arXiv subjects

Nelma Moreira

Publications and source records attributed to Nelma Moreira.

24 records · Page 2Linked to original sources

arXiv2010

State Elimination Ordering Strategies: Some Experimental Results

Recently, the problem of obtaining a short regular expression equivalent to a given finite automaton has been intensively investigated. Algorithms for converting finite automata to regular expressions have an exponential blow-up in the worst-case. To overcome this, simple heuristic methods have been proposed. In this paper we analyse some of the heuristics presented in the literature and propose new ones. We also present some experimental comparative results based on uniform random generated deterministic finite automata.

cs.FL↗

arXiv2009

Exact generation of acyclic deterministic finite automata

We give a canonical representation for trim acyclic deterministic finite automata (Adfa) with n states over an alphabet of k symbols. Using this normal form, we present a backtracking algorithm for the exact generation of Adfas. This algorithm is a non trivial adaptation of the algorithm for the exact generation of minimal acyclic deterministic finite automata, presented by Almeida et al.

cs.FL↗

arXiv2009

Testing the Equivalence of Regular Languages

The minimal deterministic finite automaton is generally used to determine regular languages equality. Antimirov and Mosses proposed a rewrite system for deciding regular expressions equivalence of which Almeida et al. presented an improved variant. Hopcroft and Karp proposed an almost linear algorithm for testing the equivalence of two deterministic finite automata that avoids minimisation. In this paper we improve the best-case running time, present an extension of this algorithm to non-deterministic finite automata, and establish a relationship between this algorithm and the one proposed in Almeida et al. We also present some experimental comparative results. All these algorithms are closely related with the recent coalgebraic approach to automata proposed by Rutten.

cs.FL↗

arXiv2009

Aspects of enumeration and generation with a string automata representation

In general, the representation of combinatorial objects is decisive for the feasibility of several enumerative tasks. In this work, we show how a (unique) string representation for (complete) initially-connected deterministic automata (ICDFAs) with n states over an alphabet of k symbols can be used for counting, exact enumeration, sampling and optimal coding, not only the set of ICDFAs but, to some extent, the set of regular languages. An exact generation algorithm can be used to partition the set of ICDFAs in order to parallelize the counting of minimal automata (and thus of regular languages). We present also a uniform random generator for ICDFAs that uses a table of pre-calculated values. Based on the same table it is also possible to obtain an optimal coding for ICDFAs.

cs.FL↗

arXiv2009

On the Representation of Finite Automata

We give an unique string representation, up to isomorphism, for initially connected deterministic finite automata (ICDFAs) with n states over an alphabet of k symbols. We show how to generate all these strings for each n and k, and how its enumeration provides an alternative way to obtain the exact number of ICDFAs.

cs.FL↗

arXiv1995

Constraint Categorial Grammars

Although unification can be used to implement a weak form of $β$-reduction, several linguistic phenomena are better handled by using some form of $λ$-calculus. In this paper we present a higher order feature description calculus based on a typed $λ$-calculus. We show how the techniques used in \CLG for resolving complex feature constraints can be efficiently extended. \CCLG is a simple formalism, based on categorial grammars, designed to test the practical feasibility of such a calculus.

cmp-lg↗