Find the component of a vector that is perpendicular to a second
   vector.  All vectors are 3-dimensional.

   None.

   VARIABLE  I/O  DESCRIPTION
   --------  ---  --------------------------------------------------
    a         I    The vector whose orthogonal component is sought.
    b         I    The vector used as the orthogonal reference.
    p         O    The component of a orthogonal to b.

   a     is a double precision, 3-dimensional vector.  It the vector
         whose component orthogonal to b is sought. (There is a
         unique decomposition of a into a sum v + p, where v is
         parallel to b and p is orthogonal to b.  We want the
         component p.)

   b     is a double precision, 3-dimensional vector.  This
         vector is the vector used as a reference for the
         decomposition of a.

   p     is a double precision, 3-dimensional vector containing
         the the component of a that is orthogonal to b.
         p may overwrite either a or b.

   None.

   Given and non-zero vector b and a vector a, there is a unique
   decomposition of a as a sum v + p such that p is orthogonal
   to b and v is parallel to b.  This routine finds the vector p.

   If b is a zero vector, p will be identical to a.

   The following table gives sample inputs and results from calling
   vperp_c.

   a                  b                 p
   ------------------------------------------
   (6, 6, 6)      ( 2, 0, 0)        (0, 6, 6)
   (6, 6, 6)      (-3, 0, 0)        (0, 6, 6)
   (6, 6, 0)      ( 0, 7, 0)        (6, 0, 0)
   (6, 0, 0)      ( 0, 0, 9)        (6, 0, 0)

   None.

   Error free.

   None.

   W.L. Taber      (JPL)

   REFERENCE: Any reasonable calculus text (for example Thomas)

   -CSPICE Version 1.2.0, 22-OCT-1998 (NJB)

      Made input vectors const.

   -CSPICE Version 1.1.0, 06-MAR-1998   (EDW)

      Removed non printing character.

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

   perpendicular component of a 3-vector