Given a set S of n points in the plane, an E-strongly convex delta-hull of S is defined as a convex polygon P with the vertices taken from S such that no point of S lies farther than 6 outside P and such that even if ...
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Given a set S of n points in the plane, an E-strongly convex delta-hull of S is defined as a convex polygon P with the vertices taken from S such that no point of S lies farther than 6 outside P and such that even if the vertices of P are perturbed by as much as e, P remains convex. This paper presents the first parallel robust method for this generalized convex hull problem (note that the convex hull of S is the 0-strongly convex 0-hull of S). We show that an e-strongly convex O(epsilon + beta)-hull of S can be constructed in O(log(3) n) time using n processors with imprecise computations, where beta is the error unit of primitive operations. This result also implies an improved sequential algorithm. Our algorithm consists of two parts: (1) computing a convex O(epsilon + beta)-hull of n points, in O(log(3) n) time using n processors, and (2) constructing an E-strongly convex O(epsilon + beta)-hull of a convex polygon with n vertices, in O(log(2) n) time with n processors. We also find an approximate bridge of two sets with n points each, in O(log(2) n) time using n processors, which we use as a subroutine. All these algorithms are fundamental and have their own applications. The parallel computationalmodel in this paper is the EREW pram. (C) 2002 Elsevier Science B.V. All rights reserved.
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