Greg Aloupis

Learn More
Several measures of data depth have been proposed, each attempting to maintain certain robustness properties. This paper lists the main approaches known to the computer science community. Properties and algorithms are mentioned, for computing the depth of a point and the location of
We study several coloring problems for geometric range-spaces. In addition to their theoretical interest, some of these problems arise in sensor networks. Given a set of points in R or R, we want to color them such that every region of a certain family (e.g., every disk containing at least a certain number of points) contains points of many (say, k)(More)
Consider two orthogonal closed chains on a cylinder. The chains are monotone with respect to the angle Θ. We wish to rigidly move one chain so that the total area between the two chains is minimized. This is a geometric measure of similarity between two repeating melodies proposed by Ó Maid́ın. We present an O(n) time algorithm to compute this measure if Θ(More)
We propose a new model of realistic input: k-guardable objects. An object is k-guardable if its boundary can be seen by k guards in the interior of the object. In this abstract, we describe a simple algorithm for triangulating k-guardable polygons. Our algorithm, which is easily implementable, takes linear time assuming that k is constant.
We prove that for every centrally symmetric convex polygonQ, there exists a constant α such that any locally finite αk-fold covering of the plane by translates of Q can be decomposed into k coverings. This improves on a quadratic upper bound proved by Pach and Tóth. The question is motivated by a sensor network problem, in which a region has to be monitored(More)
Modular robots consist of many small units that attach together and can perform local motions. By combining these motions, we can achieve a reconfiguration of the global shape. The term modular comes from the idea of grouping together a fixed number of units into a module, which behaves as a larger individual component. Recently, a fair amount of research(More)
For a set R of n red points and a set B of n blue points, a <i>BR-matching</i> is a non-crossing geometric perfect matching where each segment has one endpoint in B and one in R. Two BR-matchings are compatible if their union is also non-crossing. We prove that, for any two distinct BR-matchings M and M', there exists a sequence of BR-matchings M =(More)
In this paper we study three related problems: (i) Given a fat polygon P , we show how to find a set G of points in P such that every point on the boundary of P sees at least one point of G. The set G is said to guard the boundary of P and its cardinality depends on the shape parameters of P . Fat polygons are often used to model more realistic inputs. (ii)(More)
Given a set S of n points in R 2 , the Oja depth of a point is the sum of the areas of all triangles formed by and two elements of S. A point in R 2 with minimum depth is an Oja median. We show how an Oja median may be computed in O(n log 3 n) time. In addition, we present an algorithm for computing the Fermat-Torricelli points of n lines in O(n) time.(More)
Consider two orthogonal closed chains on a cylinder. These chains are monotone with respect to the tangential Θ direction. We wish to rigidly move one chain so that the total area between the two is minimized. This minimization is a geometric measure of similarity between two melodies proposed by Ó Maid́ın. The Θ direction represents time and the axial(More)