Procedure

   vzero_c ( Is a vector the zero vector? ) 

   SpiceBoolean vzero_c ( ConstSpiceDouble v[3] )

Abstract

   Indicate whether a 3-vector is the zero vector.

Required_Reading

   None.

Keywords

   MATH
   VECTOR

Brief_I/O

   VARIABLE  I/O  DESCRIPTION
   --------  ---  --------------------------------------------------
   v          I   Vector to be tested.

   The function returns the value SPICETRUE if and only if `v' is the
   zero vector.

Detailed_Input

   v           is a vector in 3-space.

Detailed_Output

   The function returns the value SPICETRUE if and only if `v' is the
   zero vector.

Parameters

   None.

Exceptions

   Error free.

Files

   None.

Particulars

   This function has the same truth value as the logical expression

      vnorm_c ( v )  ==  0.

   Replacing the above expression by

      vzero_c ( v );

   has several advantages: the latter expresses the test more
   clearly, looks better, and doesn't go through the work of scaling,
   squaring, taking a square root, and re-scaling (all of which
   vnorm_c must do) just to find out that a vector is non-zero.

   A related function is vzerog_c, which accepts vectors of arbitrary
   dimension.

Examples

   1)  When testing whether a vector is the zero vector, one
       normally constructs tests like

          if (  vnorm_c ( v ) ==  0.  )
             {
                      .
                      .
                      .


       These can be replaced with the code

          if (  vzero_c ( v )  )
             {
                      .
                      .
                      .


    2) Check that a normal vector is non-zero before creating
       a plane with pnv2pl_c:

       if (  vzero_c ( NORMAL )  )
          {
          [ handle error ]
          }

       else
          {
          pnv2pl_c ( POINT, NORMAL, PLANE )
                        .
                        .
                        .
          }

Restrictions

   None.

Literature_References

   None.

Author_and_Institution

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

Version

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

       Edited the header to comply with NAIF standard.

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

       Made input vector const. Removed #include of SpiceZfc.h.

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

Index_Entries

   test whether a 3-dimensional vector is the zero vector