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  • 1995-1999  (2)
  • Computational geometry  (2)
  • 51-04
  • Configuration space
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Algorithmica 15 (1996), S. 428-447 
    ISSN: 1432-0541
    Keywords: Computational geometry ; Lines in space ; Plücker coordinates ; ε-Nets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Questions about lines in space arise frequently as subproblems in three-dimensional computational geometry. In this paper we study a number of fundamental combinatorial and algorithmic problems involving arrangements ofn lines in three-dimensional space. Our main results include: 1. A tight Θ(n 2) bound on the maximum combinatorial description complexity of the set of all oriented lines that have specified orientations relative to then given lines. 2. A similar bound of Θ(n 3) for the complexity of the set of all lines passing above then given lines. 3. A preprocessing procedure usingO(n 2+ɛ) time and storage, for anyε〉0, that builds a structure supportingO(logn)-time queries for testing if a line lies above all the given lines. 4. An algorithm that tests the “towering property” inO(n 2+ɛ) time, for anyε〉0; don given red lines lie all aboven given blue lines? The tools used to obtain these and other results include Plücker coordinates for lines in space andε-nets for various geometric range spaces.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Algorithmica 16 (1996), S. 498-516 
    ISSN: 1432-0541
    Keywords: Computational geometry ; Combinatorial optimization ; Linear programming ; Smallest enclosing ball ; Smallest enclosing ellipsoid ; Randomized incremental algorithms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We present a simple randomized algorithm which solves linear programs withn constraints andd variables in expected $$\min \{ O(d^2 2^d n),e^{2\sqrt {dIn({n \mathord{\left/ {\vphantom {n {\sqrt d }}} \right. \kern-\nulldelimiterspace} {\sqrt d }})} + O(\sqrt d + Inn)} \}$$ time in the unit cost model (where we count the number of arithmetic operations on the numbers in the input); to be precise, the algorithm computes the lexicographically smallest nonnegative point satisfyingn given linear inequalities ind variables. The expectation is over the internal randomizations performed by the algorithm, and holds for any input. In conjunction with Clarkson's linear programming algorithm, this gives an expected bound of $$O(d^2 n + e^{O(\sqrt {dInd} )} ).$$ The algorithm is presented in an abstract framework, which facilitates its application to several other related problems like computing the smallest enclosing ball (smallest volume enclosing ellipsoid) ofn points ind-space, computing the distance of twon-vertex (orn-facet) polytopes ind-space, and others. The subexponential running time can also be established for some of these problems (this relies on some recent results due to Gärtner).
    Type of Medium: Electronic Resource
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