6,504 research outputs found
Basic properties for sand automata
Presented at MFCS 2005 (Gdansk, POLAND). Long version with complete proofs published in Theoretical Computer Science, 2006, under the title "From Sandpiles to Sand Automata".International audienceWe prove several results about the relations between injectivity and surjectivity for sand automata. Moreover, we begin the exploration of the dynamical behavior of sand automata proving that the property of nilpotency is undecidable. We believe that the proof technique used for this last result might reveal useful for many other results in this context
Energy constrained sandpile models
We study two driven dynamical systems with conserved energy. The two automata
contain the basic dynamical rules of the Bak, Tang and Wiesenfeld sandpile
model. In addition a global constraint on the energy contained in the lattice
is imposed. In the limit of an infinitely slow driving of the system, the
conserved energy becomes the only parameter governing the dynamical
behavior of the system. Both models show scale free behavior at a critical
value of the fixed energy. The scaling with respect to the relevant
scaling field points out that the developing of critical correlations is in a
different universality class than self-organized critical sandpiles. Despite
this difference, the activity (avalanche) probability distributions appear to
coincide with the one of the standard self-organized critical sandpile.Comment: 4 pages including 3 figure
Short period attractors and non-ergodic behavior in the deterministic fixed energy sandpile model
We study the asymptotic behaviour of the Bak, Tang, Wiesenfeld sandpile
automata as a closed system with fixed energy.
We explore the full range of energies characterizing the active phase. The
model exhibits strong non-ergodic features by settling into limit-cycles whose
period depends on the energy and initial conditions. The asymptotic activity
(topplings density) shows, as a function of energy density , a
devil's staircase behaviour defining a symmetric energy interval-set over which
also the period lengths remain constant. The properties of -
phase diagram can be traced back to the basic symmetries underlying the model's
dynamics.Comment: EPL-style, 7 pages, 3 eps figures, revised versio
Large-Scale Synchrony in Weakly Interacting Automata
We study the behavior of two spatially distributed (sandpile) models which
are weakly linked with one another. Using a Monte-Carlo implementation of the
renormalization group and algebraic methods, we describe how large-scale
correlations emerge between the two systems, leading to synchronized behavior.Comment: 6 pages, 3 figures; to appear PR
Cluster Statistics of BTW automata
The cluster statistics of BTW automata in the SOC states are obtained by
extensive computer simulation. Various moments of the clusters are calculated
and few results are compared with earlier available numerical estimates and
exact results. Reasonably good agreement is observed. An extended statistical
analysis has been made.Comment: 8 pages Latex, To appear in Acta Physica Polonica B (2011
Minimizing finite automata is computationally hard
It is known that deterministic finite automata (DFAs) can be algorithmically minimized, i.e., a DFA M can be converted to an equivalent DFA M' which has a minimal number of states. The minimization can be done efficiently [6]. On the other hand, it is known that unambiguous finite automata (UFAs) and nondeterministic finite automata (NFAs) can be algorithmically minimized too, but their minimization problems turn out to be NP-complete and PSPACE-complete [8]. In this paper, the time complexity of the minimization problem for two restricted types of finite automata is investigated. These automata are nearly deterministic, since they only allow a small amount of non determinism to be used. On the one hand, NFAs with a fixed finite branching are studied, i.e., the number of nondeterministic moves within every accepting computation is bounded by a fixed finite number. On the other hand, finite automata are investigated which are essentially deterministic except that there is a fixed number of different initial states which can be chosen nondeterministically. The main result is that the minimization problems for these models are computationally hard, namely NP-complete. Hence, even the slightest extension of the deterministic model towards a nondeterministic one, e.g., allowing at most one nondeterministic move in every accepting computation or allowing two initial states instead of one, results in computationally intractable minimization problems
Cellular Automaton for Realistic Modelling of Landslides
A numerical model is developed for the simulation of debris flow in
landslides over a complex three dimensional topography. The model is based on a
lattice, in which debris can be transferred among nearest neighbors according
to established empirical relationships for granular flows. The model is then
validated by comparing a simulation with reported field data. Our model is in
fact a realistic elaboration of simpler ``sandpile automata'', which have in
recent years been studied as supposedly paradigmatic of ``self-organized
criticality''.
Statistics and scaling properties of the simulation are examined, and show
that the model has an intermittent behavior.Comment: Revised version (gramatical and writing style cleanup mainly).
Accepted for publication by Nonlinear Processes in Geophysics. 16 pages, 98Kb
uuencoded compressed dvi file (that's the way life is easiest). Big (6Mb)
postscript figures available upon request from [email protected] /
[email protected]
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