433 research outputs found
Quasiconvex Programming
We define quasiconvex programming, a form of generalized linear programming
in which one seeks the point minimizing the pointwise maximum of a collection
of quasiconvex functions. We survey algorithms for solving quasiconvex programs
either numerically or via generalizations of the dual simplex method from
linear programming, and describe varied applications of this geometric
optimization technique in meshing, scientific computation, information
visualization, automated algorithm analysis, and robust statistics.Comment: 33 pages, 14 figure
Uncertainty Control for Reliable Video Understanding on Complex Environments
International audienceThe most popular applications for video understanding are those related to video-surveillance (e.g. alarms, abnormal behaviours, expected events, access control). Video understanding has several other applications of high impact to the society as medical supervision, traffic control, violent acts detection, crowd behaviour analysis, among many others. We propose a new generic video understanding approach able to extract and learn valuable information from noisy video scenes for real-time applications. This approach comprises motion segmentation, object classification, tracking and event learning phases. This work is focused on building the first fundamental blocks allowing a proper management of uncertainty of data in every phase of the video understanding process. The main contributions of the proposed approach are: (i) a new algorithm for tracking multiple objects in noisy environments, (ii) the utilisation of reliability measures for modelling uncertainty in data and for proper selection of valuable information extracted from noisy data, (iii) the improved capability of tracking to manage multiple visual evidence-target associations, (iv) the combination of 2D image data with 3D information in a dynamics model governed by reliability measures for proper control of uncertainty in data, and (v) a new approach for event recognition through incremental event learning, driven by reliability measures for selecting the most stable and relevant data
Dynamic movement primitives: volumetric obstacle avoidance
Dynamic Movement Primitives (DMPs) are a framework for learning a trajectory from a demonstration. The trajectory can be learned efficiently after only one demonstration, and it is immediate to adapt it to new goal positions and time duration. Moreover, the trajectory is also robust against perturbations. However, obstacle avoidance for DMPs is still an open problem. In this work, we propose an extension of DMPs to support volumetric obstacle avoidance based on the use of superquadric potentials. We show the advantages of this approach when obstacles have known shape, and we extend it to unknown objects using minimal enclosing ellipsoids. A simulation and experiments with a real robot validate the framework, and we make freely available our implementation
Simulating Hard Rigid Bodies
Several physical systems in condensed matter have been modeled approximating
their constituent particles as hard objects. The hard spheres model has been
indeed one of the cornerstones of the computational and theoretical description
in condensed matter. The next level of description is to consider particles as
rigid objects of generic shape, which would enrich the possible phenomenology
enormously. This kind of modeling will prove to be interesting in all those
situations in which steric effects play a relevant role. These include biology,
soft matter, granular materials and molecular systems. With a view to
developing a general recipe for event-driven Molecular Dynamics simulations of
hard rigid bodies, two algorithms for calculating the distance between two
convex hard rigid bodies and the contact time of two colliding hard rigid
bodies solving a non-linear set of equations will be described. Building on
these two methods, an event-driven molecular dynamics algorithm for simulating
systems of convex hard rigid bodies will be developed and illustrated in
details. In order to optimize the collision detection between very elongated
hard rigid bodies, a novel nearest-neighbor list method based on an oriented
bounding box will be introduced and fully explained. Efficiency and performance
of the new algorithm proposed will be extensively tested for uniaxial hard
ellipsoids and superquadrics. Finally applications in various scientific fields
will be reported and discussed.Comment: 36 pages, 17 figure
An investigation into the Gustafsson limit for small planar antennas using optimisation
The fundamental limit for small antennas provides a guide to the
effectiveness of designs. Gustafsson et al, Yaghjian et al, and
Mohammadpour-Aghdam et al independently deduced a variation of the
Chu-Harrington limit for planar antennas in different forms. Using a
multi-parameter optimisation technique based on the ant colony algorithm,
planar, meander dipole antenna designs were selected on the basis of lowest
resonant frequency and maximum radiation efficiency. The optimal antenna
designs across the spectrum from 570 to 1750 MHz occupying an area of were compared with these limits calculated using the
polarizability tensor. The results were compared with Sievenpiper's comparison
of published planar antenna properties. The optimised antennas have greater
than 90% polarizability compared to the containing conductive box in the range
, so verifying the optimisation algorithm. The generalized
absorption efficiency of the small meander line antennas is less than 50%, and
results are the same for both PEC and copper designs.Comment: 6 pages, 10 figures, in press article. IEEE Transactions on Antennas
and Propagation (2014
MINVO Basis: Finding Simplexes with Minimum Volume Enclosing Polynomial Curves
This paper studies the problem of finding the smallest -simplex enclosing
a given -degree polynomial curve. Although the Bernstein and
B-Spline polynomial bases provide feasible solutions to this problem, the
simplexes obtained by these bases are not the smallest possible, which leads to
undesirably conservative results in many applications. We first prove that the
polynomial basis that solves this problem (MINVO basis) also solves for the
-degree polynomial curve with largest convex hull enclosed in a
given -simplex. Then, we present a formulation that is \emph{independent} of
the -simplex or -degree polynomial curve given. By using
Sum-Of-Squares (SOS) programming, branch and bound, and moment relaxations, we
obtain high-quality feasible solutions for any and prove
numerical global optimality for . The results obtained for show
that, for any given -degree polynomial curve, the MINVO basis is
able to obtain an enclosing simplex whose volume is and times
smaller than the ones obtained by the Bernstein and B-Spline bases,
respectively. When , these ratios increase to and
, respectively.Comment: 25 pages, 16 figure
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