DOUBLE PRECISION FUNCTION KSGMAS(PW, VP, MVP)
#endif
#if !defined(CLEO_DOUBLE)
      REAL FUNCTION KSGMAS(PW, VP, MVP)
#endif
 
C  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
C  Returns the error in mass for a track in the W parameterization.
C
C  PW        real array (read)
C            Track parameters in W form (at least 4-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 4)
C
C
C   The mass can be written as
C
C         M = sqrt(E**2 - Px**2 - Py**2 - Pz**2)
C
C   so    dM = (E*dE - Px*dPx - Py*dPy - Pz*dPz) / M
C
C   The covariance matrix of the mass is then
C
C       sig**2 = A*Vx0*A(t)
C
C    where A = (-Px, -Py, -Pz, E) / M
C  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>