Classes of Transfinite Sequences Accepted by Nondeterministic Finite Automata

1984 ◽  
Vol 7 (2) ◽  
pp. 191-223
Author(s):  
Jerzy Wojciechowski
Keyword(s):  
Finite Automaton ◽  
Finite Automata ◽  
Basic Properties ◽  
Nondeterministic Finite Automata ◽  
The Family ◽  
Finite Sequences ◽  
Emptiness Problem ◽  
Nondeterministic Finite Automaton ◽  
Defining Sets

In this paper the notion of a nondeterministic finite automaton acting on arbitrary transfinite sequences is introduced. It is a generalization of the finite automaton on finite sequences and the finite automaton on ω-sequences. The basic properties of the behaviour of such automata are proved. The methods are shown how to construct automata accepting classes A ⋃ B, A ⋂ B, A ∘ B, A*, Aω, A# if we have automata accepting classes A and B. We prove that if a TF-automaton having k states accepts anything then it accepts an α-sequence for a certain, α ∈ { ∑ i = 0 m ω i · a i : ∑ i = 1 m i · a i + a 0 ⩽ k }. Using the foregoing fact, we show that the family of classes definable by TF-automata is not closed with respect to the complement operation, that nondeterministic automata are not equivalent to the deterministic ones and that the emptiness problem for TP-automata is decidable. In the last section we show the construction of TP-automata defining sets {∗α} for α < ω ω and having as few states as possible.

MAGIC NUMBERS FOR SYMMETRIC DIFFERENCE NFAS

2005 ◽  
Vol 16 (05) ◽  
pp. 1027-1038 ◽  
Author(s):  
LYNETTE VAN ZIJL
Keyword(s):  
Finite Automaton ◽  
Finite Automata ◽  
Symmetric Difference ◽  
Magic Numbers ◽  
Deterministic Finite Automaton ◽  
Nondeterministic Finite Automata ◽  
Binary Case ◽  
Nondeterministic Finite Automaton

Iwama et al. showed that there exists an n-state binary nondeterministic finite automaton such that its equivalent minimal deterministic finite automaton has exactly 2n - α states, for all n ≥ 7 and 5 ≤ α ≤ 2n-2, subject to certain coprimality conditions. We investigate the same question for both unary and binary symmetric difference nondeterministic finite automata. In the binary case, we show that for any n ≥ 4, there is an n-state symmetric difference nondeterministic finite automaton for which the equivalent minimal deterministic finite automaton has 2n - 1 + 2k - 1 - 1 states, for 2 < k ≤ n - 1. In the unary case, we consider a large practical subclass of unary symmetric difference nondeterministic finite automata: for all n ≥ 2, we argue that there are many values of α such that there is no n-state unary symmetric difference nondeterministic finite automaton with an equivalent minimal deterministic finite automaton with 2n - α states, where 0 < α < 2n - 1. For each n ≥ 2, we quantify such values of α precisely.

DETERMINISTIC BLOW-UPS OF MINIMAL NONDETERMINISTIC FINITE AUTOMATA OVER A FIXED ALPHABET

2008 ◽  
Vol 19 (03) ◽  
pp. 617-631 ◽  
Author(s):  
JOZEF JIRÁSEK ◽  
GALINA JIRÁSKOVÁ ◽  
ALEXANDER SZABARI
Keyword(s):  
Finite Automaton ◽  
Finite Automata ◽  
Magic Numbers ◽  
Deterministic Finite Automaton ◽  
Nondeterministic Finite Automata ◽  
Letter Alphabet ◽  
Input Alphabet ◽  
Nondeterministic Finite Automaton

We show that for all integers n and α such that n ⩽ α ⩽ 2n, there exists a minimal nondeterministic finite automaton of n states with a four-letter input alphabet whose equivalent minimal deterministic finite automaton has exactly α states. It follows that in the case of a four-letter alphabet, there are no "magic numbers", i.e., the holes in the hierarchy. This improves a similar result obtained by Geffert for a growing alphabet of size n + 2.

A CHARACTERIZATION OF RECOGNIZABLE PICTURE LANGUAGES

1994 ◽  
Vol 08 (02) ◽  
pp. 501-508 ◽  
Author(s):  
KATSUSHI INOUE ◽  
ITSUO TAKANAMI
Keyword(s):  
Finite Automata ◽  
Two Dimensional ◽  
Open Problems ◽  
Nondeterministic Finite Automata ◽  
Letter Alphabet ◽  
The Family ◽  
On Line ◽  
Picture Languages

This paper first shows that REC, the family of recognizable picture languages in Giammarresi and Restivo,3 is equal to the family of picture languages accepted by two-dimensional on-line tessellation acceptors in Inoue and Nakamura.5 By using this result, we then solve open problems in Giammarresi and Restivo,3 and show that (i) REC is not closed under complementation, and (ii) REC properly contains the family of picture languages accepted by two-dimensional nondeterministic finite automata even over a one letter alphabet.

SIMULATIONS OF UNARY ONE-WAY MULTI-HEAD FINITE AUTOMATA

2014 ◽  
Vol 25 (07) ◽  
pp. 877-896 ◽  
Author(s):  
MARTIN KUTRIB ◽  
ANDREAS MALCHER ◽  
MATTHIAS WENDLANDT
Keyword(s):  
Lower Bound ◽  
Lower Bounds ◽  
Finite Automaton ◽  
Finite Automata ◽  
Upper And Lower Bounds ◽  
Unary Languages ◽  
Order Of Magnitude ◽  
Simulation Results ◽  
Special Case ◽  
Nondeterministic Finite Automaton

We investigate the descriptional complexity of deterministic one-way multi-head finite automata accepting unary languages. It is known that in this case the languages accepted are regular. Thus, we study the increase of the number of states when an n-state k-head finite automaton is simulated by a classical (one-head) deterministic or nondeterministic finite automaton. In the former case upper and lower bounds that are tight in the order of magnitude are shown. For the latter case we obtain an upper bound of O(n2k) and a lower bound of Ω(nk) states. We investigate also the costs for the conversion of one-head nondeterministic finite automata to deterministic k-head finite automata, that is, we trade nondeterminism for heads. In addition, we study how the conversion costs vary in the special case of finite and, in particular, of singleton unary lanuages. Finally, as an application of the simulation results, we show that decidability problems for unary deterministic k-head finite automata such as emptiness or equivalence are LOGSPACE-complete.

The Degree of Irreversibility in Deterministic Finite Automata

2017 ◽  
Vol 28 (05) ◽  
pp. 503-522
Author(s):  
Holger Bock Axelsen ◽  
Markus Holzer ◽  
Martin Kutrib
Keyword(s):  
Finite Automaton ◽  
Regular Language ◽  
Finite Automata ◽  
Deterministic Finite Automaton ◽  
Deterministic Finite Automata ◽  
Infinite Hierarchy ◽  
Complete Problem ◽  
Nondeterministic Finite Automata ◽  
Forbidden Patterns

Recently, a method to decide the NL-complete problem of whether the language accepted by a given deterministic finite automaton (DFA) can also be accepted by some reversible deterministic finite automaton (REV-DFA) has been derived. Here, we show that the corresponding problem for nondeterministic finite automata (NFA) is PSPACE-complete. The recent DFA method essentially works by minimizing the DFA and inspecting it for a forbidden pattern. We here study the degree of irreversibility for a regular language, the minimal number of such forbidden patterns necessary in any DFA accepting the language, and show that the degree induces a strict infinite hierarchy of language families. We examine how the degree of irreversibility behaves under the usual language operations union, intersection, complement, concatenation, and Kleene star, showing tight bounds (some asymptotically) on the degree.

scholarly journals Efficient Recursive Subtyping

1992 ◽  
Vol 21 (405) ◽  
Author(s):  
Dexter Kozen ◽  
Jens Palsberg ◽  
Michael I. Schwartzbach
Keyword(s):  
Finite Automaton ◽  
Finite Automata ◽  
Lambda Calculus ◽  
Theoretic Approach ◽  
Exponential Time ◽  
Emptiness Problem ◽  
Definition Of

<p>Subtyping in the presence of recursive types for the lambda-calculus was studied by Amadio and Cardelli in 1991. They showed that the problem of deciding whether one recursive type is a subtype of another is decidable in exponential time.</p><p>In this paper we give an O(n^2) algorithm. Our algorithm is based on a simplification of the definition of the subtype relation, which allows us to reduce the problem to the emptiness problem for a certain finite automaton with quadratically many states.</p><p>It is known that equality of recursive types and the covariant Böhm order can be decided efficiently by means of finite automata. Our results extend the automata-theoretic approach to handle orderings based on contravariance.</p>

Parallel Algorithms for Minimal Nondeterministic Finite Automata Inference

2021 ◽  
Vol 178 (3) ◽  
pp. 203-227
Author(s):  
Tomasz Jastrzab ◽  
Zbigniew J. Czech ◽  
Wojciech Wieczorek
Keyword(s):  
Parallel Algorithms ◽  
Constraint Satisfaction ◽  
Finite Automaton ◽  
Regular Language ◽  
Finite Automata ◽  
Constraint Satisfaction Problem ◽  
Computational Experiments ◽  
Learning Sample ◽  
Automata Inference ◽  
Nondeterministic Finite Automaton

The goal of this paper is to develop the parallel algorithms that, on input of a learning sample, identify a regular language by means of a nondeterministic finite automaton (NFA). A sample is a pair of finite sets containing positive and negative examples. Given a sample, a minimal NFA that represents the target regular language is sought. We define the task of finding an NFA, which accepts all positive examples and rejects all negative ones, as a constraint satisfaction problem, and then propose the parallel algorithms to solve the problem. The results of comprehensive computational experiments on the variety of inference tasks are reported. The question of minimizing an NFA consistent with a learning sample is computationally hard.

Operations on Unambiguous Finite Automata

2018 ◽  
Vol 29 (05) ◽  
pp. 861-876 ◽  
Author(s):  
Jozef Jirásek ◽  
Galina Jirásková ◽  
Juraj Šebej
Keyword(s):  
Upper Bound ◽  
Finite Automaton ◽  
Finite Automata ◽  
Upper Bounds ◽  
Input String ◽  
State Complexity ◽  
Letter Alphabet ◽  
Left And Right ◽  
Nondeterministic Finite Automaton ◽  
Intersection Formula

A nondeterministic finite automaton is unambiguous if it has at most one accepting computation on every input string. We investigate the state complexity of basic regular operations on languages represented by unambiguous finite automata. We get tight upper bounds for reversal ([Formula: see text]), intersection ([Formula: see text]), left and right quotients ([Formula: see text]), positive closure ([Formula: see text]), star ([Formula: see text]), shuffle ([Formula: see text]), and concatenation ([Formula: see text]). To prove tightness, we use a binary alphabet for intersection and left and right quotients, a ternary alphabet for star and positive closure, a five-letter alphabet for shuffle, and a seven-letter alphabet for concatenation. For complementation, we reduce the trivial upper bound [Formula: see text] to [Formula: see text]. We also get some partial results for union and square.

ON THE REGULARITY OF SETS OF MULTI-ACCEPTED STRINGS OF A NON-DETERMINISTIC FINITE AUTOMATON

2009 ◽  
Vol 02 (04) ◽  
pp. 717-726
Author(s):  
L. K. Waters ◽  
J. K. Grieshop
Keyword(s):  
Finite Automaton ◽  
Finite Automata ◽  
Equivalence Classes ◽  
Deterministic Finite Automaton ◽  
Finite Sets ◽  
Nondeterministic Finite Automata ◽  
Labeling Approach ◽  
Acceptance Levels ◽  
Labeling Method

In this paper we establish the regularity of various sets of multi-accepted strings of nondeterministic finite automata. Regularity follows from the existence of accepting automata constructed by introducing a vector labeling method which generalizes the subset labeling approach. In each set the acceptance levels of the strings correspond to finite sets of additive equivalence classes of non-negative integers.

Efficient recursive subtyping

1995 ◽  
Vol 5 (1) ◽  
pp. 113-125 ◽  
Author(s):  
Dexter Kozen ◽  
Jens Palsberg ◽  
Michael I. Schwartzbach
Keyword(s):  
Finite Automaton ◽  
Finite Automata ◽  
Theoretic Approach ◽  
Exponential Time ◽  
Emptiness Problem ◽  
Definition Of

Subtyping in the presence of recursive types for the λ-calculus was studied by Amadio and Cardelli in 1991 (Amadio and Cardelli 1991). In that paper they showed that the problem of deciding whether one recursive type is a subtype of another is decidable in exponential time. In this paper we give an 0(n2) algorithm. Our algorithm is based on a simplification of the definition of the subtype relation, which allows us to reduce the problem to the emptiness problem for a certain finite automaton with quadratically many states.It is known that equality of recursive types and the covariant Bohm order can be decided efficiently by means of finite automata, since they are just language equality and language inclusion, respectively. Our results extend the automata-theoretic approach to handle orderings based on contravariance.

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