function [x1,flag1,rr1,iter1,rv1] = mypcg2(A, b)
tol = 1e-6;  maxit = 15;  M = diag([10:-1:1 1 1:10]);
[x1, flag1, rr1, iter1, rv1] = pcg(A, b, tol, maxit, M);
% @types vector, double, double, double, vector, matrix, vector 
