1,721,111 research outputs found
Two-wayness: Automata and Transducers
Full text linkThis PhD is about two natural extensions of Finite Automata (FA): the 2-way fa (2FA) and the
2-way transducers (2T).
It is well known that 2FA s are computably equivalent to FAs, even in their nondeterministic
(2nfa) variant. However, in the field of descriptional complexity, some questions remain. Raised by Sakoda and Sipser in 1978, the question of the cost of the simulation of 2NFA by 2DFA (the deterministic variant of 2FA) is still open. In this manuscript, we give an answer in a restricted case in which the nondeterministic choices of the simulated 2NFA may occur at the boundaries of the input tape only (2ONFA). We show that every 2ONFA can be simulated by a 2DFA of subexponential (but superpolynomial) size. Under the assumptions L=NL, this cost is reduced to the polynomial level. Moreover, we prove that the complementation and the simulation by a halting 2ONFA is polynomial. We also consider the anologous simulations for alternating devices.
Providing a one-way write-only output tape to FAs leads to the notion of transducer. Contrary to the case of finite automata which are acceptor, 2-way transducers strictly extends the computational power of 1-way one, even in the case where both the input and output alphabets are unary. Though 1-way transducers enjoy nice properties and characterizations (algebraic, logical, etc. . . ), 2-way variants are less known, especially the nondeterministic case. In this area, this manuscript gives a new contribution: an algebraic characterization of the relations accepted by two-way transducers when both the input and output alphabets are unary. Actually, it can be reformulated as follows: each unary two-way transducer is equivalent to a sweeping (and even rotating) transducer. We also show that the assumptions made on the size of the alphabets are required, that is, sweeping transducers weakens the 2-way transducers whenever at least one of the alphabet is non-unary. On the path, we discuss on the computational power of some algebraic operations on word relations, introduced in the aim of describing the behavior of 2-way transducers or, more generally, of 2-way weighted automata. In particular, the mirror operation, consisting in reversing the input word in order to describe a right to left scan, draws our attention.
Finally, we study another kind of operations, more adapted for binary word relations: the
composition. We consider the transitive closure of relations. When the relation belongs to some very restricted sub-family of rational relations, we are able to compute its transitive closure and we set its complexity. This quickly becomes uncomputable when higher classes are considered
Two-way automata making choices only at the endmarkers
No full textThe question of the state-size cost for simulation of two-way nondeterministic automata (2 nfas) by two-way deterministic automata (2 dfas) was raised in 1978 and, despite many attempts, it is still open. Subsequently, the problem was attacked by restricting the power of 2 dfas (e.g., using a restricted input head movement) to the degree for which it was already possible to derive some exponential gaps between the weaker model and the standard 2 nfas. Here we use an opposite approach, increasing the power of 2 dfas to the degree for which it is still possible to obtain a subexponential conversion from the stronger model to the standard 2 dfas. In particular, it turns out that subexponential conversion is possible for two-way automata that make nondeterministic choices only when the input head scans one of the input tape endmarkers. However, there is no restriction on the input head movement. This implies that an exponential gap between 2 nfas and 2 dfas can be obtained only for unrestricted 2 nfas using capabilities beyond the proposed new model. As an additional bonus, conversion into a machine for the complement of the original language is polynomial in this model. The same holds for making such machines self-verifying, halting, or unambiguous. Finally, any superpolynomial lower bound for the simulation of such machines by standard 2 dfas would imply L ≠ NL. In the same way, the alternating version of these machines is related to L over(=, ?) NL over(=, ?) P, the classical computational complexity problems. © 2014 Elsevier Inc. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Collectio Selecta SS. Ecclesiae Patrum, Complectens Exquisitissima Opera Tum Dogmatica Et Moralia, Tum Apologetica Et Oratoria; Accurantibus D. A. B. Guillon, Missionum Gallicarum Presbyteris, Nonnulisque Cleri Gallicani Presbyteris, ... Una Cum D. M. N. S. Cuillon, In Facultate Theologiae Parisensi Eloquentiae Sacrae Professore, Praedicatore Regio, Auctore Libri Cui Titulus Gallice
Full text linkCOLLECTIO SELECTA SS. ECCLESIAE PATRUM, COMPLECTENS EXQUISITISSIMA OPERA TUM DOGMATICA ET MORALIA, TUM APOLOGETICA ET ORATORIA; ACCURANTIBUS D. A. B. GUILLON, MISSIONUM GALLICARUM PRESBYTERIS, NONNULISQUE CLERI GALLICANI PRESBYTERIS, ... UNA CUM D. M. N. S. CUILLON, IN FACULTATE THEOLOGIAE PARISENSI ELOQUENTIAE SACRAE PROFESSORE, PRAEDICATORE REGIO, AUCTORE LIBRI CUI TITULUS GALLICE
Collectio Selecta SS. Ecclesiae Patrum, Complectens Exquisitissima Opera Tum Dogmatica Et Moralia, Tum Apologetica Et Oratoria; Accurantibus D. A. B. Guillon, Missionum Gallicarum Presbyteris, Nonnulisque Cleri Gallicani Presbyteris, ... Una Cum D. M. N. S. Cuillon, In Facultate Theologiae Parisensi Eloquentiae Sacrae Professore, Praedicatore Regio, Auctore Libri Cui Titulus Gallice ( - )
Programma ([1]
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Two-way automata making choices only at the endmarkers
No full textThe question of the state-size cost for simulation of two-way nondeterministic automata (2nfas) by two-way deterministic automata (2dfas) was raised in 1978 and, despite many attempts, it is still open. Subsequently, the problem was attacked by restricting the power of 2dfas (e.g., using a restricted input head movement) to the degree for which it was already possible to derive some exponential gaps between the weaker model and the standard 2nfas. Here we use an opposite approach, increasing the power of 2dfas to the degree for which it is still possible to obtain a subexponential conversion from the stronger model to the standard 2dfas. In particular, it turns out that subexponential conversion is possible for two-way automata that make nondeterministic choices only when the input head scans one of the input tape endmarkers. However, there is no restriction on the input head movement. This implies that an exponential gap between 2nfas and 2dfas can be obtained only for unrestricted 2nfas using capabilities beyond the proposed new model.
As an additional bonus, conversion into a machine for the complement of the original language is polynomial in this model. The same holds for making such machines self-verifying, halting, or unambiguous. Finally, any superpolynomial lower bound for the simulation of such machines by standard 2dfas would imply L ≠ NL. In the same way, the alternating version of these machines is related to L ≟ NL ≟ P, the classical computational complexity problems
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