def _add_node(self, idx, unique_idx, frac_coords):
        """
        Add information about a node describing a critical point.

        :param idx: unique index
        :param unique_idx: index of unique CriticalPoint,
        used to look up more information of point (field etc.)
        :param frac_coord: fractional co-ordinates of point
        :return:
        """
        self.nodes[idx] = {'unique_idx': unique_idx, 'frac_coords': frac_coords}
def _add_node ( self , idx , unique_idx , frac_coords ) : self . nodes [ idx ] = { 'unique_idx' : unique_idx , 'frac_coords' : frac_coords }
Add information about a node describing a critical point.

        :param idx: unique index
        :param unique_idx: index of unique CriticalPoint,
        used to look up more information of point (field etc.)
        :param frac_coord: fractional co-ordinates of point
        :return: