncertain multi-agent system. Finally, a numerical simulation is provided to validate the structural balance of state-dependent networks and output bipartite consensus of heterogeneous uncertain agents.

Inequality aversion and government health expenditure

This paper explores a behavioural mechanism through which income inequality may be associated with population health. We consider a model with heterogeneous agents in which agents' preferences are characterized by income inequality aversion. Our analysis shows that spending on health-producing goods is inversely related to the agents’ degree of inequality aversion. A Veblenesque mechanism drives this relation: inequality averse poor agents wish to enjoy consumption levels closer to the average consumption levels in the economy but can only do so by reducing their expenditures on health. This leads to adverse outcomes for individuals and adverse political economy implications for health. In the political economy context, agents characterized by high inequality aversion vote for lower levels of government health spending. To specifically test this mechanism, we construct empirical measures of inequality aversion. Then, using these measures for a panel of 147 countries spanning 2008–2019, we find a significant negative impact of inequality aversion on allocations of public spending for healthcare. These results remain robust to different model specifications.

Directed Distance-Based Formation Control of Nonlinear Heterogeneous Agents in 3-D Space

This paper studies distance-based formation control of a set of nonlinear multi-agent systems over directed graphs. We propose a distributed, distance-based formation control scheme for a set of heterogeneous, nonlinear agents over a particular class of minimally, structurally persistent, directed graphs in a 3-D space, namely <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">directed trilateral Laman</i> graphs. The responsibility of controlling each directed edge is assigned to only one of the adjacent agents. The state-dependent Riccati equation is used to design the control method for nonlinear agents. Based on the mathematical induction and stability theory of cascade interconnected systems, we rigorously prove the asymptotic stability of the overall formation. A combination of signed area and volume constraints is used to prevent agents from converging to the flip-ambiguous frameworks in 3-D space. The proposed control law assures collision avoidance between the neighboring pairs of agents. Simulation results are provided to verify the theoretical results.

Reinforcement Learning in a New Keynesian Model

We construct a New Keynesian (NK) behavioural macroeconomic model with bounded-rationality (BR) and heterogeneous agents. We solve and simulate the model using a third-order approximation for a given policy and evaluate its properties using this solution. The model is inhabited by fully rational (RE) and BR agents. The latter are anticipated utility learners, given their beliefs of aggregate states, and they use simple heuristic rules to forecast aggregate variables exogenous to their micro-environment. In the most general form of the model, RE and BR agents learn from their forecasting errors by observing and comparing them with each other, making the composition of the two types endogenous. This reinforcement learning is then at the core of the heterogeneous expectations model and leads to the striking result that increasing the volatility of exogenous shocks, by assisting the learning process, increases the proportion of RE agents and is welfare-increasing.

Capital flows and income inequality

We document empirical evidence that surges in capital inflows (outflows) raise (reduce) income inequality. We study the mechanism through which changes in capital flows and capital account policies can influence income distributions in a small open economy model. Our model features heterogeneous agents and financial frictions, with banks intermediating between household savings and entrepreneur investment. Inflow surges disproportionately raise entrepreneur income, exacerbating inequality, while increases in outflows boost the share of household income, alleviating inequality. Under capital-skill complementarity, capital account liberalization that induces net capital inflows raises both the skill wage premium and overall income inequality. These predictions are in line with our empirical evidence.

Pay equality among heterogeneous agents

A principal incentivizes a team of agents to work by choosing performance-contingent rewards. She desires to implement work by all agents as a unique Nash equilibrium. We identify necessary and sufficient conditions under which it is optimal to reward heterogeneous agents equally, and show that increasing inequality in the marginal productivities of agents can either increase or decrease pay inequality. Our results rationalize patterns of performance pay in many labor market settings, including professional sports leagues and the military.

Biologics for severe asthma-Which, when and why?

Asthma is a common chronic inflammatory condition of the airways that affects about 350 million people globally. In 5%-10% of individuals, it is severe, with considerable morbidity and high health care utilization. The goal of asthma management is disease control by reducing symptoms and exacerbations and reducing corticosteroid-related morbidity. The era of biologics has revolutionized the management of severe asthma. Biologics have changed our expectations for severe asthma, especially in those people with type-2 mediated immunity. We can now explore the potential for changing disease trajectory and inducing remission. However, biologics are not a panacea for all severe asthma sufferers and despite their success there remains substantial unmet clinical need. We review the pathogenesis of asthma, phenotyping the heterogeneity of asthma, currently licensed and future biologic agents, how to choose the initial biologic, assessing the response, remission and switching of biologic therapies.

El canal de renta real y las depreciaciones contractivas en un modelo de agentes heterogéneos para América Latina

Rationale In Latin America, it is not unusual to see exchange rate depreciations in excess of 20% in a single year. Although depreciation tends to stimulate a country’s net external demand, it does not always lead to increased output. It is worth understanding which channels may explain this outcome. Takeaways •In conventional macroeconomic theory, exchange rate depreciations have expansionary effects on economic activity. However, the empirical evidence shows that, in the case of emerging market economies, devaluing the exchange rate may cause output to contract. •One channel that explains this evidence, known as the real income channel, operates through the erosion of purchasing power as a result of rising prices for imported goods, which can lead to a fall in the real consumption of households with limited access to financial markets. •This article discusses a heterogeneous agent model calibrated for the main Latin American economies that allows the importance of this channel to be measured. The results show that this channel may have a sizable macroeconomic impact, particularly on economies more open to international trade.

Higher moment connectedness of cryptocurrencies: a time-frequency approach

The purpose of the study is to examine higher moment connectedness among 12 cryptocurrencies using data sampled at the 1-minute high-frequency interval. We use methods that demonstrate the heterogeneity of agents from their distinct investing horizons. This includes wavelet multiple cross-correlations, CEEMDAN-based Diebold-Yilmaz (DY) connectedness index and the Barunik-Krehlik (BK) frequency connectedness index. First, our results show that higher moment multiple correlations among the sampled cryptocurrencies are higher at all time scales and the relationship strengthens at lower frequencies. Second, the wavelet cross-correlations show different cryptocurrencies with the potential to lead and lag in the transmission of higher moment shocks to the whole system at different frequencies. Again, the multiple wavelet cross-correlations increase with increasing time scales. The results from the CEEMDAN-based DY connectedness index as well as the BK framework also reveal cyclical connectedness and differences in connectedness across different frequencies. The results show more connectedness of higher moments than the connectedness empirically reported for returns and volatility. Cryptocurrency connectedness has mostly been examined using the first two moments. We extend this line of literature by examining the third and fourth moments, which might be more useful for risk management purposes.

Decentralized coordination between active distribution network and multi-microgrids through a fast decentralized adjustable robust operation framework

Due to the autonomous characteristic and heterogeneity of the individual agents in active distribution network (ADN) with multi-microgrids (MMG), this paper proposes a fully decentralized adjustable robust operation framework achieving the coordinated operation between ADN and MMG. The improved linear decision rules (LDRs) based microgrid adjustable robust operation model is proposed to reduce the solution conservatism in dealing with renewable energy uncertainty. The LDRs model is then reformulated as a computationally tractable solution such that the proposed adjustable robust extension of decentralized operation can handle renewable energy uncertainty while reducing the computation burden of decentralized optimization. Then, a tailored fast alternating direction method of multipliers algorithm with a predictor–corrector type acceleration step is developed to improve the convergence rate of decentralized optimization. The effectiveness of the proposed model is validated on a modified IEEE 69-bus distribution system with four microgrids.

Household heterogeneity in macroeconomic models: A historical perspective

In this paper, we trace the rise of heterogeneous household models in mainstream macroeconomics from the turn of the 1980s to the early 2000s, when these models evolved into an identifiable and consistent literature. We show that different communities across the US and Europe considered heterogeneous agents for various reasons and developed models that differed in their theoretical and empirical strategies. Minnesota economists primarily focused on incorporating stochastic heterogeneity into general equilibrium models. Other researchers refined growth models or tried to find alternatives to the permanent income hypothesis, leading them to explore more structural heterogeneity. We also document the computational challenges that some of these communities faced, how they gradually became aware of each other's work, and how they faced criticisms from macro- and microeconomists, many of them trained in European countries and dissatisfied with the theoretical and empirical aggregation strategies underlying these models.

Coexisting Attractors in a Heterogeneous Agent Model in Discrete Time

In this paper, the discrete-time version of a continuous-time model with fundamentalists and momentum traders is presented. Our aim consists of studying the impact of cross-sectional momentum traders on the dynamics of the model. To this end, the continuous-time deterministic skeleton of the benchmark model is transformed using sophisticated discretization techniques. It is worth noting that the model does not always maintain the same characteristics after moving from continuous to discrete time. In spite of this, our discrete-time system preserves the dynamic properties of the continuous-time original model. Moreover, heterogeneity introduces an important non-linearity into the market dynamics, causing our deterministic financial model to generate erratic time series similar to the patterns observed in real markets. In particular, we show that the time series originated by the perturbed deterministic system capture some of the main stylized facts of the U.S. financial market. Converting the benchmark model from continuous time to discrete time allows the use of financial data available in discrete time.

Unemployment insurance design with repeated choices

Abstract This article characterizes the relation between the equilibrium unemployment insurance replacement rate and the frequency of its political choice. We first use a tractable analytical model to show how insurance, incentive, and redistribution effects interact at the equilibrium. We then examine a fully repeated choices equilibrium in a quantitative heterogeneous agents model and show that unemployment persistence, whether a policy is announced first or not, and the type of the political process are key determinants of the relation between the equilibrium replacement rate and the frequency of its choice. In a utilitarian welfare context, we find that the equilibrium replacement rate is higher if the policy is chosen more frequently but this relation is reversed in a median voter context.

Group lending, sorting, and risk sharing

This paper studies group lending with joint-liability contracts offered by Microfinance Institutions (MFIs). We develop a model of group lending where heterogeneous agents form groups, obtain capital from the MFI, and share risks among themselves. We show that the composition of the groups is not always homogeneous once risk-sharing is introduced, rationalizing the empirical evidence of risk heterogeneity within groups. Moreover, we find that joint liability introduces inefficiency for risk-averse borrowers, which explains why MFIs are moving away from joint-liability contracts. Surprisingly, the first-best outcome can be achieved even in the presence of information asymmetry.

Cerium refinement of grains and primary carbides during solidification of Cr4Mo4V bearing steel

The effect of cerium (Ce) on the solidification microstructure of Cr4Mo4V bearing steel was investigated via a combined experimental and theoretical method. With a trace amount (0.056 wt%) of Ce addition, the coarse columnar grains in as-cast microstructure transform into equiaxed ones, and the average diameter is reduced from 56 to 27 μm. The network-like and bulky primary MC and M2C carbides at the interdendritic regions become disconnected and refined, and their volume percentage decreases from 4.15 vol% to 2.1 vol%. Ce-inclusions acting as heterogeneous nucleation agents of prior-austenite grains and Ce atoms segregating at grain boundaries, both contribute to the refinement of grains. Thermodynamic calculations reveal that primary carbides are precipitated after γ-austenite forms near the end of the solidification process. The modification of primary carbides in size and amount is mainly attributed to the isolated remaining melt separated by refined γ-austenite grains in which the nucleation of carbides is promoted, while the growth is restrained owing to the less segregation of alloying elements.