9 research outputs found
Deterministic continutation of stochastic metastable equilibria via Lyapunov equations and ellipsoids
Numerical continuation methods for deterministic dynamical systems have been
one of the most successful tools in applied dynamical systems theory.
Continuation techniques have been employed in all branches of the natural
sciences as well as in engineering to analyze ordinary, partial and delay
differential equations. Here we show that the deterministic continuation
algorithm for equilibrium points can be extended to track information about
metastable equilibrium points of stochastic differential equations (SDEs). We
stress that we do not develop a new technical tool but that we combine results
and methods from probability theory, dynamical systems, numerical analysis,
optimization and control theory into an algorithm that augments classical
equilibrium continuation methods. In particular, we use ellipsoids defining
regions of high concentration of sample paths. It is shown that these
ellipsoids and the distances between them can be efficiently calculated using
iterative methods that take advantage of the numerical continuation framework.
We apply our method to a bistable neural competition model and a classical
predator-prey system. Furthermore, we show how global assumptions on the flow
can be incorporated - if they are available - by relating numerical
continuation, Kramers' formula and Rayleigh iteration.Comment: 29 pages, 7 figures [Fig.7 reduced in quality due to arXiv size
restrictions]; v2 - added Section 9 on Kramers' formula, additional
computations, corrected typos, improved explanation
The Finite Termination Property of an Algorithm for Solving the Minimum Circumscribed Ball Problem
In this paper basic mathematical tasks of coordinate measurement are briefly described and a modied optimization algorithm is proposed. Coordinate measurement devices generate huge data set and require adapted methods to solve related mathematical problems in real time. The proposed algorithm possesses a simplied step size rule and nds the solution of the minimum circumscribed ball fitting after only a nite number The iteration is of the steepest descent type applied to the related distance function. But, in contrast to standard algorithms it uses a modied step size rule that takes into account the specic properties of the occurring objective function. This small dierence in the code improves the performance of the algorithm and it enables real time use of the proposed method in coordinate measurement machines. The eciency of the prosed algorithm will be illustrated by some typical examples
Efficient collision detection for real-time simulated environments
Thesis (M.S.)--Massachusetts Institute of Technology, Program in Media Arts & Sciences, 1994.Includes bibliographical references (leaves 64-68).by Paul Jay Dworkin.M.S
Modelado, detecci贸n de colisiones y planificaci贸n de movimientos en sistemas robotizados mediante vol煤menes esf茅ricos
[EN] The efficiency of free-collision motion planning results very sensible on robot and obstacle modelling
technique selected. In this way, many works have been oriented to define models with proper
throughput to speed up the collision detection proccess. This dissertation presents a new approach to
the problem, whose complexity is reduced notably by means of using enveloping models of real
objects, allowing security regions or distances. This objective is reached by means of the definition of
a spherical model, composed of infinite spheres, generated from the application of linear or
polynomial equations to a reduced number of control spheres, giving the so-called poly-spheres and
spheroids respectively. These models, with evident simplicity, present a high modelling power, adapt
easily to the requirements need in collision-detection and path planning applications for robotics
systems.
In order to represent a complete multi-robot cell, an extended hierarchical structure has been defined,
in form of an AND-OR graph, with different degrees of accuracy, according to the different
approximation model used. In order to generate automatically this structure, a procedure has been
developed to compute the minimum volume enveloping spherical model in an off-line process with
two levels based on Downhill Simplex method and Hough transform. This procedure can be greatly
speed up by using clustering techniques to obtain appropiate initial conditions, allowing an on-line
use. With a hierarchical structure computed in such a way, a fast procedure for collision detection in a
multi-robot cell is introduced, based on several algorithms for distance computation including polyspheres
and spheroids. This methodology presents a fast and anticipativa response, in the sense that
every movement of a system has been validated before its execution, implying that not necessarily
must be done in an off-line simulation.
The use of spherical models, in addition to their fast distance computation, results suitable for the
definition of artificial potential fields allowing a path planning in robotics systems with up to six
degrees of freedom, including three for translation and three for rotation. The definition of these new
potential fields and the study of new planning techniques based on classical optimisation methods
allow their application straight forward in Cartesian space, with all their advantages.
Last but not least, with the help of some systems for robot programming, simulation and control, the
correctness of these contributions have been validated in a set of prototype applications, covering
from robot-obstacle and multi-robot collision detection, to motion planning for a robot-arm or an
auto-guided vehicle.[ES] La eficiencia de la planificaci贸n de movimientos libres de colisi贸n resulta muy sensible al modelado
de los robots y obst谩culos que se consideren, por lo que, frente al modelado tradicional con politopos,
muchos trabajos en rob贸tica han estado orientados a la definici贸n de unos modelos que presenten
buenas prestaciones de cara a acelerar el proceso de detecci贸n de colisiones. En esta Tesis se presenta
una nueva perspectiva del problema, cuya complejidad queda reducida notablemente al utilizar
envolventes de los objetos reales, lo que permite definir zonas o distancias de seguridad. Para ello se
han definido unos modelos esf茅ricos, compuestos de infinitas esferas generadas a partir de la
aplicaci贸n de unas relaciones lineales o polin贸micas a un n煤mero reducido de esferas de control,
dando lugar a las llamadas poli-esferas y esferoides respectivamente. Estos modelos, de sencillez
clara, presentan una potencia de modelado elevada, adapt谩ndose f谩cilmente a los requisitos necesarios
en las aplicaciones de detecci贸n de colisiones y planificaci贸n de movimientos en sistemas
robotizados.
Para la representaci贸n de una c茅lula multi-robot completa, se ha definido una estructura jer谩rquica
extendida, en forma de grafo AND-OR, con diferentes grados de precisi贸n, mediante diferentes
modelos de aproximaci贸n. De cara a generar autom谩ticamente esta estructura, se ha desarrollado un
procedimiento para generar el modelo esf茅rico envolvente de m铆nimo volumen en un proceso off-line
con dos niveles, basados en el m茅todo de minimizaci贸n Downhill Simplex y en la transformada de
Hough. Este procedimiento se acelera enormemente al utilizar t茅cnicas de agrupamiento para obtener
condiciones iniciales apropiadas, permitiendo su uso on-line. Con una estructura jer谩rquica generada
de esta forma, se introduce un procedimiento r谩pido de detecci贸n de colisiones aplicable a una c茅lula
multi-robot, basado en algoritmos b谩sicos de c谩lculo de distancias que pueden considerar poli-esferas
y esferoides. Esta metodolog铆a presenta una respuesta r谩pida y anticipativa, entendiendo por tal que
todo movimiento de cualquier sistema ha sido validado antes de su ejecuci贸n, por lo que no
necesariamente debe realizarse en una simulaci贸n off-line.
La utilizaci贸n de modelos esf茅ricos, as铆 como el r谩pido c谩lculo de distancias entre ellos, resulta id贸nea
para la definici贸n de campos potenciales artificiales que permitan una planificaci贸n de movimientos
en sistemas robotizados con hasta seis grados de libertad, incluyendo tres de traslaci贸n y tres de
rotaci贸n. La definici贸n de estos nuevos campos potenciales y el estudio de nuevas t茅cnicas de
planificaci贸n basados en m茅todos cl谩sicos de optimizaci贸n permiten su aplicaci贸n directamente en el
espacio cartesiano, con las claras ventajas que esto conlleva.
Finalmente, con la ayuda de varios sistemas de programaci贸n, simulaci贸n y control de robots, se ha
demostrado la validez de estas aportaciones en una serie de aplicaciones prototipo que van desde la
detecci贸n de colisiones de un robot con un obst谩culo o entre sistemas multi-robot, a la planificaci贸n
de movimientos de un brazo-robot o un veh铆culo autoguiado.Mellado Arteche, M. (1996). Modelado, detecci贸n de colisiones y planificaci贸n de movimientos en sistemas robotizados mediante vol煤menes esf茅ricos [Tesis doctoral no publicada]. Universitat Polit猫cnica de Val猫ncia. https://doi.org/10.4995/Thesis/10251/5662