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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, Note 1)
+*     JFORM    i     choice of element set (1-3; Note 3)
+*     EPOCH    d     epoch of elements (TT MJD, Note 4)
+*     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  A choice of three different element-set options is 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 elements and 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)
+*
+*     Unused arguments (DM for JFORM=2, AORL and DM for JFORM=3) are not
+*     accessed.
+*
+*  4  Each of the three element sets defines an unperturbed heliocentric
+*     orbit.  For a given epoch of observation, the position of the body
+*     in its orbit can be predicted from these elements, which are
+*     called "osculating elements", using standard two-body analytical
+*     solutions.  However, due to planetary perturbations, a given set
+*     of osculating elements remains usable for only as long as the
+*     unperturbed orbit that it describes is an adequate approximation
+*     to reality.  Attached to such a set of elements is a date called
+*     the "osculating epoch", at which the elements are, momentarily,
+*     a perfect representation of the instantaneous position and
+*     velocity of the body.
+*
+*     Therefore, for any given problem there are up to three different
+*     epochs in play, and it is vital to distinguish clearly between
+*     them:
+*
+*     . The epoch of observation:  the moment in time for which the
+*       position of the body is to be predicted.
+*
+*     . The epoch defining the position of the body:  the moment in time
+*       at which, in the absence of purturbations, the specified
+*       position (mean longitude, mean anomaly, or perihelion) is
+*       reached.
+*
+*     . The osculating epoch:  the moment in time at which the given
+*       elements are correct.
+*
+*     For the major-planet and minor-planet cases it is usual to make
+*     the epoch that defines the position of the body the same as the
+*     epoch of osculation.  Thus, only two different epochs are
+*     involved:  the epoch of the elements and the epoch of observation.
+*
+*     For comets, the epoch of perihelion fixes the position in the
+*     orbit and in general a different epoch of osculation will be
+*     chosen.  Thus, all three types of epoch are involved.
+*
+*     For the present routine:
+*
+*     . The epoch of observation is the argument DATE.
+*
+*     . The epoch defining the position of the body is the argument
+*       EPOCH.
+*
+*     . The osculating epoch is not used and is assumed to be close
+*       enough to the epoch of observation to deliver adequate accuracy.
+*       If not, a preliminary call to slPRTL may be used to update
+*       the element-set (and its associated osculating epoch) by
+*       applying planetary perturbations.
+*
+*  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   31 December 2002
+*
+*  Copyright (C) 2002 Rutherford Appleton Laboratory
+*
+*  License:
+*    This program is free software; you can redistribute it and/or modify
+*    it under the terms of the GNU General Public License as published by
+*    the Free Software Foundation; either version 2 of the License, or
+*    (at your option) any later version.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU General Public License for more details.
+*
+*    You should have received a copy of the GNU General Public License
+*    along with this program (see SLA_CONDITIONS); if not, write to the
+*    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+*    Boston, MA  02110-1301  USA
+*
+*  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
+*-
+
+      IMPLICIT NONE
+
+      DOUBLE PRECISION DATE
+      INTEGER JFORM
+      DOUBLE PRECISION EPOCH,ORBINC,ANODE,PERIH,AORQ,E,AORL,DM,PV(6)
+      INTEGER JSTAT
+
+      DOUBLE PRECISION U(13)
+      INTEGER J
+
+
+
+*  Validate elements and convert to "universal variables" parameters.
+      CALL slELUE(DATE,JFORM,
+     :               EPOCH,ORBINC,ANODE,PERIH,AORQ,E,AORL,DM,U,J)
+
+*  Determine the position and velocity.
+      IF (J.EQ.0) THEN
+         CALL slUEPV(DATE,U,PV,J)
+         IF (J.NE.0) J=-5
+      END IF
+
+*  Wrap up.
+      JSTAT = J
+
+      END