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Index Page vcrss_c

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Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries

#### Procedure

       vcrss_c ( Vector cross product, 3 dimensions )

       void vcrss_c ( ConstSpiceDouble   v1[3],
                      ConstSpiceDouble   v2[3],
                      SpiceDouble        vout[3] )

#### Abstract

       Compute the cross product of two 3-dimensional vectors.

#### Required_Reading

       None.

#### Keywords

       VECTOR

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       v1         I   Left hand vector for cross product.
       v2         I   Right hand vector for cross product.
       vout       O   Cross product v1 x v2.

#### Detailed_Input

       v1,
       v2          are two 3-dimensional vectors. Typically, these might
                   represent the (possibly unit) vector to a planet, Sun,
                   or a star which defines the orientation of axes of some
                   reference frame.

#### Detailed_Output

       vout        is the cross product of `v1' and `v2'. `vout' may overwrite
                   `v1' or `v2'.

#### Parameters

       None.

#### Exceptions

       Error free.

#### Files

       None.

#### Particulars

       vcrss_c calculates the three dimensional cross product of two
       vectors according to the definition. The cross product is stored
       in a buffer vector until the calculation is complete. Thus `vout'
       may overwrite `v1' or `v2' without interfering with intermediate
       computations.

       If `v1' and `v2' are large in magnitude (taken together, their
       magnitude surpasses the limit allowed by the computer) then it
       may be possible to generate a floating point overflow from an
       intermediate computation even though the actual cross product may
       be well within the range of double precision numbers. vcrss_c does
       NOT check the magnitude of `v1' or `v2' to insure that overflow will
       not occur.

#### 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 vectors and compute the cross product of
          each vector in first set and the corresponding vector in
          the second set.

          Example code begins here.

          /.
             Program vcrss_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {

             /.
             Local parameters.
             ./
             #define NDIM         3
             #define SETSIZ       2

             /.
             Local variables.
             ./
             SpiceDouble          vout   [NDIM];

             SpiceInt             i;

             /.
             Define the two vector sets.
             ./
             SpiceDouble          seta   [SETSIZ][NDIM] = {
                                       {0.0,  1.0,  0.0},
                                       {5.0,  5.0,  5.0} };

             SpiceDouble          setb   [SETSIZ][NDIM] = {
                                       { 1.0,  0.0,  0.0},
                                       {-1.0, -1.0, -1.0} };

             /.
             Calculate the cross product of each pair of vectors
             ./
             for ( i = 0; i < SETSIZ; i++ )
             {

                vcrss_c ( seta[i], setb[i], vout );

                printf( "Vector A     :  %4.1f %4.1f %4.1f\n",
                            seta[i][0], seta[i][1], seta[i][2] );
                printf( "Vector B     :  %4.1f %4.1f %4.1f\n",
                            setb[i][0], setb[i][1], setb[i][2] );
                printf( "Cross product:  %4.1f %4.1f %4.1f\n",
                                     vout[0], vout[1], vout[2] );
                printf( "\n" );

             }

             return ( 0 );
          }

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

          Vector A     :   0.0  1.0  0.0
          Vector B     :   1.0  0.0  0.0
          Cross product:   0.0  0.0 -1.0

          Vector A     :   5.0  5.0  5.0
          Vector B     :  -1.0 -1.0 -1.0
          Cross product:   0.0  0.0  0.0

#### Restrictions

       1)  No checking of `v1' or `v2' is done to prevent floating point
           overflow. The user is required to determine that the
           magnitude of each component of the vectors is within an
           appropriate range so as not to cause floating point overflow.
           In almost every case there will be no problem and no checking
           actually needs to be done.

#### Literature_References

       None.

#### Author_and_Institution

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

#### Version

       -CSPICE Version 1.1.1, 05-JUL-2021 (JDR)

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

       -CSPICE Version 1.1.0, 22-OCT-1998 (NJB)

           Made input vectors const.

       -CSPICE Version 1.0.1, 06-MAR-1998 (EDW)

           Minor header correction. Added use of MOVED.

       -CSPICE Version 1.0.0, 08-FEB-1998 (EDW) (WMO)

#### Index_Entries

       vector cross product

#### Link to routine vcrss_c source file vcrss_c.c

    Fri Dec 31 18:41:14 2021