function ex13x03(A,b,xmin,xmax,ymin,ymax)

[x,y] = meshgrid(linspace(xmin,xmax,8), linspace(ymin,ymax,8) ); 
z = zeros(size(x)); 
for j = 1:size(x,1)
    for k = 1:size(x,2) 
        z(j,k) = ex13x02(A,b,[x(j,k);y(j,k)]);
    end
end
z = z-max(max(z));	% lower the z-value to plot 
surf(x,y,z,'edgecolor','none'),view(2) % surf and contour in 1 figure 
hold on 
contour(x,y,z,10,'EdgeColor','w');
hold off 
axis equal, grid off, axis off