Approximating centroids for the maximum intersection of spherical polygons

This paper considers the problem of investigating the spherical regions owned by the maximum number of spherical polygons. We present a practical O(n(v+I)) time algorithm for finding the approximating centroids for the maximum intersection of spherical polygons, where n, v, and I are, respectively, the numbers of polygons, all vertices, and intersection points. In order to elude topological errors and handle geometric degeneracies, our algorithm takes the approach of edge-based partitioning of the sphere. Furthermore, the numerical complexity is avoided since the algorithm is completely spherical.     

Optimal and near-optimal algorithms for generalized intersection reporting on pointer machines

We develop efficient algorithms for a number of generalized intersection reporting problems, including orthogonal and general segment intersection, 2D range searching, rectangular point enclosure, and rectangle intersection search. Our results for orthogonal and general segment intersection, 3-sided 2D range searching, and rectangular pointer enclosure problems match the lower bounds for their corresponding standard versions under the pointer machine model. Our results for the remaining problems improve upon the best known previous algorithms.     

Convex hulls of objects bounded by algebraic curves

We present an0(n ·d ^o(1)) algorithm to compute the convex hull of a curved object bounded by0(n) algebraic curve segments of maximum degreed.Research supported in part by NSF Grant MIP-85 21356, ARO Contract DAA G29-85-C0018 under Cornell MSI, and ONR Contract N00014-88-K-0402. This paper is an updated version of a part of [6].     

Minimizing the sum of the k largest functions in linear time

Given a collection of n functions defined on , and a polyhedral set , we consider the problem of minimizing the sum of the k largest functions of the collection over Q. Specifically we focus on collections of linear functions and several classes of convex, piecewise linear functions which are defined by location models. We present simple linear programming formulations for these optimization models which give rise to linear time algorithms when the dimension d is fixed. Our results improve complexity bounds of several problems reported recently by Tamir [Discrete Appl. Math. 109 (2001) 293-307], Tokuyama [Proc. 33rd Annual ACM Symp. on Theory of Computing, 2001, pp. 75-84] and Kalcsics, Nickel, Puerto and Tamir [Oper. Res. Lett. 31 (1984) 114-127].     

A note on maximum independent sets in rectangle intersection graphs

Finding the maximum independent set in the intersection graph of n axis-parallel rectangles is NP-hard. We re-examine two known approximation results for this problem. For the case of rectangles of unit height, Agarwal, van Kreveld and Suri [Comput. Geom. Theory Appl. 11 (1998) 209-218] gave a (1+1/k)-factor algorithm with an O(nlogn+n^2k−1) time bound for any integer constant k?1; we describe a similar algorithm running in only O(nlogn+nΔ^k−1) time, where Δ?n denotes the maximum number of rectangles a point can be in. For the general case, Berman, DasGupta, Muthukrishnan and Ramaswami [J. Algorithms 41 (2001) 443-470] gave a ⌈log_kn⌉-factor algorithm with an O(n^k+1) time bound for any integer constant k?2; we describe similar algorithms running in O(nlogn+nΔ^k−2) and n^O(k/logk) time.     

Line-segment intersection reporting in parallel

In this paper we give a parallel algorithm for line-segment intersection reporting in the plane. It runs in timeO(((n +k) logn log logn)/p) usingp processors on a concurrent-read-exclusive-write (CREW)-PRAM, wheren is the number of line segments,k is the number of intersections, andp n +k.This work was supported by the DFG, SFB 124, TP B2, VLSI Entwurfsmethoden und Parallelität.     

Robustness of k-gon Voronoi diagram construction

In this paper, we present a plane sweep algorithm for constructing the Voronoi diagram of a set of non-crossing line segments in 2D space using a distance metric induced by a regular k-gon and study the robustness of the algorithm. Following the algorithmic degree model [G. Liotta, F.P. Preparata, R. Tamassia, Robust proximity queries: an illustration of degree-driven algorithm design, SIAM J. Comput. 28 (3) (1998) 864-889], we show that the Voronoi diagram of a set of arbitrarily oriented segments can be constructed with degree 14 for certain k-gon metrics (e.g., k=6,8,12). For rectilinear segments or segments with slope +1 or −1, the degree reduces to 2. The algorithm is easy to implement and finds applications in VLSI layout.     

Approximating the Maximum Agreement Forest on k trees

The Maximum Agreement Forest problem (MAF) asks for the largest common subforest of a set of binary trees. This problem is known to be MAXSNP-complete for instances consisting of 2 trees. We show that it remains MAXSNP-complete for k?2 trees.     

An optimal time and minimal space algorithm for rectangle intersection problems

Given a set ofn iso-oriented rectangles in the plane whose sides are parallel to the coordinate axes, we consider the rectangle intersection problem, i.e., finding alls intersecting pairs. The problem is well solved in the past and its solution relies heavily on unconventional data structures such as range trees, segment trees or rectangle trees. In this paper we demonstrate that classical divide-and-conquer technique and conventional data structures such as linked lists are sufficient to achieve a time bound ofO(n logn) +s, and a space bound of (n), both of which are optimal.Supported in part by the National Science Foundation under Grants MCS 8342682 and ECS 8340031.     

Smallest k-point enclosing rectangle and square of arbitrary orientation

Given a set of n points in 2D, the problem of identifying the smallest rectangle of arbitrary orientation, and containing exactly k(?n) points is studied in this paper. The worst case time and space complexities of the proposed algorithm are O(n²logn+nk(n−k)(n−k+logk)) and O(n), respectively. The algorithm is then used to identify the smallest square of arbitrary orientation, and containing exactly k points in O(n²logn+kn²(n−k)logn) time.     

Reporting intersections among thick objects

Let E be a set of n objects in fixed dimension d. We assume that each element of E has diameter smaller than D and has volume larger than V. We give a new divide and conquer algorithm that reports all the intersecting pairs in O(nlogn+(D^d/V)(n+k)) time and using O(n) space, where k is the number of intersecting pairs. It makes use of simple data structures and primitive operations, which explains why it performs very well in practice. Its restriction to unit balls in low dimensions is optimal in terms of time complexity, space complexity and algebraic degree.     

Constructing vertex-disjoint paths in (n, k)-star graphs

This work describes a novel routing algorithm for constructing a container of width n − 1 between a pair of vertices in an (n, k)-star graph with connectivity n − 1. Since Lin et al. [T.C. Lin, D.R. Duh, H.C. Cheng, Wide diameter of (n, k)-star networks, in: Proceedings of the International Conference on Computing, Communications and Control Technologies, vol. 5, 2004, pp. 160-165] already calculated the wide diameters in (n, n − 1)-star and (n, 1)-star graphs, this study only considers an (n, k)-star with 2 ? k ? n − 2. The length of the longest container among all constructed containers serves as the upper bound of the wide diameter of an (n, k)-star graph. The lower bound of the wide diameter of an (n, k)-star graph with 2 ? k ? ⌊n/2⌋ and the lower bound of the wide diameter of a regular graph with a connectivity of 2 or above are also computed. Measurement results indicate that the wide diameter of an (n, k)-star graph is its diameter plus 2 for 2 ? k ? ⌊n/2⌋, or its diameter plus a value between 1 and 2 for ⌊n/2⌋ + 1 ? k ? n − 2.     

Fast dynamic intersection searching in a set of isothetic line segments

We reconsider the (isothetic) line segment intersection searching problem: Given a set S of n horizontal and vertical line segments and a query segment q, find all t segments in S intersecting q. We describe the first dynamic solution for this problem which achieves O(log n + t) query time. This, however, has to be paid by O(n log² n) space requirements and O(log³ n) update time. If segments are defined over a grid of size N × N (the semidynamic case), then the problem can be solved in O(logN + t) query time, O(n log² N) space and O(log² N) update time. The solution is based on the use of segment tree and range tree and the halfobject technique.     

Finding the maximum turnable state for mill/turn parts

Mill/Turns are a class of machine tool on which, as their name implies, both turning and milling operations can be performed. This capability results in reduced set-ups, leading to increased production rates and better part quality. On Mill/Turns it is more efficient to remove material by turning than by milling. Knowing how much material is turnable is therefore important in creating efficient process plans. In this paper computational techniques for determining the Maximum Turnable State (MTS) of a Mill/Turn part are presented. The Maximum Turnable Volume (MTV) is the (regularized boolean) difference between the initial workpiece and the MTS. The MTS is computed incrementally with respect to the chosen workpiece axis. The technique has been implemented and several examples are included.     

Maximal intersection of spherical polygons by an arc with applications to 4-axis machining

Many geometric optimization problems in CAD/CAM can be reduced to a maximal intersection problem on the sphere: given a set of N simple spherical polygons on the unit sphere and a real number constant L≤2π, find an arc of length L on the unit sphere that intersects as many spherical polygons as possible. Past results can only solve this maximization problem for two very restricted special cases: the arc must be either a great circle or a semi-great circle. In this paper, a simple and deterministic algorithm based on domain partitioning is presented for solving this maximal arc intersection problem in the general case when the number L is arbitrary. The algorithm is made possible by reducing the domain of the arcs to a continuous sub-space in R² and then establishing a quotient space partitioning in this sub-space based on a congruence relation. The number of the constituting congruent sub-regions in this quotient space partitioning is shown to have an upper-bound O(E³), where E is the total number of edges on the polygons. The proposed algorithm has a worst-case upper bound O(ME) on its running time, where M is an output-sensitive number and is bounded by O(E³). Examples including two realistic tests for 4-axis NC machining are presented.     

Drawing K2,n: A lower bound

We give a tradeoff theorem between the area and the aspect ratio required by any planar straight-line drawing of K_2,n on the integer lattice. In particular we show that if the drawing is contained in a rectangle of area O(n) then the rectangle must have aspect ratio , and conversely, if the aspect ratio is O(1) then the area must be .     

On the density and discrepancy of a 2D point set with applications to thermal analysis of VLSI chips

In this era of giga-scale integration, thermal analysis has become one of the hot topics in VLSI chip design. Active thermal sources may be abstracted as a set of weighted points on a 2D chip-floor. The conventional notion of discrepancy that deals with the congestion properties of a set of scattered points may not be able to capture properly all real-life instances in this context. In this paper, we have introduced a new concept, called the density of a region to study some of the properties of the distribution of these weighted points. We prove several counter-intuitive results concerning the properties of the regions that have maximum or minimum density. We then outline algorithms for recognizing these regions. We also compare the attributes of density with the existing concept of discrepancy.     

A new algorithm for the largest empty rectangle problem

A rectangleA and a setS ofn points inA are given. We present a new simple algorithm for the so-called largest empty rectangle problem, i.e., the problem of finding a maximum area rectangle contained inA and not containing any point ofS in its interior. The computational complexity of the presented algorithm isO(n logn + s), where s is the number of possible restricted rectangles considered. Moreover, the expected performance isO(n · logn).