def __init__(self, groups=None):
        super(GroupedRequirements, self).__init__(NamedRequirements)
        self.groups = groups or self.default_groups
        self.filename = None
        self.create_default_groups()
def __calculate_initial_clusters(self, centers):
        """!
        @brief Calculate Euclidean distance to each point from the each cluster. 
        @brief Nearest points are captured by according clusters and as a result clusters are updated.