arXiv subjects

Alonso Castillo-Ramirez

Publications and source records attributed to Alonso Castillo-Ramirez.

28 records · Page 2Linked to original sources

arXiv2019

Elementary, Finite and Linear vN-Regular Cellular Automata

Let $G$ be a group and $A$ a set. A cellular automaton (CA) $τ$ over $A^G$ is von Neumann regular (vN-regular) if there exists a CA $σ$ over $A^G$ such that $τστ= τ$, and in such case, $σ$ is called a generalised inverse of $τ$. In this paper, we investigate vN-regularity of various kinds of CA. First, we establish that, over any nontrivial configuration space, there always exist CA that are not vN-regular. Then, we obtain a partial classification of elementary vN-regular CA over $\{ 0,1\}^{\mathbb{Z}}$; in particular, we show that rules like 128 and 254 are vN-regular (and actually generalised inverses of each other), while others, like the well-known rules $90$ and $110$, are not vN-regular. Next, when $A$ and $G$ are both finite, we obtain a full characterisation of vN-regular CA over $A^G$. Finally, we study vN-regular linear CA when $A= V$ is a vector space over a field $\mathbb{F}$; we show that every vN-regular linear CA is invertible when $V= \mathbb{F}$ and $G$ is torsion-free elementary amenable (e.g. when $G=\mathbb{Z}^d, \ d \in \mathbb{N}$), and that every linear CA is vN-regular when $V$ is finite-dimensional and $G$ is locally finite with $Char(\mathbb{F}) \nmid o(g)$ for all $g \in G$.

math.GR↗

arXiv2018

Code algebras which are axial algebras and their $\mathbb{Z}_2$-gradings

A code algebra $A_C$ is a non-associative commutative algebra defined via a binary linear code $C$. We study certain idempotents in code algebras, which we call small idempotents, that are determined by a single non-zero codeword. For a general code $C$, we show that small idempotents are primitive and semisimple and we calculate their fusion law. If $C$ is a projective code generated by a conjugacy class of codewords, we show that $A_C$ is generated by small idempotents and so is, in fact, an axial algebra. Furthermore, we classify when the fusion law is $\mathbb{Z}_2$-graded. In doing so, we exhibit an infinite family of $\mathbb{Z}_2 \times \mathbb{Z}_2$-graded axial algebras - these are the first known examples of axial algebras with a non-trivial grading other than a $\mathbb{Z}_2$-grading.

math.RA↗

arXiv2018

Code algebras, axial algebras and VOAs

Inspired by code vertex operator algebras (VOAs) and their representation theory, we define code algebras, a new class of commutative non-associative algebras constructed from binary linear codes. Let $C$ be a binary linear code of length $n$. A basis for the code algebra $A_C$ consists of $n$ idempotents and a vector for each non-constant codeword of $C$. We show that code algebras are almost always simple and, under mild conditions on their structure constants, admit an associating bilinear form. We determine the Peirce decomposition and the fusion law for the idempotents in the basis, and we give a construction to find additional idempotents, called the $s$-map, which comes from the code structure. For a general code algebra, we classify the eigenvalues and eigenvectors of the smallest examples of the $s$-map construction, and hence show that certain code algebras are axial algebras. We give some examples, including that for a Hamming code $H_8$ where the code algebra $A_{H_8}$ is an axial algebra and embeds in the code VOA $V_{H_8}$.

math.RA↗

arXiv2018

Complete Simulation of Automata Networks

Consider a finite set $A$ and an integer $n \geq 1$. This paper studies the concept of complete simulation in the context of semigroups of transformations of $A^n$, also known as finite state-homogeneous automata networks. For $m \geq n$, a transformation of $A^m$ is \emph{$n$-complete of size $m$} if it may simulate every transformation of $A^n$ by updating one coordinate (or register) at a time. Using tools from memoryless computation, it is established that there is no $n$-complete transformation of size $n$, but there is such a transformation of size $n+1$. By studying the the time of simulation of various $n$-complete transformations, it is conjectured that the maximal time of simulation of any $n$-complete transformation is at least $2n$. A transformation of $A^m$ is \emph{sequentially $n$-complete of size $m$} if it may sequentially simulate every finite sequence of transformations of $A^n$; in this case, minimal examples and bounds for the size and time of simulation are determined. It is also shown that there is no $n$-complete transformation that updates all the registers in parallel, but that there exists a sequentally $n$-complete transformation that updates all but one register in parallel. This illustrates the strengths and weaknesses of parallel models of computation, such as cellular automata.

cs.FL↗

arXiv2018

Associative subalgebras of low-dimensional Majorana algebras

A Majorana algebra is a commutative nonassociative real algebra generated by a finite set of idempotents, called Majorana axes, that satisfy some of the properties of the $2A$-axes of the Monster Griess algebra. The term was introduced by A. A. Ivanov in 2009 inspired by the work of S. Sakuma and M. Miyamoto. In the present paper, we revisit Mayer and Neutsch's theorem on associative subalgebras of the Griess algebra in the context of Majorana theory. We apply this result to determine all the maximal associative subalgebras of some low-dimensional Majorana algebras; namely, the Majorana algebras generated by two Majorana axes and the Majorana representations of the symmetric group of degree $4$ involving $3C$-algebras.

math.RA↗

arXiv2017

Von Neumann Regular Cellular Automata

For any group $G$ and any set $A$, a cellular automaton (CA) is a transformation of the configuration space $A^G$ defined via a finite memory set and a local function. Let $\text{CA}(G;A)$ be the monoid of all CA over $A^G$. In this paper, we investigate a generalisation of the inverse of a CA from the semigroup-theoretic perspective. An element $τ\in \text{CA}(G;A)$ is von Neumann regular (or simply regular) if there exists $σ\in \text{CA}(G;A)$ such that $τ\circ σ\circ τ= τ$ and $σ\circ τ\circ σ= σ$, where $\circ$ is the composition of functions. Such an element $σ$ is called a generalised inverse of $τ$. The monoid $\text{CA}(G;A)$ itself is regular if all its elements are regular. We establish that $\text{CA}(G;A)$ is regular if and only if $\vert G \vert = 1$ or $\vert A \vert = 1$, and we characterise all regular elements in $\text{CA}(G;A)$ when $G$ and $A$ are both finite. Furthermore, we study regular linear CA when $A= V$ is a vector space over a field $\mathbb{F}$; in particular, we show that every regular linear CA is invertible when $G$ is torsion-free elementary amenable (e.g. when $G=\mathbb{Z}^d, \ d \in \mathbb{N}$) and $V=\mathbb{F}$, and that every linear CA is regular when $V$ is finite-dimensional and $G$ is locally finite with $\text{Char}(\mathbb{F}) \nmid o(g)$ for all $g \in G$.

math.GR↗

arXiv2017

Cellular Automata and Finite Groups

For a finite group $G$ and a finite set $A$, we study various algebraic aspects of cellular automata over the configuration space $A^G$. In this situation, the set $\text{CA}(G;A)$ of all cellular automata over $A^G$ is a finite monoid whose basic algebraic properties had remained unknown. First, we investigate the structure of the group of units $\text{ICA}(G;A)$ of $\text{CA}(G;A)$. We obtain a decomposition of $\text{ICA}(G;A)$ into a direct product of wreath products of groups that depends on the numbers $α_{[H]}$ of periodic configurations for conjugacy classes $[H]$ of subgroups of $G$. We show how the numbers $α_{[H]}$ may be computed using the Möbius function of the subgroup lattice of $G$, and we use this to improve the lower bound recently found by Gao, Jackson and Seward on the number of aperiodic configurations of $A^G$. Furthermore, we study generating sets of $\text{CA}(G;A)$; in particular, we prove that $\text{CA}(G;A)$ cannot be generated by cellular automata with small memory set, and, when all subgroups of $G$ are normal, we determine the relative rank of $\text{ICA}(G;A)$ on $\text{CA}(G;A)$, i.e. the minimal size of a set $V \subseteq \text{CA}(G;A)$ such that $\text{CA}(G;A) = \langle \text{ICA}(G;A) \cup V \rangle$.

math.GR↗

arXiv2016

On Finite Monoids of Cellular Automata

For any group $G$ and set $A$, a cellular automaton over $G$ and $A$ is a transformation $τ: A^G \to A^G$ defined via a finite neighborhood $S \subseteq G$ (called a memory set of $τ$) and a local function $μ: A^S \to A$. In this paper, we assume that $G$ and $A$ are both finite and study various algebraic properties of the finite monoid $\text{CA}(G,A)$ consisting of all cellular automata over $G$ and $A$. Let $\text{ICA}(G;A)$ be the group of invertible cellular automata over $G$ and $A$. In the first part, using information on the conjugacy classes of subgroups of $G$, we give a detailed description of the structure of $\text{ICA}(G;A)$ in terms of direct and wreath products. In the second part, we study generating sets of $\text{CA}(G;A)$. In particular, we prove that $\text{CA}(G,A)$ cannot be generated by cellular automata with small memory set, and, when $G$ is finite abelian, we determine the minimal size of a set $V \subseteq \text{CA}(G;A)$ such that $\text{CA}(G;A) = \langle \text{ICA}(G;A) \cup V \rangle$.

math.GR↗

arXiv2016

Ranks of finite semigroups of one-dimensional cellular automata

Since first introduced by John von Neumann, the notion of cellular automaton has grown into a key concept in computer science, physics and theoretical biology. In its classical setting, a cellular automaton is a transformation of the set of all configurations of a regular grid such that the image of any particular cell of the grid is determined by a fixed local function that only depends on a fixed finite neighbourhood. In recent years, with the introduction of a generalised definition in terms of transformations of the form $τ: A^G \to A^G$ (where $G$ is any group and $A$ is any set), the theory of cellular automata has been greatly enriched by its connections with group theory and topology. In this paper, we begin the finite semigroup theoretic study of cellular automata by investigating the rank (i.e. the cardinality of a smallest generating set) of the semigroup $\text{CA}(\mathbb{Z}_n; A)$ consisting of all cellular automata over the cyclic group $\mathbb{Z}_n$ and a finite set $A$. In particular, we determine this rank when $n$ is equal to $p$, $2^k$ or $2^kp$, for any odd prime $p$ and $k \geq 1$, and we give upper and lower bounds for the general case.

math.GR↗

arXiv2015

Some special features of Cayley algebras, and $G_2$, in low characteristics

Some features of Cayley algebras (or algebras of octonions) and their Lie algebras of derivations over fields of low characteristic are presented. More specifically, over fields of characteristic $7$, explicit embeddings of any twisted form of the Witt algebra into the simple split Lie algebra of type $G_2$ are given. Over fields of characteristic $3$, even though the Lie algebra of derivations of a Cayley algebra is not simple, it is shown that still two Cayley algebras are isomorphic if and only if their Lie algebras of derivations are isomorphic. Finally, over fields of characteristic $2$, it is shown that the Lie algebra of derivations of any Cayley algebra is always isomorphic to the projective special linear Lie algebra of degree four. The twisted forms of this latter algebra are described too.

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