.help planel Jun99 "Slalib Package"
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      SUBROUTINE slPLNE (DATE, JFORM, EPOCH, ORBINC, ANODE, PERIH,
     :                       AORQ, E, AORL, DM, PV, JSTAT)

     - - - - - - -
      P L N L
     - - - - - - -

  Heliocentric position and velocity of a planet, asteroid or comet,
  starting from orbital elements.

  Given:
     DATE      d      date, Modified Julian Date (JD - 2400000.5)
     JFORM     i      choice of element set (1-3; Note 3)
     EPOCH     d      epoch of elements (TT MJD)
     ORBINC    d      inclination (radians)
     ANODE     d      longitude of the ascending node (radians)
     PERIH     d      longitude or argument of perihelion (radians)
     AORQ      d      mean distance or perihelion distance (AU)
     E         d      eccentricity
     AORL      d      mean anomaly or longitude (radians, JFORM=1,2 only)
     DM        d      daily motion (radians, JFORM=1 only)

  Returned:
     PV        d(6)   heliocentric x,y,z,xdot,ydot,zdot of date,
                                       J2000 equatorial triad (AU,AU/s)
     JSTAT     i      status:  0 = OK
                              -1 = illegal JFORM
                              -2 = illegal E
                              -3 = illegal AORQ
                              -4 = illegal DM
                              -5 = numerical error

  Called:  slELUE, slUEPV

  Notes

  1  DATE is the instant for which the prediction is required.  It is
     in the TT timescale (formerly Ephemeris Time, ET) and is a
     Modified Julian Date (JD-2400000.5).

  2  The elements are with respect to the J2000 ecliptic and equinox.

  3  Three different element-format options are available:

     Option JFORM=1, suitable for the major planets:

     EPOCH  = epoch of elements (TT MJD)
     ORBINC = inclination i (radians)
     ANODE  = longitude of the ascending node, big omega (radians)
     PERIH  = longitude of perihelion, curly pi (radians)
     AORQ   = mean distance, a (AU)
     E      = eccentricity, e (range 0 to <1)
     AORL   = mean longitude L (radians)
     DM     = daily motion (radians)

     Option JFORM=2, suitable for minor planets:

     EPOCH  = epoch of elements (TT MJD)
     ORBINC = inclination i (radians)
     ANODE  = longitude of the ascending node, big omega (radians)
     PERIH  = argument of perihelion, little omega (radians)
     AORQ   = mean distance, a (AU)
     E      = eccentricity, e (range 0 to <1)
     AORL   = mean anomaly M (radians)

     Option JFORM=3, suitable for comets:

     EPOCH  = epoch of perihelion (TT MJD)
     ORBINC = inclination i (radians)
     ANODE  = longitude of the ascending node, big omega (radians)
     PERIH  = argument of perihelion, little omega (radians)
     AORQ   = perihelion distance, q (AU)
     E      = eccentricity, e (range 0 to 10)

  4  Unused elements (DM for JFORM=2, AORL and DM for JFORM=3) are
     not accessed.

  5  The reference frame for the result is with respect to the mean
     equator and equinox of epoch J2000.

  6  The algorithm was originally adapted from the EPHSLA program of
     D.H.P.Jones (private communication, 1996).  The method is based
     on Stumpff's Universal Variables.

  Reference:  Everhart, E. & Pitkin, E.T., Am.J.Phys. 51, 712, 1983.

  P.T.Wallace   Starlink   18 March 1999

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

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