improve precision in jacobianCurvilinearToCartesian

Author: slava77

DataFormats/GeometryVector/src/TrackingJacobians.cc

@@ -36,11 +36,9 @@ AlgebraicMatrix65 jacobianCurvilinearToCartesian(const GlobalVector& momentum, i
   R(5, 5) = 1.;
 
   double p = pvec.mag(), p2 = p * p;
-  double lambda = 0.5 * M_PI - pvec.theta();
-  double phi = pvec.phi();
-  double sinlambda = sin(lambda), coslambda = cos(lambda);
-  double sinphi = sin(phi), cosphi = cos(phi);
-
+  double sinlambda = pvec.z()/p, coslambda = pt/p;
+  double sinphi = pvec.y()/pt, cosphi = pvec.x()/pt;
+  
   theJacobian(1, 3) = 1.;
   theJacobian(2, 4) = 1.;
   theJacobian(3, 0) = -q * p2 * coslambda * cosphi;