MR2344960 Dana, M.; Ikramov, Kh. D. A numerical comparison of two
minimal residual methods for linear polynomials in unitary
matrices. (Russian) Zh. Vychisl. Mat. Mat. Fiz. 46 (2006), no. 12,
2138--2148. 65Fxx


Numerical performance of the two specific methods adapted to the
problems $(\alpha U + \beta I)=b$ with unitary $U$ is compared. A
persuasively and increasingly better performance of the method
using the generalized rather than standard Krylov subspaces is
found at the growing ratio $|\alpha|/|\beta|>1$.