* create factory with the standard homogenous rave::ConstantMagneticField,
  * 4 Tesla in "z". No material effects (because we use the "VacuumPropagator").
  * Default reconstruction method is "avr",
  * verbosity level is "0".
  */
  rave::VertexFactory factory ( rave::ConstantMagneticField(0.,0.,4.),
                                rave::VacuumPropagator(), "avr", 0 );
 

 /* from "tracks" ( std::vector < rave::Track > ) create "vertices",
  * using the Multivertex "mvf" method "cutting" at sigma=3.0.
  * (I.e. a track is considered incompatible with a vertex if
  * the reduced distance > 3.0)
  */
  std::vector < rave::Vertex > vertices = factory.create( tracks, "mvf-sigmacut:3.0" );

 /* We fit vertices again, this time using
  * the iterative adaptive fitter technique.
  * For the primary vertex we "cut the tracks" at sigma=3.0
  * all subsequent vertices have sigma=6.0.
  */
  std::vector < rave::Vertex > v2 = factory.create( tracks, "avr-primcut:3.0-seccut:6.0" );