23 research outputs found
Aspects Topologiques des Représentations en Analyse Calculable
Computable analysis provides a formalization of algorithmic computations over infinite mathematical objects. The central notion of this theory is the symbolic representation of objects, which determines the computation power of the machine, and has a direct impact on the difficulty to solve any given problem. The friction between the discrete nature of computations and the continuous nature of mathematical objects is captured by topology, which expresses the idea of finite approximations of infinite objects.We thoroughly study the multiple interactions between computations and topology, analysing the information that can be algorithmically extracted from a representation. In particular, we focus on the comparison between two representations of a single family of objects, on the precise relationship between algorithmic and topological complexity of problems, and on the relationship between finite and infinite representations.L’analyse calculable permet de formaliser le traitement algorithmique d’objets mathématiques infinis. La théorie repose sur une représentation symbolique des objets, dont le choix détermine les capacités de calcul de la machine, notamment sa difficulté à résoudre chaque problème donné. La friction entre le caractère discret du calcul et la nature continue des objets est capturée par la topologie, qui exprime l’idée d’approximation finie d’objets infinis.Nous étudions en profondeur les multiples interactions entre calcul et topologie, cherchant à analyser l’information qui peut être extraite algorithmiquement d’une représentation. Je me penche plus particulièrement sur la comparaison entre deux représentations d’une même famille d’objets, sur les liens détaillés entre complexité algorithmique et topologique des problèmes, ainsi que sur les relations entre représentations finies et infinies
The Speedup Theorem in a Primitive Recursive Framework
Blum’s speedup theorem is a major theorem in computational com-plexity, showing the existence of computable functions for which no optimal program can exist: for any speedup function r there ex-ists a function fr such that for any program computing fr we can find an alternative program computing it with the desired speedup r. The main corollary is that algorithmic problems do not have, in general, a inherent complexity. Traditional proofs of the speedup theorem make an essential use of Kleene’s fix point theorem to close a suitable diagonal argument. As a consequence, very little is known about its validity in subrecursive settings, where there is no universal machine, and no fixpoints. In this article we discuss an alternative, formal proof of the speedup theorem that allows us to spare the invocation of the fix point theorem and sheds more light on the actual complexity of the function fr
The prospects for mathematical logic in the twenty-first century
The four authors present their speculations about the future developments of
mathematical logic in the twenty-first century. The areas of recursion theory,
proof theory and logic for computer science, model theory, and set theory are
discussed independently.Comment: Association for Symbolic Logi
The independence of control structures in abstract programming systems
AbstractAn instance of a control structure is a mapping which takes one or more programs into a new program whose behavior is based on that of the original programs. An instance of a control structure is effective iff it is effectively computable. In order to study the interrelationships of control structures, . we consider abstract programming systems (numberings of the partial recursive functions) in which some control structures, effective or otherwise, are present, but others are not. This paper uses the techniques of recursive function theory, including recursion theorems and priority arguments to prove the independence of certain control structures in abstract programming systems. For example, we have obtained the following results. In effective numberings of the partial recursive functions, the one-one effective Kleene recursion theorem and the one-one effective (partial) if-then-else control structure are independent, but together, they yield all effective control structures. In any effective numbering, the effective Kleene form of the double recursion theorem yields all effective control structures
Complexity of Acyclic Term Graph Rewriting
Term rewriting has been used as a formal model to reason about the
complexity of logic, functional, and imperative programs. In contrast
to term rewriting, term graph rewriting permits sharing of
common sub-expressions, and consequently is able to capture more
closely reasonable implementations of rule based languages. However,
the automated complexity analysis of term graph rewriting has received
little to no attention.
With this work, we provide first steps towards overcoming this
situation. We present adaptions of two prominent complexity techniques
from term rewriting, viz, the interpretation method and
dependency tuples. Our adaptions are non-trivial, in the sense
that they can observe not only term but also graph structures, i.e.
take sharing into account. In turn, the developed methods allow us to
more precisely estimate the runtime complexity of programs where
sharing of sub-expressions is essential
Relativization of the theory of computational complexity.
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 1972.Vita.Bibliography: leaves 123-124.Ph.D