How can I evaluate Jacobian matrix?

I have a problem. I made a program for "Newton-Raphson method for vectorial function" but I have a problem. Let's suppose to have the function f(x,y)=(x-y,x+y^2). The jacobian matrix is [1,-1;1,2*y]. Then I put r=symvar(jacobian) and to evaluate I use subs(jacobian,r,x0): So my problem is: how can I evaluate the matrix in x0=(0,0) if the first variable x doesn't appear?

Here it is my Matlab code:

function [ x0,iter ] = newtonvect( f1,x0,tol,imax )
%UNTITLED3 Summary of this function goes here
%   Detailed explanation goes here

f2=sym(f1);
t=symvar(f2);
j=jacobian(f1,t);
r=symvar(j);
val=subs(f1,t,x0);
m=length(r);
iter=0;
while norm(val)>tol & iter<imax
  *x1=x0(1:m);*
  jac=subs(j,r,x1);
  z=Gausselpiv(jac,-val);
  x0=x0+z';
  iter=iter+1;
  val=subs(f1,t,x0);
end

Obviously bold line is wrong and the code does not work in every case.Could you help me please?