def bisect_value(self):
return self.total_weight_in_all_comms()<EOL>
Give the value on which we can perform bisectioning.

        If p1 and p2 are two different optimal partitions for two different
        resolution parameters g1 and g2, then if p1.bisect_value() ==
        p2.bisect_value() the two partitions should be optimal for both g1 and g2.