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Search Results: 1 - 10 of 2288 matches for " Ichiro Takeuchi "
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Suboptimal Solution Path Algorithm for Support Vector Machine
Masayuki Karasuyama,Ichiro Takeuchi
Computer Science , 2011,
Abstract: We consider a suboptimal solution path algorithm for the Support Vector Machine. The solution path algorithm is an effective tool for solving a sequence of a parametrized optimization problems in machine learning. The path of the solutions provided by this algorithm are very accurate and they satisfy the optimality conditions more strictly than other SVM optimization algorithms. In many machine learning application, however, this strict optimality is often unnecessary, and it adversely affects the computational efficiency. Our algorithm can generate the path of suboptimal solutions within an arbitrary user-specified tolerance level. It allows us to control the trade-off between the accuracy of the solution and the computational cost. Moreover, We also show that our suboptimal solutions can be interpreted as the solution of a \emph{perturbed optimization problem} from the original one. We provide some theoretical analyses of our algorithm based on this novel interpretation. The experimental results also demonstrate the effectiveness of our algorithm.
Redescription of the rare amphipod crustacean Pseudaeginella montoucheti (Quitete, 1971) from Brazil
Mariana Lacerda,Ichiro Takeuchi,Setuko Masunari
ZooKeys , 2011, DOI: 10.3897/zookeys.146.1856
Abstract: Pseudaeginella montoucheti (Quitete, 1971) is redescribed based on newly collected specimens from red and brown algae and tubiculous polychaete colony that were obtained from shallow waters at Tamboretes Archipelago, Balneário Barra do Sul and Sepultura Beach, Bombinhas, Santa Catarina State, Brazil. Of 10 species of Pseudaeginella so far reported, P. montoucheti is closest to P. sanctipauli Laubitz, 1995, but differs from the latter bymore numerous body spines including ventro-lateral ones over gills on pereonites 3 and 4, and the antenna 1 length measuring half body length. An identification key for Pseudaeginella species and a checklist of Caprellidea occurring along the Brazilian coasts are also presented.
Quick sensitivity analysis for incremental data modification and its application to leave-one-out CV in linear classification problems
Shota Okumura,Yoshiki Suzuki,Ichiro Takeuchi
Computer Science , 2015,
Abstract: We introduce a novel sensitivity analysis framework for large scale classification problems that can be used when a small number of instances are incrementally added or removed. For quickly updating the classifier in such a situation, incremental learning algorithms have been intensively studied in the literature. Although they are much more efficient than solving the optimization problem from scratch, their computational complexity yet depends on the entire training set size. It means that, if the original training set is large, completely solving an incremental learning problem might be still rather expensive. To circumvent this computational issue, we propose a novel framework that allows us to make an inference about the updated classifier without actually re-optimizing it. Specifically, the proposed framework can quickly provide a lower and an upper bounds of a quantity on the unknown updated classifier. The main advantage of the proposed framework is that the computational cost of computing these bounds depends only on the number of updated instances. This property is quite advantageous in a typical sensitivity analysis task where only a small number of instances are updated. In this paper we demonstrate that the proposed framework is applicable to various practical sensitivity analysis tasks, and the bounds provided by the framework are often sufficiently tight for making desired inferences.
Short-range YN interactions in the Quark Cluster Model
Ken-ichiro Ogawa,Sachiko Takeuchi,Makoto Oka
Physics , 1993,
Abstract: A phenomenological model for the hyperon-nucleon interactions is constructed by using the quark cluster model approach to the short-distance baryon-baryon interactions. The model contains the SU(3) symmetric meson exchange interaction at large distances and the quark-exchange short-distance interaction. The main feature of the model is that strong channel dependences of the short range repulsions due to the quark model symmetry. It is pointed out that two channels, ($I$, $S$)= (1/2, 0) and (3/2, 1), of the S-wave sigma-nucleon interactions have extremely strong repulsions at short-distances.
Charge current driven by spin dynamics in disordered Rashba spin-orbit system
Jun-ichiro Ohe,Akihito Takeuchi,Gen Tatara
Physics , 2007, DOI: 10.1103/PhysRevLett.99.266603
Abstract: Pumping of charge current by spin dynamics in the presence of the Rashba spin-orbit interaction is theoretically studied. Considering disordered electron, the exchange coupling and spin-orbit interactions are treated perturbatively. It is found that dominant current induced by the spin dynamics is interpreted as a consequence of the conversion from spin current via the inverse spin Hall effect. We also found that the current has an additional component from a fictitious conservative field. Results are applied to the case of moving domain wall.
Sparse selection of bases in neural-network potential for crystalline and liquid Si
Ryo Kobayashi,Tomoyuki Tamura,Ichiro Takeuchi,Shuji Ogata
Physics , 2015,
Abstract: The neural-network interatomic potential for crystalline and liquid Si has been developed using the forward stepwise regression technique to reduce the number of bases with keeping the accuracy of the potential. This approach of making the neural-network potential enables us to construct the accurate interatomic potentials with less and important bases selected systematically and less heuristically. The evaluation of bulk crystalline properties, and dynamic properties of liquid Si show good agreements between the neural-network potential and ab-initio results.
Multi-parametric Solution-path Algorithm for Instance-weighted Support Vector Machines
Masayuki Karasuyama,Naoyuki Harada,Masashi Sugiyama,Ichiro Takeuchi
Computer Science , 2010,
Abstract: An instance-weighted variant of the support vector machine (SVM) has attracted considerable attention recently since they are useful in various machine learning tasks such as non-stationary data analysis, heteroscedastic data modeling, transfer learning, learning to rank, and transduction. An important challenge in these scenarios is to overcome the computational bottleneck---instance weights often change dynamically or adaptively, and thus the weighted SVM solutions must be repeatedly computed. In this paper, we develop an algorithm that can efficiently and exactly update the weighted SVM solutions for arbitrary change of instance weights. Technically, this contribution can be regarded as an extension of the conventional solution-path algorithm for a single regularization parameter to multiple instance-weight parameters. However, this extension gives rise to a significant problem that breakpoints (at which the solution path turns) have to be identified in high-dimensional space. To facilitate this, we introduce a parametric representation of instance weights. We also provide a geometric interpretation in weight space using a notion of critical region: a polyhedron in which the current affine solution remains to be optimal. Then we find breakpoints at intersections of the solution path and boundaries of polyhedrons. Through extensive experiments on various practical applications, we demonstrate the usefulness of the proposed algorithm.
Homotopy Continuation Approaches for Robust SV Classification and Regression
Shinya Suzumura,Kohei Ogawa,Masashi Sugiyama,Masayuki Karasuyama,Ichiro Takeuchi
Computer Science , 2015,
Abstract: In support vector machine (SVM) applications with unreliable data that contains a portion of outliers, non-robustness of SVMs often causes considerable performance deterioration. Although many approaches for improving the robustness of SVMs have been studied, two major challenges remain in robust SVM learning. First, robust learning algorithms are essentially formulated as non-convex optimization problems. It is thus important to develop a non-convex optimization method for robust SVM that can find a good local optimal solution. The second practical issue is how one can tune the hyperparameter that controls the balance between robustness and efficiency. Unfortunately, due to the non-convexity, robust SVM solutions with slightly different hyper-parameter values can be significantly different, which makes model selection highly unstable. In this paper, we address these two issues simultaneously by introducing a novel homotopy approach to non-convex robust SVM learning. Our basic idea is to introduce parametrized formulations of robust SVM which bridge the standard SVM and fully robust SVM via the parameter that represents the influence of outliers. We characterize the necessary and sufficient conditions of the local optimal solutions of robust SVM, and develop an algorithm that can trace a path of local optimal solutions when the influence of outliers is gradually decreased. An advantage of our homotopy approach is that it can be interpreted as simulated annealing, a common approach for finding a good local optimal solution in non-convex optimization problems. In addition, our homotopy method allows stable and efficient model selection based on the path of local optimal solutions. Empirical performances of the proposed approach are demonstrated through intensive numerical experiments both on robust classification and regression problems.
Safe Sample Screening for Support Vector Machines
Kohei Ogawa,Yoshiki Suzuki,Shinya Suzumura,Ichiro Takeuchi
Statistics , 2014,
Abstract: Sparse classifiers such as the support vector machines (SVM) are efficient in test-phases because the classifier is characterized only by a subset of the samples called support vectors (SVs), and the rest of the samples (non SVs) have no influence on the classification result. However, the advantage of the sparsity has not been fully exploited in training phases because it is generally difficult to know which sample turns out to be SV beforehand. In this paper, we introduce a new approach called safe sample screening that enables us to identify a subset of the non-SVs and screen them out prior to the training phase. Our approach is different from existing heuristic approaches in the sense that the screened samples are guaranteed to be non-SVs at the optimal solution. We investigate the advantage of the safe sample screening approach through intensive numerical experiments, and demonstrate that it can substantially decrease the computational cost of the state-of-the-art SVM solvers such as LIBSVM. In the current big data era, we believe that safe sample screening would be of great practical importance since the data size can be reduced without sacrificing the optimality of the final solution.
An Algorithmic Framework for Computing Validation Performance Bounds by Using Suboptimal Models
Yoshiki Suzuki,Kohei Ogawa,Yuki Shinmura,Ichiro Takeuchi
Statistics , 2014,
Abstract: Practical model building processes are often time-consuming because many different models must be trained and validated. In this paper, we introduce a novel algorithm that can be used for computing the lower and the upper bounds of model validation errors without actually training the model itself. A key idea behind our algorithm is using a side information available from a suboptimal model. If a reasonably good suboptimal model is available, our algorithm can compute lower and upper bounds of many useful quantities for making inferences on the unknown target model. We demonstrate the advantage of our algorithm in the context of model selection for regularized learning problems.
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