This paper focuses on the convergence of information in distributed systems of agents communicating over a network.

The information on which the convergence is sought is not represented by real numbers, as often in the literature, rather by sets. The dynamics of the evolution of information across the network is accordingly described by set-valued iterative maps. While the study of convergence of set-valued iterative maps is highly complex in general, this paper focuses on Boolean maps, which are comprised of arbitrary combinations of unions, intersections, and complements of sets. For these important class of systems, we provide tools to study both global and local convergence. A distributed geographic information system, leading to successful information reconstruction from partial and corrupted data, is used to illustrate the applications of the proposed methods.

VL - 61
UR - http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7272075
IS - 6
ER -
TY - JOUR
T1 - An equivalent of Kronecker's Theorem for powers of an Algebraic Number and Structure of Linear Recurrences of fixed length
JF - Acta Arithmetica
Y1 - 2012
A1 - N. Dubbini
A1 - M. Monge
KW - Robotics
AB - After defining a notion of epsilon-density, we provide for any integer m>1 and real algebraic number alpha an estimate of the smallest epsilon such that the set of vectors of the form (t,t^alpha,...,t alpha^{m-1}) for tR is epsilon-dense modulo 1 in terms of the multiplicative Mahler measure M(A(x)) of the minimal integral polynomial A(x) of alpha, which is independent of m. In particular, we show that if alpha has degree d it is possible to take epsilon = 2^{[d/2]}/M(A(x)). On the other side we show using asymptotic estimates for Toeplitz determinants that we cannot have epsilon$-density for sufficiently large m whenever epsilon is strictly smaller than 1/M(A(x)). In the process of proving this we obtain a result of independent interest about the structure of the Z-module of integral linear recurrences of fixed length determined by a non-monic polynomial.

VL - 153 UR - http://journals.impan.pl/cgi-bin/doi?aa153-1-2 IS - 1 N1 -accepted for publication

ER - TY - CONF T1 - Causality as a unifying approach between activation and connectivity analysis of fMRI data T2 - 17-th annual meeting of the Organization for Human Brain Mapping Y1 - 2011 A1 - N. Dubbini A1 - E. Ricciardi A1 - A. Gaglianese A1 - S. Marmi A1 - P. Pietrini JF - 17-th annual meeting of the Organization for Human Brain Mapping N1 - Abstract ER - TY - JOUR T1 - Left invertibility of discrete-time output-quantized systems: the linear case with finite inputs JF - Mathematics of Control, Signals, and Systems Y1 - 2011 A1 - N. Dubbini A1 - B. Piccoli A1 - A. Bicchi KW - Robotics AB -This paper studies left invertibility of discrete-time linear outputquantized systems. Quantized outputs are generated according to a given partition of the state-space, while inputs are sequences on a nite alphabet. Left invertibility, i.e. injectivity of I/O map, is reduced to left D-invertibility, under suitable conditions. While left invertibility takes into account membership to sets of a given partition, left D-invertibility considers only membership to a single set, and is much easier to detect. The condition under which left invertibility and left D-invertibility are equivalent is that the elements of the dynamic matrix of the system form an algebraically independent set. Our main result is a method to compute left D-invertibility (so also left invertibility for a full measure matrix set) for all linear systems with no eigenvalue of modulus one. Therefore we are able to check left invertibility of output-quantized linear systems for a full measure matrices set. Some examples are presented to show the application of the proposed method.

VL - 23 N1 -published online 8 Sept. 2011

ER - TY - CONF T1 - Left invertibility of output-quantized MISO linear systems T2 - 2011 Congress of the International Federation of Automatic Control - IFAC2011 Y1 - 2011 A1 - N. Dubbini A1 - M. Monge A1 - A. Bicchi KW - Embedded Control KW - Robotics AB -This paper studies left invertibility of single-output discrete-time quantized linear systems. Quantized outputs are generated according to a given partition of the state-space, while inputs are sequences on a finite alphabet. Left invertibility deals with the possibility of recovering unknown inputs from the only knowledge of the outputs. It is reduced, under suitable conditions, to left D-invertibility: while left invertibility takes into account membership to sets of a given partition, left D-invertibility considers only membership to a single set, and is easily (and algorithmically) detectable. Our main result is a sufficient condition for the equivalence between left invertibility and left D-invertibility in MISO system. In unidimensional systems the equivalence is valid except at most a finite (and computable) number of cases. These results allows the effective detection of left invertibility by means of left Dinvertibility, which is algorithmically detectable. An example with effective computations is presented to show the application of the proposed method.

JF - 2011 Congress of the International Federation of Automatic Control - IFAC2011 CY - Milano, italy ER - TY - JOUR T1 - Left invertibility of discrete systems with finite inputs and quantized output JF - International Journal Of Control Y1 - 2010 A1 - N. Dubbini A1 - B. Piccoli A1 - A. Bicchi KW - Embedded Control KW - Robotics AB -The aim of this paper is to address left invertibility for dynamical systems with inputs and outputs in discrete sets. We study systems which evolve in discrete time within a continuous state-space; quantized outputs are generated by the system according to a given partition of the state-space, while inputs are arbitrary sequences of symbols in a finite alphabet, which are associated to specific actions on the system. Our main results are obtained under some contractivity hypotheses. The problem of left invertibility, i.e. recovering an unknown input sequence from the knowledge of the corresponding output string, is addressed using the theory of Iterated Function Systems (IFS), a tool developed for the study of fractals. We show how the IFS naturally associated to a system and the geometric properties of its attractor are linked to the invertibility property of the system. Our main result is a necessary and sufficient condition for left invertibility and uniform left invertibility for joint contractive systems. In addition, an algorithm is proposed to recover inputs from output strings. A few examples are presented to illustrate the application of the proposed method.

VL - 83 ER - TY - CONF T1 - Left invertibility of output-quantized systems: an application to cryptography T2 - International Conference on Decision and Control - CDC 2010 Y1 - 2010 A1 - N. Dubbini A1 - A. Carluccio A1 - A. Bicchi KW - Robotics AB -In this paper a secure communication method is proposed, based on left invertibility of output-quantized dynamical systems. The sender uses an output-quantized linear system with a feedback function to encode messages, which are sequences of inputs of the system. So left invertibility property enables the receiver to recover the messages. The secret key is formed by the system

JF - International Conference on Decision and Control - CDC 2010 CY - Atlanta, USA ER - TY - CONF T1 - Distributed Consensus on Boolean Information T2 - 1st IFAC Workshop on Estimation and Control of Networked Systems (NecSys'09) Y1 - 2009 A1 - A. Fagiolini A1 - S. Martini A1 - N. Dubbini A1 - A. Bicchi KW - Embedded Control KW - Robotics AB -In this paper we study the convergence towards consensus on information in a distributed system of agents communicating over a network. The particularity of this study is that the information on which the consensus is seeked is not represented by real numbers, rather by logical values or compact sets. Whereas the problems of allowing a network of agents to reach a consensus on logical functions of input events, and that of agreeing on set-valued information, have been separately addressed in previous work, in this paper we show that these problems can indeed be attacked in a unified way in the framework of Boolean distributed information systems. Based on a notion of contractivity for Boolean dynamical systems, a necessary and suficient condition ensuring the global convergence toward a unique equilibrium point is presented. This result can be seen as a first step toward the denition of a unified framework to uniformly address all consensus problems on Boolean algebras.

JF - 1st IFAC Workshop on Estimation and Control of Networked Systems (NecSys'09) CY - Venice, Italy ER - TY - CONF T1 - Left invertibility of discrete systems with finite inputs and quantized output T2 - Proc. IEEE Int. Conf. on Decision and Control Y1 - 2008 A1 - N. Dubbini A1 - B. Piccoli A1 - A. Bicchi KW - Embedded Control KW - Robotics AB -The aim of this paper is to address left invertibility for dynamical systems with inputs and outputs in discrete sets. We study systems that evolve in discrete time within a continuous state-space. Quantized outputs are generated by the system according to a given partition of the state-space, while inputs are arbitrary sequences of symbols in a finite alphabet, which are associated to specific actions on the system. We restrict to the case of contractive dynamics for fixed inputs. The problem of left invertibility, i.e. recovering an unknown input sequence from the knowledge of the corresponding output string, is addressed using the theory of Iterated Function Systems (IFS), a tool developed for the study of fractals. We show how the IFS naturally associated to a system and the geometric properties of its attractor are linked to the left invertibility property of the system. Our main results are a necessary and sufficient condition for a given system to be left invertible with probability one on the space of inputs (i.e. for almost all input sequences), and necessary and sufficient conditions for left invertibility and uniform left invertibility under some weak additional hypotheses. A few examples are presented to illustrate the application of the proposed method.

JF - Proc. IEEE Int. Conf. on Decision and Control ER -