Procedure

   vnormg_c ( Vector norm, general dimension ) 

   SpiceDouble vnormg_c ( ConstSpiceDouble   * v1,
                          SpiceInt             ndim )

Abstract

   Compute the magnitude of a double precision vector of arbitrary
   dimension.

Required_Reading

   None.

Keywords

   VECTOR

Brief_I/O

   VARIABLE  I/O  DESCRIPTION
   --------  ---  --------------------------------------------------
   v1         I   Vector whose magnitude is to be found.
   ndim       I   Dimension of `v1'.

   The function returns the magnitude of `v1'.

Detailed_Input

   v1          is any double precision vector of arbitrary dimension.

   ndim        is the dimension of the input vector `v1'.

Detailed_Output

   The function returns the magnitude of `v1' calculated in a
   numerically stable way.

Parameters

   None.

Exceptions

   Error free.

Files

   None.

Particulars

   vnormg_c finds the component of v1 whose magnitude is the largest.
   If the absolute magnitude of that component indicates that a
   numeric overflow would occur when it is squared, or if it
   indicates that an underflow would occur when squared (falsely
   giving a magnitude of zero) then the following expression is
   used:

      vnormg_c = v1max * MAGNITUDE OF [ (1/v1max)*v1 ]

   Otherwise a simpler expression is used:

      vnormg_c = MAGNITUDE OF [ v1 ]

   Beyond the logic described above, no further checking of the
   validity of the input is performed.

Examples

   The numerical results shown for these examples 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 a four-dimensional vector and calculate its magnitude.

      Example code begins here.


      /.
         Program vnormg_ex1
      ./
      #include <stdio.h>
      #include "SpiceUsr.h"

      int main( )
      {

         /.
         Local parameters.
         ./
         #define NDIM         4

         /.
         Local variables.
         ./
         SpiceDouble          v1    [NDIM] = { 12.3, -4.32, 76.0, 1.87 };

         /.
         Compute the magnitude of `v1'
         ./
         printf(" Magnitude of v1: %f\n", vnormg_c( v1, NDIM ) );

         return ( 0 );
      }


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


       Magnitude of v1: 77.132673


   2) The following table show the correlation between various input
      vectors `v1' and vnormg_c:

         ndim     v1[ndim]                          vnormg_c
         ---------------------------------------------------
          1      (-7.0e20)                            7.e20
          3      (1., 2., 2.)                         3.
          4      (3., 3., 3., 3.)                     6.
          5      (5., 12., 0., 0., 0.)               13.
          3      (-5.e-17, 0.0, 12.e-17)             13.e-17

Restrictions

   None.

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 1.2.0, 13-AUG-2021 (JDR)

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

       Removed check for "ndim" being positive in order to replicate
       behavior of SPICELIB equivalent routine.

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

       Made input vector const.

   -CSPICE Version 1.0.0, 01-APR-1998 (EDW) (WMO)

Index_Entries

   norm of n-dimensional vector