Covering many points with a small-area box

Let $P$ be a set of $n$ points in the plane. We show how to find, for a given integer $k>0$, the smallest-area axis-parallel rectangle that covers $k$ points of $P$ in $O(nk^2 \log n+ n\log^2 n)$ time. We also consider the problem of, given a value $\alpha>0$, covering as many points of $P$ as possible with an axis-parallel rectangle of area at most $\alpha$. For this problem we give a probabilistic $(1-\varepsilon)$-approximation that works in near-linear time: In $O((n/\varepsilon^4)\log^3 n \log (1/\varepsilon))$ time we find an axis-parallel rectangle of area at most $\alpha$ that, with high probability, covers at least $(1-\varepsilon)\mathrm{\kappa^*}$ points, where $\mathrm{\kappa^*}$ is the maximum possible number of points that could be covered

Generalized dynamical entropies in weakly chaotic systems

A large class of technically non-chaotic systems, involving scatterings of light particles by flat surfaces with sharp boundaries, is nonetheless characterized by complex random looking motion in phase space. For these systems one may define a generalized, Tsallis type dynamical entropy that increases linearly with time. It characterizes a maximal gain of information about the system that increases as a power of time. However, this entropy cannot be chosen independently from the choice of coarse graining lengths and it assigns positive dynamical entropies also to fully integrable systems. By considering these dependencies in detail one usually will be able to distinguish weakly chaotic from fully integrable systems.Comment: Submitted to Physica D for the proceedings of the Santa Fe workshop of November 6-9, 2002 on Anomalous Distributions, Nonlinear Dynamics and Nonextensivity. 8 pages and two figure

Harmonic Currents of Finite Energy and Laminations

We introduce, on a complex Kahler manifold (M,\omega), a notion of energy for harmonic currents of bidegree (1,1). This allows us to define $\int T \wedge T \wedge \omega^{k-2},$ for positive harmonic currents. We then show that for a lamination with singularities of a compact set in P^2 there is a unique positive harmonic current which minimizes energy. If X is a compact laminated set in P^2 of class C^1 it carries a unique positive harmonic current T of mass 1. The current T can be obtained by an Ahlfors type construction starting with a arbitrary leaf of X.Comment: 29 page