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1.
J. R. Iglesias R. M. C. de Almeida 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(3):85
Many recent models of trade dynamics use the simple idea of wealth exchanges among
economic agents in order to obtain a stable or equilibrium distribution of wealth among
the agents. In particular, a plain analogy compares the wealth in a society with the
energy in a physical system, and the trade between agents to the energy exchange between
molecules during collisions. In physical systems, the energy exchange among molecules
leads to a state of equipartition of the energy and to an equilibrium
situation where the entropy is a maximum. On the other hand, in a large class of exchange
models, the system converges to a very unequal condensed state, where one
or a few agents concentrate all the wealth of the society while the wide majority of
agents shares zero or almost zero fraction of the wealth. So, in those economic systems a
minimum entropy state is attained. We propose here an analytical model where we
investigate the effects of a particular class of economic exchanges that minimize the
entropy. By solving the model we discuss the conditions that can drive the system to a
state of minimum entropy, as well as the mechanisms to recover a kind of equipartition of
wealth. 相似文献
2.
Els Heinsalu Marco Patriarca 《The European Physical Journal B - Condensed Matter and Complex Systems》2014,87(8):1-10
We propose a novel kinetic exchange model differing from previous ones in two main aspects. First, the basic dynamics is modified in order to represent economies where immediate wealth exchanges are carried out, instead of reshufflings or uni-directional movements of wealth. Such dynamics produces wealth distributions that describe more faithfully real data at small values of wealth. Secondly, a general probabilistic trading criterion is introduced, so that two economic units can decide independently whether to trade or not depending on their profit. It is found that the type of the equilibrium wealth distribution is the same for a large class of trading criteria formulated in a symmetrical way with respect to the two interacting units. This establishes unexpected links between and provides a microscopic foundations of various kinetic exchange models in which the existence of a saving propensity is postulated. We also study the generalized heterogeneous version of the model in which units use different trading criteria and show that suitable sets of diversified parameter values with a moderate level of heterogeneity can reproduce realistic wealth distributions with a Pareto power law. 相似文献
3.
G. M. Caon S. Gonçalves J. R. Iglesias 《The European physical journal. Special topics》2007,143(1):69-74
Simple agent based exchange models are a commonplace in the study of
wealth distribution of artificial societies. Generally, each agent
is characterized by its wealth and by a risk-aversion factor, and
random exchanges between agents allow for a redistribution of the
wealth. However, the detailed influence of the amount of capital
exchanged has not been fully analyzed yet. Here we present a
comparison of two exchange rules and also a systematic study of the
time evolution of the wealth distribution, its functional
dependence, the Gini coefficient and time correlation functions. In
many cases a stable state is attained, but, interesting, some
particular cases are found in which a very slow dynamics develops.
Finally, we observe that the time evolution and the final wealth
distribution are strongly dependent on the exchange rules in a
nontrivial way. 相似文献
4.
C. F. Moukarzel S. Gonçalves J. R. Iglesias M. Rodríguez-Achach R. Huerta-Quintanilla 《The European physical journal. Special topics》2007,143(1):75-79
Random Asset Exchange (RAE) models, despite a number of simplifying
assumptions, serve the purpose of establishing direct relationships between
microscopic exchange mechanisms and observed economical data. In this work
a conservative multiplicative RAE model is discussed in which, at each
timestep, two agents “bet” for a fraction f of the poorest agent's
wealth. When the poorest agent wins the bet with probability p, we show
that, in a well defined region of the (p,f) phase space, there is
wealth condensation. This means that all wealth ends up owned by only
one agent, in the long run. We derive the condensation conditions
analytically by two different procedures, and find results in accordance
with previous numerical estimates. In the non-condensed phase, the
equilibrium wealth distribution is a power law for small wealths. The
associated exponent is derived analytically and it is found that it tends to
-1 on the condensation interface. I turns out that wealth condensation
happens also for values of p much larger than 0.5, that is under
microscopic exchange rules that, apparently, favor the poor. We argue that
the observed “rich get richer” effect is enhanced by the
multiplicative character of the dynamics. 相似文献
5.
Pareto law, which states that wealth distribution in societies has a power-law tail, has been the subject of intensive investigations in the statistical physics community. Several models have been employed to explain this behavior. However, most of the agent based models assume the conservation of number of agents and wealth. Both these assumptions are unrealistic. In this paper, we study the limiting wealth distribution when one or both of these assumptions are not valid. Given the universality of the law, we have tried to study the wealth distribution from the asset exchange models point of view. We consider models in which (a) new agents enter the market at a constant rate (b) richer agents fragment with higher probability introducing newer agents in the system (c) both fragmentation and entry of new agents is taking place. While models (a) and (c) do not conserve total wealth or number of agents, model (b) conserves total wealth. All these models lead to a power-law tail in the wealth distribution pointing to the possibility that more generalized asset exchange models could help us to explain the emergence of a power-law tail in wealth distribution. 相似文献
6.
Urna Basu P. K. Mohanty 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(4):585-589
We introduce an auto-regressive model which captures the growing nature of realistic markets. In our model agents do not trade
with other agents, they interact indirectly only through a market. Change of their wealth depends, linearly on how much they
invest, and stochastically on how much they gain from the noisy market. The average wealth of the market could be fixed or
growing. We show that in a market where investment capacity of agents differ, average wealth of agents generically follow
the Pareto-law. In few cases, the individual distribution of wealth of every agentcould also be obtained exactly. We also
show that the underlying dynamics of other well studied kinetic models of markets can be mapped to the dynamics of our auto-regressive
model. 相似文献
7.
Many models of market dynamics make use of the idea of conservative wealth exchanges among economic agents. A few years ago an exchange model using extremal dynamics was developed and a very interesting result was obtained: a self-generated minimum wealth or poverty line. On the other hand, the wealth distribution exhibited an exponential shape as a function of the square of the wealth. These results have been obtained both considering exchanges between nearest neighbors or in a mean field scheme. In the present paper we study the effect of distributing the agents on a complex network. We have considered archetypical complex networks: Erdös–Rényi random networks and scale-free networks. The presence of a poverty line with finite wealth is preserved but spatial correlations are important, particularly between the degree of the node and the wealth. We present a detailed study of the correlations, as well as the changes in the Gini coefficient, that measures the inequality, as a function of the type and average degree of the considered networks. 相似文献
8.
M. Ali Saif 《Physica A》2007,384(2):448-456
We investigate the problem of wealth distribution from the viewpoint of asset exchange. Robust nature of Pareto's law across economies, ideologies and nations suggests that this could be an outcome of trading strategies. However, the simple asset exchange models fail to reproduce this feature. A Yardsale (YS) model in which amount put on the bet is a fraction of minimum of the two players leads to condensation of wealth in hands of some agent while theft and fraud (TF) model in which the amount to be exchanged is a fraction of loser's wealth leads to an exponential distribution of wealth. We show that if we allow few agents to follow a different model than others, i.e., there are some agents following TF model while rest follow YS model, it leads to distribution with power-law tails. Similar effect is observed when one carries out transactions for a fraction of one's wealth using TF model and for the rest YS model is used. We also observe a power-law tail in wealth distribution if we allow the agents to follow either of the models with some probability. 相似文献
9.
U. Garibaldi E. Scalas P. Viarengo 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(2):241-246
We propose a simple stochastic exchange game mimicking
taxation and redistribution. There are g agents and n coins;
taxation is modeled by randomly extracting some coins; then, these
coins are redistributed to agents following Polya's scheme. The
individual wealth equilibrium distribution for the resulting Markov
chain is the multivariate symmetric Polya distribution. In the
continuum limit, the wealth distribution converges to a Gamma
distribution, whose form factor is just the initial redistribution
weight. The relationship between this taxation-and-redistribution
scheme and other simple conservative stochastic exchange games (such
as the BDY game) is discussed. 相似文献
10.
In this paper we explore the physical interpretation of statistical data collected from complex black-box systems. Given the output statistics of a black-box system, and considering a class of relevant Markov dynamics which are physically meaningful, we reverse-engineer the Markov dynamics to obtain an equilibrium distribution that coincides with the output statistics observed. This reverse-engineering scheme provides us with a conceptual physical interpretation of the black-box system investigated. Five specific reverse-engineering methodologies are developed, based on the following dynamics: Langevin, geometric Langevin, diffusion, growth-collapse, and decay-surge. In turn, these methodologies yield physical interpretations of the black-box system in terms of conceptual intrinsic forces, temperatures, and instabilities. The application of these methodologies is exemplified in the context of the distribution of wealth and income in human societies, which are outputs of the complex black-box system called “the economy”. 相似文献
11.
We present and analyze a model for the evolution of the wealth distribution within a heterogeneous economic environment. The model considers a system of rational agents interacting in a game theoretical framework, through fairly general assumptions on the cost function. This evolution drives the dynamic of the agents in both wealth and economic configuration variables. We consider a regime of scale separation where the large scale dynamics is given by a hydrodynamic closure with a Nash equilibrium serving as the local thermodynamic equilibrium. The result is a system of gas dynamics-type equations for the density and average wealth of the agents on large scales. We recover the inverse gamma distribution as an equilibrium in the particular case of quadratic cost functions which has been previously considered in the literature. 相似文献
12.
The distribution of wealth in human populations displays a Log–Gauss–Pareto composite statistical structure: its density is Log–Gauss in its central body, and follows power-law decay in its tails. This composite statistical structure is further observed in other complex systems, and on a logarithmic scale it displays a Gauss-Exponential structure: its density is Gauss in its central body, and follows exponential decay in its tails. In this paper we establish an equilibrium Langevin explanation for this statistical phenomenon, and show that: (i) the stationary distributions of Langevin dynamics with sigmoidal force functions display a Gauss-Exponential composite statistical structure; (ii) the stationary distributions of geometric Langevin dynamics with sigmoidal force functions display a Log–Gauss–Pareto composite statistical structure. This equilibrium Langevin explanation is universal — as it is invariant with respect to the specific details of the sigmoidal force functions applied, and as it is invariant with respect to the specific statistics of the underlying noise. 相似文献
13.
《Physica A》2006,361(1):309-318
We study the effect of altruism in two simple asset exchange models: the yard sale model (winner gets a random fraction of the poorer player's wealth) and the theft and fraud model (winner gets a random fraction of the loser's wealth). We also introduce in these models the concept of bargaining efficiency, which makes the poorer trader more aggressive in getting a favorable deal thus augmenting his winning probabilities. The altruistic behavior is controlled by varying the number of traders who behave altruistically and by the degree of altruism that they show. The resulting wealth distribution is characterized using the Gini index. We compare the resulting values of the Gini index at different levels of altruism in both models. It is found that altruistic behavior does lead to a more equitable wealth distribution but only for unreasonable high values of altruism that are difficult to expect in a real economic system. 相似文献
14.
S. Ispolatov P.L. Krapivsky S. Redner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):267-276
A model for the evolution of the wealth distribution in an economically interacting population is introduced, in which a specified
amount of assets are exchanged between two individuals when they interact. The resulting wealth distributions are determined
for a variety of exchange rules. For “random” exchange, either individual is equally likely to gain in a trade, while “greedy”
exchange, the richer individual gains. When the amount of asset traded is fixed, random exchange leads to a Gaussian wealth
distribution, while greedy exchange gives a Fermi-like scaled wealth distribution in the long-time limit. Multiplicative processes
are also investigated, where the amount of asset exchanged is a finite fraction of the wealth of one of the traders. For random
multiplicative exchange, a steady state occurs, while in greedy multiplicative exchange a continuously evolving power law
wealth distribution arises.
Received: 13 August 1997 / Revised: 31 December 1997 / Accepted: 26
January 1998 相似文献
15.
A. Dragulescu V.M. Yakovenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):723-729
In a closed economic system, money is conserved. Thus, by analogy with energy, the equilibrium probability distribution of
money must follow the exponential Boltzmann-Gibbs law characterized by an effective temperature equal to the average amount
of money per economic agent. We demonstrate how the Boltzmann-Gibbs distribution emerges in computer simulations of economic
models. Then we consider a thermal machine, in which the difference of temperatures allows one to extract a monetary profit.
We also discuss the role of debt, and models with broken time-reversal symmetry for which the Boltzmann-Gibbs law does not
hold. The instantaneous distribution of money among the agents of a system should not be confused with the distribution of
wealth. The latter also includes material wealth, which is not conserved, and thus may have a different (e.g. power-law) distribution.
Received 22 June 2000 相似文献
16.
《Physica A》2006,371(1):112-117
Different models to study the wealth distribution in an artificial society have considered a transactional dynamics as the driving force. Those models include a risk aversion factor, but also a finite probability of favoring the poorer agent in a transaction. Here, we study the case where the partners in the transaction have a previous knowledge of the winning probability and adjust their risk aversion taking this information into consideration. The results indicate that a relatively equalitarian society is obtained when the agents risk in direct proportion to their winning probabilities. However, it is the opposite case that delivers wealth distribution curves and Gini indices closer to empirical data. This indicates that, at least for this very simple model, either agents have no knowledge of their winning probabilities, either they exhibit an “irrational” behavior risking more than reasonable. 相似文献
17.
A. Chatterjee B. K. Chakrabarti 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(3):399-404
We study here numerically the behavior of an ideal gas like model of markets having
only one non-consumable commodity. We investigate the behavior of the
steady-state distributions of money, commodity and total wealth,
as the dynamics of trading or exchange of money and commodity proceeds,
with local (in time) fluctuations in the price of the commodity.
These distributions are studied in markets with agents having uniform and
random saving factors. The self-organizing features in money distribution
are similar to the cases without any commodity (or with consumable
commodities), while the commodity distribution shows an exponential decay.
The wealth distribution shows interesting behavior: gamma like
distribution for uniform saving propensity and has the same power-law tail,
as that of the money distribution, for
a market with agents having random saving propensity. 相似文献
18.
A. Chatterjee 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(4):593-598
We propose some kinetic models of wealth exchange and investigate their behavior on directed networks though numerical simulations.
We observe that network topology and directedness yields a variety of interesting features in these models. The nature of
asset distribution
in such directed networks show varied results, the degree of asset inequality increased with the degree of disorder in the
graphs. 相似文献
19.
Anindya S. Chakrabarti 《Physica A》2011,390(23-24):4370-4378
We propose a stochastic map model of economic dynamics. In the past decade, an array of observations in economics has been investigated in the econophysics literature, a major example being the universal features of inequality in terms of income and wealth. Another area of enquiry is the formation of opinion in a society. The model proposed attempts to produce positively skewed distributions and power law distributions as has been observed in the real data of income and wealth. Also, it shows a non-trivial phase transition in the opinion of a society (opinion formation). A number of physical models also generate similar results. In particular, kinetic exchange models have been successful especially in this regard. Therefore, we compare the results obtained from these two approaches and discuss a number of new features and drawbacks of this model. 相似文献
20.
《Physica A》2005,356(1):107-113
We study the effect of the social stratification on the wealth distribution on a system of interacting economic agents that are constrained to interact only within their own economic class. The economical mobility of the agents is related to its success in exchange transactions. Different wealth distributions are obtained as a function of the width of the economic class. We find a range of widths in which the society is divided in two classes separated by a deep gap that prevents further exchange between poor and rich agents. As a consequence, the middle wealth class is eliminated. The high values of the Gini indices obtained in these cases indicate a highly unequal society. On the other hand, lower and higher widths induce lower Gini indices and a fairer wealth distribution. 相似文献