Global Versus Local Computations: Fast Computing with Identifiers

This paper studies what can be computed by using probabilistic local interactions with agents with a very restricted power in polylogarithmic parallel time. It is known that if agents are only finite state (corresponding to the Population Protocol model by Angluin et al.), then only semilinear predicates over the global input can be computed. In fact, if the population starts with a unique leader, these predicates can even be computed in a polylogarithmic parallel time. If identifiers are added (corresponding to the Community Protocol model by Guerraoui and Ruppert), then more global predicates over the input multiset can be computed. Local predicates over the input sorted according to the identifiers can also be computed, as long as the identifiers are ordered. The time of some of those predicates might require exponential parallel time. In this paper, we consider what can be computed with Community Protocol in a polylogarithmic number of parallel interactions. We introduce the class CPPL corresponding to protocols that use $O(n\log^k n)$, for some k, expected interactions to compute their predicates, or equivalently a polylogarithmic number of parallel expected interactions. We provide some computable protocols, some boundaries of the class, using the fact that the population can compute its size. We also prove two impossibility results providing some arguments showing that local computations are no longer easy: the population does not have the time to compare a linear number of consecutive identifiers. The Linearly Local languages, such that the rational language $(ab)^*$, are not computable.Comment: Long version of SSS 2016 publication, appendixed version of SIROCCO 201

« Orientation client » et (in)civilité : le cas d’une ligne de transport public collectif

Cet article vise à articuler politique d’orientation client d’une entreprise publique de transport, d’une part, et (in)civilité des voyageurs à l’égard des salariés aux guichets, d’autre part, à partir du cas d’une nouvelle ligne de transport public collectif voulant inaugurer de nouveaux modes de relations entre agents et clients, basés sur l’attention et la convivialité. En fait de convivialité, c’est essentiellement l’incivilité que les salariés doivent régulièrement subir. L’énoncé, par la direction de la ligne, de la position centrale des clients dans l’organisation ainsi que l’évolution des missions confiées aux agents en contact avec les clients, viennent modifier la nature des rapports sociaux de service entre agents et clients, qui évoluent vers des rapports de pouvoir en faveur des clients et au détriment de la civilité dans l’espace public.A new public transit line set up a programme entitled “focus on the client” [orientation client] intended to found relations between employees and clients on attention and interaction. In practice, interaction essentially brings incivility, which the employees confront regularly. The transit authority’s announcement that clients were central to the organisation as well as the evolution of employees’ responsibilities when in contact with clients has altered the service relationship. It is shifting the power relationship in the clients’ favour and at the loss of civility in public space

LES JUIFS ET LE NOUVEAU MESSIE DE L’ART

Transcript of LES JUIFS ET LE NOUVEAU MESSIE DE L’ART by Ch. Beauquier, appearing in L'ART MUSICAL, 8 avril 1869, pp. 149-150

Quelle gestion des incivilités dans les entreprises accueillant du public ?

La notion d’incivilité regroupe un très large éventail de conduites : indifférence, impolitesse, dégradations, agressivité verbale. Les espaces publics de la Société nationale des Chemins de fer (SNCF) comme ceux de La Poste sont des lieux de brassage social, d’attente prolongée, de mélange entre besoins individuels et traitement de masse. La qualité de service y est intimement liée à la qualité du lien social. Les salariés de ces entreprises font remonter régulièrement le poids croissant des incivilités dont ils sont les témoins ou l’objet. Face à ces actes problématiques, la SNCF et La Poste ont engagé des travaux de recherche analysant les facteurs de dégradation et les leviers de régulation de la civilité dans leurs espaces.Incivility covers a wide range of behaviours – indifference, rudeness, insults, verbal aggression. The public spaces of the railways [SNCF] and the post office are places of social encounter, long waits, and a mix of mass treatment and individual needs. The quality of service is intimately linked to the quality of social ties. Employees in these companies must regularly overcome an increasing burden of incivilities of which they are the object or a witness. Faced with such problem behaviours, the railway companies and the postal service are engaged in research to analyse the factors that account for this degradation and the mechanisms for regulating civility in their public spaces

Beeping a Deterministic Time-Optimal Leader Election

The beeping model is an extremely restrictive broadcast communication model that relies only on carrier sensing. In this model, we solve the leader election problem with an asymptotically optimal round complexity of O(D + log n), for a network of unknown size n and unknown diameter D (but with unique identifiers). Contrary to the best previously known algorithms in the same setting, the proposed one is deterministic. The techniques we introduce give a new insight as to how local constraints on the exchangeable messages can result in efficient algorithms, when dealing with the beeping model. Using this deterministic leader election algorithm, we obtain a randomized leader election algorithm for anonymous networks with an asymptotically optimal round complexity of O(D + log n) w.h.p. In previous works this complexity was obtained in expectation only. Moreover, using deterministic leader election, we obtain efficient algorithms for symmetry-breaking and communication procedures: O(log n) time MIS and 5-coloring for tree networks (which is time-optimal), as well as k-source multi-broadcast for general graphs in O(min(k,log n) * D + k log{(n M)/k}) rounds (for messages in {1,..., M}). This latter result improves on previous solutions when the number of sources k is sublogarithmic (k = o(log n))

Broadcasting in WDM Optical Rings and Tori

The well-known spanning binomial tree broadcast algorithm is generalized to obtain two families of broadcast algorithms for optical rings and two-dimensional toroidal meshes (tori) using {\em Wavelength Division Multiplexing (WDM)}. These generalizations take advantage of the concurrent transmission through optical links offered by WDM. Their performances are measured under the {\em linear cost model} : the cost of sending a message of $L$ bits is defined as $\alpha +L\tau$, where $\alpha$ is the latency and $\tau$ is the per-byte transmission cost. It is assumed that each node can concurrently transmit one message and receive one message. Our algorithms are based on the familiar spanning binomial tree and on the dimensional exchanges commonly used on hypercubes. We restrict the number of nodes in a ring and in each dimension of a torus to be a power of two. The algorithms described in this paper offer significant performance improvements over the basic spanning tree broadcast

Non-deterministic Population Protocols (Extended Version)

In this paper we show that, in terms of generated output languages, non-deterministic \textit{population protocols} are strictly more powerful than deterministic ones. Analyzing the reason for this negative result, we propose two slightly enhanced models, in which non-deterministic population protocols can be \emph{exactly} simulated by deterministic ones. First, we consider a model in which interactions are not only between couples of agents, but also between triples and in which non-uniform initial states are allowed. We generalize this transformation and we prove a general property for a model with interactions between any number of agents. Second, we simulate any non-deterministic population protocol by a deterministic one in a model where a \emph{configuration} can have an \textit{empty output}. Non-deterministic and deterministic population protocols are then compared in terms of inclusion of their output languages, that is, in terms of solvability of problems. Two transformations, which realize this inclusion, are presented. The first one uses (again) the natural model with interactions of triples, but does not need non-uniform initial states. As before, this result is generalized for the natural model with interactions between any number of agents. The second transformation is a parameterized one with parameters depending on the transition graph of the considered non-deterministic protocol and on the population. Note that the transformations in the paper apply to a whole class of non-deterministic population protocols (for a proposed model), in contrast with the transformations proposed in previous works, which apply only to a specific sub-class of protocols (satisfying a so called ''elasticity'' condition)

The Benefits of Entropy in Population Protocols

A distributed computing system can be viewed as the result of the interplay between a distributed algorithm specifying the effects of a local event (e.g. reception of a message), and an adversary choosing the interleaving (schedule) of these events in the execution. In the context of large networks of mobile pairwise interacting agents (population protocols), the adversary models the mobility of the agents by choosing the successive pairs of interacting agents. For some problems, assuming that the adversary selects the schedule according to some probability distribution greatly helps to devise (almost) correct solutions. But how much randomness is really necessary? To what extent does a problem admit implementations that are robust against a "not so random" schedule? This paper takes a first step in addressing this question by borrowing the concept of T-randomness, 0 <= T <= 1, from algorithmic information theory. Roughly speaking, the value T fixes the entropy rate of the considered schedules. For instance, the case T = 1 corresponds, in a specific sense, to schedules in which the pairs of interacting agents are chosen independently and uniformly (perfect randomness). The holy grail question can then be precisely stated as determining the optimal entropy rate to solve a given problem. We first show that perfect randomness is never required. Precisely, if a finite-state algorithm solves a problem with 1-randomness, then this algorithm still solves the same problem with T-randomness for some T < 1. Second, we illustrate how to compute bounds on the optimal entropy rate of a specific problem, namely the leader election problem