arXiv subjects
Publications and source records attributed to Dietrich Stauffer.
Capital usually leads to income, and income is more accurately and easily measured. Thus we summarize income distributions in USA, Germany, etc.
Various aspects of recent sociophysics research are shortly reviewed: Schelling model as an example for lack of interdisciplinary cooperation, opinion dynamics, combat, and citation statistics as an example for strong interdisciplinarity.
Revolution dynamics is studied through a minimal Ising model with three main influences (fields): personal conservatism (power-law distributed), inter-personal and group pressure, and a global field incorporating peer-to-peer and mass communications, which is generated bottom-up from the revolutionary faction. A rich phase diagram appears separating possible terminal stages of the revolution, characterizing failure phases by the features of the individuals who had joined the revolution. An exhaustive solution of the model is produced, allowing predictions to be made on the revolution's outcome.
The image of physics is connected with simple "mechanical" deterministic events: that an apple always falls down, that force equals mass times acceleleration. Indeed, applications of such concept to social or historical problems go back two centuries (population growth and stabilisation, by Malthus and by Verhulst) and use "differential equations", as recently revierwed by Vitanov and Ausloos [2011]. However, since even today's computers cannot follow the motion of all air molecules within one cubic centimeter, the probabilistic approach has become fashionable since Ludwig Boltzmann invented Statistical Physics in the 19th century. Computer simulations in Statistical Physics deal with single particles, a method called agent-based modelling in fields which adopted it later. Particularly simple are binary models where each particle has only two choices, called spin up and spin down by physicists, bit zero and bit one by computer scientists, and voters for the Republicans or for the Democrats in American politics (where one human is simulated as one particle). Neighbouring particles may influence each other, and the Ising model of 1925 is the best-studied example of such models. This text will explain to the reader how to program the Ising model on a square lattice (in Fortran language); starting from there the readers can build their own computer programs. Some applications of Statistical Physics outside the natural sciences will be listed.
If in the sexual Penna ageing model conditions are applied leading to complementary bit-strings, then marriages between brothers and sisters, or between close cousins, may lead to more offspring than for unrelated couples.
We discuss two different ways of chromosomes' and genomes' evolution. Purifying selection dominates in large panmictic populations, where Mendelian law of independent gene assortment is valid. If the populations are small, recombination processes are not effective enough to ensure an independent assortment of linked genes and larger clusters of genes could be inherited as the genetic units. There are whole clusters of genes which tend to complement in such conditions instead of single pairs of alleles like in the case of purifying selection. Computer simulations have shown that switching in-between complementation and purification strategies has a character of a phase transition. This is also responsible for specific distribution of recombination events observed along eukaryotic chromosomes - higher recombination rate is observed in subtelomeric regions than in central parts of chromosomes - for sympatric speciation and probably for non-monotonous relation between reproduction potential and genetic distance between parents.
Using Monte Carlo simulations, we study the evolution of contigent cooperation and ethnocentrism in the one-move game. Interactions and reproduction among computational agents are simulated on {\it undirected} and {\it directed} Barabási-Albert (BA) networks. We first replicate the Hammond-Axelrod model of in-group favoritism on a square lattice and then generalize this model on {\it undirected} and {\it directed} BA networks for both asexual and sexual reproduction cases. Our simulations demonstrate that irrespective of the mode of reproduction, ethnocentric strategy becomes common even though cooperation is individually costly and mechanisms such as reciprocity or conformity are absent. Moreover, our results indicate that the spread of favoritism toward similar others highly depends on the network topology and the associated heterogeneity of the studied population.
This paper presents Monte Carlo simulations of language populations and the development of language families, showing how a simple model can lead to distributions similar to the ones observed empirically. The model used combines features of two models used in earlier work by phycisists for the simulation of competition among languages: the "Viviane" model for the migration of people and propagation of languages and the "Schulze" model, which uses bitstrings as a way of characterising structural features of languages.
Thousands of different forms (words) are associated with thousands of different meanings (concepts) in a language computer model. Reasonable agreement with reality is found for the number of languages in a family and the Hamming distances between languages.
In Hopfield neural networks with up to 10^8 nodes we store two patterns through Hebb couplings. Then we start with a third random pattern which is supposed to evolve into one of the two stored patterns, simulating the cognitive process of associative memory leading to one of two possible opinions. With probability p each neuron independently, instead of following the Hopfield rule, takes over the corresponding value of another network, thus simulating how different people can convince each other. A consensus is achieved for high p.
Monte Carlo simulations mix the opinion dynamics of Deffuant et al with the cultural transfer model of Axelrod, using ten discrete possible opinions on ten different themes. As Jacobmeier's simulations of the pure Deffuant case, people preferably agree on nearly all or nearly no theme.
We investigate the impact of an exogenous environment on the emergence of social herding of economic sentiment. An interactions-driven dynamics of economic sentiment is modeled by an Ising model on a large (two-dimensional) square lattice. The individual states are called optimism and pessimism. The exogenous environment is modeled as a sequence of random events, which might have a positive or negative influence on economic sentiment. These exogenous events can be frequent or rare, have a lasting impact or a non-lasting impact. Impact of events is inhomogeneous over the lattice, as individuals might fail to perceive particular events. We introduce two notions of social herding: permanent herding refers to the situation where an ordered state (i.e. a state with an overwhelming majority of optimists or pessimists) persists over an infinite time horizon, while temporary herding refers to the situation where ordered states appear, persist for some time and decay. The parameter of the inter-agent interaction strength is such as to engender permanent herding without the influence of the environment. To investigate the impact of an environment we determine whether an initially ordered state decays. We consider two cases: in the first case positive and negative events have both the same empirical frequencies and strengths, while in the second case events have the same empirical frequencies but different strengths. (In the first case the environment is ``neutral''in the long term), In the neutral case we find temporary herding if events are sufficiently ``strong'' and/or perceived by a sufficiently large proportion of agents, and our results suggest that permanent herding occurs for small values of the parameters. In the ``non-neutral'' case we find only temporary herding.
The possible coexistence of one host, one aggressive parasite and one non-lethal parasite is simulated using the Penna model of biological ageing. If the aggressive parasites survive the difficult initial times where they have to adjust genetically to the proper host age, all three species may survive, though the host number may be diminished by increasing parasite aggressivity.
We develop a model of tax evasion based on the Ising model. We augment the model using an appropriate enforcement mechanism that may allow policy makers to curb tax evasion. With a certain probability tax evaders are subject to an audit. If they get caught they behave honestly for a certain number of periods. Simulating the model for a range of parameter combinations, we show that tax evasion may be controlled effectively by using punishment as an enforcement mechanism.
Urban segregation of different communities, like blacks and whites in the USA, has been simulated by Ising-like models since Schelling 1971. This research was accompanied by a scientific segregation, with sociologists and physicists ignoring each other until 2000. We review recent progress and also present some new two-temperature multi-cultural simulations.
When a region is conquered by people speaking another language, we assume within the Schulze model that at each iteration each person with probability s shifts to the conquering language. The time needed for the conquering language to become dominating is about 2/s for directed Barabasi-Albert networks, but diverges on the square lattice for decreasing s at some critical value sc
The Schelling model of 1971 is a complicated version of a square-lattice Ising model at zero temperature, to explain urban segregation, based on the neighbour preferences of the residents, without external reasons. Various versions between Ising and Schelling models give about the same results. Inhomogeneous "temperatures" T do not change the results much, while a feedback between segregation and T leads to a self-organisation of an average T.
An earlier study (Nettle 1999b) concluded, based on computer simulations and some inferences from empirical data, that languages will change the more slowly the larger the population gets. We replicate this study using a more complete language model for simulations (the Schulze model combined with a Barabasi-Albert net- work) and a richer empirical dataset (the World Atlas of Language Structures edited by Haspelmath et al. 2005). Our simulations show either a weak or stronger dependence of language change on population sizes depending on the parameter settings, and empirical data, like some of the simulations, show a weak dependence.