Over the past several years a number of hybrid algorithms have been proposed for solving large sparse systems of linear algebraic equations. In this paper we consider the hybrid GMRES algorithm by Nachtigal, Reichel and Trefethen (1992) and show that in the floating-point arithmetic there exist some cases in which the properties of this algorithm are lost, e.g., the result is false, or the coef...

This work is the follow-up of the experimental study presented in [3]. It is based on and extends some theoretical results in [15, 18]. In a backward error framework we study the convergence of GMRES when the matrixvector products are performed inaccurately. This inaccuracy is modeled by a perturbation of the original matrix. We prove the convergence of GMRES when the perturbation size is propo...

Low complexity equalization with LSRQ and GMRES algorithm is compared with traditional equalization methods. As the next generation technologies like LTE and WiMax have a large number of subcarriers the traditional equalization methods like MF, ZF, MMSE, VBLAST, and SAGE which require matrix inversion become highly complex in time and consume a lot of time to equalize the received signal. An al...

The generalized minimum residual method (GMRES) [Y. Saad and M. Schultz, SIAM J. Sci. Statist. Comput., 7 (1986), pp. 856–869] for solving linear systems Ax = b is implemented as a sequence of least squares problems involving Krylov subspaces of increasing dimensions. The most usual implementation is Modified Gram-Schmidt GMRES (MGS-GMRES). Here we show that MGS-GMRES is backward stable. The re...

The solution of nonsymmetric systems of linear equations continues to be a diicult problem. A main algorithm for solving nonsymmetric problems is restarted GMRES. The algorithm is based on restarting full GMRES every s iterations, for some integer s>0. This paper considers the impact of the restart frequency s on the convergence and work requirements of the method. It is shown that a good choic...

Standard multigrid algorithms have proven ineffective for the solution of discretizations of Helmholtz equations. In this work we modify the standard algorithm by adding GMRES iterations at coarse levels and as an outer iteration. We demonstrate the algorithm’s effectiveness through theoretical analysis of a model problem and experimental results. In particular, we show that the combined use of...

Direction of arrival estimation LFM signal is an essential task in radar, sonar, acoustics and biomedical. In this paper, a short time Fourier transform multi-step knowledge aided iterative generalized minimum residual (STFT-MS-KAI-GMRES) approach presented to amend the angle measurement signal. A three stage algorithm proposed. First, process initiated with formulating for carrier frequency ch...

A b s t r a c t . A procedure for soìving nonìinear time-marching problems is presented. The nonsymmetric systems of equations arising from Newton-type linearizations are solved using an iterativestrategy based on the Generalized Minimal RESidual (GMRES) algorithm. Matrix-free techniques ìeading to reduction in Storage are presented. Incorporation of a linesearch algorithm in the Newton-GMRES s...

We investigate using the gmres method with the differentiation operator. This operator is unbounded, and thus does not fall into the framework of existing Krylov subspace theory. We establish conditions under which a function can be approximated by its own derivatives in a domain of the complex plane. These conditions are used to determine when gmres converges. This algorithm outperforms tradit...

Standard Krylov subspace methods only allow the user to choose a single preconditioner, although in many situations there may be a number of possibilities. Here we describe an extension of GMRES, multi-preconditioned GMRES, which allows the use of more than one preconditioner. We give some theoretical results, propose a practical algorithm, and present numerical results from problems in domain ...