1,720,975 research outputs found
General forbidden configuration theorems
No full textAbstractResults in this paper gives bounds on the number of columns in a matrix when certain submatrices are forbidden. Let F be a k by l (0, 1)-matrix with no repeated columns, column sums at least s. Let A be a m by n (0, 1)-matrix with no repeated column, column sums at least s and no submatrix F nor any row and column permutation of F. Then n⩽(mk−1) + (mk−2) + ⋯ + (ms). This bound is best possible for numerous F. The bound, with s = 0, is an easy corollary to a bound of Sauer and Perles and Shelah. The bounds can be extended to any F and to any F where we do not allow row and column permutations. The results follow from a configuration theorem that says, in essence, that matrices without a configuration are determined by row intersections of sets of rows of various sizes. A linear independence argument yields the bound. Results of Ryser, Frankl and Pach, Quinn and the author are obtained
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Properties of (0, 1)-matrices without certain configurations
No full textAbstractWe generalize results of Ryser on (0, 1)-matrices without triangles, 3 × 3 submatrices with row and column sums 2. The extremal case of matrices without triangles was previously studied by the author. Let the row intersection of row i and row j (i ≠ j) of some matrix, when regarded as a vector, have a 1 in a given column if both row i and row j do not 0 otherwise. For matrices satisfying some conditions on forbidden configurations and column sums ⩾ 2, we find that the number of linearly independent row intersections is equal to the number of distinct columns. The extremal matrices with m rows and (m2) distinct columns have a unique SDR of pairs of rows with 1's. A triangle bordered with a column of 0's and its (0, 1)-complement are also considered as forbidden configurations. Similar results are obtained and the extremal matrices are closely related to the extremal matrices without triangles
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
A forbidden configuration theorem of Alon
No full textAbstractThe paper studies the maximum possible number of distinct rows in a matrix with n columns with entries in column i in {0, 1, …, qi − 1} that does not contain certain forbidden submatrices. The results might have algorithmic significance if, for example, these matrices are the constraint matrix of a linear program. Combinatorial problems often yield a forbidden submatrix structure. Let (n; q1, q2, …, qn)-matrices be matrices on n columns with entries in column i in {0, 1, …, qi − 1} and let S be a family of subsets of {1, 2, …, n}. Let f(n, S) be the number of (n; q1, q2, …, qn)-rows which for each S ϵ S do not have 0's in all columns S. Noga Alon proved that if A is an m × n (n; q1, q2, …, qn)-matrix with no repeated rows, and for each S ϵ S, not all possible rows on columns S, then m ⩽ f(n, S). This paper provides an inductive proof and new f(n, S) × n matrices A as above. A linear algebra proof is given for the case q1 = q2 = … = qn = 2. Alon's shift proof technique is extended to handle the case A does not have all possible rows on S, each row occurring at least t times. Some other results concerning the extremal f(n, S) × n matrices are presented
Forbidden Configurations, Discrepancy and Determinants
No full textAn m × n matrix A is said to have hereditary discrepancy d if the maximum over submatrices B of A of the minimum over (−1/2, +1/2)-vectors x of ‖Bx‖∞. If A is integral and has no repeated rows then we show that m is bounded by a polynomial in n for fixed d. This improves a result of Lovász and Vesztergombi for fixed d. Let A be an m × n matrix with no repeated rows and with each square submatrix having determinant {0, ±1, ±2,..., ±k} . Then m is bounded by a polynomial in n for fixed k. This extends a result of Heller for totally unimodular matrices. (A result of Kung combined with results of J. Lee provides a much better bound.) Both bounds follow from repeated applications of the forbidden configuration theorem of Sauer, Perles and Shelah, which states that an m × n (0, 1)-matrix with no repeated rows and no 2kxk submatrix of all (0, 1)-rows on k columns has m at most (nk−1)+(nk−2)+⋯+(n0)
- …
