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2001


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Hardness-depth profiling on nanometer scale

Kunert, M., Baretzky, B., Baker, S. P., Mittemeijer, E. J.

{Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science}, 32(5):1201-1209, 2001 (article)

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[BibTex]

2001


[BibTex]


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Compound formation and abrasion resistance of ion-implanted Ti6Al4V

Schmidt, H., Schminke, A., Schmiedgen, M., Baretzky, B.

{Acta Materialia}, 49(3):487-495, 2001 (article)

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[BibTex]

[BibTex]


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Influence of vortex-vortex interaction on critical currents across low-angle grain boundaries in YBa2Cu3O7-δthin films

Albrecht, J., Leonhardt, S., Kronmüller, H.

{Physical Review B}, 63, 2001 (article)

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[BibTex]

[BibTex]


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Structure of superconducting [BaCuOx]2/[CaCuO2]n superlattices on SrTiO3(001) investigated by x-ray scattering

Aruta, C., Zegenhagen, J., Cowie, B., Balestrino, G., Pasquini, G., Medaglia, P. G., Ricci, F., Luebbert, D., Baumbach, T., Riedo, E., Ortega, L., Kremer, R., Albrecht, J.

{Physica Status Solidi (A)}, 183, pages: 353-364, 2001 (article)

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[BibTex]

[BibTex]


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Flux-line pinning in low-angle grain boundaries.

Albrecht, J., Leonhardt, S., Kronmüller, H.

In Proceedings 10th International Workshop on Critical Currents (IWCC 2001), pages: 41-43, Göttingen, Germany, 2001 (inproceedings)

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[BibTex]

[BibTex]


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Transmission X-ray microscopy using X-MCD

Eimüller, T., Fischer, P., Köhler, M., Scholz, M., Guttmann, P., Denbeaux, G., Glück, S., Bayreuther, G., Schmahl, G., Attwood, D., Schütz, G.

{Applied Physics A}, 73, pages: 697-701, 2001 (article)

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[BibTex]

[BibTex]


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Soft X-ray microscopy to 25 nm with applications to biology and magnetic materials

Denbeaux, G., Anderson, E., Chao, W., Eimüller, T., Johnson, L., Köhler, M., Larabell, C., Legros, M., Fischer, P., Pearson, A., Schütz, G., Yager, D., Attwood, D.

{Nuclear Instruments and Methods in Physics Research A}, 467-468, pages: 841-844, 2001 (article)

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[BibTex]

[BibTex]


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Study of in-plane magnetic domains with magnetic transmission X-ray microscopy

Fischer, P., Eimüller, T., Schütz, G., Köhler, M., Bayreuther, G., Denbeaux, G., Attwood, D.

{Journal of Applied Physics}, 89, pages: 7159-7161, 2001 (article)

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[BibTex]

[BibTex]


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Influence of vortex-vortex interaction on critical currents across low-angle grain boundaries in YBa2Cu3O7-δthin films

Albrecht, J., Leonhardt, S., Kronmüller, H.

{Physical Review B}, 63, 2001 (article)

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[BibTex]

[BibTex]


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Non-symmetric influences in the total electron yield X-ray magnetic circular dichroism signal in applied magnetic fields

Goering, E., Gold, S., Bayer, A., Schütz, G.

{Journal of Synchrotron Radiation}, 8, pages: 434-436, 2001 (article)

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DOI [BibTex]

DOI [BibTex]


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Effect of Ga substitution on the magnetocrystalline anisotropy of arc-melted Sm2Co17-xGax (x\textequals5,6) compounds

Liang, B., Kleinschroth, I., Kronmüller, H.

{Journal of Applied Physics}, 89(1):488-491, 2001 (article)

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[BibTex]

[BibTex]


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Influence of grain boundary phase transitions on the properties of Cu-Bi polycrystals

Straumal, B. B., Sluchanko, N.E., Gust, W.

In Defects and Diffusion in Metals III: An Annual Retrospective III, 188-1, pages: 185-194, Defect and Diffusion Forum, 2001 (incollection)

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[BibTex]

[BibTex]


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Learning inverse kinematics

D’Souza, A., Vijayakumar, S., Schaal, S.

In IEEE International Conference on Intelligent Robots and Systems (IROS 2001), Piscataway, NJ: IEEE, Maui, Hawaii, Oct.29-Nov.3, 2001, clmc (inproceedings)

Abstract
Real-time control of the endeffector of a humanoid robot in external coordinates requires computationally efficient solutions of the inverse kinematics problem. In this context, this paper investigates learning of inverse kinematics for resolved motion rate control (RMRC) employing an optimization criterion to resolve kinematic redundancies. Our learning approach is based on the key observations that learning an inverse of a non uniquely invertible function can be accomplished by augmenting the input representation to the inverse model and by using a spatially localized learning approach. We apply this strategy to inverse kinematics learning and demonstrate how a recently developed statistical learning algorithm, Locally Weighted Projection Regression, allows efficient learning of inverse kinematic mappings in an incremental fashion even when input spaces become rather high dimensional. The resulting performance of the inverse kinematics is comparable to Liegeois ([1]) analytical pseudo inverse with optimization. Our results are illustrated with a 30 degree-of-freedom humanoid robot.

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link (url) [BibTex]

link (url) [BibTex]


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Biomimetic smooth pursuit based on fast learning of the target dynamics

Shibata, T., Schaal, S.

In IEEE International Conference on Intelligent Robots and Systems (IROS 2001), 2001, clmc (inproceedings)

Abstract
Following a moving target with a narrow-view foveal vision system is one of the essential oculomotor behaviors of humans and humanoids. This oculomotor behavior, called ``Smooth Pursuit'', requires accurate tracking control which cannot be achieved by a simple visual negative feedback controller due to the significant delays in visual information processing. In this paper, we present a biologically inspired and control theoretically sound smooth pursuit controller consisting of two cascaded subsystems. One is an inverse model controller for the oculomotor system, and the other is a learning controller for the dynamics of the visual target. The latter controller learns how to predict the target's motion in head coordinates such that tracking performance can be improved. We investigate our smooth pursuit system in simulations and experiments on a humanoid robot. By using a fast on-line statistical learning network, our humanoid oculomotor system is able to acquire high performance smooth pursuit after about 5 seconds of learning despite significant processing delays in the syste

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link (url) [BibTex]

link (url) [BibTex]


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Biomimetic oculomotor control

Shibata, T., Vijayakumar, S., Conradt, J., Schaal, S.

Adaptive Behavior, 9(3/4):189-207, 2001, clmc (article)

Abstract
Oculomotor control in a humanoid robot faces similar problems as biological oculomotor systems, i.e., capturing targets accurately on a very narrow fovea, dealing with large delays in the control system, the stabilization of gaze in face of unknown perturbations of the body, selective attention, and the complexity of stereo vision. In this paper, we suggest control circuits to realize three of the most basic oculomotor behaviors and their integration - the vestibulo-ocular and optokinetic reflex (VOR-OKR) for gaze stabilization, smooth pursuit for tracking moving objects, and saccades for overt visual attention. Each of these behaviors and the mechanism for their integration was derived with inspiration from computational theories as well as behavioral and physiological data in neuroscience. Our implementations on a humanoid robot demonstrate good performance of the oculomotor behaviors, which proves to be a viable strategy to explore novel control mechanisms for humanoid robotics. Conversely, insights gained from our models have been able to directly influence views and provide new directions for computational neuroscience research.

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link (url) [BibTex]

link (url) [BibTex]


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Development of a scaled teleoperation system for nano scale interaction and manipulation

Sitti, M., Aruk, B., Shintani, H., Hashimoto, H.

In Robotics and Automation, 2001. Proceedings 2001 ICRA. IEEE International Conference on, 1, pages: 860-867, 2001 (inproceedings)

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[BibTex]

[BibTex]


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Irradiation-induced electron tunnelling and small-polaron hopping in single-crystalline YIG

Walz, F., Brabers, J. H. V. J., Torres, L., Kronmüller, H.

{Physica Status Solidi B-Basic Research}, 228(3):717-730, 2001 (article)

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[BibTex]

[BibTex]


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Kernspinresonanzuntersuchungen zur Diffusion von Wasserstoff in den Di- und Trihydriden der Übergangsmetalle

Gottwald, J.

Universität Stuttgart, Stuttgart, 2001 (phdthesis)

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[BibTex]


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Hexagonally ordered 100 nm period nickel nanowire arrays

Nielsch, K., Wehrspohn, R. B., Barthel, J., Kirschner, J., Gösele, U., Fischer, S. F., Kronmüller, H.

{Applied Physics Letters}, 79(9):1360-1362, 2001 (article)

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[BibTex]

[BibTex]


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Magnetization processes in isotropic and textured Nd2Fe14B- films

Melsheimer, A., Kronmüller, H.

{Physica B}, 299(3-4):251-259, 2001 (article)

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[BibTex]

[BibTex]


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Critical magnetic properties of disordered Cr-rich FeCr alloys

Fischer, S. F., Kaul, S. N., Kronmüller, H.

{Journal of Magnetism and Magnetic Materials}, 226(Sp. Iss. SI):540-541, 2001 (article)

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[BibTex]

[BibTex]


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Fast ab initio methods for the calculation of adiabatic spin wave spectra in complex systems

Grotheer, O., Ederer, C., Fähnle, M.

{Physical Review B}, 63(10):100401-100401, 2001 (article)

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[BibTex]

[BibTex]


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Hydrogen storage in sonicated carbon materials

Hirscher, M., Becher, M., Haluska, M., Dettlaff-Weglikowska, U., Quintel, A., Duesberg, G. S., Choi, Y. M., Downes, P., Hulman, M., Roth, S., Stepanek, I., Bernier, P.

{Applied Physics A-Materials Science \& Processing}, 72(2):129-132, 2001 (article)

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[BibTex]

[BibTex]


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Measurement of the low-temperature self-diffusivity of lithium by elastic recoil detection analysis

Wieland, O., Carstanjen, H. D.

In Proceedings of DIMAT 2000, the Fifth International Conference on Diffusion in Materials, 194/199, pages: 35-41, Defect and Diffusion Forum, Scitec Publications Ltd., Paris, France, 2001 (inproceedings)

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[BibTex]

[BibTex]


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Co(NH3)2Cl2 and Co(ND3)2Cl2: Order-Disorder Behaviour of N(H,D)3 and Antiferromagnetic Structure

Leineweber, A., Jacobs, H., E\ssmann, P., Allenspach, F., Fauth, F., Fischer, P.

{Zeitschrift f\"ur Anorganische und Allgemeine Chemie}, 627, pages: 2063-2069, 2001 (article)

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[BibTex]

[BibTex]


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Critical magnetic properties of disordered polycrystalline Fe75Fe25 and Cr70Fe30 alloys

Fischer, S. F., Kaul, S. N., Kronmüller, H.

{Physical Review B}, 65, 2001 (article)

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[BibTex]

[BibTex]


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From the electronic structure to the macroscopic behaviour: a multi-scale analysis of plasticity in intermetallic compounds

Fähnle, M., Kohlhammer, S., Bester, G.

In Influences of Interface and Dislocation Behavior on Microstructure Evolution, 652, pages: Y.4.5.1-Y.4.5.12, Materials Research Society Symposium Proceedings, MRS, Boston, Mass., 2001 (inproceedings)

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[BibTex]

[BibTex]


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Enhancement of the critical current density of YBa2Cu3O7-8-films by substracte irradiation

Leonhardt, S., Albrecht, J., Warthmann, R., Kronmüller, H.

In High-Tc Superconductors and Related Applications: Materials Science, Fundamental Properties, and Some Future Electronic Applications. Proceedings of the NATO Advanced Study Institute, 86, pages: 529-534, NATO Science Series 3. High Technology, Kluwer Academic Publishers, Albena, Bulgaria, 2001 (inproceedings)

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[BibTex]

[BibTex]


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Diffusion of 23Na and 35K in the eutectic melt Na0.32K0.69

Feinauer, A., Majer, G.

{Physical Review B}, 64, 2001 (article)

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[BibTex]

[BibTex]


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AMOC studies of positronium in fine MgO powder

van Waeyenberge, B., Dauwe, C., Stoll, H.

In Positron Annihilation. Proceedings of the 12th International Conference on Positron Annihilation, 363/365, pages: 401-403, Materials Science Forum, Trans Tech Publications Ltd., München, 2001 (inproceedings)

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[BibTex]

[BibTex]


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Influence of nanocrystallization on the evolution of domain patterns and the magnetoimpedance effect in amorphous Fe73.5Cu1Nb3Si13.5B9 ribbons

Guo, H. Q., Kronmüller, H., Dragon, T., Cheng, Z. H., Shen, B. G.

{Journal of Applied Physics}, 89(1):514-520, 2001 (article)

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[BibTex]

[BibTex]


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Ab-initio statistical mechanics for the phase diagram of NiAl including the effect of vacancies

Lechermann, F., Fähnle, M.

{Physica Status Solidi (B)}, 224, pages: R4-R6, 2001 (article)

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[BibTex]

[BibTex]


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Atomic defects and electronic structure of B2-FeAl, CoAl and NiAl

Fähnle, M., Meyer, B., Bester, G., Majer, J., Börnsen, N.

In Proceedings of DIMAT 2000, the Fifth International Conference on Diffusion in Materials, 194/199, pages: 279-285, Defect and Diffusion Forum, Scitec Publications Ltd., Paris, France, 2001 (inproceedings)

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[BibTex]

[BibTex]

1994


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Robot juggling: An implementation of memory-based learning

Schaal, S., Atkeson, C. G.

Control Systems Magazine, 14(1):57-71, 1994, clmc (article)

Abstract
This paper explores issues involved in implementing robot learning for a challenging dynamic task, using a case study from robot juggling. We use a memory-based local modeling approach (locally weighted regression) to represent a learned model of the task to be performed. Statistical tests are given to examine the uncertainty of a model, to optimize its prediction quality, and to deal with noisy and corrupted data. We develop an exploration algorithm that explicitly deals with prediction accuracy requirements during exploration. Using all these ingredients in combination with methods from optimal control, our robot achieves fast real-time learning of the task within 40 to 100 trials.

am

link (url) [BibTex]

1994


link (url) [BibTex]


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Robot learning by nonparametric regression

Schaal, S., Atkeson, C. G.

In Proceedings of the International Conference on Intelligent Robots and Systems (IROS’94), pages: 478-485, Munich Germany, 1994, clmc (inproceedings)

Abstract
We present an approach to robot learning grounded on a nonparametric regression technique, locally weighted regression. The model of the task to be performed is represented by infinitely many local linear models, i.e., the (hyper-) tangent planes at every query point. Such a model, however, is only generated when a query is performed and is not retained. This is in contrast to other methods using a finite set of linear models to accomplish a piecewise linear model. Architectural parameters of our approach, such as distance metrics, are also a function of the current query point instead of being global. Statistical tests are presented for when a local model is good enough such that it can be reliably used to build a local controller. These statistical measures also direct the exploration of the robot. We explicitly deal with the case where prediction accuracy requirements exist during exploration: By gradually shifting a center of exploration and controlling the speed of the shift with local prediction accuracy, a goal-directed exploration of state space takes place along the fringes of the current data support until the task goal is achieved. We illustrate this approach by describing how it has been used to enable a robot to learn a challenging juggling task: Within 40 to 100 trials the robot accomplished the task goal starting out with no initial experiences.

am

[BibTex]

[BibTex]


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Assessing the quality of learned local models

Schaal, S., Atkeson, C. G.

In Advances in Neural Information Processing Systems 6, pages: 160-167, (Editors: Cowan, J.;Tesauro, G.;Alspector, J.), Morgan Kaufmann, San Mateo, CA, 1994, clmc (inproceedings)

Abstract
An approach is presented to learning high dimensional functions in the case where the learning algorithm can affect the generation of new data. A local modeling algorithm, locally weighted regression, is used to represent the learned function. Architectural parameters of the approach, such as distance metrics, are also localized and become a function of the query point instead of being global. Statistical tests are given for when a local model is good enough and sampling should be moved to a new area. Our methods explicitly deal with the case where prediction accuracy requirements exist during exploration: By gradually shifting a "center of exploration" and controlling the speed of the shift with local prediction accuracy, a goal-directed exploration of state space takes place along the fringes of the current data support until the task goal is achieved. We illustrate this approach with simulation results and results from a real robot learning a complex juggling task.

am

link (url) [BibTex]

link (url) [BibTex]


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Memory-based robot learning

Schaal, S., Atkeson, C. G.

In IEEE International Conference on Robotics and Automation, 3, pages: 2928-2933, San Diego, CA, 1994, clmc (inproceedings)

Abstract
We present a memory-based local modeling approach to robot learning using a nonparametric regression technique, locally weighted regression. The model of the task to be performed is represented by infinitely many local linear models, the (hyper-) tangent planes at every query point. This is in contrast to other methods using a finite set of linear models to accomplish a piece-wise linear model. Architectural parameters of our approach, such as distance metrics, are a function of the current query point instead of being global. Statistical tests are presented for when a local model is good enough such that it can be reliably used to build a local controller. These statistical measures also direct the exploration of the robot. We explicitly deal with the case where prediction accuracy requirements exist during exploration: By gradually shifting a center of exploration and controlling the speed of the shift with local prediction accuracy, a goal-directed exploration of state space takes place along the fringes of the current data support until the task goal is achieved. We illustrate this approach by describing how it has been used to enable a robot to learn a challenging juggling task: within 40 to 100 trials the robot accomplished the task goal starting out with no initial experiences.

am

[BibTex]

[BibTex]


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Nonparametric regression for learning

Schaal, S.

In Conference on Adaptive Behavior and Learning, Center of Interdisciplinary Research (ZIF) Bielefeld Germany, also technical report TR-H-098 of the ATR Human Information Processing Research Laboratories, 1994, clmc (inproceedings)

Abstract
In recent years, learning theory has been increasingly influenced by the fact that many learning algorithms have at least in part a comprehensive interpretation in terms of well established statistical theories. Furthermore, with little modification, several statistical methods can be directly cast into learning algorithms. One family of such methods stems from nonparametric regression. This paper compares nonparametric learning with the more widely used parametric counterparts and investigates how these two families differ in their properties and their applicability. 

am

link (url) [BibTex]

link (url) [BibTex]