.help pertel Jun99 "Slalib Package"
.nf

      SUBROUTINE slPRTL (JFORM, DATE0, DATE1,
     :                 EPOCH0, ORBI0, ANODE0, PERIH0, AORQ0, E0, AM0,
     :                 EPOCH1, ORBI1, ANODE1, PERIH1, AORQ1, E1, AM1,
     :                       JSTAT)

     - - - - - - -
      P R T L
     - - - - - - -

  Update the osculating orbital elements of an asteroid or comet by
  applying planetary perturbations.

  Given (format and dates):
     JFORM   i    choice of element set (2 or 3; Note 1)
     DATE0   d    date of osculation (TT MJD) for the given elements
     DATE1   d    date of osculation (TT MJD) for the updated elements

  Given (the unperturbed elements):
     EPOCH0  d    epoch (TT MJD) of the given element set (Note 2)
     ORBI0   d    inclination (radians)
     ANODE0  d    longitude of the ascending node (radians)
     PERIH0  d    argument of perihelion (radians)
     AORQ0   d    mean distance or perihelion distance (AU)
     E0      d    eccentricity
     AM0     d    mean anomaly (radians, JFORM=2 only)

  Returned (the updated elements):
     EPOCH1  d    epoch (TT MJD) of the updated element set (Note 2)
     ORBI1   d    inclination (radians)
     ANODE1  d    longitude of the ascending node (radians)
     PERIH1  d    argument of perihelion (radians)
     AORQ1   d    mean distance or perihelion distance (AU)
     E1      d    eccentricity
     AM1     d    mean anomaly (radians, JFORM=2 only)

  Returned (status flag):
     JSTAT   i    status: +102 = warning, distant epoch
                          +101 = warning, large timespan ( > 100 years)
                      +1 to +8 = coincident with major planet (Note 6)
                             0 = OK
                            -1 = illegal JFORM
                            -2 = illegal E0
                            -3 = illegal AORQ0
                            -4 = internal error
                            -5 = numerical error

  Notes:

  1  Two different element-format options are available:

     Option JFORM=2, suitable for minor planets:

     EPOCH   = epoch of elements (TT MJD)
     ORBI    = 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
     AM      = mean anomaly M (radians)

     Option JFORM=3, suitable for comets:

     EPOCH   = epoch of perihelion (TT MJD)
     ORBI    = 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

  2  DATE0, DATE1, EPOCH0 and EPOCH1 are all instants of time in
     the TT timescale (formerly Ephemeris Time, ET), expressed
     as Modified Julian Dates (JD-2400000.5).

     DATE0 is the instant at which the given (i.e. unperturbed)
     osculating elements are correct.

     DATE1 is the specified instant at which the updated osculating
     elements are correct.

     EPOCH0 and EPOCH1 will be the same as DATE0 and DATE1
     (respectively) for the JFORM=2 case, normally used for minor
     planets.  For the JFORM=3 case, the two epochs will refer to
     perihelion passage and so will not, in general, be the same as
     DATE0 and/or DATE1 though they may be similar to one another.

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

  4  Unused elements (AM0 and AM1 for JFORM=3) are not accessed.

  5  See the slPRTE routine for details of the algorithm used.

  6  This routine is not intended to be used for major planets, which
     is why JFORM=1 is not available and why there is no opportunity
     to specify either the longitude of perihelion or the daily
     motion.  However, if JFORM=2 elements are somehow obtained for a
     major planet and supplied to the routine, sensible results will,
     in fact, be produced.  This happens because the slPRTE routine
     that is called to perform the calculations checks the separation
     between the body and each of the planets and interprets a
     suspiciously small value (0.001 AU) as an attempt to apply it to
     the planet concerned.  If this condition is detected, the
     contribution from that planet is ignored, and the status is set to
     the planet number (Mercury=1,...,Neptune=8) as a warning.

  Reference:

     Sterne, Theodore E., "An Introduction to Celestial Mechanics",
     Interscience Publishers Inc., 1960.  Section 6.7, p199.

  Called:  slELUE, slPRTE, slUEEL

  P.T.Wallace   Starlink   14 March 1999

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

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