1,720,995 research outputs found
The complexity of flow on fat terrains and its I/O-efficient computation
No full textWe study the complexity and the i/o-efficient computation of flow on triangulated terrains. We present an acyclic graph, the descent graph, that enables us to trace flow paths in triangulations i/o-efficiently. We use the descent graph to obtain i/o-efficient algorithms for computing river networks and watershed-area maps in O(Sort(d+r)) i/o's, where r is the complexity of the river network and d of the descent graph. Furthermore we describe a data structure based on the subdivision of the terrain induced by the edges of the triangulation and paths of steepest ascent and descent from its vertices. This data structure can be used to report the boundary of the watershed of a query point q or the flow path from q in O(l(s)+Scan(k)) i/o's, where s is the complexity of the subdivision underlying the data structure, l(s) is the number of i/o's used for planar point location in this subdivision, and k is the size of the reported output.
On a-fat terrains, that is, triangulated terrains where the minimum angle of any triangle is bounded from below by a, we show that the worst-case complexity of the descent graph and of any path of steepest descent is O(n/a2), where n is the number of triangles in the terrain. The worst-case complexity of the river network and the above-mentioned data structure on such terrains is O(n2/a2). When a is a positive constant this improves the corresponding bounds for arbitrary terrains by a linear factor. We prove that similar bounds cannot be proven for Delaunay triangulations: these can have river networks of complexity T(n3)
Computing a minimum-dilation spanning tree is NP-hard
No full textGiven a set S of n points in the plane, a minimumdilation spanning tree of S is a tree with vertex set S of smallest possible dilation. We show that given a set S of n points and a dilation δ> 1, it is NP-hard to determine whether a spanning tree of S with dilation at most δ exists
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
최소-Dilation 신장 트리 찾기의 NP-hard 증명
No full text학위논문(석사) - 한국과학기술원 : 전산학전공, 2007.2, [ v, 31 p. ]In a geometric network G=(S,E), the graph distance between two vertices u, v∈S is the length of the shortest path in G connecting u to v. The dilation of G is the maximum factor by which graph distance differs from the Euclidean distance between every pair of vertices. We show that given a set S of n points and a dilation >1, it is NP-hard to determine whether a spanning tree of S with dilation at most exists.한국과학기술원 : 전산학전공
- …
