function Y=imp_fn2(x,y)
Tx=1.0001;
Ty=1.0001;
Tx2=(Tx-1)/2;
Ty2=(Ty-1)/2;
rectx=0.5*(sign(x+Tx2)-sign(x-Tx2));
recty=0.5*(sign(y+Ty2)-sign(y-Ty2));
Y=recty'*rectx;