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991.
Huimin Zhao 《Knowledge and Information Systems》2008,15(3):321-334
In real-world classification problems, different types of misclassification errors often have asymmetric costs, thus demanding cost-sensitive learning methods that attempt to minimize average misclassification cost rather than plain error rate. Instance weighting and post hoc threshold adjusting are two major approaches to cost-sensitive classifier learning. This paper compares the effects of these two approaches on several standard, off-the-shelf classification methods. The comparison indicates that the two approaches lead to similar results for some classification methods, such as Naïve Bayes, logistic regression, and backpropagation neural network, but very different results for other methods, such as decision tree, decision table, and decision rule learners. The findings from this research have important implications on the selection of the cost-sensitive classifier learning approach as well as on the interpretation of a recently published finding about the relative performance of Naïve Bayes and decision trees. 相似文献
992.
We study the problem of segmenting a sequence into k pieces so that the resulting segmentation satisfies monotonicity or unimodality constraints. Unimodal functions can be used
to model phenomena in which a measured variable first increases to a certain level and then decreases. We combine a well-known
unimodal regression algorithm with a simple dynamic-programming approach to obtain an optimal quadratic-time algorithm for
the problem of unimodal k-segmentation. In addition, we describe a more efficient greedy-merging heuristic that is experimentally shown to give solutions
very close to the optimal. As a concrete application of our algorithms, we describe methods for testing if a sequence behaves
unimodally or not. The methods include segmentation error comparisons, permutation testing, and a BIC-based scoring scheme.
Our experimental evaluation shows that our algorithms and the proposed unimodality tests give very intuitive results, for
both real-valued and binary data.
Niina Haiminen received the M.Sc. degree from the University of Helsinki in 2004. She is currently a Graduate Student at the Department
of Computer Science of University of Helsinki, and a Researcher at the Basic Research Unit of Helsinki Institute for Information
Technology. Her research interests include algorithms, bioinformatics, and data mining.
Aristides Gionis received the Ph.D. degree from Stanford University in 2003, and he is currently a Senior Researcher at the Basic Research
Unit of Helsinki Institute for Information Technology. His research experience includes summer internship positions at Bell
Labs, AT&T Labs, and Microsoft Research. His research areas are data mining, algorithms, and databases.
Kari Laasonen received the M.Sc. degree in Theoretical Physics in 1995 from the University of Helsinki. He is currently a Graduate Student
in Computer Science at the University of Helsinki and a Researcher at the Basic Research Unit of Helsinki Institute for Information
Technology. His research is focused on algorithms and data analysis methods for pervasive computing. 相似文献
993.
In this paper, we describe an implementation of use in demonstrating the effectiveness of architectures for real-time multi-agent
systems. The implementation provides a simulation of a simplified RoboCup Search and Rescue environment, with unexpected events,
and includes a simulator for both a real-time operating system and a CPU. We present experimental evidence to demonstrate
the benefit of the implementation in the context of a particular hybrid architecture for multi-agent systems that allows certain
agents to remain fully autonomous, while others are fully controlled by a coordinating agent. In addition, we discuss the
value of the implementation for testing any models for the construction of real-time multi-agent systems and include a comparison
to related work.
相似文献
Robin CohenEmail: |
994.
Biomechanics of human head has been widely studied since several decades. At a mechanical level, the use of engineering allowed investigating injury mechanisms developing numerical models of adult head. For children, the problem is more difficult and evaluating child injury mechanisms using data obtained from scaling adult injury criteria does not account for differences in morphology and structure between adults and children. During growth, child head undergoes different modifications in morphology and structure. The present paper compares the anthropometry and numerical simulations of a child head model based on medical CT scans to a child head model developed by scaling an adult head model using the method proposed by Mertz [H.J. Mertz, A procedure for normalizing impact response data, SAE paper 840884, 1984]. These analysis point out significant differences showing that scaling down an adult head to obtain a child head does not appear relevant. Biofidelic and specific child geometry is needed to investigate child injury mechanisms. 相似文献
995.
The main purpose of a gene interaction network is to map the relationships of the genes that are out of sight when a genomic study is tackled. DNA microarrays allow the measure of gene expression of thousands of genes at the same time. These data constitute the numeric seed for the induction of the gene networks. In this paper, we propose a new approach to build gene networks by means of Bayesian classifiers, variable selection and bootstrap resampling. The interactions induced by the Bayesian classifiers are based both on the expression levels and on the phenotype information of the supervised variable. Feature selection and bootstrap resampling add reliability and robustness to the overall process removing the false positive findings. The consensus among all the induced models produces a hierarchy of dependences and, thus, of variables. Biologists can define the depth level of the model hierarchy so the set of interactions and genes involved can vary from a sparse to a dense set. Experimental results show how these networks perform well on classification tasks. The biological validation matches previous biological findings and opens new hypothesis for future studies. 相似文献
996.
Peter Baumann 《Informatik-Spektrum》2008,31(5):435-450
Zusammenfassung Navigationssysteme, ortsbezogene Suchdienste wie Google Maps, interaktive Augmented-Reality-Spiele, Handy-basierte FindMe-Dienste
– diese wenige Beispiele zeigen bereits, wie direkt oder indirekt raumbezogene Dienste unser Alltagsleben immer mehr durchdringen.
Wir beobachten, wie sich die Nutzung von Geodaten schrittweise vom pers?nlichen Desktop-Geoinformationssystem (GIS) über hausinternen
Zugriff auf die Geodatenbank bis zum Webzugriff durch Clients und Servern unterschiedlicher Provenienz ausweitet (,,Web-GIS“).
Klassische Aufgaben wie Kartenproduktion und Beauskunftung treten dabei gegenüber komplexen, situationsbezogenen Verknüpfungen
von Geo- mit anderen Daten eher in den Hintergrund. Damit geht offensichtlich ein Paradigmenwechsel von der einfachen, passiven
Geodatenbereitstellung via WWW zu funktional komplexeren Geodiensten einher.
Sollen solche Mehrwertdienste offen und flexibel orchestrierbar sein, so müssen Geodaten systemübergreifend ad hoc abgefragt werden k?nnen. Unabdingbar sind dafür offene Standards, nicht nur auf der Ebene von Datenaustauschformaten, sondern
auch bei den Zugriffsdiensten; diese Geoservice-Standardisierung leistet das Open GeoSpatial Consortium (OGC).
Im vorliegenden Beitrag geben wir einen überblick über die Modellierung von Web-basierten Geodiensten auf Basis ausgew?hlter
OGC-Standards. Modellierung bedeutet in diesem Kontext die Gestaltung von Funktionalit?t und Schnittstellen eines potenziell
komplexen Dienstes auf Basis offener Standards und ihrer Basisdienste und -operationen. Diskutiert werden Standards für den
Meta-, Vektor- und Rasterdatenzugriff sowie ein anwendungsorientierter Standard für Sensordaten. 相似文献
997.
Sabine Timpf 《Informatik-Spektrum》2008,31(1):70-74
Zusammenfassung Im Zeitalter der Informationsgesellschaft, so wurde postuliert, spielten r?umliche Distanzen keine Rolle mehr und unsere r?umliche
Mobilit?t n?hme ab. Die Mobilit?t in den letzten Jahren, speziell die Freizeitmobilit?t, hat hingegen zugenommen. Die Bereitstellung
ortsbezogener Dienste – ,,Location-based Services“ – unterstützt und f?rdert dieses Verhalten. 相似文献
998.
Fabrice Rousselle Petrik Clarberg Luc Leblanc Victor Ostromoukhov Pierre Poulin 《The Visual computer》2008,24(7-9):465-474
We present an efficient method for importance sampling the product of multiple functions. Our algorithm computes a quick approximation of the product on the fly, based on hierarchical representations of the local maxima and averages of the individual terms. Samples are generated by exploiting the hierarchical properties of many low-discrepancy sequences, and thresholded against the estimated product. We evaluate direct illumination by sampling the triple product of environment map lighting, surface reflectance, and a visibility function estimated per pixel. Our results show considerable noise reduction compared to existing state-of-the-art methods using only the product of lighting and BRDF. 相似文献
999.
We study the complexity issues for Walrasian equilibrium in a special case of combinatorial auction, called single-minded
auction, in which every participant is interested in only one subset of commodities. Chen et al. (J. Comput. Syst. Sci. 69(4):
675–687, 2004) showed that it is NP-hard to decide the existence of a Walrasian equilibrium for a single-minded auction and proposed a
notion of approximate Walrasian equilibrium called relaxed Walrasian equilibrium. We show that every single-minded auction
has a relaxed Walrasian equilibrium that satisfies at least two-thirds of the participants, proving a conjecture posed in
Chen et al. (J. Comput. Syst. Sci. 69(4): 675–687, 2004). Motivated by practical considerations, we introduce another concept of approximate Walrasian equilibrium called weak Walrasian
equilibrium. We show NP-completeness and hardness of approximation results for weak Walrasian equilibria.
In search of positive results, we restrict our attention to the tollbooth problem (Guruswami et al. in Proceedings of the
Symposium on Discrete Algorithms (SODA), pp. 1164–1173, 2005), where every participant is interested in a single path in some underlying graph. We give a polynomial time algorithm to
determine the existence of a Walrasian equilibrium and compute one (if it exists), when the graph is a tree. However, the
problem is still NP-hard for general graphs. 相似文献
1000.
In this paper we consider the p-ary transitive reduction (TR
p
) problem where p>0 is an integer; for p=2 this problem arises in inferring a sparsest possible (biological) signal transduction network consistent with a set of
experimental observations with a goal to minimize false positive inferences even if risking false negatives. Special cases
of TR
p
have been investigated before in different contexts; the best previous results are as follows:
In this paper, our contributions are as follows:
R. Albert’s research was partly supported by a Sloan Research Fellowship in Science and Technology.
B. DasGupta’s research was partly supported by NSF grants DBI-0543365, IIS-0612044 and IIS-0346973.
E. Sontag’s research was partly supported by NSF grants EIA 0205116 and DMS-0504557. 相似文献
(1) | The minimum equivalent digraph problem, that correspond to a special case of TR1 with no critical edges, is known to be MAX-SNP-hard, admits a polynomial time algorithm with an approximation ratio of 1.617+ε for any constant ε>0 (Chiu and Liu in Sci. Sin. 4:1396–1400, 1965) and can be solved in linear time for directed acyclic graphs (Aho et al. in SIAM J. Comput. 1(2):131–137, 1972). |
(2) | A 2-approximation algorithm exists for TR1 (Frederickson and JàJà in SIAM J. Comput. 10(2):270–283, 1981; Khuller et al. in 19th Annual ACM-SIAM Symposium on Discrete Algorithms, pp. 937–938, 1999). |
• | We observe that TR p , for any integer p>0, can be solved in linear time for directed acyclic graphs using the ideas in Aho et al. (SIAM J. Comput. 1(2):131–137, 1972). |
• | We provide a 1.78-approximation for TR1 that improves the 2-approximation mentioned in (2) above. |
• | We provide a 2+o(1)-approximation for TR p on general graphs for any fixed prime p>1. |