Geometrical interpretation and applications of membership functions with fuzzy rough sets

  • Authors:

  • Degang Chen;Sam Kwong;Qiang He;Hui Wang

  • Affiliations:

  • Department of Mathematics and Physics, North China Electric Power University, Beijing 102206, PR China;Department of Computer Science, City University of Hong Kong, Kowloon, Hong Kong;Department of Mathematics and Computer Science, Hebei University, Baoding 071002, PR China;School of Computing and Mathematics, Faculty of Computing and Engineering, University of Ulster, Jordanstown, Newtownabbey, Co. Antrim, N. Ireland BT37 0QB, UK

  • Venue:
  • Fuzzy Sets and Systems
  • Year:
  • 2012

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Abstract

Fuzzy rough sets are a generalization of crisp rough sets for measuring inconsistency between conditional attributes and decision attributes for many decision systems. In many classification problems a membership function for the training sample belonging to a certain class can be computed by methods in fuzzy rough sets. In this paper, we present a geometrical interpretation and its applications of this kind of membership functions. First, we prove that every fuzzy similarity relation in fuzzy rough sets is a reproducing kernel which is related to a Krein space, thus, fuzzy similarity relations can be geometrically explained in a Krein space. Second, we will present the interpretation of several types of membership functions geometrically by using the lower approximations in fuzzy rough sets, in terms of square distances in Krein spaces. As practical applications of these membership functions, we develop a new algorithm to find reducts and reformulate soft margin support vector machines by taking the membership degree for every training sample into considerations. Experimental results also demonstrate the effectiveness of the work proposed in this paper.