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COULOMB-FRICTION IN TWO-DIMENSIONAL RIGID BODY SYSTEMS

ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND MECHANIK 1981年第12期61卷 605-615页

作者： LOTSTEDT, P Department of Numerical Analysis and Computing Science Royal Institute of Technology S-10044 Stockholm 70 Sweden

Die Lösungen des Coulombschen Reibungsproblems für starre Körper in zwei Dimensionen werden analysiert. Das bestimmende System von gewöhnlichen Differentialgleichungen und Ungleichungen wird aufgestellt. Beispiele werden vorgelegt, die einige ungewünschte Eigenschaften dieses speziellen Reibungsgesetzes nachweisen. Hinreichende Bedingungen für Existenz und Eindeutigkeit werden mit Hilfe der Theorie der linearen Komplementarität hergeleitet. The solutions to the Coulomb friction problem for rigid bodies in two dimensions are analyzed. The governing system of ordinary differential equations and inequalities is derived. Examples are presented demonstrating undesirable properties of this particular law of friction. Sufficient conditions for existence and uniqueness are given using the theory of linear complementarity.

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Consolidation of concentrated suspensions – numerical simulations using a two-phase fluid model

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computing and Visualization in science 2014年第1期3卷 39-45页

作者： Gustavsson, Katarina Oppelstrup, Jesper Department of Numerical Analysis and Computing Science Royal Institute of Technology S-100 44 Stockholm Sweden SE

We investigate numerically a mathematical model of a consolidation process of a dense, flocculated suspension. The suspension is treated as a two-constituent mixture of a fluid and solid particles by an Eulerian two-phase fluid model. We characterize the suspension by constitutive relations concerning the stresses, interaction forces and inter-particle forces. A numerical solver for a two dimensional test case is developed using finite difference methods both in time and space. In the numerical experiments, the suspension is confined to a closed box and consolidates due to a constant gravity field directed toward the bottom. To study the effect of shear, 2D simulations are performed where the bottom wall of the box is moving with a constant speed.

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A lower bound for perceptrons and an oracle separation of the PP/sup PH/ hierarchy

A lower bound for perceptrons and an oracle separation of th...

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Annual IEEE Conference on Computational Complexity

作者： C. Berg S. Ulfberg Department of Numerical Analysis and Computing Science Royal Institute of Technology Stockholm Sweden

We show that there are functions computable by linear size boolean circuits of depth k that require superpolynomial size perceptrons of depth k-1, for k

关键词： Circuits Polynomials numerical analysis Ear

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Efficient parallel algorithms for tree-decomposition and related problems

Efficient parallel algorithms for tree-decomposition and rel...

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Annual IEEE Symposium on Foundations of Computer science

作者： J. Lagergren Department of Numerical Analysis and Computing Science Royal Institute of Technology Stockholm Sweden

An efficient parallel algorithm for the tree-decomposition problem for fixed width w is presented. The algorithm runs in time O(log/sup 3/ n) and uses O(n) processors on a concurrent-read, concurrent-write parallel random access machine (CRCW PRAM). This result can be used to construct efficient parallel algorithms for three important classes of problems: MS (monadic second-order) properties, linear EMS (extended monadic second-order) extremum problems, and enumeration problems for MS properties, for graphs of tree width at most w. The sequential time complexity of the tree-composition problem for fixed w is improved, and some implications for this improvement are stated.< >

关键词： Parallel algorithms Tree graphs Phase change random access memory Medical services Logic numerical analysis Computational modeling Concurrent computing Polynomials Stress

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Iterated greedy algorithms for the maximal covering location problem

Iterated greedy algorithms for the maximal covering location...

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12th European Conference on Evolutionary Computation in Combinatorial Optimization, EvoCOP 2012

作者： Rodriguez, Francisco J. Blum, Christian Lozano, Manuel García-Martínez, Carlos Department of Computer Science and Artificial Intelligence University of Granada Granada Spain ALBCOM Research Group Technical University of Catalonia Barcelona Spain Department of Computing and Numerical Analysis University of Córdoba Córdoba Spain

ISBN: (纸本)9783642291234

The problem of allocating a set of facilities in order to maximise the sum of the demands of the covered clients is known as the maximal covering location problem. In this work we tackle this problem by means of iterated greedy algorithms. These algorithms iteratively refine a solution by partial destruction and reconstruction, using a greedy constructive procedure. Iterated greedy algorithms have been applied successfully to solve a considerable number of problems. With the aim of providing additional results and insights along this line of research, this paper proposes two new iterated greedy algorithms that incorporate two innovative components: a population of solutions optimised in parallel by the iterated greedy algorithm, and an improvement procedure that explores a large neighbourhood by means of an exact solver. The benefits of the proposal in comparison to a recently proposed decomposition heuristic and a standalone exact solver are experimentally shown. © 2012 Springer-Verlag.

关键词： Iterative methods

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An artificial bee colony algorithm for the unrelated parallel machines scheduling problem

An artificial bee colony algorithm for the unrelated paralle...

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12th International Conference on Parallel Problem Solving from Nature, PPSN 2012

作者： Rodriguez, Francisco J. García-Martínez, Carlos Blum, Christian Lozano, Manuel Department of Computer Science and Artificial Intelligence University of Granada Granada Spain ALBCOM Research Group Technical University of Catalonia Barcelona Spain Department of Computing and Numerical Analysis University of Córdoba Córdoba Spain

ISBN: (纸本)9783642329630

In this work, we tackle the problem of scheduling a set of jobs on a set of non-identical parallel machines with the goal of minimising the total weighted completion times. Artificial bee colony (ABC) algorithm is a new optimization technique inspired by the intelligent foraging behaviour of honey-bee swarm. These algorithms have shown a better or similar performance to those of other population-based algorithms, with the advantage of employing fewer control parameters. This paper proposes an ABC algorithm that combines the basic scheme with two significant elements: (1) a local search method to enhance the exploitation capability of basic ABC and (2) a neighbourhood operator based on iterated greedy constructive-destructive procedure. The benefits of the proposal in comparison to three different metaheuristic proposed in the literature are experimentally shown. © 2012 Springer-Verlag.

关键词： Scheduling

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Barycentre Averaging for the Move-Split-Merge Time Series Distance Measure 15

Barycentre Averaging for the Move-Split-Merge Time Series Di...

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15th International Conference on Knowledge Discovery and Information Retrieval, KDIR 2023 as part of the 15th International Joint Conference on Knowledge Discovery, Knowledge Engineering and Knowledge Management, IC3K 2023

作者： Holder, Christopher Guijo-Rubio, David Bagnall, Anthony School of Computing Sciences University of East Anglia Norwich United Kingdom Department of Computer Science and Numerical Analysis University of Córdoba Córdoba Spain School of Electronics and Computer Science University of Southampton Southampton United Kingdom

ISBN: (纸本)9789897586712

Distance functions play a core role in many time series machine learning algorithms for tasks such as clustering, classification and regression. Time series often require bespoke distance functions because small offsets in time can lead to large distances between series that are conceptually similar. Elastic distances compensate for misalignment by creating a path through a cost matrix by warping and/or editing time series. Time series are most commonly clustered with partitional algorithms such as k-means and k-medoids using elastic distance measures such as Dynamic Time Warping (DTW). The distance is used to assign cases to the closest cluster representative. k-means requires the averaging of time series to find these representative centroids. If DTW is used to assign membership, but the arithmetic mean is used to find centroids, k-means performance degrades significantly. An averaging technique specific to DTW, called DTW Barycentre Averaging (DBA), overcomes the averaging problem however, can only be used with DTW. As such alternative distance functions such as Move-Split-Merge (MSM) are forced to use the arithmetic mean to compute new centroids and suffer similar degraded performance as k-means-DTW without DBA. To address this we propose a averaging method for MSM distance, MSM Barycentre Averaging (MBA) and show that when used to find centroids it significantly improves MSM based k-means and is better than commonly used alternatives. Copyright © 2023 by SCITEPRESS - science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

关键词： Time series

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A person following behaviour for a mobile robot

A person following behaviour for a mobile robot

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IEEE International Conference on Robotics and Automation (ICRA)

作者： H. Sidenbladh D. Kragic H.I. Christensen Computer Vision and Active Perception Lab Department of Numerical Analysis and Computing Science Royal Institute of Technology Stockholm Sweden Centre for Autonomous Systems Department of Numerical Analysis and Computing Science Royal Institute of Technology Stockholm Sweden

In this paper, a person following behaviour for a mobile robot is presented. The head of the person is located using skin colour detection. Then, a control loop is fed with the camera movements required to put the upper part of the person in the center of the image. The algorithm was tested in different rooms of a research lab. It performed well in all lighting conditions except in direct sunlight. Since the background and lighting cannot be controlled, the vision algorithm must be robust to such changes. However, since the computing power is quite limited, the algorithm must have as low complexity as possible.

关键词： Mobile robots Robot vision systems Cameras Computer vision Skin Image motion analysis numerical analysis Lighting control Humans Machine vision

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Tracking techniques for visual servoing tasks

Tracking techniques for visual servoing tasks

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IEEE International Conference on Robotics and Automation (ICRA)

作者： D. Kragic H.I. Christensen Computer Vision and Active Perception Lab Department of Numerical Analysis and Computing Science Royal Institute of Technology Stockholm Sweden Centre for Autonomous Sys Department of Numerical Analysis and Computing Science Royal Institute of Technology Stockholm Sweden

Many of today's visual servoing systems rely on the use of markers on the object to provide features for control. There is thus a need for a visual system that provides control features regardless of the appearance of the object. Region based tracking is a natural approach since it does not require any special type of features. In this paper we present two different approaches to region based tracking: 1) a multi-resolution gradient based approach (using optical flow); and 2) a discrete feature based search approach. We present experiments conducted with both techniques for different types of image motions. Finally, the performance, drawbacks and limitations of used techniques are discussed.

关键词： Visual servoing Robots Tracking Computer vision numerical analysis Control systems Grippers Image motion analysis Motion estimation Visual system

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Seeing the obvious [robot vision]

Seeing the obvious [robot vision]

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13th International Conference on Pattern Recognition, ICPR 1996

作者： Bräutigam, Carsten G. Garding, Jonas Eklundh, Jan-Olof Department of Numerical Analysis and Computing Science Royal Institute of Technology S-100 44 Stockholm Sweden DeeMed International Centre Equation 2 AV de Vignate F-3861O Gières France

ISBN: (纸本)081867282X

We propose an approach to determine the occurrence of low-parametric qualitative models from images by a hypothesis-and-test approach based on the coincidence of multiple cues, thereby avoiding complete reconstruction of the scene. A system is presented which applies the approach to finding instances of planar surfaces, as it is important in many tasks for mobile or manipulating robots. The system uses monocularly determined L-junctions and binocular disparities. A notable feature of the approach is that it finds the most conspicuous exemplar of the model first. This property seems quite relevant for an agent using vision to guide its behaviors, since the simplest solution becomes available early on. © 1996 IEEE.

关键词： Computer vision

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