pcg.m with 'null' and 'flex' options by Andrew Knyazev

Preconditioned Conjugate Gradients handles homogeneous equations and nonsymmetric preconditioning (linear algebra, preconditioned, conjugate)

pcg(A,b,tol,maxit,M1,M2,x0,opts1,opts2,varargin)

cpcg.m by Leevan Ling

CPCG -CIRCULANT PRECONDITIONED CONJUGATE GRADIENT METHOD. (linear algebra, circulant, preconditioned)

cpcg(a, b, tol, max_it, c, x0)