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SUBROUTINE sla_PERTEL (JFORM, DATE0, DATE1,
: EPOCH0, ORBI0, ANODE0, PERIH0, AORQ0, E0, AM0,
: EPOCH1, ORBI1, ANODE1, PERIH1, AORQ1, E1, AM1,
: JSTAT)
*+
* - - - - - - -
* P E R T E 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 sla_PERTUE 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 sla_PERTUE 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: sla_EL2UE, sla_PERTUE, sla_UE2EL
*
* P.T.Wallace Starlink 14 March 1999
*
* Copyright (C) 1999 Rutherford Appleton Laboratory
*-
IMPLICIT NONE
INTEGER JFORM
DOUBLE PRECISION DATE0,DATE1,
: EPOCH0,ORBI0,ANODE0,PERIH0,AORQ0,E0,AM0,
: EPOCH1,ORBI1,ANODE1,PERIH1,AORQ1,E1,AM1
INTEGER JSTAT
DOUBLE PRECISION U(13),DM
INTEGER J,JF
* Check that the elements are either minor-planet or comet format.
IF (JFORM.LT.2.OR.JFORM.GT.3) THEN
JSTAT = -1
GO TO 9999
END IF
* Transform the elements from conventional to universal form.
CALL sla_EL2UE(DATE0,JFORM,EPOCH0,ORBI0,ANODE0,PERIH0,
: AORQ0,E0,AM0,0D0,U,J)
IF (J.NE.0) THEN
JSTAT = J
GO TO 9999
END IF
* Update the universal elements.
CALL sla_PERTUE(DATE1,U,J)
IF (J.GT.0) THEN
JSTAT = J
ELSE IF (J.LT.0) THEN
JSTAT = -5
GO TO 9999
END IF
* Transform from universal to conventional elements.
CALL sla_UE2EL(U,2,
: JF, EPOCH1, ORBI1, ANODE1, PERIH1,
: AORQ1, E1, AM1, DM, J)
IF (JF.NE.JFORM.OR.J.NE.0) JSTAT=-5
9999 CONTINUE
END
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