function d = der(xx)
  d(1,1)=2*xx(1);
d(1,2)=2*xx(2);
d(1,3)=2*xx(3);
d(2,1)=xx(2)*xx(3);
d(2,2)=xx(1)*xx(3);
d(2,3)=xx(1)*xx(2);
d(3,1)=1;
d(3,2)=-1;
d(3,3)=-cos(xx(3));
end