2,645 research outputs found
Cost and dimension of words of zero topological entropy
Let denote the free monoid generated by a finite nonempty set In
this paper we introduce a new measure of complexity of languages defined in terms of the semigroup structure on For each we define its {\it cost} as the infimum of all real numbers
for which there exist a language with
and a positive integer with We also
define the {\it cost dimension} as the infimum of the set of all
positive integers such that for some language with
We are primarily interested in languages given by the
set of factors of an infinite word of zero
topological entropy, in which case We establish the following
characterisation of words of linear factor complexity: Let and
Fac be the set of factors of Then if and only
and In other words, if and only if
Fac for some language of bounded complexity
(meaning In general the cost of a language
reflects deeply the underlying combinatorial structure induced by the semigroup
structure on For example, in contrast to the above characterisation of
languages generated by words of sub-linear complexity, there exist non
factorial languages of complexity (and hence of cost
equal to and of cost dimension In this paper we investigate the
cost and cost dimension of languages defined by infinite words of zero
topological entropy
Subproduct systems and Cartesian systems; new results on factorial languages and their relations with other areas
We point out that a sequence of natural numbers is the dimension sequence of
a subproduct system if and only if it is the cardinality sequence of a word
system (or factorial language). Determining such sequences is, therefore,
reduced to a purely combinatorial problem in the combinatorics of words. A
corresponding (and equivalent) result for graded algebras has been known in
abstract algebra, but this connection with pure combinatorics has not yet been
noticed by the product systems community. We also introduce Cartesian systems,
which can be seen either as a set theoretic version of subproduct systems or an
abstract version of word systems. Applying this, we provide several new results
on the cardinality sequences of word systems and the dimension sequences of
subproduct systems.Comment: New title; added references; to appear in Journal of Stochastic
Analysi
Generating functions for generating trees
Certain families of combinatorial objects admit recursive descriptions in
terms of generating trees: each node of the tree corresponds to an object, and
the branch leading to the node encodes the choices made in the construction of
the object. Generating trees lead to a fast computation of enumeration
sequences (sometimes, to explicit formulae as well) and provide efficient
random generation algorithms. We investigate the links between the structural
properties of the rewriting rules defining such trees and the rationality,
algebraicity, or transcendence of the corresponding generating function.Comment: This article corresponds, up to minor typo corrections, to the
article submitted to Discrete Mathematics (Elsevier) in Nov. 1999, and
published in its vol. 246(1-3), March 2002, pp. 29-5
Computational aerodynamics and artificial intelligence
The general principles of artificial intelligence are reviewed and speculations are made concerning how knowledge based systems can accelerate the process of acquiring new knowledge in aerodynamics, how computational fluid dynamics may use expert systems, and how expert systems may speed the design and development process. In addition, the anatomy of an idealized expert system called AERODYNAMICIST is discussed. Resource requirements for using artificial intelligence in computational fluid dynamics and aerodynamics are examined. Three main conclusions are presented. First, there are two related aspects of computational aerodynamics: reasoning and calculating. Second, a substantial portion of reasoning can be achieved with artificial intelligence. It offers the opportunity of using computers as reasoning machines to set the stage for efficient calculating. Third, expert systems are likely to be new assets of institutions involved in aeronautics for various tasks of computational aerodynamics
Profinite Groups Associated to Sofic Shifts are Free
We show that the maximal subgroup of the free profinite semigroup associated
by Almeida to an irreducible sofic shift is a free profinite group,
generalizing an earlier result of the second author for the case of the full
shift (whose corresponding maximal subgroup is the maximal subgroup of the
minimal ideal). A corresponding result is proved for certain relatively free
profinite semigroups. We also establish some other analogies between the kernel
of the free profinite semigroup and the \J-class associated to an irreducible
sofic shift
Refrain from Standards? French, Cavemen and Computers. A (short) Story of Multidimensional Analysis in French Prehistoric Archaeology
Focusing on the history of prehistoric archaeology in the 20th century, this papers shows (1) that statistical multidimensional analyses were carried out by a new kind of actors who challenged the previous common language shared by prehistorians. This fundamental change was important, considering that (2) language is a fundamental point for the epistemology of archaeology. However, a comparison of multidimensional analyses applications over time shall make clear that (3) the differences are mostly a generational matter: the transmission processes between them will be addressed
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