SLA_EVP - Earth Position & Velocity

ACTION:
     Barycentric and heliocentric velocity and position of the Earth.
CALL:
     CALL sla_EVP (DATE, DEQX, DVB, DPB, DVH, DPH)

GIVEN:

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

      DEQX D Julian Epoch (e.g. 2000D0) of mean equator and equinox of the vectors returned. If DEQX <0, all vectors are referred to the mean equator and equinox (FK5) of date DATE.

RETURNED:

      DVB D(3) barycentric [$[\,\dot{x},\dot{y},\dot{z}\,]$], AU s-1

      DPB D(3) barycentric [$[\,x,y,z\,]$], AU

      DVH D(3) heliocentric [$[\,\dot{x},\dot{y},\dot{z}\,]$], AU s-1

      DPH D(3) heliocentric [$[\,x,y,z\,]$], AU

NOTES:
     1.   This routine is used when accuracy is more important than CPU
          time, yet the extra complication of reading a pre-computed
          ephemeris is not justified. The maximum deviations from the
          JPL DE96 ephemeris are as follows:
             + velocity (barycentric or heliocentric): 420 mm s-1
             + position (barycentric): 6900 km
             + position (heliocentric): 1600 km
     2.   The routine is an adaption of the BARVEL and BARCOR subroutines of
          P.Stumpff, which are described in Astr.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 slightly better numerical accuracy could be achieved if
          the various polynomial evaluations were to be so arranged that the
          smallest terms were computed first. Note also that one of
          Stumpff's precession constants differs by
          [$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.001$] from
          the value given in the Explanatory Supplement.