nd V2.
                  It is defined as:
                                              || v1 - v2 ||
                            <b>vrel_c</b>   =   ----------------------
                                       max ( ||v1||, ||v2|| )

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

                  <b>vrel_c</b> assumes values in the range [0,2]. If both
                  v1 and v2 are zero vectors then <b>vrel_c</b> is defined
  