  With the recent advances of networking technology, connections among people
are unprecedentedly enhanced. People with different ideologies and backgrounds
interact with each other, and there may exist severe opinion polarization and
disagreement in the social network. There have been a lot of reviews on
modeling opinion formation. However, less attention has been paid to opinion
polarization and disagreement. In this work, we review recent advances in
opinion polarization and disagreement and pay attention to how they are
evaluated and controlled. In literature, three metrics: polarization,
disagreement, and polarization-disagreement index (PDI) are usually adopted,
and there is a tradeoff between polarization and disagreement. Different
strategies have been proposed in literature which can significantly control
opinion polarization and disagreement based on these metrics. This review is of
crucial importance to summarize works on opinion polarization and disagreement,
and to the better understanding and control of them.
