Procedure

     PACKAD ( Pack a double precision array )

     SUBROUTINE PACKAD ( IN,
    .                    PACK,   NPACK,
    .                    MAXOUT, NOUT,   OUT )

Abstract

     Pack the contents of a double precision array. That is,
     take a set of arbitrarily spaced elements from an input
     array, and make them adjacent elements in an output array.

Required_Reading

     None.

Keywords

     ARRAY
     ASSIGNMENT
     UTILITY

Declarations

     IMPLICIT NONE

     DOUBLE PRECISION   IN      ( * )
     INTEGER            PACK    ( * )
     INTEGER            NPACK
     INTEGER            MAXOUT

     INTEGER            NOUT
     DOUBLE PRECISION   OUT     ( * )

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     IN         I   Input array.
     PACK       I   Indices of elements to be packed.
     NPACK      I   Number of indices.
     MAXOUT     I   Maximum number of elements in the output array.
     NOUT       O   Number of elements in the output array.
     OUT        O   Output array.

Detailed_Input

     IN       is the input array.

     PACK     is the set of elements to be packed into the output
              array. PACK(i) is the index of the element in the
              input array that is to become the i'th element of the
              output array.

     NPACK    is the number of elements to be packed into the
              output array.

     MAXOUT   is the maximum number of elements to be packed into
              the output array. If NPACK is larger than MAXOUT, the
              extra items are ignored.

Detailed_Output

     NOUT     is the number of elements in the output array.

     OUT      is the output array. This array contains up to
              MAXOUT elements from the input array, located
              in the first NOUT elements of the array.

Parameters

     None.

Exceptions

     1)  If an element in the PACK array is less than 1, the error
         SPICE(INVALIDINDEX) is signaled.

Files

     None.

Particulars

     The indicated elements are moved from their current locations
     in the input array to consecutive positions in the output array.

        OUT(   1) = IN(PACK(   1))
        OUT(   2) = IN(PACK(   2))
             .
             .
       OUT(NOUT) = IN(PACK(NOUT))

     NOUT is either NPACK or MAXOUT, whichever is smaller.

Examples

     The most common use for this routine is to remove unwanted items
     from an array or set of arrays. For example, suppose that the
     arrays NAME, CODE, RADIUS and MASS contain the names, NAIF
     integer ID codes, radii, and masses of a set of NSAT satellites.
     Suppose further that the user selects a subset of the original
     set of satellites from a menu of some sort. Let the indices of
     these satellites be the NSEL elements of the array SEL. The
     following sequence would remove the names, codes, etc., of the
     unselected satellites from the arrays.

        CALL PACKAC ( NAME,   SEL, NSEL, NSAT, NOUT, NAME2   )
        CALL PACKAI ( CODE,   SEL, NSEL, NSAT, NOUT, CODE2   )
        CALL PACKAD ( RADIUS, SEL, NSEL, NSAT, NOUT, RADIUS2 )
        CALL PACKAD ( MASS,   SEL, NSEL, NSAT, NOUT, MASS2   )

     In the example above, suppose that NAME and PACK contain
     the following:

        NAME = 'MIMAS'          PACK = 2, 4, 6, 7
               'ENCELADUS'
               'TETHYS'
               'DIONE'
               'RHEA'
               'TITAN'
               'HYPERION'
               'IAPETUS'
               'PHOEBE'

     Then, following the call to PACKAC, NOUT and NAME2 contain
     the following:

        NOUT = 4                 NAME2 = 'ENCELADUS'
                                         'DIONE'
                                         'TITAN'
                                         'HYPERION'

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     H.A. Neilan        (JPL)
     W.L. Taber         (JPL)
     I.M. Underwood     (JPL)

Version

    SPICELIB Version 1.1.0, 20-AUG-2021 (JDR)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard.

    SPICELIB Version 1.0.2, 23-APR-2010 (NJB)

        Header correction: assertions that the output
        can overwrite the input have been removed.

    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.0, 31-JAN-1990 (WLT) (IMU) (HAN)