On the impact of treewidth in the computational complexity of freezing dynamics

An automata network is a network of entities, each holding a state from a finite set and evolving according to a local update rule which depends only on its neighbors in the network's graph. It is freezing if there is an order on states such that the state evolution of any node is non-decreasing in any orbit. They are commonly used to model epidemic propagation, diffusion phenomena like bootstrap percolation or cristal growth. In this paper we establish how treewidth and maximum degree of the underlying graph are key parameters which influence the overall computational complexity of finite freezing automata networks. First, we define a general model checking formalism that captures many classical decision problems: prediction, nilpotency, predecessor, asynchronous reachability. Then, on one hand, we present an efficient parallel algorithm that solves the general model checking problem in NC for any graph with bounded degree and bounded treewidth. On the other hand, we show that these problems are hard in their respective classes when restricted to families of graph with polynomially growing treewidth. For prediction, predecessor and asynchronous reachability, we establish the hardness result with a fixed set-defiend update rule that is universally hard on any input graph of such families

Collision-based Computing

International audienceCollision-based computing is an implementation of logical circuits, mathematical machines or other computing and information processing devices in homogeneous uniform unstructured media with traveling mobile localizations. A quanta of information is represented by a compact propagating pattern (glider in cellular automata, soliton in optical system, wave-fragment in excitable chemical system). Logical truth corresponds to presence of the localization, logical false to absence of the localization; logical values can be also represented by a particular state of the localization. When two more or more traveling localizations collide they change their velocity vectors and/or states. Post-collision trajectories and/or states of the localizations represent results of a logical operations implemented by the collision. One of the principle advantages of the a collision-based computing medium —hidden in 1D systems but obvious in 2D and 3D media— is that the medium is architecture-less: nothing is hardwired, there are no stationary wires or gates, a trajectory of a propagating information quanta can be see as a momentary wire. We introduce basics of collision-based computing, and overview the collision-based computing schemes in 1D and 2D cellular automata and continuous excitable media. Also we provide an overview of collision-based schemes where particles/collisions are dimensionless

On the development of slime mould morphological, intracellular and heterotic computing devices

The use of live biological substrates in the fabrication of unconventional computing (UC) devices is steadily transcending the barriers between science fiction and reality, but efforts in this direction are impeded by ethical considerations, the field’s restrictively broad multidisciplinarity and our incomplete knowledge of fundamental biological processes. As such, very few functional prototypes of biological UC devices have been produced to date. This thesis aims to demonstrate the computational polymorphism and polyfunctionality of a chosen biological substrate — slime mould Physarum polycephalum, an arguably ‘simple’ single-celled organism — and how these properties can be harnessed to create laboratory experimental prototypes of functionally-useful biological UC prototypes. Computing devices utilising live slime mould as their key constituent element can be developed into a) heterotic, or hybrid devices, which are based on electrical recognition of slime mould behaviour via machine-organism interfaces, b) whole-organism-scale morphological processors, whose output is the organism’s morphological adaptation to environmental stimuli (input) and c) intracellular processors wherein data are represented by energetic signalling events mediated by the cytoskeleton, a nano-scale protein network. It is demonstrated that each category of device is capable of implementing logic and furthermore, specific applications for each class may be engineered, such as image processing applications for morphological processors and biosensors in the case of heterotic devices. The results presented are supported by a range of computer modelling experiments using cellular automata and multi-agent modelling. We conclude that P. polycephalum is a polymorphic UC substrate insofar as it can process multimodal sensory input and polyfunctional in its demonstrable ability to undertake a variety of computing problems. Furthermore, our results are highly applicable to the study of other living UC substrates and will inform future work in UC, biosensing, and biomedicine

Task Allocation in Foraging Robot Swarms:The Role of Information Sharing

Autonomous task allocation is a desirable feature of robot swarms that collect and deliver items in scenarios where congestion, caused by accumulated items or robots, can temporarily interfere with swarm behaviour. In such settings, self-regulation of workforce can prevent unnecessary energy consumption. We explore two types of self-regulation: non-social, where robots become idle upon experiencing congestion, and social, where robots broadcast information about congestion to their team mates in order to socially inhibit foraging. We show that while both types of self-regulation can lead to improved energy efficiency and increase the amount of resource collected, the speed with which information about congestion flows through a swarm affects the scalability of these algorithms

TOWARDS A MODEL FOR ARTIFICIAL AESTHETICS - Contributions to the Study of Creative Practices in Procedural and Computational Systems

Este trabalho propõe o desenvolvimento de um modelo analítico e da terminologia a ele associada para o estudo de artefactos estéticos computacionais. Reconhecendo a presença e uso crescentes dos media computacionais, começamos por estudar como através da remediação eles transformam quantitativamente os media precedentes, e como as suas propriedades procedimentais e computacionais os afectam qualitativamente. Para perceber o potencial criativo e a especificidade dos media computacionais, desenvolvemos um modelo para a sua prática, crítica e análise. Como ponto de partida recorremos à tipologia desenvolvida por Espen Aarseth para o estudo de cibertextos, avaliando a sua adequação à análise de peças ergódicas visuais e audiovisuais, adaptando-a e expandindo-a com novas variáveis e respectivos valores. O modelo é testado através da análise de um conjunto de peças que representam diversas abordagens à criação procedimental e diversas áreas de actividade criativa contemporânea. É posteriormente desenvolvida uma análise de controlo para avaliar a usabilidade e utilidade do modelo, a sua capacidade para a elaboração de classificações objectivas e o rigor da análise. Demonstramos a adequação parcial do modelo de Aarseth para o estudo de artefactos não textuais e expandimo-lo para melhor descrever as peças estudadas. Concluímos que o modelo apresentado produz boas descrições das peças, agrupando-as logicamente, reflectindo afinidades estilísticas e procedimentais entre sistemas que, se estudados com base nas suas propriedades sensoriais ou nas suas estruturas de superfície provavelmente não revelariam muitas semelhanças. As afinidades reveladas pelo modelo são estruturais e procedimentais, e atestam a importância das características computacionais para a apreciação estética das obras. Verificamos a nossa conjectura inicial sobre a importância da procedimentalidade não só nas fases de desenvolvimento e implementação das obras mas também como base conceptual e estética na criação e apreciação artísticas, como um prazer estético