EXTREMAL POLYNOMIALS WITH PPLICATION TO RICHARDSON ITERATION

The application of Richardson iteration to a symmetric, but indefinite linear system requires certain parameters which can be determined from the zeros in the error of a certain best polynomial approximant on some set S known to contain the spectrum of the coefficient matrix. It is pointed out that this error can also be obtained as a multiple of the extremal polynomial for the linear functional p- p(O), and this leads to an efficient Remes type algorithm for its determination. A program incorporating this algorithm for the case that S consists of two intervals bracketing zero is also given. AMS(MOS) Subject Classification- 65F10, 65D15, 41A10 Key Words- Richardson iteration, symmetric indefinite, Remes, norm preserving extension, norm calculation for linea