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Index Page vrel_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

       vrel_c ( Vector relative difference, 3 dimensions )

       SpiceDouble vrel_c ( ConstSpiceDouble v1[3],
                            ConstSpiceDouble v2[3]  )

#### Abstract

       Return the relative difference between two 3-dimensional vectors.

#### Required_Reading

       None.

#### Keywords

       MATH
       VECTOR

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       v1,
       v2         I   Input vectors.

       The function returns the relative difference between two
       3-dimensional vectors.

#### Detailed_Input

       v1,
       v2          are two 3-dimensional vectors for which the relative
                   difference is to be computed.

#### Detailed_Output

       The function returns the relative difference between the two input
       3-dimensional vectors `v1' and `v2'.

       It is defined as:

                            || v1 - v2 ||
          vrel_c   =   ------------------------
                        max ( ||v1||, ||v2|| )

       where ||x|| indicates the Euclidean norm of the vector `x'.

       vrel_c assumes values in the range [0,2]. If both `v1' and `v2' are zero
       vectors then vrel_c is defined to be zero.

#### Parameters

       None.

#### Exceptions

       Error free.

       1)  If both `v1' and `v2' are zero vectors, then vrel_c is defined
           to be zero.

#### Files

       None.

#### Particulars

       This function computes the relative difference between two
       3-dimensional vectors as defined above.

       The function vrelg_c may be used to find the relative difference
       for two vectors of general dimension.

#### Examples

       This example code fragment computes the relative difference
       between the geometric and light time corrected state of Io
       with respect to Voyager 2 at a given UTC time.

             #include "SpiceUsr.h"
                   .
                   .
                   .
             /.
             The NAIF integer code for Io is 501 and the code for
             Voyager 2 is -32.
             ./

             #define           IO    501
             #define           VG2   -32

             /.
             Local variables
             ./
             SpiceDouble       state [ 6 ];
             SpiceDouble       pos1  [ 3 ];
             SpiceDouble       pos2  [ 3 ];
             SpiceDouble       diff;
             SpiceDouble       lt;
             SpiceDouble       et;

             SpiceChar       * utc = "1979 JUN 25 12:00:00";

             /.
             Load the sample SPK ephemeris file.
            ./
             furnsh_c ( "VG2_JUP.BSP" );

             /.
             Convert the UTC time string to ephemeris time.
             ./
             utc2et_c ( utc, &et );

             /.
             First calculate the geometric state and then the light
             time corrected state.
             ./
             spkez_c ( IO, et, "J2000", "none", VG2, state, &lt );

             vequ_c  ( state, pos1 );

             spkez_c ( IO, et, "J2000", "lt", VG2, state, &lt );

             vequ_c  ( state, pos2 );

             /.
             Call vrel_c to find the relative difference between the
             two states.
             ./
             diff = vrel_c ( pos1, pos2 );

             .
             .
             .

#### Restrictions

       None.

#### Literature_References

       None.

#### Author_and_Institution

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

#### Version

       -CSPICE Version 1.1.1, 09-APR-2021 (JDR)

           Edited the header to comply with NAIF standard.

       -CSPICE Version 1.1.0, 28-AUG-2001 (NJB)

           Include interface macro definition file SpiceZim.h.

       -CSPICE Version 1.0.1, 13-APR-2000 (NJB)

           Made some minor updates and corrections in the code example.

       -CSPICE Version 1.0.0, 06-JUL-1999 (EDW) (JML)

#### Index_Entries

       relative difference of 3-dimensional vectors

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

    Fri Dec 31 18:41:15 2021