function f=shili02fun(x,x0,y0,theta,sigma,d4,sigma4)
for i=1:3
   f(i)=(atan2(x(1)-x0(i),x(2)-y0(i))-theta(i))/sigma(i);
 end
 f(4)=(sqrt((x(1)-x0(4))^2+(x(2)-y0(4))^2)-d4)/sigma4;