我用牛顿迭代法对非线性方组求解时出现问题,请高手帮忙看下啊
  程序如下:function [r,n]=mulNewton3(F,x0,eps)
if nargin==1
    eps=1.0e-4;
end
J=jacobian(sym(F));
fa=subs(sym(F),x0);
fb=subs(sym(J),x0);
r=x0-fa/fb;
n=1;
tol=1;
while tol>eps
    x0=r;
    r=x0-fa/fb;
    tol=norm(r-x0);
    n=n+1;
    if(n>100000)
        disp('******');
        return;
    end
end

出错部分如下:
J=jacobian(sym(F));
fa=subs(sym(F),x0);
fb=subs(sym(J),x0);