On a class of transformations of copulas and quasi-copulas

  • Authors:
  • Elisabetta Alvoni;Pier Luigi Papini;Fabio Spizzichino

  • Affiliations:
  • Department of Mathematics for Economic and Social Sciences, University of Bologna, Viale Filopanti, 5, I 40126 Bologna, Italy;Department of Mathematics, University of Bologna, I 40126 Bologna, Italy;Department of Mathematics, University “La Sapienza”, I-00185 Rome, Italy

  • Venue:
  • Fuzzy Sets and Systems
  • Year:
  • 2009

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Abstract

The theory of copulas is by now a very well established one. Recently, larger classes of functions C:[0,1]^n-[0,1], that are increasing in each variable and satisfy some conditions at the boundary (like quasi-copulas), have been the object of fruitful research. Several authors have considered the action of a class of transformations on some aggregation operators, as t-norms, copulas, quasi-copulas and so on. These simple transformations do not preserve in general all properties of copulas (or quasi-copulas): in particular, the fact that only some properties are preserved by these transformations, suggested the introduction of semi-copulas. The purpose of the present contribution is to give a fairly complete picture concerning such action on copulas and quasi-copulas; in particular, we prove results concerning inclusions and strict inclusions among these classes of operators, and those of their transforms.