Abstract

   CSPICE_VREL returns the relative difference between two
   double precision 3-vectors.

I/O

   Given:

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

               help, v1
                  DOUBLE = Array[3]
               help, v2
                  DOUBLE = Array[3]

   the call:

      vrel = cspice_vrel( v1, v2 )

   returns:

      vrel     the scalar double precision relative difference between between
               `v1' and `v2'.

               help, vrel
                  DOUBLE = Scalar

               It is defined as:

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

               where || x || indicates the Euclidean norm of
               the vector `x' ( ||x|| = sqrt( x . x ) ).

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

Parameters

   None.

Examples

   Any numerical results shown for this example may differ between
   platforms as the results depend on the SPICE kernels used as input
   and the machine specific arithmetic implementation.

   1) Compute the relative difference between two three-dimensional
      vectors.

      Example code begins here.


      PRO vrel_ex1

         vec1 = [ 12.3d   , -4.32d ,  76.d  ]
         vec2 = [ 23.0423d, -11.99d, -0.10d ]

         ;;
         ;; Compute the relative difference between `vec1' and `vec2'
         ;;
         diff = cspice_vrel( vec1, vec2 )

         print, 'Relative difference between v1 and v2:', diff

      END


      When this program was executed on a Mac/Intel/IDL8.x/64-bit
      platform, the output was:


      Relative difference between v1 and v2:       1.0016370

Particulars

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

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

Exceptions

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

   2)  If any of the input arguments, `v1' or `v2', is undefined, an
       error is signaled by the IDL error handling system.

   3)  If any of the input arguments, `v1' or `v2', is not of the
       expected type, or it does not have the expected dimensions and
       size, an error is signaled by the Icy interface.

Files

   None.

Restrictions

   None.

Required_Reading

   ICY.REQ

Literature_References

   None.

Author_and_Institution

   J. Diaz del Rio     (ODC Space)
   E.D. Wright         (JPL)

Version

   -Icy Version 1.0.2, 01-JUN-2021 (JDR)

       Edited the header to comply with NAIF standard. Added
       example's problem statement and reformatted example's output.

       Added -Parameters, -Exceptions, -Files, -Restrictions,
       -Literature_References and -Author_and_Institution sections, and
       completed -Particulars section.

       Removed reference to the routine's corresponding CSPICE header from
       -Abstract section.

       Added arguments' type and size information in the -I/O section.

   -Icy Version 1.0.1, 13-JUN-2011 (EDW)

       Edits to comply with NAIF standard for Icy headers.

   -Icy Version 1.0.0, 16-JUN-2003 (EDW)

Index_Entries

   relative difference of 3-dimensional vectors