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In probability theory and information theory, adjusted mutual information, a variation of mutual information may be used for comparing clusterings. It corrects the effect of agreement solely due to chance between clusterings, similar to the way the adjusted rand index corrects the Rand index. It is closely related to variation of information: when a similar adjustment is made to the VI index, it becomes equivalent to the AMI.〔 The adjusted measure however is no longer metrical. ==Mutual Information of two Partitions== Given a set ''S'' of ''N'' elements , consider two partitions of ''S'', namely with ''R'' clusters, and with ''C'' clusters. It is presumed here that the partitions are so-called ''hard clusters;'' the partitions are pairwise disjoint: : for all , and complete: : The mutual information of cluster overlap between ''U'' and ''V'' can be summarized in the form of an ''R''x''C'' contingency table , where denotes the number of objects that are common to clusters and . That is, : Suppose an object is picked at random from ''S''; the probability that the object falls into cluster is: : The entropy associated with the partitioning ''U'' is: : ''H(U)'' is non-negative and takes the value 0 only when there is no uncertainty determining an object's cluster membership, ''i.e.'', when there is only one cluster. Similarly, the entropy of the clustering ''V'' can be calculated as: : where . The mutual information (MI) between two partitions: : where ''P(i,j)'' denotes the probability that a point belongs to both the cluster in ''U'' and cluster in ''V'': : MI is a non-negative quantity upper bounded by the entropies ''H''(''U'') and ''H''(''V''). It quantifies the information shared by the two clusterings and thus can be employed as a clustering similarity measure. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Adjusted mutual information」の詳細全文を読む スポンサード リンク
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