.help evp Jun99 "Slalib Package"
.nf

      SUBROUTINE slEVP (DATE, DEQX, DVB, DPB, DVH, DPH)

     - - - -
      E V P
     - - - -

  Barycentric and heliocentric velocity and position of the Earth

  All arguments are double precision

  Given:

     DATE          TDB (loosely ET) as a Modified Julian Date
                                         (JD-2400000.5)

     DEQX          Julian Epoch (e.g. 2000.0D0) of mean equator and
                   equinox of the vectors returned.  If DEQX .LE. 0D0,
                   all vectors are referred to the mean equator and
                   equinox (FK5) of epoch DATE.

  Returned (all 3D Cartesian vectors):

     DVB,DPB       barycentric velocity, position

     DVH,DPH       heliocentric velocity, position

  (Units are AU/s for velocity and AU for position)

  Called:  slEPJ, slPREC

  Accuracy:

     The maximum deviations from the JPL DE96 ephemeris are as
     follows:

     barycentric velocity         0.42  m/s
     barycentric position         6900  km

     heliocentric velocity        0.42  m/s
     heliocentric position        1600  km

  This routine is adapted from the BARVEL and BARCOR
  subroutines of P.Stumpff, which are described in
  Astron. Astrophys. Suppl. Ser. 41, 1-8 (1980).  Most of the
  changes are merely cosmetic and do not affect the results at
  all.  However, some adjustments have been made so as to give
  results that refer to the new (IAU 1976 'FK5') equinox
  and precession, although the differences these changes make
  relative to the results from Stumpff's original 'FK4' version
  are smaller than the inherent accuracy of the algorithm.  One
  minor shortcoming in the original routines that has NOT been
  corrected is that better numerical accuracy could be achieved
  if the various polynomial evaluations were nested.  Note also
  that one of Stumpff's precession constants differs by 0.001 arcsec
  from the value given in the Explanatory Supplement to the A.E.

  P.T.Wallace   Starlink   21 March 1999

  Copyright (C) 1999 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

.fi
.endhelp
