Procedure

     SPKE21 ( S/P Kernel, evaluate, type 21 )

     SUBROUTINE SPKE21 ( ET, RECORD, STATE )

Abstract

     Evaluate a single SPK data record from a segment of type 21
     (Extended Difference Lines).

Required_Reading

     SPK
     TIME

Keywords

     EPHEMERIS

Declarations

     IMPLICIT NONE

     INCLUDE 'spk21.inc'

     DOUBLE PRECISION      ET
     DOUBLE PRECISION      RECORD   ( * )
     DOUBLE PRECISION      STATE    ( 6 )

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     ET         I   Evaluation epoch.
     RECORD     I   Data record.
     STATE      O   State (position and velocity).
     MAXTRM     P   Maximum number of terms per difference table
                    component.

Detailed_Input

     ET       is an epoch at which a state vector is to be
              computed. The epoch is represented as seconds past
              J2000 TDB.

     RECORD   is a data record which, when evaluated at epoch ET,
              will give the state (position and velocity) of an
              ephemeris object, relative to its center of motion,
              in an inertial reference frame.

              The contents of RECORD are as follows:

                 RECORD(1):         The difference table size per
                                    Cartesian component. Call this
                                    size MAXDIM; then the difference
                                    line (MDA) size DLSIZE is

                                      ( 4 * MAXDIM ) + 11

                 RECORD(2)
                    ...
                 RECORD(1+DLSIZE):  An extended difference line.
                                    The contents are:

                    Dimension  Description
                    ---------  ----------------------------------
                    1          Reference epoch of difference line
                    MAXDIM     Stepsize function vector
                    1          Reference position vector,  x
                    1          Reference velocity vector,  x
                    1          Reference position vector,  y
                    1          Reference velocity vector,  y
                    1          Reference position vector,  z
                    1          Reference velocity vector,  z
                    MAXDIM,3   Modified divided difference
                               arrays (MDAs)
                    1          Maximum integration order plus 1
                    3          Integration order array

Detailed_Output

     STATE    is the state resulting from evaluation of the input
              record at ET. Units are km and km/sec.

Parameters

     MAXTRM   is the maximum number of terms allowed in
              each component of the difference table
              contained in the input argument RECORD.
              See the INCLUDE file spk21.inc for the value
              of MAXTRM.

Exceptions

     1)  If the maximum table size of the input record exceeds
         MAXTRM, the error SPICE(DIFFLINETOOLARGE) is signaled.

Files

     None.

Particulars

     The exact format and structure of type 21 (difference lines)
     segments are described in the SPK Required Reading file.

     SPKE21 is a modified version of SPKE01. The routine has been
     generalized to support variable size difference lines.

Examples

     None.

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     F.T. Krogh         (JPL)
     W.L. Taber         (JPL)
     I.M. Underwood     (JPL)

Version

    SPICELIB Version 1.1.0, 14-APR-2021 (JDR)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard. Moved SPK
        required reading from $Literature_References to
        $Required_Reading section.

    SPICELIB Version 1.0.0, 03-FEB-2014 (NJB) (FTK) (WLT) (IMU)