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2008


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Energy Functionals for Manifold-valued Mappings and Their Properties

Hein, M., Steinke, F., Schölkopf, B.

(167), Max Planck Institute for Biological Cybernetics, Tübingen, January 2008 (techreport)

Abstract
This technical report is merely an extended version of the appendix of Steinke et.al. "Manifold-valued Thin-Plate Splines with Applications in Computer Graphics" (2008) with complete proofs, which had to be omitted due to space restrictions. This technical report requires a basic knowledge of differential geometry. However, apart from that requirement the technical report is self-contained.

PDF [BibTex]

2008

PDF [BibTex]


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Methods for feature selection in a learning machine

Weston, J., Elisseeff, A., Schölkopf, B., Pérez-Cruz, F.

United States Patent, No 7318051, January 2008 (patent)

[BibTex]

[BibTex]


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A Robot System for Biomimetic Navigation: From Snapshots to Metric Embeddings of View Graphs

Franz, MO., Stürzl, W., Reichardt, W., Mallot, HA.

In Robotics and Cognitive Approaches to Spatial Mapping, pages: 297-314, Springer Tracts in Advanced Robotics ; 38, (Editors: Jefferies, M.E. , W.-K. Yeap), Springer, Berlin, Germany, 2008 (inbook)

Abstract
Complex navigation behaviour (way-finding) involves recognizing several places and encoding a spatial relationship between them. Way-finding skills can be classified into a hierarchy according to the complexity of the tasks that can be performed [8]. The most basic form of way-finding is route navigation, followed by topological navigation where several routes are integrated into a graph-like representation. The highest level, survey navigation, is reached when this graph can be embedded into a common reference frame. In this chapter, we present the building blocks for a biomimetic robot navigation system that encompasses all levels of this hierarchy. As a local navigation method, we use scene-based homing. In this scheme, a goal location is characterized either by a panoramic snapshot of the light intensities as seen from the place, or by a record of the distances to the surrounding objects. The goal is found by moving in the direction that minimizes the discrepancy between the recorded intensities or distances and the current sensory input. For learning routes, the robot selects distinct views during exploration that are close enough to be reached by snapshot-based homing. When it encounters already visited places during route learning, it connects the routes and thus forms a topological representation of its environment termed a view graph. The final stage, survey navigation, is achieved by a graph embedding procedure which complements the topologic information of the view graph with odometric position estimates. Calculation of the graph embedding is done with a modified multidimensional scaling algorithm which makes use of distances and angles between nodes.

PDF PDF DOI [BibTex]

PDF PDF DOI [BibTex]


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Haptic Device For Cell Manipulation

Lee, DY., Son, HI., Woo, HJ.

Max-Planck-Gesellschaft, Biologische Kybernetik, 2008 (patent)

[BibTex]

[BibTex]


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Minimal Nonlinear Distortion Principle for Nonlinear Independent Component Analysis

Zhang, K., Chan, L.

Journal of Machine Learning Research, 9, pages: 2455-2487, 2008 (article)

Abstract
It is well known that solutions to the nonlinear independent component analysis (ICA) problem are highly non-unique. In this paper we propose the "minimal nonlinear distortion" (MND) principle for tackling the ill-posedness of nonlinear ICA problems. MND prefers the nonlinear ICA solution with the estimated mixing procedure as close as possible to linear, among all possible solutions. It also helps to avoid local optima in the solutions. To achieve MND, we exploit a regularization term to minimize the mean square error between the nonlinear mixing mapping and the best-fitting linear one. The effect of MND on the inherent trivial and non-trivial indeterminacies in nonlinear ICA solutions is investigated. Moreover, we show that local MND is closely related to the smoothness regularizer penalizing large curvature, which provides another useful regularization condition for nonlinear ICA. Experiments on synthetic data show the usefulness of the MND principle for separating various nonlinear mixtures. Finally, as an application, we use nonlinear ICA with MND to separate daily returns of a set of stocks in Hong Kong, and the linear causal relations among them are successfully discovered. The resulting causal relations give some interesting insights into the stock market. Such a result can not be achieved by linear ICA. Simulation studies also verify that when doing causality discovery, sometimes one should not ignore the nonlinear distortion in the data generation procedure, even if it is weak.

Web [BibTex]

Web [BibTex]


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Transport processes in networks with scattering ramification nodes

Radl, A.

Journal of Applied Functional Analysis, 3, pages: 461-483, 2008 (article)

Web [BibTex]

Web [BibTex]


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Learning to control in operational space

Peters, J., Schaal, S.

International Journal of Robotics Research, 27, pages: 197-212, 2008, clmc (article)

Abstract
One of the most general frameworks for phrasing control problems for complex, redundant robots is operational space control. However, while this framework is of essential importance for robotics and well-understood from an analytical point of view, it can be prohibitively hard to achieve accurate control in face of modeling errors, which are inevitable in com- plex robots, e.g., humanoid robots. In this paper, we suggest a learning approach for opertional space control as a direct inverse model learning problem. A first important insight for this paper is that a physically cor- rect solution to the inverse problem with redundant degrees-of-freedom does exist when learning of the inverse map is performed in a suitable piecewise linear way. The second crucial component for our work is based on the insight that many operational space controllers can be understood in terms of a constrained optimal control problem. The cost function as- sociated with this optimal control problem allows us to formulate a learn- ing algorithm that automatically synthesizes a globally consistent desired resolution of redundancy while learning the operational space controller. From the machine learning point of view, this learning problem corre- sponds to a reinforcement learning problem that maximizes an immediate reward. We employ an expectation-maximization policy search algorithm in order to solve this problem. Evaluations on a three degrees of freedom robot arm are used to illustrate the suggested approach. The applica- tion to a physically realistic simulator of the anthropomorphic SARCOS Master arm demonstrates feasibility for complex high degree-of-freedom robots. We also show that the proposed method works in the setting of learning resolved motion rate control on real, physical Mitsubishi PA-10 medical robotics arm.

link (url) DOI [BibTex]

link (url) DOI [BibTex]