A METHOD FOR SOLVING SYSTEMS OF LINEAR EQUATIONS WHOSE COEFFICIENT MATRICES ARE NORMAL AND SPECIAL.

A minimal residual method, called MINRES-N2 that is based on the use of unconventional Krylov subspaces was previously proposed by the authors for solving a system of linear equations Ax=b with a normal conefficient matrix whose spectrum belongs to an algebriac second-degree curve Γ. However, the computational scheme of this method dose not cover matrices of the from A=αU+βI, where U is an arbitrary unitary matrix; for such matrices, Γ. is a circle.