DOUBLE PRECISION FUNCTION KSGTHE(PW, VP, MVP)
#endif
#if !defined(CLEO_DOUBLE)
      REAL FUNCTION KSGTHE(PW, VP, MVP)
#endif
 
C  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
C  Returns the error in theta for a track in the W parameterization.
C
C  PW        real array (read)
C            Track parameters in W form (at least 3-vector part)
C
C  VP        real array (read)
C            Covariance matrix
C
C  MVP       integer variable (read)
C            First dimension of VP (must be at least 3)
C
C
C   The equation for theta can be written as
C
C         cos(theta) = Pz / sqrt(Px**2 + Py**2 + Pz**2)
C
C   so    dtheta = (Px*Pz*dPx + Py*Pz*dPy - Pt**2*dPz) / (P**2*Pt)
C
C   The covariance matrix of the momentum is then
C
C       sig**2 = A*Vx0*A(t)
C
C    where A = (Px*Pz, Py*Pz, -Pt**2, 0) / (P**2*Pt)
C  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>