Procedure

     WNDIFD ( Difference two DP windows )

     SUBROUTINE WNDIFD ( A, B, C )

Abstract

     Place the difference of two double precision windows into
     a third window.

Required_Reading

     WINDOWS

Keywords

     WINDOWS

Declarations

     IMPLICIT NONE

     INTEGER               LBCELL
     PARAMETER           ( LBCELL = -5 )

     DOUBLE PRECISION      A        ( LBCELL:* )
     DOUBLE PRECISION      B        ( LBCELL:* )
     DOUBLE PRECISION      C        ( LBCELL:* )

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     A,
     B          I   Input windows.
     C          O   Difference of A and B.

Detailed_Input

     A,
     B        are SPICE windows, each of which contains zero or more
              intervals.

Detailed_Output

     C        is the output SPICE window, containing the difference
              of A and B --- every point contained in A, but not
              contained in B.

              C must be distinct from both A and B.

Parameters

     None.

Exceptions

     1)  If the difference of the two windows results in an excess of
         elements, the error SPICE(WINDOWEXCESS) is signaled.

     2)  The cardinality of the input windows must be even. Left
         endpoints of stored intervals must be strictly greater than
         preceding right endpoints. Right endpoints must be greater
         than or equal to corresponding left endpoints. Invalid window
         data are not diagnosed by this routine and may lead to
         unpredictable results.

Files

     None.

Particulars

     Mathematically, the difference of two windows contains every
     point contained in the first window but not contained in the
     second window.

     Fortran offers no satisfactory floating point representation
     of open intervals. Thus, for floating point windows we must
     return the closure of the set theoretical difference: that is,
     the difference plus the endpoints of the first window that are
     contained in the second window.

Examples

     Let A contain the intervals

           [ 1, 3 ]  [ 7, 11 ]  [ 23, 27 ]

     and B contain the intervals

           [ 2, 4 ]  [ 8, 10 ]  [ 16, 18 ]

     Then the difference of A and B contains the intervals

           [ 1, 2 ]  [ 7, 8 ]  [ 10, 11 ]  [ 23, 27 ]

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 2.1.0, 24-AUG-2021 (JDR) (NJB)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard. Fixed I/O type
        of argument C in $Brief_I/O table.

        Added entry #2 in $Exceptions section.

    SPICELIB Version 2.0.0, 16-SEP-1998 (WLT)

        The previous version did not work when removing
        singletons. This has been corrected.

    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)