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Tversky index : ウィキペディア英語版
Tversky index
The Tversky index, named after Amos Tversky, is an asymmetric similarity measure on sets that compares a variant to a prototype. The Tversky index can be seen as a generalization of Dice's coefficient and Tanimoto coefficient.
For sets ''X'' and ''Y'' the Tversky index is a number between 0 and 1 given by
S(X, Y) = \frac ,
Here, X - Y denotes the relative complement of Y in X.
Further, \alpha, \beta \ge 0 are parameters of the Tversky index. Setting \alpha = \beta = 1 produces the Tanimoto coefficient; setting \alpha = \beta = 0.5 produces Dice's coefficient.
If we consider ''X'' to be the prototype and ''Y'' to be the variant, then \alpha corresponds to the weight of the prototype and \beta corresponds to the weight of the variant. Tversky measures with \alpha + \beta = 1 are of special interest.〔http://www.daylight.com/dayhtml/doc/theory/theory.finger.html〕
Because of the inherent asymmetry, the Tversky index does not meet the criteria for a similarity metric. However, if symmetry is needed a variant of the original formulation has been proposed using max and min functions 〔Jimenez, S., Becerra, C., Gelbukh, A. (SOFTCARDINALITY-CORE: Improving Text Overlap with Distributional Measures for Semantic Textual Similarity ). Second Joint Conference on Lexical and Computational Semantics (
*SEM), Volume 1: Proceedings of the Main Conference and the Shared Task: Semantic Textual Similarity, p.194-201, June 7–8, 2013, Atlanta, Georgia, USA.〕
.
S(X,Y)=\frac,
a=\min\left(|X-Y|,|Y-X|\right) ,
b=\max\left(|X-Y|,|Y-X|\right) ,
This formulation also re-arranges parameters \alpha and \beta . Thus, \alpha controls the balance between |X - Y| and |Y - X| in the denominator. Similarly, \beta controls the effect of the symmetric difference |X\,\triangle\,Y\,| versus | X \cap Y | in the denominator.
==Notes==


抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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