1,721,018 research outputs found
A novel estimation procedure for robust CP model fitting
No full textThe usual way of parameter estimation in CANDECOM/PARAFAC (CP) is an alternating least squares (ALS) procedure that yields least-squares solutions and provides consistent outcomes but at the same time has several deficiencies, like sensitivity to the presence of outliers in the data, slow convergence, and susceptibility to degeneracy conditions. A number of works have addressed these weaknesses, but to our knowledge, there is no outlier-robust procedure that is highly computationally efficient at the same time, especially for large data sets. We propose a robust procedure based on an integrated estimation algorithm, alternative to ALS, which guards against outliers and is computationally efficient at the same time
A novel estimation procedure for robust CANDECOMP/PARAFAC model fitting
No full textThe parameter estimation in CANDECOMP/PARAFAC (CP) is carried out by alternating least squares (ALS) that yields least-squares solutions and provides consistent outcomes. At the same time, it has several drawbacks, like sensitivity to the presence of outliers in the data, issues with the computational efficiency in terms of processing time and memory requirements, as well as susceptibility to degeneracy conditions. These weaknesses have been addressed, but there is no outlier-robust procedure that at the same time is highly computationally efficient, especially for large data sets. A novel procedure based on an integrated estimation algorithm is proposed. This is an alternative to ALS, which guards against outliers and is computationally efficient at the same time. The performance of the new method is demonstrated in an extensive simulation study and an empirical example
Comparing three robust procedures for CANDECOMP/PARAFAC estimation
Full text linkCANDECOMP/PARAFAC aims to identify the true components underlying data with a
trilinear configuration. The search for a unique solution is not always an easy task, as degeneracies may occur. The presence of outlier contamination further complicates the matter
by requiring the implementation of robust procedures. The most used robust approach RALS is based on the iterative repetition of the standard alternating least squares algorithm,
which is known to be slow and vulnerable to over-factoring, collinearity, and bad initial
values. Here the faster and stable robust alternative R-INT1, based on the SWATLD-ALS
integrated scheme INT-1, is implemented. Its performance is tested against ALS, R-ALS,
and R-INT2 (built on INT-2, an ATLD-ALS procedure already proposed in the literature).
Performance is assessed in a simulation study with varied levels of outlier contamination
Fast CP Model Fitting with Integrated ASD-ALS Procedure
No full textThe CP decomposition is the most appropriate tool for modeling data arrays with a trilinear structure. Model fitting can be hindered by several issues, including computational inefficiency, bad initialization, excessive modeled noise, sensitivity to over-factoring and collinearity. Many algorithms have been proposed for parameter estimation, each with specific strengths and weaknesses. Fast procedures tend to be less stable and vice-versa. Stability is usually prioritized by preferring the least-square approach ALS, albeit slow and sensitive to excess factors. As a solution integrated methods have been proposed in the literature. First, estimation is initialized with a fast procedure to ensure competitive speed then results are refined with ALS to improve precision. In this work, we implement a novel integrated algorithm called INT-3 where ASD steps are concatenated with ALS. ASD was selected because of its remarkable speed and low memory consumption requirements. INT-3 performance is tested against ALS on artificial data
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
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