double precision function kget_track_err_momentum(ktrk) * * begin_doc * * Returns the momentum error of a track to the caller. * * Input Parameters: * ktrk integer variable * Track number * * Output Parameters: * None * * Return value: * Error on mass * * Other routines: * * Notes: * * The momentum can be written as * * P = sqrt(Px**2 + Py**2 + Pz**2) * * so dP = (Px*dPx + Py*dPy + Pz*dPz) / P * * The covariance matrix of the momentum is then * * sig**2 = A*Vx0*A(t) * * where A = (Px, Py, Pz, 0) / P * * Author: Paul Avery Created: Tue Aug 26 19:35:08 EDT 1997 * * Major revisions: * * * end_doc