'When updating scores the score of the highest-weighted incoming
arc is subtracted upon collapse.  This returns the correct
amount to subtract from that edge.
:type column_index: integer.
:param column_index: A index representing the column of incoming arcs
to a particular node being updated
:type cycle_indexes: A list of integers.
:param cycle_indexes: Only arcs from cycle nodes are considered.  This
is a list of such nodes addresses.'

def compute_max_subtract_score(self, column_index, cycle_indexes):

    max_score = (-100000)
    for row_index in cycle_indexes:
        for subtract_val in self.scores[row_index][column_index]:
            if (subtract_val > max_score):
                max_score = subtract_val
    return max_score
