The positive preference flow \phi^{+}(a_i) quantifies how a given action a_i is globally preferred to all the other actions while the negative preference flow \phi^{-}(a_i) quantifies how a given action a_i is being globally preferred by all the other actions. An ideal action would have a positive preference flow equal to 1 and a negative preference flow equal to 0. The two preference flows induce two generally different complete rankings on the set of actions. The first one is obtained by ranking the actions according to the decreasing values of their positive flow scores. The second one is obtained by ranking the actions according to the increasing values of their negative flow scores. The Promethee I partial ranking is defined as the intersection of these two rankings. As a consequence, an action a_i will be as good as another action a_j if \phi^{-}(a_i) \ge \phi^{-}(a_j) and \phi^{-}(a_i)\le \phi^{-}(a_j)
