We provide an efficient algorithm deciding chaos for linear cellular automata (LCA) over (Z/mZ)n, a large and important class of cellular automata (CA) which may exhibit many of the complex features typical of general CA and are used in many applications. The efficiency of our algorithm is mainly due to fact that it avoids the computation of the prime factor decomposition of m which is a well-known difficult task. Instead of factoring m we make use of a new and efficient generalized technique for computing the greatest common divisor (gcd) of polynomials with coefficients not belonging to a field, which in itself is an interesting result. We wish also to emphasize that the gcd computations required by our algorithm always involve polynomials of degree at most n. We also illustrate the impact of our algorithm in real-world applications regarding the growing domain of cryptosystems, the latter being often based on LCA over (Z/mZ)n with n>1. As a matter of facts, since cryptosystems have to satisfy the so-called confusion and diffusion properties (which are ensured if the involved LCA is chaotic) our algorithm turns out to be an important tool for building chaotic LCA over (Z/mZ)n and, hence, for improving the existing methods based on them.

Abstract This work introduces the new class of pure reaction automata, as well as a new update manner, called maximal reactive manner, that can also be applied to standard reaction automata. Pure reaction automata differ from the standard model in that they don’t have permanence: the entities that are not consumed by the reactions happening at a certain state are not conserved in the result states. We prove that the set of languages accepted by the new class under the maximal reactive manner contains the set of languages accepted by standard reaction automata under the same manner or under the maximal parallel manner. We also prove that a strict subclass of pure reaction automata can compute any partial recursive function.

Let $\mathbb{K}$ be a finite commutative ring, and let $\mathbb{L}$ be a commutative $\mathbb{K}$-algebra. Let $A$ and $B$ be two $n \times n$-matrices over $\mathbb{L}$ that have the same characteristic polynomial. The main result of this paper states that the set $\left\{ A^0,A^1,A^2,\ldots\right\}$ is finite if and only if the set $\left\{ B^0,B^1,B^2,\ldots\right\}$ is finite. We apply this result to Cellular Automata (CA). Indeed, it gives a complete and easy-to-check characterization of sensitivity to initial conditions and equicontinuity for linear CA over the alphabet $\mathbb{K}^n$ for $\mathbb{K} = \mathbb{Z}/m\mathbb{Z}$ i.e., CA in which the local rule is defined by $n\times n$-matrices with elements in $\mathbb{Z}/m\mathbb{Z}$. To prove our main result, we derive an integrality criterion for matrices that is likely of independent interest. Namely, let $\mathbb{K}$ be any commutative ring (not necessarily finite), and let $\mathbb{L}$ be a commutative $\mathbb{K}$-algebra. Consider any $n \times n$-matrix $A$ over $\mathbb{L}$. Then, $A \in \mathbb{L}^{n \times n}$ is integral over $\mathbb{K}$ (that is, there exists a monic polynomial $f \in \mathbb{K}\left[t\right]$ satisfying $f\left(A\right) = 0$) if and only if all coefficients of the characteristic polynomial of $A$ are integral over $\mathbb{K}$. The proof of this fact relies on a strategic use of exterior powers (a trick pioneered by Gert Almkvist). Furthermore, we extend the decidability result concerning sensitivity and equicontinuity to the wider class of additive CA over a finite abelian group. For such CA, we also prove the decidability of injectivity, surjectivity, topological transitivity and all the properties (as, for instance, ergodicity) that are equivalent to the latter.

Since their introduction in the 80s, sandpile models have raised interest for their simple definition and their surprising dynamical properties. In this survey we focus on the computational complexity of the prediction problem, namely, the complexity of knowing, given a finite configuration c and a cell x in c, if cell x will eventually become unstable. This is an attempt to formalize the intuitive notion of “behavioral complexity” that one easily observes in simulations. However, despite many efforts and nice results, the original question remains open: how hard is it to predict the two-dimensional sandpile model of Bak, Tang and Wiesenfeld?

We study the dynamical behavior of D-dimensional (D >= 1) additive cellular automata where the alphabet is any finite abelian group. This class of discrete time dynamical systems is a generalization of the systems extensively studied by many authors among which one may list [Masanobu Ito et al., 1983; Giovanni Manzini and Luciano Margara, 1999; Giovanni Manzini and Luciano Margara, 1999; Jarkko Kari, 2000; Gianpiero Cattaneo et al., 2000; Gianpiero Cattaneo et al., 2004]. Our main contribution is the proof that topologically transitive additive cellular automata are ergodic. This result represents a solid bridge between the world of measure theory and that of topology theory and greatly extends previous results obtained in [Gianpiero Cattaneo et al., 2000; Giovanni Manzini and Luciano Margara, 1999] for linear CA over Z_m i.e. additive CA in which the alphabet is the cyclic group Z_m and the local rules are linear combinations with coefficients in Z_m. In our scenario, the alphabet is any finite abelian group and the global rule is any additive map. This class of CA strictly contains the class of linear CA over Z_m^n, i.e. , with the local rule defined by n x n matrices with elements in Z_m which, in turn, strictly contains the class of linear CA over Z_m. In order to further emphasize that finite abelian groups are more expressive than Z_m we prove that, contrary to what happens in Z_m, there exist additive CA over suitable finite abelian groups which are roots (with arbitrarily large indices) of the shift map. As a consequence of our results, we have that, for additive CA, ergodic mixing, weak ergodic mixing, ergodicity, topological mixing, weak topological mixing, topological total transitivity and topological transitivity are all equivalent properties. As a corollary, we have that invertible transitive additive CA are isomorphic to Bernoulli shifts. Finally, we provide a first characterization of strong transitivity for additive CA which we suspect it might be true also for the general case.

This issue contains seven papers presented during the "Third Symposium on Cellular Automata-Journes Automates Cellulaires" (JAC 2012), held in La Marana, Corsica (France) in the period September 19th-21th

We investigate the relationships between dynamical complexity and the set of periodic configurations of surjective Cellular Automata. We focus on the set of strictly temporally periodic configurations, i.e., the set of those configurations which are

This work studies some aspects of the computational power of fully asynchronous cellular automata (ACA). We deal with some notions of simulation between ACA and Turing Machines. In particular, we characterize the updating sequences specifying which are “universal”, i.e., allowing a (specific family of) ACA to simulate any Turing machine on any input. We also consider the computational cost of such simulations. Finally, we deal with ACA equipped with peculiar updating sequences, namely those generated by random walks.

This paper investigates the avalanche problem AP for the Kadanoff sandpile model (KSPM). We prove that (a slight restriction of) AP is in NC1 in dimension one, leaving the general case open. Moreover, we prove that AP is P-complete in dimension two.

A cellular automaton (CA) is a parallel synchronous computing model, which consists in a juxtaposition of finite automata (cells) whose state evolves according to that of their neighbors. Its trace is the set of infinite words representing the sequence of states taken by some particular cell. In this paper we study the ultimate trace of CA and partial CA (a CA restricted to a particular subshift). The ultimate trace is the trace observed after a long time run of the CA. We give sufficient conditions for a set of infinite words to be the trace of some CA and prove the undecidability of all properties over traces that are stable by ultimate coincidence.