% Sitzung S. 197

tol = 1e-11; kmax = 14; m = 129; norm = 2;
P = spdiags(diag(A),0,n,n); P(:,1:m) = A(:,1:m); M = inv(P); 
[x,fail,r,k] = pri(A,b,tol,kmax,M,norm);
if not(fail), k, x1 = x(1), err = r/x1, end