arXiv subjects

Roberto D'Autilia

Publications and source records attributed to Roberto D'Autilia.

8 recordsLinked to original sources

arXiv2022

Shaken dynamics: an easy way to parallel Markov Chain Monte Carlo

We define a class of Markovian parallel dynamics for spin systems on arbitrary graphs with nearest neighbor interaction described by a Hamiltonian function $H(σ)$. These dynamics turn out to be reversible and their stationary measure is explicitly determined. Convergence to equilibrium and relation of the stationary measure to the usual Gibbs measure are discussed when the dynamics is defined on $\mathbb{Z}^2$. Further it is shown how these dynamics can be used to define natively parallel algorithms to face problems in the context of combinatorial optimization.

math-ph↗

arXiv2019

Parallel simulation of two--dimensional Ising models using Probabilistic Cellular Automata

We perform a numerical investigation of the \emph{shaken dynamics}, a parallel Markovian dynamics for spin systems with local interaction and whose transition probabilities depend on two parameters, $q$ and $J$, that tune the geometry of the underlying lattice. We determine a phase transition curve, in the $(q, J)$ plane, separating the disordered phase from the ordered one, study the mixing time of the Markov chain and evaluate the spin-spin correlations as $q$ and $J$ vary. Further, we investigate the relation between the equilibrium measure of the shaken dynamics and the Gibbs measure for the Ising model. Two different approaches are considered for the implementation of the dynamics: a multicore CPU approach, with code written in Julia and a GPU approach with code written in CUDA.

physics.comp-ph↗

arXiv2019

Criticality of measures on 2-d Ising configurations: from square to hexagonal graphs

On the space of Ising configurations on the 2-d square lattice, we consider a family of non Gibbsian measures introduced by using a pair Hamiltonian, depending on an additional inertial parameter $q$. These measures are related to the usual Gibbs measure on $\Z^2$ and turn out to be the marginal of the Gibbs measure of a suitable Ising model on the hexagonal lattice. The inertial parameter $q$ tunes the geometry of the system. The critical behaviour and the decay of correlation functions of these measures are studied thanks to relation with the Random Cluster model.

math-ph↗

arXiv2017

Simulation tools to compare and optimize the mobility plans

In the last decades, mobility planning has been a fundamental issue for the development of cities. A full knowledge of the way a mobility system influences the traffic behavior of a whole city is needed in order to propose plans aligned with the municipalities' goals. In particular, a tool to compare different plans and the respective costs and benefits is necessary to forecast the consequences of the changes in mobility plans. The aim of this research is to show how two different mobility models can be compared, based on different plans, and how to use this comparison strategy to develop or review a mobility plan. As a case study we analyzed the city of Barcelona, where in the last 10 years the municipality applied a new urban mobility plan, reviewed every 5 years (PMU 2007 and 2012). By using MATSim simulation tools, we realized two models of the infrastructure network: in both we built metro, train, tram and car networks. The main differences between the two models are the speed limit of the car network and the presence or absence of the bicycle network. The results show that if we set low speed limits and increase bike infrastructures, the average travel time decreases and the number of users of the bicycle network increases to the detriment of public and private transport. In particular, we show that the number of users of public transport decreases more than the private transport users. This behavior is related to the lack of the bus network, not simulated in these models, suggesting that the metro network works properly only when it is integrated with a bus network.

physics.soc-ph↗

arXiv2016

Shaping ideal cities: the graph representation of the urban utopia

The ideal Renaissance city is designed as a star-shaped fortress, where the streets and squares are organized to speed the movement of people and soldiers. Symmetry and accessibility represent the key features for the organization of the urban space. The resulting city is hierarchized and does not always guarantee an optimal degree of connectivity. Taking the baton from the work done by space syntax in the definition of properties of spatial graph representation, we introduce a method to compute urban graphs from the Euclidean representation, the corresponding line graph and the contraction of nodes with the same urban function. We analyze the urban graphs of five historic cities: Vitry le François, Avola, Neuf Brisach, Grammichele and Palmanova and compare the analysis restults with the corresponding results from space syntax. Analysis of the spectral gap and the relative asymmetry distribution show a similar structure for these cities. The irregular or reticular housing structure seems to ensure connectivity and accessibility more than the regular grids. However connectivity is ensured by the most peripheral streets, which in the space syntax representation play a marginal role.

physics.soc-ph↗

arXiv2015

Line graphs e contrazioni: un approccio rigoroso alla space syntax

The methods of the space syntax have been the subject of extensive discussion, and several techniques to identify the axis lines have been proposed. The space syntax can be represented in terms of line graph, a graphs defined on the edge of a given primary graph. By means of the line graph algorithms, a system of labels defined on the edges of the primary graph is transformed into a system of labels on the vertices of the line graph. The contraction of adjacent edges with the same label allows to build a more general graph than those generated with the methods of the space syntax. By means of the functions implemented in Mathematica is therefore possible to redefine the space syntax on any system of urban quantities (labels) and reproduce the results of the axial lines as a special case. As an example is discussed a possible application of the method to the urban noise analysis.

physics.soc-ph↗

arXiv2014

Is there enough fertile soil to feed a planet of growing cities?

We analyze a scaling law for the consumption of agricultural soil by cities. The nonlinear dependence of the size of the city on the number of inhabitants gives rise to an equation for population dynamics. We found the asymptotic limit of the solution for this equation, given by the carrying capacity in terms of number of inhabitants that can be fed. The carrying capacity as a function of the scaling law exponent is computed numerically, showing that the exponent must be very small to ensure a food sustainability. We suggest a bound for the value of this exponent and analyze the reliability of the scaling law for major cities.

physics.soc-ph↗

arXiv2004

The prosody and the music of the human speech

We propose the use of a self-oscillating dynamical system --the pre-Galileian clock equation-- for modeling the laryngeal tone. The parameters are shown to be the minimal control needed for generating the prosody of the human speech. Based on this model, we outline a peak delay detection algorithm for extracting the prosody of the real speech.

physics.bio-ph↗