Procedure

     VSUB ( Vector subtraction, 3 dimensions )

     SUBROUTINE VSUB ( V1, V2, VOUT )

Abstract

     Compute the difference between two double precision 3-dimensional
     vectors.

Required_Reading

     None.

Keywords

     VECTOR

Declarations

     IMPLICIT NONE

     DOUBLE PRECISION  V1   ( 3 )
     DOUBLE PRECISION  V2   ( 3 )
     DOUBLE PRECISION  VOUT ( 3 )

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     V1         I   First vector (minuend).
     V2         I   Second vector (subtrahend).
     VOUT       O   Difference vector, V1 - V2.

Detailed_Input

     V1       is a double precision 3-dimensional vector which is the
              minuend (i.e. first or left-hand member) in the vector
              subtraction.

     V2       is a double precision 3-dimensional vector which is the
              subtrahend (i.e. second or right-hand member) in the
              vector subtraction.

Detailed_Output

     VOUT     is a double precision 3-dimensional vector which
              represents the vector difference, V1 - V2.

Parameters

     None.

Exceptions

     Error free.

Files

     None.

Particulars

     For each value of the index I from 1 to 3, this routine performs
     the following subtraction:

        VOUT(I) = V1(I) - V2(I)

     No error checking is performed to guard against numeric overflow
     or underflow.

Examples

     The numerical results shown for this example may differ across
     platforms. The results depend on the SPICE kernels used as
     input, the compiler and supporting libraries, and the machine
     specific arithmetic implementation.

     1) Define two sets of 3-dimensional vectors and compute the
        difference from each vector in first set with the
        corresponding vector in the second set.


        Example code begins here.


              PROGRAM VSUB_EX1
              IMPLICIT NONE

        C
        C     Local parameters.
        C
              INTEGER               SETSIZ
              PARAMETER           ( SETSIZ = 3 )

        C
        C     Local variables.
        C
              DOUBLE PRECISION      V1   ( 3, SETSIZ )
              DOUBLE PRECISION      V2   ( 3, SETSIZ )
              DOUBLE PRECISION      VOUT ( 3         )

              INTEGER               I
              INTEGER               J

        C
        C     Define the two vector sets.
        C
              DATA                  V1 / 1.D0,  2.D0,  3.D0,
             .                           1.D0,  2.D0,  3.D0,
             .                           1.D0,  2.D0,  3.D0  /

              DATA                  V2 / 1.D0,  1.D0,  1.D0,
             .                          -1.D0, -2.D0, -3.D0,
             .                          -1.D0,  2.D0, -3.D0  /

        C
        C     Calculate the difference between each pair of vectors
        C
              DO I=1, SETSIZ

                 CALL VSUB ( V1(1,I), V2(1,I), VOUT )

                 WRITE(*,'(A,3F6.1)') 'First vector : ',
             .                        ( V1(J,I), J=1,3 )
                 WRITE(*,'(A,3F6.1)') 'Second vector: ',
             .                        ( V2(J,I), J=1,3 )
                 WRITE(*,'(A,3F6.1)') 'Difference   : ', VOUT
                 WRITE(*,*)

              END DO

              END


        When this program was executed on a Mac/Intel/gfortran/64-bit
        platform, the output was:


        First vector :    1.0   2.0   3.0
        Second vector:    1.0   1.0   1.0
        Difference   :    0.0   1.0   2.0

        First vector :    1.0   2.0   3.0
        Second vector:   -1.0  -2.0  -3.0
        Difference   :    2.0   4.0   6.0

        First vector :    1.0   2.0   3.0
        Second vector:   -1.0   2.0  -3.0
        Difference   :    2.0   0.0   6.0

Restrictions

     1)  The user is required to determine that the magnitude each
         component of the vectors is within the appropriate range so as
         not to cause floating point overflow. No error recovery or
         reporting scheme is incorporated in this routine.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     W.M. Owen          (JPL)
     W.L. Taber         (JPL)
     E.D. Wright        (JPL)

Version

    SPICELIB Version 1.0.4, 03-JUL-2020 (JDR)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard. Added complete
        code example based on existing example.

    SPICELIB Version 1.0.3, 22-APR-2010 (NJB)

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

    SPICELIB Version 1.0.2, 07-NOV-2003 (EDW)

        Corrected a mistake in the second example's value
        for VOUT, i.e. replaced (1D24, 2D23, 0.0) with
        (-1D24, 0.0, 0.0).

    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 (WMO)