1,720,977 research outputs found
Permutations Avoiding a Simsun Pattern
Full text linkA permutation π avoids the simsun pattern τ if π avoids the consecutive pattern τ and the same condition applies to the restriction of π to any interval [k]. Permutations avoiding the simsun pattern 321 are the usual simsun permutation introduced by Simion and Sundaram. Deutsch and Elizalde enumerated the set of simsun permutations that avoid in addition any set of patterns of length 3 in the classical sense. In this paper we enumerate the set of permutations avoiding any other simsun pattern of length 3 together with any set of classical patterns of length 3.
The main tool in the proofs is a massive use of a bijection between permutations and increasing binary trees
Pattern avoiding alternating involutions
Full text linkWe enumerate and characterize some classes of alternating and reverse
alternating involutions avoiding a single pattern of length three or four. If
on one hand the case of patterns of length three is trivial, on the other hand,
the length four case is more challenging and involves sequences of
combinatorial interest, such as Motzkin and Fibonacci numbers
Two descent statistics over 321-avoiding centrosymmetric involutions
Full text linkCentrosymmetric involutions in the symmetric group S_{2n} are permutations pi such that pi = pi^{- 1} and pi(i)+ pi(2n + 1 - i) = 2n + 1 for all i, and they are in bijection with involutions of the hyperoctahedral group. We describe the distribu- tion of some natural descent statistics on 321-avoiding centrosymmetric involutions, including the number of descents in the rst half of the involution, and the sum of the positions of these descents. Our results are based on two new bijections, one between centrosymmetric involutions in S_{2n} and subsets of {1; ...; n}, and another one showing that certain statistics on Young diagrams that fit inside a rectangle are equidistributed. We also use the latter bijection to rene a known result stating that the distribution of the major index on 321-avoiding involutions is given by the q-analogue of the central binomial coefficients
Some permutations on Dyck words
No full textWe examine three permutations on Dyck words. The first one, α, is related to the Baker and Norine theorem on graphs, the second one, β, is the symmetry, and the third one is the composition of these two. The first two permutations are involutions and it is not difficult to compute the number of their fixed points, while the third one has cycles of different lengths. We show that the lengths of these cycles are odd numbers. This result allows us to give some information about the interplay between α and β , and a characterization of the fixed points of α∘β
Ascending runs in permutations and valued Dyck paths
No full textAbstract
We define a bijection between permutations and valued Dyck paths, namely, Dyck
paths whose odd vertices are labelled with an integer that does not exceed their height.
This map allows us to characterize the set of permutations avoiding the pattern 132 as
the preimage of the set of Dyck paths with minimal labeling. Moreover, exploiting this
bijection we associate to the set of n-permutations a polynomial that generalizes at the
same time Eulerian polynomials, Motzkin numbers, super-Catalan numbers, little Schr ̈oder
numbers, and other combinatorial sequences. Lastly, we determine the Hankel transform
of the sequence of such polynomials
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
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
- …
