Structure preserving quaternion conjugate gradient-type methods for solving non-Hermitian quaternion linear systems

TL;DR

This paper introduces two structure-preserving quaternion conjugate gradient methods, QNHERLQ and QNHERQR, for solving non-Hermitian quaternion linear systems, with applications in image and signal processing.

Contribution

The paper develops novel quaternion conjugate gradient-type algorithms based on a new tridiagonalization procedure, enhancing robustness and efficiency over existing methods.

Findings

Algorithms have finite termination property.

Numerical results show improved robustness and effectiveness.

Convergence depends on the singular values of the matrix.

Abstract

In this paper, we consider the non-Hermitian quaternion linear systems arising from color image restoration and three-dimensional signal filtering problems. For exploring to solve such systems, we present two innovative structure-preserving conjugate gradient-type methods, QNHERLQ and QNHERQR, which are based on the unitary equivalence transformations of the non-Hermitian quaternion matrices to tridiagonal forms, called quaternion Saunders-Simon-Yip tridiagonalization procedure. The proposed tridiagonalization procedure for non-Hermitian quaternion matrices is closely related to the quaternion Lanczos process for Hermitian matrices, and is very different from the quaternion Lanczos biorthogonalization process for non-Hermitian matrices. The convergence of QNHERLQ and QNHERQR is discussed, which depends on the singular values of the coefficient matrix. Also we show that both algorithms have the finite termination property and constant costs per iteration step. Numerical results illustrate that the proposed algorithms are with the robustness and effectiveness compared with QGMRES and QQMR.