function [y,iter] = my_gs_res_28_04(x,v,z,b,tol,maxiter)
%Jacobi method for arrow matrices
n=length(x); 
y=zeros(n,1);
iter=0;
nb=norm(b,2);
for k=1:n
    if(x(k)==0) 
        disp('metodo non applicabile');
        return
    end
end
err=norm(mat_prod_arrow(x,v,z,y)-b,2)/nb;
while(err>tol & iter<=maxiter)
    %calcolare ynew da yold
    y(1)=(b(1)-v'*y(2:n))/x(1);
        for k=2:n
            y(k)=(b(k)-z(k-1)*y(1))/x(k);
        end
        err=norm(mat_prod_arrow(x,v,z,y)-b,2)/nb;
        iter=iter+1;
end

end