function [x,n]=twostep(A,b,x0,eps,varargin)if nargin==3    eps= 1.0e-6;    M  = 200;elseif nargin<3    error    returnelseif nargin ==5    M  = varargin{1};end  D=diag(diag(A));    %求A的對角矩陣L=-tril(A,-1);      %求A的下三角陣U=-triu(A,1);       %求A的上三角陣B1=(D-L)\U;B2=(D-U)\L;f1=(D-L)\b;f2=(D-U)\b;x12=B1*x0+f1;x  =B2*x12+f2;n=1;                  %迭代次數while norm(x-x0)>=eps    x0 =x;    x12=B1*x0+f1;    x  =B2*x12+f2;    n=n+1;    if(n>=M)        disp('Warning: 迭代次數太多，可能不收斂！');        return;    endend