Published online by Cambridge University Press: 10 November 2015
For any given matrix A ∈ℂnxn, a preconditioner tU(A) called thesuperoptimal preconditioner was proposed in 1992 by Tyrtyshnikov. It has beenshown that tU(A) is an efficient preconditioner forsolving various structured systems, for instance, Toeplitz-like systems. In thispaper, we construct the superoptimal preconditioners for different functions ofmatrices. Let f be a function of matrices from ℂnxn to ℂnxn. For any A ∈ ℂ nxn, one may construct two superoptimal preconditioners for f(A):tU(f(A)) and f(tU(A)).We establish basic properties of tU(f(A)) andf(tU(A)) for different functions ofmatrices. Some numerical tests demonstrate that the proposed preconditioners arevery efficient for solving the system f(A)x = b.