About the Algebraic Solutions of Smallest Enclosing Cylinders Problems

Given n points in Euclidean space E^d, we propose an algebraic algorithm to compute the best fitting (d-1)-cylinder. This algorithm computes the unknown direction of the axis of the cylinder. The location of the axis and the radius of the cylinder are deduced analytically from this direction. Special attention is paid to the case d=3 when n=4 and n=5. For the former, the minimal radius enclosing cylinder is computed algebrically from constrained minimization of a quartic form of the unknown direction of the axis. For the latter, an analytical condition of existence of the circumscribed cylinder is given, and the algorithm reduces to find the zeroes of an one unknown polynomial of degree at most 6. In both cases, the other parameters of the cylinder are deduced analytically. The minimal radius enclosing cylinder is computed analytically for the regular tetrahedron and for a trigonal bipyramids family with a symmetry axis of order 3.Comment: 13 pages, 0 figure; revised version submitted to publication (previous version is a copy of the original one of 2010

Spheres Unions and Intersections and Some of their Applications in Molecular Modeling

Accepted manuscript was chapter 2, pp.17-39, then was published as chapter 4, pp.61-83.International audienceThe geometrical and computational aspects of spheres unions and intersections are described. A practical analytical calculation of their surfaces and volumes is given in the general case: any number of intersecting spheres of any radii. Applications to trilateration and van der Waals surfaces and volumes calculation are considered. The results are compared to those of other algorithms, such as Monte-Carlo methods, regular grid methods, or incomplete analytical algorithms. For molecular modeling, these latter algorithms are shown to give strongly overestimated values when the radii values are in the ranges recommended in the literature, while regular grid methods are shown to give a poor accuracy. Other concepts related to surfaces and volumes of unions of spheres are evoked, such as Connolly's surfaces, accessible surface areas, and solvent excluded volumes