262 research outputs found
Ultimate periodicity of b-recognisable sets : a quasilinear procedure
It is decidable if a set of numbers, whose representation in a base b is a
regular language, is ultimately periodic. This was established by Honkala in
1986.
We give here a structural description of minimal automata that accept an
ultimately periodic set of numbers. We then show that it can verified in linear
time if a given minimal automaton meets this description.
This thus yields a O(n log(n)) procedure for deciding whether a general
deterministic automaton accepts an ultimately periodic set of numbers.Comment: presented at DLT 201
Discussion quality diffuses in the digital public square
Studies of online social influence have demonstrated that friends have
important effects on many types of behavior in a wide variety of settings.
However, we know much less about how influence works among relative strangers
in digital public squares, despite important conversations happening in such
spaces. We present the results of a study on large public Facebook pages where
we randomly used two different methods--most recent and social feedback--to
order comments on posts. We find that the social feedback condition results in
higher quality viewed comments and response comments. After measuring the
average quality of comments written by users before the study, we find that
social feedback has a positive effect on response quality for both low and high
quality commenters. We draw on a theoretical framework of social norms to
explain this empirical result. In order to examine the influence mechanism
further, we measure the similarity between comments viewed and written during
the study, finding that similarity increases for the highest quality
contributors under the social feedback condition. This suggests that, in
addition to norms, some individuals may respond with increased relevance to
high-quality comments.Comment: 10 pages, 6 figures, 2 table
A model for dynamic communicators
We develop and test an intuitively simple dynamic network model to describe the type of time-varying connectivity structure present in many technological settings. The model assumes that nodes have an inherent hierarchy governing the emergence of new connections. This idea draws on newly established concepts in online human behaviour concerning the existence of discussion catalysts, who initiate long threads, and online leaders, who trigger feedback. We show that the model captures an important property found in e-mail and voice call data â âdynamic communicatorsâ with sufficient foresight or impact to generate effective links and having an influence that is grossly underestimated by static measures based on snaphots or aggregated data
Algorithmic statistics revisited
The mission of statistics is to provide adequate statistical hypotheses
(models) for observed data. But what is an "adequate" model? To answer this
question, one needs to use the notions of algorithmic information theory. It
turns out that for every data string one can naturally define
"stochasticity profile", a curve that represents a trade-off between complexity
of a model and its adequacy. This curve has four different equivalent
definitions in terms of (1)~randomness deficiency, (2)~minimal description
length, (3)~position in the lists of simple strings and (4)~Kolmogorov
complexity with decompression time bounded by busy beaver function. We present
a survey of the corresponding definitions and results relating them to each
other
Fabrication de chikwangue au Congo
Ce rapport fait Ă©tat, d'une part, des rĂ©sultats obtenus dans le cadre de recherches entreprises pour dĂ©finir les contextes dans lesquels il est prĂ©vu de diffuser un produit nouveau, la "chiwangue Agricongo", ainsi que les procĂ©dĂ©s et les Ă©quipements mis au point de fabrication et, d'autre part, des actions menĂ©es Ă l'Ă©chelle pilote en vue d'assurer la diffusion de ces innovations. A partir d'enquĂȘtes rĂ©alisĂ©es, Ă Brazzaville et sur toute l'Ă©tendue du territoire, les modalitĂ©s de consommation de la chikwangue au Congo ont Ă©tĂ© dĂ©crites et son importance dans la ration alimentaire des congolais prĂ©cisĂ©e. Les prĂ©fĂ©rences exprimĂ©es et le comportement des consommateurs de chikwangue vis-Ă vis de leur aliment de base ont Ă©tĂ© analysĂ©s. Si la chikwangue reste l'aliment de base prĂ©fĂ©rĂ© des congolais, l'importance de sa consommation varie en fonction de certains facteurs Ă©co-socioĂ©conomiques. D'autres enquĂȘtes rĂ©alisĂ©es dans le mĂȘme temps ont permis d'inventorier et de dĂ©crire les variantes et les innovations endogĂšnes apparues dans les procĂ©dĂ©s de fabrication de la chikwangue en zones rurales et le mode de fonctionnement des ateliers urbains de fabrication. Le rendement des transformations et la durĂ©e et la pĂ©nibilitĂ© des diffĂ©rentes Ă©tapes ont Ă©tĂ© mesurĂ©s. Les procĂ©dĂ©s et les Ă©quipements mis au point Ă partir de 1987 par Agricongo sont dĂ©crits ainsi que, en comparaison avec les systĂšmes traditionnels, le systĂšme de production du groupement de producteurs agricoles dans lequel une ligne de fabrication a Ă©tĂ© installĂ©e en 1991. Les Ă©tudes rĂ©alisĂ©es pour Ă©valuer le rĂ©seau mis en place pour assurer la distribution du produit et l'acceptabilitĂ© des produits, des procĂ©dĂ©s et des Ă©quipements montrent que le produit est trĂšs bien acceptĂ© et que le choix de le commercialiser dans un rĂ©seau de petits commerces est judicieux. Malheureusement, les Ă©quipements se sont rĂ©vĂ©lĂ©s mal adaptĂ©s aux contextes socio-Ă©conomiques, insuffisamment analysĂ©s au moment du dĂ©marrage du projet. D'autre part, le coĂ»t de l'amortissement des machines et la chertĂ© de la matiĂšre premiĂšre en ville ne permet pas d'envisager d'installer des lignes de fabrication en zones urbaines. D'autre part, une fiabilitĂ© encore insuffisante des machines rend alĂ©atoire leur installation prĂšs des zones de production en raison des problĂšmes de maintenance. Par ailleurs, la diffusion des Ă©quipements pris sĂ©parĂ©ment est difficile, compte tenu de leur coĂ»t et du faible niveau habituel d'investissement des ateliers traditionnels. Toutefois, la description rigoureuse des modalitĂ©s de consommation et de transformation de la chikwangue existant actuellement au Congo permet Ă Agricongo, promoteur du projet, de dresser un cahier des charges prĂ©cis pour les amĂ©nagements Ă faire subir aux procĂ©dĂ©s et aux Ă©quipements en vue de les rendre complĂštement adaptĂ©s aux contestes technologiques et Ă©conomiques qui prĂ©valent au Congo. (RĂ©sumĂ© d'auteur
Anyone Can Become a Troll: Causes of Trolling Behavior in Online Discussions
In online communities, antisocial behavior such as trolling disrupts
constructive discussion. While prior work suggests that trolling behavior is
confined to a vocal and antisocial minority, we demonstrate that ordinary
people can engage in such behavior as well. We propose two primary trigger
mechanisms: the individual's mood, and the surrounding context of a discussion
(e.g., exposure to prior trolling behavior). Through an experiment simulating
an online discussion, we find that both negative mood and seeing troll posts by
others significantly increases the probability of a user trolling, and together
double this probability. To support and extend these results, we study how
these same mechanisms play out in the wild via a data-driven, longitudinal
analysis of a large online news discussion community. This analysis reveals
temporal mood effects, and explores long range patterns of repeated exposure to
trolling. A predictive model of trolling behavior shows that mood and
discussion context together can explain trolling behavior better than an
individual's history of trolling. These results combine to suggest that
ordinary people can, under the right circumstances, behave like trolls.Comment: Best Paper Award at CSCW 201
Two-dimensional ranking of Wikipedia articles
The Library of Babel, described by Jorge Luis Borges, stores an enormous
amount of information. The Library exists {\it ab aeterno}. Wikipedia, a free
online encyclopaedia, becomes a modern analogue of such a Library. Information
retrieval and ranking of Wikipedia articles become the challenge of modern
society. While PageRank highlights very well known nodes with many ingoing
links, CheiRank highlights very communicative nodes with many outgoing links.
In this way the ranking becomes two-dimensional. Using CheiRank and PageRank we
analyze the properties of two-dimensional ranking of all Wikipedia English
articles and show that it gives their reliable classification with rich and
nontrivial features. Detailed studies are done for countries, universities,
personalities, physicists, chess players, Dow-Jones companies and other
categories.Comment: RevTex 9 pages, data, discussion added, more data at
http://www.quantware.ups-tlse.fr/QWLIB/2drankwikipedia
An output-sensitive algorithm for the minimization of 2-dimensional String Covers
String covers are a powerful tool for analyzing the quasi-periodicity of
1-dimensional data and find applications in automata theory, computational
biology, coding and the analysis of transactional data. A \emph{cover} of a
string is a string for which every letter of lies within some
occurrence of . String covers have been generalized in many ways, leading to
\emph{k-covers}, \emph{-covers}, \emph{approximate covers} and were
studied in different contexts such as \emph{indeterminate strings}.
In this paper we generalize string covers to the context of 2-dimensional
data, such as images. We show how they can be used for the extraction of
textures from images and identification of primitive cells in lattice data.
This has interesting applications in image compression, procedural terrain
generation and crystallography
Studies of the limit order book around large price changes
We study the dynamics of the limit order book of liquid stocks after
experiencing large intra-day price changes. In the data we find large
variations in several microscopical measures, e.g., the volatility the bid-ask
spread, the bid-ask imbalance, the number of queuing limit orders, the activity
(number and volume) of limit orders placed and canceled, etc. The relaxation of
the quantities is generally very slow that can be described by a power law of
exponent . We introduce a numerical model in order to understand
the empirical results better. We find that with a zero intelligence deposition
model of the order flow the empirical results can be reproduced qualitatively.
This suggests that the slow relaxations might not be results of agents'
strategic behaviour. Studying the difference between the exponents found
empirically and numerically helps us to better identify the role of strategic
behaviour in the phenomena.Comment: 19 pages, 7 figure
A complementary view on the growth of directory trees
Trees are a special sub-class of networks with unique properties, such as the
level distribution which has often been overlooked. We analyse a general tree
growth model proposed by Klemm {\em et. al.} (2005) to explain the growth of
user-generated directory structures in computers. The model has a single
parameter which interpolates between preferential attachment and random
growth. Our analysis results in three contributions: First, we propose a more
efficient estimation method for based on the degree distribution, which is
one specific representation of the model. Next, we introduce the concept of a
level distribution and analytically solve the model for this representation.
This allows for an alternative and independent measure of . We argue that,
to capture real growth processes, the estimations from the degree and the
level distributions should coincide. Thus, we finally apply both
representations to validate the model with synthetically generated tree
structures, as well as with collected data of user directories. In the case of
real directory structures, we show that measured from the level
distribution are incompatible with measured from the degree distribution.
In contrast to this, we find perfect agreement in the case of simulated data.
Thus, we conclude that the model is an incomplete description of the growth of
real directory structures as it fails to reproduce the level distribution. This
insight can be generalised to point out the importance of the level
distribution for modeling tree growth.Comment: 16 pages, 7 figure
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