Faculty Profiles - SOGABE, Tomohiro

A preconditioning technique of Gauss–Legendre quadrature for the logarithm of symmetric positive definite matrices

Fuminori Tatsuoka, Tomohiro Sogabe, Tomoya Kemmochi, Shao-Liang Zhang

Applied Mathematics Letters Vol. 167 page： 109552 - 109552 2025.8

GPBi-CG revisited: a hybrid of the CGS method and the GPBi-CG method for nonsymmetric linear systems

Sogabe, T; Zhang, SL

JAPAN JOURNAL OF INDUSTRIAL AND APPLIED MATHEMATICS 2025.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Japan Journal of Industrial and Applied Mathematics

Toward the end of the 20th century, S.-L. Zhang constructed the so-called Zhang’s framework that successfully incorporated the CGS and Bi-CGSTAB methods and subsequently introduced the GPBi-CG method derived from the framework. While the GPBi-CG method often converges faster than the CGS and Bi-CGSTAB methods, there are still cases where the CGS method performs the best. This observation has motivated us to revisit the framework to find a hybrid algorithm, combining the GPBi-CG and CGS methods. In this paper, we introduce the hybrid algorithm, show its efficiency in some numerical experiments, and discuss a possible reason behind its effectiveness.

DOI： 10.1007/s13160-025-00716-3

Variational Quantum Algorithm for Solving Second-Order Linear Differential Equations

Sugaya, R; Sogabe, T; Kemmochi, T; Zhang, SL

QUANTUM INFORMATION & COMPUTATION Vol. 25 ( 3 ) page： 232 - 247 2025.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Quantum Information and Computation

Variational quantum algorithms (VQAs) have attracted attention as quantum algorithms employing on noisy intermediate-scale quantum devices. VQAs for solving the Poisson equation were recently proposed, as this method transforms the linear equation with a symmetric positive definite matrix obtained by discretizing the Poisson equation into a minimization problem. In this study, we propose a VQA for second-order linear differential equations including the Poisson equation on the basis of the referenced study, where the coefficient matrix obtained through discretization is a non-symmetric matrix. Furthermore, in our VQAs, we succeeded in decomposing the coefficient matrices arising from the periodic and the Dirichlet boundary condition into linear combinations of measurement operators and unitary matrices.

DOI： 10.2478/qic-2025-0012

A tensor Alternating Anderson-Richardson method for solving multilinear systems with M-tensors Reviewed

Niu, J; Du, L; Sogabe, T; Zhang, SL

JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS Vol. 461 2025.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Computational and Applied Mathematics

It is well-known that a multilinear system with a nonsingular M-tensor and a positive right-hand side has a unique positive solution. Tensor splitting methods generalizing the classical iterative methods for linear systems have been proposed for finding the unique positive solution. The Alternating Anderson–Richardson (AAR) method is an effective method to accelerate the classical iterative methods. In this study, we apply the idea of AAR for finding the unique positive solution quickly. We first present a tensor Richardson method based on tensor regular splittings, then apply Anderson acceleration to the tensor Richardson method and derive a tensor Anderson–Richardson method, finally, we periodically employ the tensor Anderson–Richardson method within the tensor Richardson method and propose a tensor AAR method. Numerical experiments show that the proposed method is effective in accelerating tensor splitting methods.

DOI： 10.1016/j.cam.2024.116419

電磁界解析の複素対称行列向け積型反復法 Reviewed

杉本振一郎，曽我部知広，張紹良，荻野正雄，武居周

電気学会論文誌 Vol. 145 ( 2 ) page： 87 - 97 2025.2

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IEEJ Transactions on Industry Applications

This paper deals with time-harmonic problems with complex symmetric matrices in the electromagnetic field analysis. To solve such problems more stably and quickly, the Product-type Krylov Subspace Methods based on the COCG and COCR methods are proposed, and verified in finite element analyses of the time-harmonic eddy current and high-frequency electromagnetic field problems. As a result, in some cases, the number of iterations and the computational time have been reduced.

DOI： 10.1541/ieejias.145.87

Computing the matrix exponential with the double exponential formula Reviewed

Fuminori Tatsuoka, Tomohiro Sogabe, Tomoya Kemmochi, Shao Liang Zhang

Special Matrices Vol. 12 ( 1 ) 2024.10

Language：English Publishing type：Research paper (scientific journal)

This article considers the computation of the matrix exponential eA with numerical quadrature. Although several quadrature-based algorithms have been proposed, they focus on (near) Hermitian matrices. In order to deal with non-Hermitian matrices, we use another integral representation including an oscillatory term and consider applying the double exponential (DE) formula specialized to Fourier integrals. The DE formula transforms the given integral into another integral whose interval is infinite, and therefore, it is necessary to truncate the infinite interval. In this article, to utilize the DE formula, we analyze the truncation error and propose two algorithms. The first one approximates eA with the fixed mesh size, which is a parameter in the DE formula affecting the accuracy. The second one computes eA based on the first one with automatic selection of the mesh size depending on the given error tolerance.

DOI： 10.1515/spma-2024-0013

Adaptive projected SOR algorithms for nonnegative quadratic programming Reviewed

Miyatake, Y; Sogabe, T

JAPAN JOURNAL OF INDUSTRIAL AND APPLIED MATHEMATICS 2024.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Japan Journal of Industrial and Applied Mathematics

The choice of relaxation parameter in the projected successive overrelaxation (PSOR) method for nonnegative quadratic programming problems is problem-dependent. We present novel adaptive PSOR algorithms that adaptively control the relaxation parameter using the Wolfe conditions. The method and its variants can be applied to various problems without requiring additional assumptions, barring the positive semidefiniteness concerning the matrix that defines the objective function, and the cost for updating the parameter is negligible in the whole iteration. Numerical experiments show that the proposed methods often perform comparably to (or sometimes superior to) the PSOR method with a nearly optimal relaxation parameter.

DOI： 10.1007/s13160-024-00672-4

Matrix equation representation of the convolution equation and its unique solvability Reviewed

Yuki Satake, Tomohiro Sogabe, Tomoya Kemmochi, Shao-Liang Zhang

Special Matrices Vol. 12 ( 1 ) 2024.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Walter de Gruyter GmbH

Abstract

We consider the convolution equation F * X = B F* X=B , where F ∈ R 3 × 3 F\in { { \mathbb{R } } }^{3\times 3} and B ∈ R m × n B\in { { \mathbb{R } } }^{m\times n} are given and X ∈ R m × n X\in { { \mathbb{R } } }^{m\times n} is to be determined. The convolution equation can be regarded as a linear system with a coefficient matrix of special structure. This fact has led to many studies including efficient numerical algorithms for solving the convolution equation. In this study, we show that the convolution equation can be represented as a generalized Sylvester equation. Furthermore, for some realistic examples arising from image processing, we show that the generalized Sylvester equation can be reduced to a simpler form, and we analyze the unique solvability of the convolution equation.

DOI： 10.1515/spma-2024-0001

Shifted LOPBiCG: A locally orthogonal product-type method for solving nonsymmetric shifted linear systems based on Bi-CGSTAB Reviewed

Other Link： https://www.degruyter.com/document/doi/10.1515/spma-2024-0001/pdf

Zhao, RJ; Sogabe, T; Kemmochi, T; Zhang, SL

NUMERICAL LINEAR ALGEBRA WITH APPLICATIONS Vol. 31 ( 2 ) 2024.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Numerical Linear Algebra with Applications

When solving shifted linear systems using shifted Krylov subspace methods, selecting a seed system is necessary, and an unsuitable seed may result in many shifted systems being unsolved. To avoid this problem, a seed-switching technique has been proposed to help switch the seed system to another linear system as a new seed system without losing the dimension of the constructed Krylov subspace. Nevertheless, this technique requires collinear residual vectors when applying Krylov subspace methods to the seed and shifted systems. Since the product-type shifted Krylov subspace methods cannot provide such collinearity, these methods cannot use this technique. In this article, we propose a variant of the shifted BiCGstab method, which possesses the collinearity of residuals, and apply the seed-switching technique to it. Some numerical experiments show that the problem of choosing the initial seed system is circumvented.

DOI： 10.1002/nla.2538

Tensor product-type methods for solving Sylvester tensor equations Reviewed

Niu Jing, Sogabe Tomohiro, Du Lei, Kemmochi Tomoya, Zhang Shao-Liang

APPLIED MATHEMATICS AND COMPUTATION Vol. 457 2023.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Mathematics and Computation

The tensor biconjugate gradient (TBiCG) method has recently been proposed for solving Sylvester tensor equations. The TBiCG method is based on the BiCG method that may exhibit irregular convergence behavior. To overcome the limitations, product-type methods, such as BiCGSTAB and GPBiCG, have been proposed. In this study, we apply the idea of product-type methods to solve Sylvester tensor equations and propose tensor GPBiCG and BiCGSTAB methods. Furthermore, we consider preconditioned algorithms of the tensor GPBiCG and BiCGSTAB methods using the nearest Kronecker product preconditioner. Numerical experiments illustrate that the proposed methods are competitive with some existing methods.

DOI： 10.1016/j.amc.2023.128155

Quantum algorithms based on the block-encoding framework for matrix functions by contour integrals Reviewed International journal

Souichi Takahira, Asuka Ohashi, Tomohiro Sogabe, Tsuyoshi S. Usuda

Quantum Information and Computation Vol. 22 ( 11&12 ) page： 965 - 979 2022.8

Publishing type：Research paper (scientific journal) Publisher：Rinton Press

he matrix functions can be defined by Cauchy's integral formula and can be approximated by the linear combination of inverses of shifted matrices using a quadrature formula. In this paper, we propose a quantum algorithm for matrix functions based on a procedure to implement the linear combination of the inverses on quantum computers. Compared with the previous study [S. Takahira, A. Ohashi, T. Sogabe, and T.S. Usuda, Quant. Inf. Comput., \textbf{20}, 1\&2, 14--36, (Feb. 2020)] that proposed a quantum algorithm to compute a quantum state for the matrix function based on the circular contour centered at the origin, the quantum algorithm in the present paper can be applied to a more general contour. Moreover, the algorithm is described by the block-encoding framework. Similarly to the previous study, the algorithm can be applied even if the input matrix is not a Hermitian or normal matrix. This is an advantage compared with quantum singular value transformation.

DOI： 10.26421/qic22.11-12-4

Recent development for computing singular values of a generalized tensor sum Reviewed

Ohashi Asuka, Sogabe Tomohiro

Journal of Advanced Simulation in Science and Engineering Vol. 9 ( 1 ) page： 136 - 149 2022

Numerical Algorithms for Computing an Arbitrary Singular Value of a Tensor Sum Reviewed Open Access

Ohashi Asuka, Sogabe Tomohiro

AXIOMS Vol. 10 ( 3 ) 2021.9

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Axioms

We consider computing an arbitrary singular value of a tensor sum: (Formula presented). We focus on the shift-and-invert Lanczos method, which solves a shift-and-invert eigenvalue problem of (TT T − ˜σ2 Iℓmn)−1, where ˜σ is set to a scalar value close to the desired singular value. The desired singular value is computed by the maximum eigenvalue of the eigenvalue problem. This shift-and-invert Lanczos method needs to solve large-scale linear systems with the coefficient matrix TT T − ˜σ2 Iℓmn. The preconditioned conjugate gradient (PCG) method is applied since the direct methods cannot be applied due to the nonzero structure of the coefficient matrix. However, it is difficult in terms of memory requirements to simply implement the shift-and-invert Lanczos and the PCG methods since the size of T grows rapidly by the sizes of A, B, and C. In this paper, we present the following two techniques: (1) efficient implementations of the shift-and-invert Lanczos method for the eigenvalue problem of TT T and the PCG method for TT T − ˜σ2 Iℓmn using three-dimensional arrays (third-order tensors) and the n-mode products, and (2) preconditioning matrices of the PCG method based on the eigenvalue and the Schur decomposition of T. Finally, we show the effectiveness of the proposed methods through numerical experiments.

DOI： 10.3390/axioms10030211

A thick-restart Lanczos type method for HermitianJ-symmetric eigenvalue problems Reviewed Open Access

Ken-Ichi Ishikawa, Tomohiro Sogabe

JAPAN JOURNAL OF INDUSTRIAL AND APPLIED MATHEMATICS Vol. 38 ( 1 ) page： 233 - 256 2021.2

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER JAPAN KK

A thick-restart Lanczos type algorithm is proposed for HermitianJ-symmetric matrices. Since HermitianJ-symmetric matrices possess doubly degenerate spectra or doubly multiple eigenvalues with a simple relation between the degenerate eigenvectors, we can improve the convergence of the Lanczos algorithm by restricting the search space of the Krylov subspace to that spanned by one of each pair of the degenerate eigenvector pairs. We show that the Lanczos iteration is compatible with theJ-symmetry, so that the subspace can be split into two subspaces that are orthogonal to each other. The proposed algorithm searches for eigenvectors in one of the two subspaces without the multiplicity. The other eigenvectors paired to them can be easily reconstructed with the simple relation from theJ-symmetry. We test our algorithm on randomly generated small dense matrices and a sparse large matrix originating from a quantum field theory.

DOI： 10.1007/s13160-020-00435-x

Other Link： http://link.springer.com/article/10.1007/s13160-020-00435-x/fulltext.html

K omega - Open-source library for the shifted Krylov subspace method of the form(zI - H)x = b Reviewed Open Access

Takeo Hoshi, Mitsuaki Kawamura, Kazuyoshi Yoshimi, Yuichi Motoyama, Takahiro Misawa, Youhei Yamaji, Synge Todo, Naoki Kawashima, Tomohiro Sogabe

COMPUTER PHYSICS COMMUNICATIONS Vol. 258 2021.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER

We develop K omega, an open-source linear algebra library for the shifted Krylov subspace methods. The methods solve a set of shifted linear equations (z(k)l - H)x((k)) = b(k = 0, 1, 2, ...) for a given matrix H and a vector b, simultaneously. The leading order of the operational cost is the same as that for a single equation. The shift invariance of the Krylov subspace is the mathematical foundation of the shifted Krylov subspace methods. Applications in materials science are presented to demonstrate the advantages of the algorithm over the standard Krylov subspace methods such as the Lanczos method. We introduce benchmark calculations of (i) an excited (optical) spectrum and (ii) intermediate eigenvalues by the contour integral on the complex plane. In combination with the quantum lattice solver H Phi, K omega can realize parallel computation of excitation spectra and intermediate eigenvalues for various quantum lattice models.Program summaryProgram Title: K omega [kei-oumig@]CPC Library link to program files: http://dx.doi.org/10.17632/mt928nz5r3.1Developer's repository link: https://github.com/issp-center-dev/KomegaLicensing provisions: GNU Lesser General Public License Version 3.Programming language: Fortran 90External routines/libraries: BLAS library, LAPACK library (Used in the sample program), MPI library (Optional).Nature of problem: Efficient algorithms, called shifted Krylov subspace algorithms, designed to solve the shifted linear equations.Solution method: Shifted conjugate gradient method, Shifted conjugate orthogonal conjugate gradient method, shifted bi-conjugate gradient method.Additional comments: The present paper is accompanied by a frozen copy of K omega release 2.0.0 that is made publicly available on GitHub (repository https://github.com/issp-center-dev/Komega commit hash fd5455328b102ec4fa13432496e41c404a0f5a9d). (C) 2020 The Authors. Published by Elsevier B.V.

DOI： 10.1016/j.cpc.2020.107536

Computing the matrix fractional power with the double exponential formula Reviewed Open Access

Tatsuoka F., Sogabe T., Miyatake Y., Kemmochi T., Zhang S.L.

Electronic Transactions on Numerical Analysis Vol. 54 page： 558 - 580 2021

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Electronic Transactions on Numerical Analysis

Two quadrature-based algorithms for computing the matrix fractional power Aα are presented in this paper. These algorithms are based on the double exponential (DE) formula, which is well-known for its effectiveness in computing improper integrals as well as in treating nearly arbitrary endpoint singularities. The DE formula transforms a given integral into another integral that is suited for the trapezoidal rule; in this process, the integral interval is transformed into an infinite interval. Therefore, it is necessary to truncate the infinite interval to an appropriate finite interval. In this paper, a truncation method, which is based on a truncation error analysis specialized to the computation of Aα, is proposed. Then, two algorithms are presented-one where Aα is computed with a fixed number of abscissa points and one with Aα computed adaptively. Subsequently, the convergence rate of the DE formula for Hermitian positive definite matrices is analyzed. The convergence rate analysis shows that the DE formula converges faster than Gaussian quadrature when A is ill-conditioned and α is a non-unit fraction. Numerical results show that our algorithms achieve the required accuracy and are faster than other algorithms in several situations.

DOI： 10.1553/0X003CC757

On a transformation of the (*)-congruence Sylvester equation for the least squares optimization Reviewed

Yuki Satake, Tomohiro Sogabe, Tomoya Kemmochi, Shao-Liang Zhang

OPTIMIZATION METHODS & SOFTWARE Vol. 35 ( 5 ) page： 974 - 981 2020.9

Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD

The star-congruence Sylvester equation is the matrix equation AX + (XB)-B-star = C, where A is an element of F-mxm, B is an element of F-nxm and C is an element of F-mxm are given, whereas X is an element of F-nxm is to be determined. Here, F = R or C, and star = T (transposed) or (*) (conjugate transposed). Very recently, Satake et al. showed that under some conditions, the matrix equation for the case star = T is equivalent to the generalized Sylvester equation. In this paper, we demonstrate that the result can be extended to the case star = (*). Through this extension, the least squares solution of the (*)-congruence Sylvester equation may be obtained using well-researched results on the least squares solution of the generalized Sylvester equation.

DOI： 10.1080/10556788.2020.1734004

Algorithms for the computation of the matrix logarithm based on the double exponential formula Reviewed Open Access

Fuminori Tatsuoka, Tomohiro Sogabe, Yuto Miyatake, Shao-Liang Zhang

JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS Vol. 373 2020.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER

We consider the computation of the matrix logarithm by using numerical quadrature. The efficiency of numerical quadrature depends on the integrand and the choice of quadrature formula. The Gauss-Legendre quadrature has been conventionally employed; however, the convergence could be slow for ill-conditioned matrices. This effect may stem from the rapid change of the integrand values. To avoid such situations, we focus on the double exponential formula, which has been developed to address integrands with endpoint singularity. In order to utilize the double exponential formula, we must determine a suitable finite integration interval, which provides the required accuracy and efficiency. In this paper, we present a method for selecting a suitable finite interval based on an error analysis as well as two algorithms, and one of these algorithms is an adaptive quadrature algorithm. (C) 2019 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cam.2019.112396

Generalized Sherman-Morrison-Woodbury formula based algorithm for the inverses of opposite-bordered tridiagonal matrices Reviewed

Ji-Teng Jia, Tomohiro Sogabe

JOURNAL OF MATHEMATICAL CHEMISTRY Vol. 58 ( 7 ) page： 1466 - 1480 2020.8

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

Matrix inverse computation is one of the fundamental mathematical problems of linear algebra and has been widely used in many fields of science and engineering. In this paper, we consider the inverse computation of an opposite-bordered tridiagonal matrix which has attracted much attention in recent years. By exploiting the low-rank structure of the matrix, first we show that an explicit formula for the inverse of the opposite-bordered tridiagonal matrix can be obtained based on the combination of a specific matrix splitting and the generalized Sherman-Morrison-Woodbury formula. Accordingly, a numerical algorithm is outlined. Second, we present a breakdown-free symbolic algorithm of O(n(2)) for computing the inverse of an n-by-n opposite-bordered tridiagonal matrix, which is based on the use of GTINV algorithm and the generalized symbolic Thomas algorithm. Finally, we have provided the results of some numerical experiments for the sake of illustration.

DOI： 10.1007/s10910-020-01138-x

Adaptive SOR methods based on the Wolfe conditions Reviewed

Yuto Miyatake, Tomohiro Sogabe, Shao-Liang Zhang

NUMERICAL ALGORITHMS Vol. 84 ( 1 ) page： 117 - 132 2020.5

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

Because the expense of estimating the optimal value of the relaxation parameter in the successive over-relaxation (SOR) method is usually prohibitive, the parameter is often adaptively controlled. In this paper, new adaptive SOR methods are presented that are applicable to a variety of symmetric positive definite linear systems and do not require additional matrix-vector products when updating the parameter. To this end, we regard the SOR method as an algorithm for minimising a certain objective function, which yields an interpretation of the relaxation parameter as the step size following a certain change of variables. This interpretation enables us to adaptively control the step size based on some line search techniques, such as the Wolfe conditions. Numerical examples demonstrate the favourable behaviour of the proposed methods.

DOI： 10.1007/s11075-019-00748-0

An Implicit Evaluation Method of Vector 2-Norms Arising from Sphere Constrained Quadratic Optimizations Invited Reviewed Open Access

Sogabe T., Suzuki A., Zhang S-L

CSIAM TRANSACTIONS ON APPLIED MATHEMATICS Vol. 1 ( 1 ) page： 142 - 154 2020.3

QUANTUM ALGORITHM FOR MATRIX FUNCTIONS BY CAUCHY'S INTEGRAL FORMULA Reviewed

Takahira Souichi, Ohashi Asuka, Sogabe Tomohiro, Usuda Tsuyoshi Sasaki

QUANTUM INFORMATION & COMPUTATION Vol. 20 ( 1-2 ) page： 14 - 36 2020.2

Relation between the T-congruence Sylvester equation and the generalized Sylvester equation Reviewed Open Access

Yuki Satake, Masaya Oozawa, Tomohiro Sogabe, Yuto Miyatake, Tomoya Kemmochi, Shao-Liang Zhang

APPLIED MATHEMATICS LETTERS Vol. 96 page： 7 - 13 2019.10

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

The T-congruence Sylvester equation is the matrix equation AX + (XB)-B-T = C, where A is an element of R-mxn, B is an element of R-nxm, and C is an element of R-mxm are given, and X is an element of R-nxm is to be determined. Recently, Oozawa et al. discovered a transformation that the matrix equation is equivalent to one of the well-studied matrix equations (the Lyapunov equation); however, the condition of the transformation seems to be too limited because matrices A and B are assumed to be square matrices (m = n). In this paper, two transformations are provided for rectangular matrices A and B. One of them is an extension of the result of Oozawa et al. for the case m >= n, and the other is a novel transformation for the case m <= n. (C) 2019 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.aml.2019.04.007

Bidiagonalization of (k, k + 1)-tridiagonal matrices Reviewed Open Access

Takahira S., Sogabe T., Usuda T. S.

SPECIAL MATRICES Vol. 7 ( 1 ) page： 20-26 2019.1

On computing the minimum singular value of a tensor sum Reviewed Open Access

A. Ohashi, T. Sogabe

Special Matrices Vol. 7 ( 1 ) page： 95 - 106 2019.1

Language：English Publishing type：Research paper (scientific journal)

© 2019 A. Ohashi et al., published by De Gruyter. Recently, the Lanczos bidiagonalization method over tensor space has been proposed for computing the maximum and minimum singular values of a tensor sum T. The method over tensor space is practical in memory and has a simple implementation due to recent developments in tensor computations; however, there is still room for improvement in the convergence to the minimum singular value. This study reconstructed an invert Lanczos bidiagonalization method from vector space to tensor space. The resulting algorithm requires solving linear systems at each iteration step. Using standard direct methods, such as the LU decomposition for solving the linear systems requires a huge memory of O(n6). Therefore, this paper proposes a tensor-structure-preserving direct methods of T whose memory requirements are of O(n3), which is equivalent to the order of iterative methods. Numerical examples indicate that the number of iterations tends to be much smaller than that of the conventional method.

DOI： 10.1515/spma-2019-0009

A structure-preserving fourier pseudo-spectral linearly implicit scheme for the space-fractional nonlinear schrödinger equation Reviewed

Yuto Miyatake, Tai Nakagawa, Tomohiro Sogabe, Shao Liang Zhang

Journal of Computational Dynamics Vol. 6 ( 2 ) page： 361 - 383 2019

Language：English Publishing type：Research paper (scientific journal)

©2019 American Institute of Mathematical Sciences. We propose a Fourier pseudo-spectral scheme for the space-fractional nonlinear Schrödinger equation. The proposedscheme has the following features:it is linearly implicit, it preserves two invariants of the equation, its unique solvability is guaranteed without any restrictions on space and time step sizes. The scheme requires solving a complex symmetric linear system per time step. To solve the system efficiently, we also present a certain variable transformation and preconditioner.

DOI： 10.3934/jcd.2019018

On Computing the k-th Singular Triplet Reviewed Open Access

Lee Dongjin, 曽我部知広, 宮武勇登, Zhang Shao-Liang

日本応用数理学会論文誌(Web) Vol. 29 ( 1 ) page： 121‐140(J‐STAGE) - 140 2019

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society for Industrial and Applied Mathematics

Abstract. We propose a numerical algorithm for the problem of computing the k-th singular triplet of a large sparse matrix. In the proposed algorithm, the problem is divided into subproblems, and then eigenvalue problems equivalent to the singular value problem are solved in each subproblem. We discuss the accuracy of the proposed algorithm and show that it can handle large matrices in numerical experiments.

DOI： 10.11540/jsiamt.29.1_121

J-GLOBAL

Modified Strang splitting for semilinear parabolic problems Reviewed Open Access

Kosuke Nakano, Tomoya Kemmochi, Yuto Miyatake, Tomohiro Sogabe, Shao-Liang Zhang

JSIAM LETTERS Vol. 11 ( 0 ) page： 77 - 80 2019

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN SOC INDUSTRIAL & APPLIED MATHEMATICS-JSIAM

We consider applying the Strang splitting to semilinear parabolic problems. The key ingredients of the Strang splitting are the decomposition of the equation into several parts and the computation of approximate solutions by combining the time evolution of each split equation. However, when the Dirichlet boundary condition is imposed, order reduction could occur due to the incompatibility of the split equations with the boundary condition. In this paper, to overcome the order reduction, a modified Strang splitting procedure is presented for the one-dimensional semilinear parabolic equation with first-order spatial derivatives, like the Burgers equation.

DOI： 10.14495/jsiaml.11.77

On the equivalence between SOR-type methods for linear systems and the discrete gradient methods for gradient systems Reviewed Open Access

Miyatake Yuto, Sogabe Tomohiro, Zhang Shao-Liang

JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS Vol. 342 page： 58-69 2018.11

Solution of the k-th eigenvalue problem in large-scale electronic structure calculations Reviewed Open Access

Lee Dongjin, Hoshi Takeo, Sogabe Tomohiro, Miyatake Yuto, Zhang Shao-Liang

JOURNAL OF COMPUTATIONAL PHYSICS Vol. 371 page： 618-632 2018.10

A Look-Back-type restart for the restarted Krylov subspace methods for solving non-Hermitian linear systems Reviewed

Imakura Akira, Sogabe Tomohiro, Zhang Shao-Liang

JAPAN JOURNAL OF INDUSTRIAL AND APPLIED MATHEMATICS Vol. 35 ( 2 ) page： 835-859 2018.7

On a relationship between the T-congruence Sylvester equation and the Lyapunov equation Reviewed Open Access

Oozawa Masaya, Sogabe Tomohiro, Miyatake Yuto, Zhang Shao-Liang

JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS Vol. 329 page： 51-56 2018.2

A fast algorithm for solving tridiagonal quasi-Toeplitz linear systems Reviewed

Lei Du, Tomohiro Sogabe, Shao-Liang Zhang

APPLIED MATHEMATICS LETTERS Vol. 75 page： 74 - 81 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

In this paper, we consider the solution of tridiagonal quasi-Toeplitz linear systems. By exploiting the special quasi-Toeplitz structure, we give a new decomposition form of the coefficient matrix. Based on this matrix decomposition form and combined with the Sherman Morrison formula, we propose an efficient algorithm for solving the tridiagonal quasi-Toeplitz linear systems. Although our algorithm takes more floating-point operations (FLOPS) than the LU decomposition method, it needs less memory storage and data transmission and is about twice faster than the LU decomposition method. Numerical examples are given to illustrate the efficiency of our algorithm. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.aml.2017.06.016

A Note on Computing the Matrix Fractional Power Using the Double Exponential Formula Reviewed Open Access

立岡文理, 曽我部知広, 宮武勇登, Zhang Shao-Liang

日本応用数理学会論文誌(Web) Vol. 28 ( 3 ) page： 142‐161(J‐STAGE) - 161 2018

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society for Industrial and Applied Mathematics

Abstract. The matrix fractional power Aα can be represented as an improper integral for a slowly decaying function over the half infinite interval. Conventional approaches to approximating the integral are to apply Gaussian quadrature after some variable transformations; however, the convergence could be slow for an ill-conditioned matrix or a specific value of α. To avoid such situation, we consider the Double Exponential (DE) formula instead of conventional approaches, propose algorithms with settings of the integration interval, and then we show some numerical results.

DOI： 10.11540/jsiamt.28.3_142

J-GLOBAL

Solution of a Nonlinear Eigenvalue Problem Using Signed Singular Values Reviewed

Ooi Kouhei, Mizuno Yoshinori, Sogabe Tomohiro, Yamamoto Yusaku, Zhang Shao-Liang

EAST ASIAN JOURNAL ON APPLIED MATHEMATICS Vol. 7 ( 4 ) page： 799-809 2017.11

The Discrete Gradient Method for Differential Equations Can Be a Generator of Linear Solvers Reviewed Open Access

宮武勇登, 曽我部知広, ZHANG Shao-Liang

日本応用数理学会論文誌(Web) Vol. 27 ( 3 ) page： 239‐249(J‐STAGE) - 249 2017

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society for Industrial and Applied Mathematics

Abstract. A novel framework of generating iterative solvers for symmetric positive definite linear systems is proposed. In the framework, iterative solvers are generated by applying the discrete gradient method to initial value problems whose equilibrium coincides with the exact solution of the linear systems. The framework can generate potentially a large number of linear solvers with unconditional convergence property. As a simple example, we show that the framework includes the SOR method.

DOI： 10.11540/jsiamt.27.3_239

J-GLOBAL

On The Pfaflians and Determinants of Some Skew-Centrosymmetric Matrices Reviewed

Fatih Yilmaz, Tomohiro Sogabe, Emrullah Kirklar

JOURNAL OF INTEGER SEQUENCES Vol. 20 ( 4 ) page： 1 - 9 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：UNIV WATERLOO

This paper shows that the Pfaffians and determinants of some skew centrosymmetric matrices can be computed by a paired two-term recurrence relation, or a general number sequence of second order. As a result, the complexities of the formulas are of order It. Furthermore, the formulas have no divisions at all, i.e., they fall into the class of breakdown-free algorithms.

Energy-preserving $H^1$-Galerkin schemes for the Hunter--Saxton equation Reviewed

Yuto Miyatake, Geonsik Eom, Tomohiro Sogabe, Shao-Liang Zhang

Journal of Mathematical Research with Applications Vol. 37 page： 107 - 118 2017

A cost-efficient variant of the incremental Newton iteration for the matrix $p$th root Reviewed

Fuminori Tatsuoka, Tomohiro Sogabe, Yuto Miyatake, Shao-Liang Zhang

Journal of Mathematical Research with Applications ( 37 ) page： 97 - 106 2016.11

An initial guess of Newton's method for the matrix square root based on a sphere constrained optimization problem. Reviewed Open Access

Sho Mizuno, Yosuke Moriizumi, Tsuyoshi Sasaki Usuda, Tomohiro Sogabe

JSIAM Lett. Vol. 8 ( 0 ) page： 17 - 20 2016

A generalized symbolic Thomas algorithm for the solution of opposite-bordered tridiagonal linear systems Reviewed Open Access

Jiteng Jia, Tomohiro Sogabe, Sumei Li

JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS Vol. 290 page： 423 - 432 2015.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

In the current paper, we present a generalized symbolic Thomas algorithm, that never suffers from breakdown, for solving the opposite-bordered tridiagonal (OBT) linear systems. The algorithm uses a fill-in matrix factorization and can solve an OBT linear system in 0(n) operations. Meanwhile, an efficient method of evaluating the determinant of an opposite-bordered tridiagonal matrix is derived. The computational costs of the proposed algorithms are also discussed. Moreover, three numerical examples are provided in order to demonstrate the performance and effectiveness of our algorithms and their competitiveness with some already existing algorithms. All of the experiments are performed on a computer with the aid of programs written in Matlab. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cam.2015.05.026

IDR(s) for solving shifted nonsymmetric linear systems Reviewed

Lei Du, Tomohiro Sogabe, Shao-Liang Zhang

JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS Vol. 274 page： 35 - 43 2015.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER

The IDR(s) method by Sonneveld and van Gijzen (2008) has recently received tremendous attention since it is effective for solving nonsymmetric linear systems. In this paper, we generalize this method to solve shifted nonsymmetric linear systems. When solving this kind of problem by existing shifted Krylov subspace methods, we know one just needs to generate one basis of the Krylov subspaces due to the shift-invariance property of Krylov subspaces. Thus the computation cost required by the basis generation of all shifted linear systems, in terms of matrix vector products, can be reduced. For the IDR(s) method, we find that there also exists a shift-invariance property of the Sonneveld subspaces. This inspires us to develop a shifted version of the IDR(s) method for solving the shifted linear systems. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cam.2014.07.004

On decomposition of k-tridiagonal ℓ-Toeplitz matrices and its applications Reviewed

A. Ohashi, T. Sogabe, T. S. Usuda

Special Matrices Vol. 3 ( 1 ) page： 200 - 206 2015.1

Language：English Publishing type：Research paper (scientific journal)

© 2015 A. Ohashis et al., licensee De Gruyter Open. We consider a k-tridiagonal ℓ-Toeplitz matrix as one of generalizations of a tridiagonal Toeplitz matrix. In the present paper, we provide a decomposition of the matrix under a certain condition. By the decomposition, the matrix is easily analyzed since one only needs to analyze the small matrix obtained from the decomposition. Using the decomposition, eigenpairs and arbitrary integer powers of the matrix are easily shown as applications.

DOI： 10.1515/spma-2015-0019

On tensor product decomposition of k-tridiagonal Toeplitz matrices Reviewed Open Access

Asuka Ohashi, Tsuyoshi Sasaki Usuda, Tomohiro Sogabe, Fatih Yilmaz

International Journal of Pure and Applied Mathematics Vol. 103 ( 3 ) page： 537 - 545 2015

Language：English Publishing type：Research paper (scientific journal)

© 2015 Academic Publications, Ltd. In the present paper, we provide a decomposition of a k-tridiagonal Toeplitz matrix via tensor product. By the decomposition, the required memory of the matrix is reduced and the matrix is easily analyzed since we can use properties of tensor product.

DOI： 10.12732/ijpam.v103i3.14

AN EXTENSION OF TWO CONJUGATE DIRECTION METHODS TO MARKOV CHAIN PROBLEMS Reviewed

Chun Wen, Ting-Zhu Huang, Tomohiro Sogabe

COMPUTING AND INFORMATICS Vol. 34 ( 2 ) page： 495 - 516 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：SLOVAK ACAD SCIENCES INST INFORMATICS

Motivated by the recent applications of the conjugate residual method to nonsymmetric lineal systems by Sogabe, Sugihara and Zhang [An extension of the conjugate residual method to nonsymmetric linear systems. J. Comput. Appl. Math., Vol. 266, 2009, pp. 103-113], this paper describes two conjugate direction methods, BiCR and BiCG, and attempts to extend their applications to compute the stationary probability distribution for an irreducible Markov chain with the aim of finding an alternative basic solver. Numerical experiments show the feasibility of the BiCR and BiCG to some extent, with applications to several practical Markov chain problems.

Quasi-minimal residual variants of the COCG and COCR methods for complex symmetric linear systems in electromagnetic simulations Reviewed

IEEE Trans. Microw. Theory Techn. Vol. 62 page： 2859-2867 2014.12

A note on a fast breakdown-free algorithm for computing the determinants and the permanents of k-tridiagonal matrices Reviewed

Tomohiro Sogabe, Fatih Yilmaz

APPLIED MATHEMATICS AND COMPUTATION Vol. 249 page： 98 - 102 2014.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE INC

k-Tridiagonal matrices have attracted much attention in recent years, which are a generalization of tridiagonal matrices. In this note, a breakdown-free numerical algorithm of O(n) is presented for computing the determinants and the permanents of k-tridiagonal matrices. Even though the algorithm is not a symbolic algorithm, it never suffers from breakdown. Furthermore, it produces exact values when all entries of the k-tridiagonal matrices are given in integer. In addition, the algorithm can be simplified for a general symmetric Toeplitz case, and it generates the kth powers of Fibonacci, Pell, and Jacobsthal numbers for a certain symmetric Toeplitz case. (C) 2014 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.amc.2014.10.040

An algorithm for solving nonsymmetric penta-diagonal Toeplitz linear systems Reviewed

Lei Du, Tomohiro Sogabe, Shao-Liang Zhang

APPLIED MATHEMATICS AND COMPUTATION Vol. 244 page： 10 - 15 2014.10

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE INC

Fast algorithms for solving symmetric penta-diagonal Toeplitz linear systems have been proposed in McNally (2010) [7], Nemani (2010) [8] and Xu (2010) [11]. In this paper, we discuss the general nonsymmetric problem and propose an algorithm for solving nonsymmetric penta-diagonal Toeplitz linear systems. Numerical examples are given to illustrate the efficiency of our algorithm. (C) 2014 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.amc.2014.06.104

BiCR-type methods for families of shifted linear systems Reviewed Open Access

Xian-Ming Gu, Ting-Zhu Huang, Jing Meng, Tomohiro Sogabe, Hou-Biao Li, Liang Li

COMPUTERS & MATHEMATICS WITH APPLICATIONS Vol. 68 ( 7 ) page： 746 - 758 2014.10

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

The shifted linear systems with non-Hermitian matrices often arise from the numerical solutions for time-dependent PDEs, computing the large-scale eigenvalue problems, control theory and so on. In the present paper, we develop two shifted variants of BiCR-type methods for solving such linear systems. These variants of BiCR-type methods take advantage of the shifted structure, so that the number of matrix-vector multiplications and the number of inner products are the same as a single linear system. Finally, extensive numerical examples are reported to illustrate the performance and effectiveness of the proposed methods. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.camwa.2014.07.029

A note on symmetric k-Tridiagonal matrix family and the Fibonacci numbers Reviewed

Fatih Yilmaz, Tomohiro Sogabe

International Journal of Pure and Applied Mathematics Vol. 96 ( 2 ) page： 289 - 298 2014

A novel algorithm for solving quasi penta-diagonal linear systems Reviewed

Ji-Teng Jia, Tomohiro Sogabe

JOURNAL OF MATHEMATICAL CHEMISTRY Vol. 51 ( 3 ) page： 881 - 889 2013.3

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

In this paper, a novel numerical algorithm for solving quasi penta-diagonal linear systems is presented. The computational costs of the algorithm is less than those of three successful algorithms given by El-Mikkawy and Rahmo (Comput Math Appl 59:1386-1396, 2010), by Lv and Le (Appl Math Comput 204:707-712, 2008), and by Jia et al. (Int J Comput Math 89:851-860, 2012). In addition, a new recursive method for inverting the quasi penta-diagonal matrices is also discussed. The implementation of the algorithm using Computer Algebra Systems (CASs) such as MATLAB and MAPLE is straightforward. Two numerical examples are given in order to demonstrate the performance and efficiency of our algorithm.

DOI： 10.1007/s10910-012-0122-7

A novel algorithm and its parallelization for solving nearly penta-diagonal linear systems Reviewed

Ji-Teng Jia, Tomohiro Sogabe

INTERNATIONAL JOURNAL OF COMPUTER MATHEMATICS Vol. 90 ( 2 ) page： 435 - 444 2013.2

Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD

In the current paper, a new serial algorithm for solving nearly penta-diagonal linear systems is presented. The computational cost of the algorithm is less than or almost equal to those of recent successful algorithms [J. Jia, Q. Kong, and T. Sogabe, A fast numerical algorithm for solving nearly penta-diagonal linear systems, Int. J. Comput. Math. 89 (2012), pp. 851860; X.G. Lv and J. Le, A note on solving nearly penta-diagonal linear systems, Appl. Math. Comput. 204 (2008), pp. 707712; S.N. Neossi Nguetchue and S. Abelman, A computational algorithm for solving nearly penta-diagonal linear systems, Appl. Math. Comput. 203 (2008), pp. 629634]. Moreover, it is suitable for developing its parallel algorithms. One of the parallel algorithms is given and is shown to be promising. The implementation of the algorithms using Computer Algebra Systems such as MATLAB and MAPLE is straightforward. Two numerical examples are given in order to illustrate the validity and efficiency of our algorithms.

DOI： 10.1080/00207160.2012.725845

On particular solution of ordinary differential equations with constant coefficients Reviewed

Jiteng Jia, Tomohiro Sogabe

APPLIED MATHEMATICS AND COMPUTATION Vol. 219 ( 12 ) page： 6761 - 6767 2013.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE INC

In this paper, a new method is presented for obtaining the particular solution of ordinary differential equations with constant coefficients. An explicit formula of the particular solution is derived from the use of an upper triangular Toeplitz matrix. The validity of the approach is illustrated by some examples. (C) 2013 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.amc.2012.12.080

Inversion of k-tridiagonal matrices with Toeplitz structure Reviewed Open Access

Jiteng Jia, Tomohiro Sogabe, Moawwad El-Mikkawy

COMPUTERS & MATHEMATICS WITH APPLICATIONS Vol. 65 ( 1 ) page： 116 - 125 2013.1

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

In this paper, we consider an inverse problem with the k-tridiagonal Toeplitz matrices. A theoretical result is obtained that under certain assumptions the explicit inverse of a k-tridiagonal Toeplitz matrix can be derived immediately. Two numerical examples are given to demonstrate the validity of our results. (c) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.camwa.2012.11.001

An interior eigenvalue problem from electronic structure calculations Reviewed

Dongjin Lee, Takafumi Miyata, Tomohiro Sogabe, Takeo Hoshi, Shao-Liang Zhang

JAPAN JOURNAL OF INDUSTRIAL AND APPLIED MATHEMATICS Vol. 30 ( 3 ) page： 625 - 633 2013

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER JAPAN KK

We consider the generalized eigenvalue problem Ax = lambda Bx, where A and B are real symmetric matrices and B is also positive definite. All the eigenvalues of this problem are real, and it is often necessary to compute only a few eigenvalues which are important for applications. In electronic structure calculations of materials, specific interior eigenvalues are of fundamental interest, since they play crucial roles in various industrial applications. In this paper, we propose an approach based on the inertia of the linear matrix pencil of A and B. The eigenvalue problem is restated, and a class of algorithms is presented for separating the target eigenvalues from the others.

DOI： 10.1007/s13160-013-0118-0

An Efficient Variant of the Restarted Shifted GMRES Method for Solving Shifted Linear Systems Reviewed

Imakura,Akira, Tomohiro,Sogabe, Shao-Liang,Zhang

Journal of Mathematical Research with Applications Vol. 33 ( 2 ) page： 127 - 141 2013

Language：English Publishing type：Research paper (scientific journal)

We investigate the restart of the Restarted Shifted GMRES method for solving shifted linear systems. Recently the variant of the GMRES($m$) method with the {\it unfixed update} has been proposed to improve the convergence of the GMRES($m$) method for solving linear systems, and shown to have an efficient convergence property. In this paper, by applying the unfixed update to the Restarted Shifted GMRES method, we propose a variant of the Restarted Shifted GMRES method. We show a potentiality for efficient convergence within the variant by some numerical results.

Solution of generalized shifted linear systems with complex symmetric matrices Reviewed

Tomohiro Sogabe, Takeo Hoshi, Shao-Liang Zhang, Takeo Fujiwara

JOURNAL OF COMPUTATIONAL PHYSICS Vol. 231 ( 17 ) page： 5669 - 5684 2012.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE

We develop the shifted COCG method [R. Takayama, T. Hoshi, T. Sogabe, S.-L. Zhang, T. Fujiwara, Linear algebraic calculation of Green's function for large-scale electronic structure theory, Phys. Rev. B 73 (165108) (2006) 1-9] and the shifted WQMR method [T. Sogabe, T. Hoshi, S.-L. Zhang, T. Fujiwara, On a weighted quasi-residual minimization strategy of the QMR method for solving complex symmetric shifted linear systems, Electron. Trans. Numer. Anal. 31 (2008) 126-140] for solving generalized shifted linear systems with complex symmetric matrices that arise from the electronic structure theory. The complex symmetric Lanczos process with a suitable bilinear form plays an important role in the development of the methods. The numerical examples indicate that the methods are highly attractive when the inner linear systems can efficiently be solved. (C) 2012 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jcp.2012.04.046

An order-N electronic structure theory with generalized eigenvalue equations and its application to a ten-million-atom system Reviewed Open Access

T. Hoshi, S. Yamamoto, T. Fujiwara, T. Sogabe, S-L Zhang

JOURNAL OF PHYSICS-CONDENSED MATTER Vol. 24 ( 16 ) 2012.4

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

A linear algebraic theory called the 'multiple Arnoldi method' is presented and realizes large-scale (order-N) electronic structure calculations with generalized eigenvalue equations. A set of linear equations, in the form of (zS - H)x = b, are solved simultaneously with multiple Krylov subspaces. The method is implemented in a simulation package ELSES (www.elses.jp) with tight-binding-form Hamiltonians. A finite-temperature molecular dynamics simulation is carried out for metallic and insulating materials. A calculation with 10(7) atoms was realized by a workstation. The parallel efficiency is shown up to 1024 CPU cores.

DOI： 10.1088/0953-8984/24/16/165502

A new algorithm for solving nearly penta-diagonal Toeplitz linear systems Reviewed Open Access

Jiteng Jia, Qiongxiang Kong, Tomohiro Sogabe

COMPUTERS & MATHEMATICS WITH APPLICATIONS Vol. 63 ( 7 ) page： 1238 - 1243 2012.4

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

A new numerical algorithm for solving nearly penta-diagonal Toeplitz linear systems is presented. The algorithm is suited for implementation using Computer Algebra Systems (CASs) such as MATLAB, MACSYMA and MAPLE. Numerical examples are given in order to illustrate the efficiency of our algorithm. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.camwa.2011.12.044

An Efficient Variant of the GMRES(m) Method Based on the Error Equations Reviewed

Akira Imakura, Tomohiro Sogabe, Shao-Liang Zhang

EAST ASIAN JOURNAL ON APPLIED MATHEMATICS Vol. 2 ( 1 ) page： 19 - 32 2012.2

Language：English Publishing type：Research paper (scientific journal) Publisher：GLOBAL SCIENCE PRESS

The GMRES(m) method proposed by Saad and Schultz is one of the most successful Krylov subspace methods for solving nonsymmetric linear systems. In this paper, we investigate how to update the initial guess to make it converge faster, and in particular propose an efficient variant of the method that exploits an unfixed update. The mathematical background of the unfixed update variant is based on the error equations, and its potential for efficient convergence is explored in some numerical experiments.

DOI： 10.4208/eajam.280611.030911a

On Convergence Behavior of the GMRES(m) Method with the Deflation-Type Restart and the Look-Back-Type Restart Reviewed Open Access

Imakura Akira, Yang Ji-Rong, Sogabe Tomohiro, Zhang Shao-Liang

Transactions of the Japan Society for Industrial and Applied Mathematics Vol. 22 ( 3 ) page： 117-141 2012

Language：English Publishing type：Research paper (scientific journal)

We investigate two types of the improvement techniques for the GMRES(m) method to solve nonsymmetric linear systems: the deflation-type restart and the Look-Back-type restart. From the analysis based on the residual polynomials, we show in this paper that these restart techniques modify the convergence behavior of the GMRES(m) method by different mathematical backgrounds. Then under the knowledge from the analysis, we propose an efficient improvement of the GMRES(m) method with these restart techniques. The numerical experiments indicate that the proposed method shows the efficient convergence behavior.

DOI： 10.11540/jsiamt.22.3_117

A Look-Back GMRES(m) Method for Solving Nonsymmetric Linear Systems Reviewed Open Access

Imakura Akira, Sogabe Tomohiro, Zhang Shao-Liang

Transactions of the Japan Society for Industrial and Applied Mathematics Vol. 22 ( 1 ) page： 1-21 2012

Language：English Publishing type：Research paper (scientific journal)

In recent years, we have focused on the restart of the GMRES(m) method, and proposed an extension of the GMRES(m) method based on the error equations. In this paper, from the analysis on the residual polynomial of the extension of the GMRES(m) method, we propose a Look-Back GMRES(m) method under a Look-Back strategy which reconstructs the past residual polynomials of the GMRES(m) method. Some numerical experiments indicate that the Look-Back GMRES(m) method has a higher performance for efficient convergence than the GMRES(m) method.

DOI： 10.11540/jsiamt.22.1_1

A fast numerical algorithm for solving nearly penta-diagonal linear systems Reviewed

Ji-teng Jia, Qiong-xiang Kong, Tomohiro Sogabe

INTERNATIONAL JOURNAL OF COMPUTER MATHEMATICS Vol. 89 ( 6 ) page： 851 - 860 2012

Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD

In this paper, we present a fast numerical algorithm for solving nearly penta-diagonal linear systems and show that the computational cost is less than those of three algorithms in El-Mikkawy and Rahmo, [Symbolic algorithm for inverting cyclic penta-diagonal matrices recursively-Derivation and implementation, Comput. Math. Appl. 59 (2010), pp. 1386-1396], Lv and Le [A note on solving nearly penta-diagonal linear systems, Appl. Math. Comput. 204 (2008), pp. 707-712] and Neossi Nguetchue and Abelman [A computational algorithm for solving nearly penta-diagonal linear systems, Appl. Math. Comput. 203 (2008), pp. 629-634.]. In addition, an efficient way of evaluating the determinant of a nearly penta-diagonal matrix is also discussed. The algorithm is suited for implementation using computer algebra systems (CAS) such as MATLAB, MACSYMA and MAPLE. Some numerical examples are given in order to illustrate the efficiency of our algorithm.

DOI： 10.1080/00207160.2012.665903

Fast block diagonalization of k-tridiagonal matrices Reviewed

Tomohiro Sogabe, Moawwad El-Mikkawy

APPLIED MATHEMATICS AND COMPUTATION Vol. 218 ( 6 ) page： 2740 - 2743 2011.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE INC

In the present paper, we give a fast algorithm for block diagonalization of k-tridiagonal matrices. The block diagonalization provides us with some useful results: e. g., another derivation of a very recent result on generalized k-Fibonacci numbers in [M. E. A. El-Mikkawy, T. Sogabe, A new family of k-Fibonacci numbers, Appl. Math. Comput. 215 (2010) 4456-4461]; efficient (symbolic) algorithm for computing the matrix determinant. (C) 2011 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.amc.2011.08.014

A variant of the IDR(s) method with the quasi-minimal residual strategy Reviewed Open Access

Lei Du, Tomohiro Sogabe, Shao-Liang Zhang

JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS Vol. 236 ( 5 ) page： 621 - 630 2011.10

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER

The IDR(s) method proposed by Sonneveld and van Gijzen is an effective method for solving nonsymmetric linear systems, but usually with irregular convergence behavior. In this paper, we reformulate the relations of residuals and their auxiliary vectors generated by the IDR(s) method in matrix form. Then, using this new formulation and motivated by other QMR-type methods, we propose a variant of the IDR(s) method, called QMRIDR(s), for overcoming the disadvantage of its irregular convergence behavior. Both fast and smooth convergence behaviors of the QMRIDR(s) method can be shown. Numerical experiments are reported to show the efficiency of our proposed method. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cam.2011.07.027

A block IDR(s) method for nonsymmetric linear systems with multiple right-hand sides Reviewed

An Arnoldi(M,W,G) Method for Generalized Eigenvalue Problems Reviewed Open Access

山下達也, 宮田考史, 曽我部知広, 星健夫, 藤原毅夫, ZHANG Shao‐Liang

日本応用数理学会論文誌 Vol. 21 ( 3 ) page： 241 - 254 2011.9

L. Du, T. Sogabe, B. Yu, Y. Yamamoto, S. -L. Zhang

JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS Vol. 235 ( 14 ) page： 4095 - 4106 2011.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The IDR(s) based on the induced dimension reduction (IDR) theorem, is a new class of efficient algorithms for large nonsymmetric linear systems. IDR(1) is mathematically equivalent to BiCGStab at the even IDR(1) residuals, and IDR(s) with s > 1 is competitive with most Bi-CG based methods. For these reasons, we extend the IDR(s) to solve large nonsymmetric linear systems with multiple right-hand sides. In this paper, a variant of the IDR theorem is given at first, then the block IDR(s), an extension of IDR(s) based on the variant IDR(s) theorem, is proposed. By analysis, the upper bound on the number of matrix-vector products of block IDR(s) is the same as that of the IDR(s) for a single right-hand side in generic case, i.e., the total number of matrix-vector products of IDR(s) may be m times that of of block IDR(s), where in is the number of right-hand sides. Numerical experiments are presented to show the effectiveness of our proposed method. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cam.2011.02.035

Efficient and accurate linear algebraic methods for large-scale electronic structure calculations with nonorthogonal atomic orbitals Reviewed Open Access

H. Teng, T. Fujiwara, T. Hoshi, T. Sogabe, S. -L. Zhang, S. Yamamoto

PHYSICAL REVIEW B Vol. 83 ( 16 ) 2011.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

The need for large-scale electronic structure calculations arises recently in the field of material physics, and efficient and accurate algebraic methods for large simultaneous linear equations become greatly important. We investigate the generalized shifted conjugate orthogonal conjugate gradient method, the generalized Lanczos method, and the generalized Arnoldi method. They are the solver methods of large simultaneous linear equations of the one-electron Schrodinger equation and map the whole Hilbert space to a small subspace called the Krylov subspace. These methods are applied to systems of fcc Au with the NRL tight-binding Hamiltonian [F. Kirchhoff et al., Phys. Rev. B 63, 195101 (2001)]. We compare results by these methods and the exact calculation and show them to be equally accurate. The system size dependence of the CPU time is also discussed. The generalized Lanczos method and the generalized Arnoldi method are the most suitable for the large-scale molecular dynamics simulations from the viewpoint of CPU time and memory size.

DOI： 10.1103/PhysRevB.83.165103

Four-point correlation function of a passive scalar field in rapidly fluctuating turbulence: Numerical analysis of an exact closure equation Reviewed

Quasi-minimal residual smoothing technique for the IDR($s$) method Reviewed Open Access

Du Lei, Sogabe Tomohiro, Zhang Shao-Liang

JSIAM Letters Vol. 3 ( 0 ) page： 13-16 2011

Y. Mizuno, K. Ohi, T. Sogabe, Y. Yamamoto, Y. Kaneda

PHYSICAL REVIEW E Vol. 82 ( 3 ) 2010.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

A numerical analysis is made on the four-point correlation function in a similarity range of a model of two-dimensional passive scalar field psi advected by a turbulent velocity field with infinitely small correlation time. The model yields an exact closure equation for the four-point correlation Psi(4) of psi, which may be casted into the form of an eigenvalue problem in the similarity range. The analysis of the eigenvalue problem gives not only the scale dependence of Psi(4), but also the dependence on the configuration of the four points. The numerical analysis gives S-4(R) alpha R-zeta 4 in the similarity range in which S-2(R) alpha R-zeta 2, where S-N is the structure function defined by S-N(R) equivalent to <[psi(x + R) - psi(x)](N) and zeta(4) not equal 2 zeta(2). The estimate of zeta(4) by the numerical analysis of the eigenvalue problem is in good agreement with numerical simulations so far reported. The agreement supports the idea of universality of the exponent zeta(4) in the sense that zeta(4) is insensitive to conditions of psi outside the similarity range. The numerical analysis also shows that the correlation C(R, r) equivalent to <[psi(x + R) - psi(x)](2) X[psi(x+r) - psi(x)](2) is stronger than that given by the joint-normal approximation, and scales like C(R, r) alpha (r/R)(chi) for r/R << 1 with R and r in the similarity range, where chi is a constant depending on the angle between R and r.

DOI： 10.1103/PhysRevE.82.036316

An Approach to the Correction Equation in the Jacobi‐Davidson Method―Based on a Shift Invariance Property of the Krylov Subspace on a Projected Space― Reviewed Open Access

宮田考史, 曽我部知広, ZHANG Shao‐Liang

日本応用数理学会論文誌 Vol. 20 ( 2 ) page： 115 - 129 2010.6

Novel algorithm of large-scale simultaneous linear equations Reviewed

T. Fujiwara, T. Hoshi, S. Yamamoto, T. Sogabe, S-L Zhang

JOURNAL OF PHYSICS-CONDENSED MATTER Vol. 22 ( 7 ) 2010.2

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

We review our recently developed methods of solving large-scale simultaneous linear equations and applications to electronic structure calculations both in one-electron theory and many-electron theory. This is the shifted COCG (conjugate orthogonal conjugate gradient) method based on the Krylov subspace, and the most important issue for applications is the shift equation and the seed switching method, which greatly reduce the computational cost. The applications to nano-scale Si crystals and the double orbital extended Hubbard model are presented.

DOI： 10.1088/0953-8984/22/7/074206

PubMed

A new family of k-Fibonacci numbers Reviewed Open Access

Moawwad El-Mikkawy, Tomohiro Sogabe

APPLIED MATHEMATICS AND COMPUTATION Vol. 215 ( 12 ) page： 4456 - 4461 2010.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE INC

In the present paper, we give a new family of k-Fibonacci numbers and establish some properties of the relation to the ordinary Fibonacci numbers. Furthermore, we describe the recurrence relations and the generating functions of the new family for k = 2 and k = 3, and presents a few identity formulas for the family and the ordinary Fibonacci numbers. (C) 2010 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.amc.2009.12.069

Notes on particular symmetric polynomials with applications Reviewed

Moawwad El-Mikkawy, Tomohiro Sogabe

APPLIED MATHEMATICS AND COMPUTATION Vol. 215 ( 9 ) page： 3311 - 3317 2010.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE INC

This paper presents some applications using several properties of three important symmetric polynomials: elementary symmetric polynomials, complete symmetric polynomials and the power sum symmetric polynomials. The applications includes a simple proof of El-Mikkawy conjecture in [M. E. A. El-Mikkawy, Appl. Math. Comput. 146 (2003) 759-769] and a very easy proof of the Newton-Girard formula. In addition, a generalization of Stirling numbers is obtained. (C) 2009 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.amc.2009.10.019

An Approach to the Correction Equation in the Jacobi-Davidson Method : Based on a Shift Invariance Property of the Krylov Subspace on a Projected Space(Theory) Open Access

Miyata Takafumi, Sogabe Tomohiro, Zhang Shao-Liang

Transactions of the Japan Society for Industrial and Applied Mathematics Vol. 20 ( 2 ) page： 115 - 129 2010

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society for Industrial and Applied Mathematics

The Jacobi-Davidson (JD) iteration method was recently proposed to compute a few eigenpairs of a large-scale and sparse matrix. In the JD method, the correction equation is solved approximately to generate the basis of a subspace for the iterative computation of eigenpairs. It is empirically known that the speed of the convergence of the JD method depends on the method for solving the correction equation. In this paper, we show a shift invariance property of the Krylov subspace on a projected space and propose a new method based on the property for solving the correction equation.

DOI： 10.11540/jsiamt.20.2_115

On the Restart of the GMRES(m) Method Reviewed Open Access

今倉暁, 曽我部知広, ZHANG Shao‐Liang

日本応用数理学会論文誌 Vol. 19 ( 4 ) page： 551 - 564 2009.12

An Extension of the Sakurai‐Sugiura Method for Eigenvalue Problems of Multiply Connected Region Reviewed Open Access

宮田考史, DU Lei, 曽我部知広, 山本有作, ZHANG Shao‐Liang

日本応用数理学会論文誌 Vol. 19 ( 4 ) page： 537 - 550 2009.12

大規模シフト線形方程式の数値解法―クリロフ部分空間の性質に着目して Reviewed Open Access

曽我部知広, 張紹良

応用数理 Vol. 19 ( 3 ) page： 163 - 178 2009.9

An extension of the conjugate residual method to nonsymmetric linear systems Reviewed

T. Sogabe, M. Sugihara, S. -L. Zhang

JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS Vol. 226 ( 1 ) page： 103 - 113 2009.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The Conjugate Gradient (CG) method and the Conjugate Residual (CR) method are Krylov subspace methods for solving symmetric (positive definite) linear systems. To solve nonsymmetric linear systems, the Bi-Conjugate Gradient (Bi-CG) method has been proposed as an extension of CG. Bi-CG has attractive short-term recurrences, and it is the basis for the successful variants such as Bi-CGSTAB. In this paper, we extend CR to nonsymmetric linear systems with the aim of finding an alternative basic solver. Numerical experiments show that the resulting algorithm with short-term recurrences often gives smoother convergence behavior than Bi-CG. Hence, it may take the place of Bi-CG for the successful variants. (c) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cam.2008.05.018

An implicit wavelet sparse approximate inverse preconditioner using block finger pattern Reviewed

A. Imakura, T. Sogabe, S. -L. Zhang

NUMERICAL LINEAR ALGEBRA WITH APPLICATIONS Vol. 16 ( 11-12 ) page： 915 - 928 2009

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

Recently, an implicit wavelet sparse approximate inverse (IW-SPAI hereafter) preconditioner has been proposed by Hawkins and Chen for nonsymmetric linear systems. The preconditioning matrix of the IW-SPAI is characterized by a special sparse structure, the so-called finger pattern, which makes it possible to construct a good sparse approximate inverse. Since the IW-SPAI requires a number of QR factorizations with substantial costs to construct the preconditioner, there is a strong need to construct the IW-SPAI more efficiently. The target of this paper is to reduce the costs of the IW-SPAI using Haar basis. Under the strategy of classifying the QR factorizations into several groups and reducing the number of QR factorizations, in this paper, we introduce a block finger pattern for Haar basis in the place of the finger pattern as the nonzero pattern of the preconditioning matrix. From the block finger pattern, we propose an implicit wavelet sparse approximate inverse preconditioner using block finger pattern (BIW-SPAI hereafter). Numerical experiments indicate that the BIW-SPAI is often more efficient than the IW-SPAI. Copyright (C) 2009 John Wiley & Sons, Ltd.

DOI： 10.1002/nla.657

Shifted Conjugate-Orthogonal-Conjugate-Gradient Method and Its Application to Double Orbital Extended Hubbard Model Reviewed

Yamamoto Susumu, Sogabe Tomohiro, Hoshi Takeo, ZHANG Shao-Liang, FUJIWARA Takeo

Journal of the Physical Society of Japan Vol. 77 ( 11 ) page： "114713-1"-"114713-8" 2008.11

New algorithms for solving periodic tridiagonal and periodic pentadiagonal linear systems Reviewed

Tomohiro Sogabe

APPLIED MATHEMATICS AND COMPUTATION Vol. 202 ( 2 ) page： 850 - 856 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE INC

Recently, an efficient computational algorithm for solving periodic pentadiagonal linear systems has been proposed by Karawia [ A. A. Karawia, A computational algorithm for solving periodic pentadiagonal linear systems, Appl. Math. Comput. 174 ( 2006) 613-618]. The algorithm is based on the LU factorization of the periodic pentadiagonal matrix. In this paper, new algorithms are presented for solving periodic pentadiagonal linear systems based on the use of any pentadiagonal linear solver. In addition, an efficient way of evaluating the determinant of a periodic pentadiagonal matrix is discussed. The corresponding results in this paper can be readily obtained for solving periodic tridiagonal linear systems. (C) 2008 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.amc.2008.03.030

A note on "A fast numerical algorithm for the determinant of a pentadiagonal matrix" Reviewed

Tomohiro Sogabe

APPLIED MATHEMATICS AND COMPUTATION Vol. 201 ( 1-2 ) page： 561 - 564 2008.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE INC

A fast numerical algorithm for evaluating the determinant of a pentadiagonal matrix has been recently proposed [T. Sogabe, A fast numerical algorithm for the determinant of a pentadiagonal matrix, Appl. Math. Comput. 196 (2008) 835-841]. The algorithm whose cost is 14n - 28, where n(>= 3) denotes the size of the matrix, is composed of two steps: first, transform a pentadiagonal matrix into sparse Hessenberg form; second, run a numerical algorithm for computing the determinant of the sparse Hessenberg matrix. In this note, it is shown that we have an algorithm with the cost of 13n - 24 by applying twice the idea of the sparse Hessenberg transformation to a pentadiagonal matrix. (c) 2008 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.amc.2007.12.047

Numerical algorithms for solving comrade linear systems based on tridiagonal solvers Reviewed

Tomohiro Sogabe

APPLIED MATHEMATICS AND COMPUTATION Vol. 198 ( 1 ) page： 117 - 122 2008.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE INC

Recently, two efficient algorithms for solving comrade linear systems have been proposed by Karawia [A. A. Karawia, Two algorithms for solving comrade linear systems, Appl. Math. Comput. 189 (2007) 291-297]. The two algorithms are based on the LU decomposition of the comrade matrix. In this paper, two algorithms are presented for solving the comrade linear systems based on the use of conventional fast tridiagonal solvers and an efficient way of evaluating the determinant of the comrade matrix is discussed. (C) 2007 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.amc.2007.08.029

A fast numerical algorithm for the determinant of a pentadiagonal matrix Reviewed

Tomohiro Sogabe

APPLIED MATHEMATICS AND COMPUTATION Vol. 196 ( 2 ) page： 835 - 841 2008.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE INC

Recently, a two-term recurrence for the determinant of a general matrix has been found [T. Sogabe, On a two-term recurrence for the determinant of a general matrix, Appl. Math. Comput., 187 (2007) 785-788] and it leads to a natural generalization of the DETGTRI algorithm [M. El-Mikkawy, A fast algorithm for evaluating nth order tridiagonal determinants, J. Comput. Appl. Math. 166 (2004) 581-584] for computing the determinant of a tridiagonal matrix. In this paper, we derive a fast numerical algorithm for computing the determinant of a pentadiagonal matrix from the generalization of the DETGTRI algorithm. (C) 2007 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.amc.2007.07.015

ON A WEIGHTED QUASI-RESIDUAL MINIMIZATION STRATEGY FOR SOLVING COMPLEX SYMMETRIC SHIFTED LINEAR SYSTEMS Reviewed

AOR法を用いた可変的前処理付き一般化共役残差法 Reviewed Open Access

前田祥兵, 阿部邦美, 曽我部知広, 張紹良

日本応用数理学会論文誌 Vol. 18 ( 1 ) page： 155-170 2008

T. Sogabe, T. Hoshi, S. -L. Zhang, T. Fujiwara

ELECTRONIC TRANSACTIONS ON NUMERICAL ANALYSIS Vol. 31 page： 126 - 140 2008

Language：English Publishing type：Research paper (scientific journal) Publisher：KENT STATE UNIVERSITY

We consider the solution of complex symmetric shifted linear systems. Such systems arise in large-scale electronic structure simulations, and there is a strong need of algorithms for their fast solution. With the aim of solving the systems efficiently, we consider a special case of the QMR method for non-Hermitian shifted linear systems and propose its weighted quasi-minimal residual approach. A numerical algorithm, referred to as shifted QMR_SYM(B), is obtained by the choice of a weight which is particularly cost-effective. Numerical examples are presented to show the performance of the shifted QMR_SYM(B) method.

An Efficient Implicit Wavelet Sparse Approximate Inverse Preconditioner Using Blocked Finger Pattern Reviewed Open Access

今倉暁, 曽我部知広, ZHANG Shao‐Liang

日本応用数理学会論文誌 Vol. 17 ( 4 ) page： 523 - 542 2007.12

On an application of the QMR approach to the Bi‐CR method Reviewed Open Access

南さつき, 曽我部知広, 杉原正顯, ZHANG Shao‐Liang

日本応用数理学会論文誌 Vol. 17 ( 3 ) page： 301 - 317 2007.9

A Product-type Krylov Subspace Method Based on Conjugate Residual Method for Nonsymmetric Coefficient Matrices Reviewed Open Access

ABE KUNIYOSHI, SOGABE TOMOHIRO, FUJINO SEIJI, ZHANG SHAO-LIANG

Vol. 48 ( 8 ) page： 11-21 2007.5

Language：English Publishing type：Research paper (scientific journal)

We propose a product-type Krylov subspace method based on the conjugate residual (CR) method for nonsymmetric coefficient matrices. The recurrence formulas for updating an approximation and a residual vector are the same as those of the original product-type Krylov subspace method, while the recurrence coefficients α_κ and β_κ are determined so as to compute the coefficients of the residual polynomial of CR for nonsymmetric coefficient matrices. Numerical experiments show that our proposed product-type Krylov subspace method is more effective than the original.

A COCR method for solving complex symmetric linear systems Reviewed

T. Sogabe and S.-L. Zhang

Vol. 199 page： 297-303 2007

On a two-term recurrence for the determinant of a general matrix Reviewed

T. Sogabe

Appl. Math. Comput. Vol. 187 page： 785-788 2007

A numerical method for calculating the green's function arising from electronic structure theory Reviewed

Tomohiro Sogabe, Takeo Hoshi, Shao-Liang Zhang, Takeo Fujiwara

FRONTIERS OF COMPUTATIONAL SCIENCE page： 189 - + 2007

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPRINGER-VERLAG BERLIN

We developed a fast numerical method for complex symmetric shifted linear systems, which is motivated by the quantum-mechanical (electronic-structure) theory in nanoscale materials. The method is named shifted Conjugate Orthogonal Conjugate Gradient (shifted COCG) method. The formulation is given and several numerical aspects are discussed.

DOI： 10.1007/978-3-540-46375-7_24