function f = fsurf(y,t)
global A, global B, global epsr
f(1)=cos(y(3));
f(2)=sin(y(3));
if (y(1)>epsr)
 f(3)=A-B*y(2)-sin(y(3))/y(1);
else
 f(3)=(A-B*y(2))/2;
end
f(4)=pi*y(1)^2*f(2);
f(5)=2*pi*y(1);
end