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Dietrich Stauffer

Publications and source records attributed to Dietrich Stauffer.

At least 91 records · Page 5Linked to original sources
arXiv2002

Adjustment and social choice

We discuss the influence of information contagion on the dynamics of choices in social networks of heterogeneous buyers. Starting from an inhomogeneous cellular automata model of buyers dynamics, we show that when agents try to adjust their reservation price, the tatonement process does not converge to equilibrium at some intermediate market share and that large amplitude fluctuations are actually observed. When the tatonnement dynamics is slow with respect to the contagion dynamics, large periodic oscillations reminiscent of business cycles appear.

cond-mat.dis-nn↗
arXiv2002

Phase transition in hierarchy model of Bonabeau et al

The model of Bonabeau explains the emergence of social hierarchies from the memory of fights in an initially egalitarian society. Introducing a feedback from the social inequality into the probability to win a fight, we find a sharp transition between egalitarian society at low population density and hierarchical society at high population density.

cond-mat.stat-mech↗
arXiv2002

Simulation consensus model of never changed opinions in Sznajd consensus model using multi-spin coding

The density of never changed opinions during the Sznajd consensus-finding process decays with time t as 1/t^{theta}. We find theta ~= 3/8 for a chain, compatible with the exact Ising result of Derrida et al. In higher dimensions, however, the exponent differs from the Ising theta. With simultaneous updating of sublattices instead of the usual random sequential updating, the number of persistent opinions decays roughly exponentially. Some of the simulations used multi-spin coding.

cond-mat.stat-mech↗
arXiv2002

Frustration from Simultaneous Updating in Sznajd Consensus Model

In the Sznajd model of 2000, a pair of neighbouring agents on a square lattice convinces its six neighbours of the pair opinion iff the two agents of the pair share the same opinion. Now we replace the usual random sequential updating rule by simultaneous updating and find that this change makes a complete consenus much more difficult. The larger the lattice is, the higher must be the initial majority for one of the two competing opinions to become the consensus.

cond-mat.stat-mech↗
arXiv2002

Sole-Manrubia model of biological evolution: some new insights

The Sole-Manrubia model of ``macro''-evolution describes the origination, evolution and extinction of species on geological time scales. We report some properties of this model which provide deep insight into this simple model which captures several realistic features.

cond-mat.stat-mech↗
arXiv2002

Simple tools for extrapolations of human mortality in rich countries

Suitable assumptions for the Gompertz mortality law take into account the break in the time development observed recently by Wilmoth et al. They show how a drastic reduction in the birth rate and improved living conditions lead to a drastic increase in the fraction of old people in the population, and how immigration of half a percent of the population per year can mostly stop this increase.

cond-mat.stat-mech↗
arXiv2002

Percolation and Galam Theory of Minority Opinion Spreading

The way in which an opinion rejecting reform can finally become the consensus of everyone was studied by Galam (2002) in a probabilistic model. We now replace his clusters by those formed via random percolation by letting particles diffuse on a lattice. Galam's rejection of reform is reproduced below the percolation threshold, whereas at and above the threshold, also approval of a reform becomes possible.

cond-mat.stat-mech↗
arXiv2002

Better be third then second in a search for a majority opinion

Monte Carlo simulations of a Sznajd model show that if a near-consensus is formed out of four initially equally widespread opinions, the one which at intermediate times is second in the number of adherents usually loses out against the third-placed opinion.

cond-mat.stat-mech↗
arXiv2002

Monte Carlo simulations of Sznajd models

The Sznajd model in less than a year has found several followers. An isolated person does not convince others; a group of people sharing the same opinions influences the neighbours much more easily. Thus on a square lattice, with variables +1 (Democrats) and --1 (Republicans) on every lattice site, a pair (or plaquette) of neighbours convinces its six (eight) nearest neighbours of its own opinion if and only if all members of the pair (plaquette) share the same opinion. The generalization to many possible states is used to explain the distribution of votes among candidates in Brazilian local elections. Review; published in Journal of Artificial Societies and Social Simulation 5, No. 1, paper 4 (2002), available only electronically

cond-mat.stat-mech↗
arXiv2002

Scaling in a simple model for surface growth in a random medium

Surface growth in random media is usually governed by both the surface tension and the random local forces. Simulations on lattices mimic the former by imposing a maximum gradient $m$ on the surface heights, and the latter by site-dependent random growth probabilities. Here we consider the limit $m \to \infty$, where the surface grows at the site with minimal random number, {\it independent} of its neighbors. The resulting height distribution obeys a simple scaling law, which is destroyed when local surface tension is included. Our model is equivalent to Yee's simplification of the Bak-Sneppen model for the extinction of biological species, where the height represents the number of times a biological species is exchanged.

cond-mat.stat-mech↗
arXiv2001

Ferromagnetic Phase Transition in Barabasi-Albert Networks

Ising spins put onto a Barabasi-Albert scale-free network show an effective phase transition from ferromagnetism to paramagnetism upon heating, with an effective critical temperature increasing as the logarithm of the system size. Starting with all spins up and upon equilibration pinning the few most-connected spins down nucleates the phase with most of the spins down.

cond-mat.stat-mech↗
arXiv2001

Nucleation of Market Shocks in Sornette-Ide model

The Sornette-Ide differential equation of herding and rational trader behaviour together with very small random noise is shown to lead to crashes or bubbles where the price change goes to infinity after an unpredictable time. About 100 time steps before this singularity, a few predictable roughly log-periodic oscillations are seen.

cond-mat.stat-mech↗
arXiv2001

Social Effects in Simple Computer Model of Ageing

A simple evolutionary model for biological ageing is modified such that it requires a minimum population for survival, like in human society. This social effect leads to a transition between extinction and survival of the species.

cond-mat.stat-mech↗
arXiv2001

Dynamics of a simple evolutionary process

We study the simple evolutionary process in which we repeatedly find the least fit agent in a population of agents and give it a new fitness which is chosen independently at random from a specified distribution. We show that many of the average properties of this process can be calculated exactly using analytic methods. In particular we find the distribution of fitnesses at arbitrary time, and the distribution of the lengths of runs of hits on the same agent, the latter being found to follow a power law with exponent -1, similar to the distribution of times between evolutionary events in the Bak-Sneppen model and models based on the so-called record dynamics. We confirm our analytic results with extensive numerical simulations.

nlin.AO↗