Maximal Consistent Subsystems of Max-T Fuzzy Relational Equations

Abstract: In this article, we study the inconsistency of a system of $\max-T$ fuzzy relational equations of the form $A \Box_{T}^{\max} x = b$, where $T$ is a t-norm among $\min$, the product or Lukasiewicz's t-norm. For an inconsistent $\max-T$ system, we directly construct a canonical maximal consistent subsystem (w.r.t the inclusion order). The main tool used to obtain it is the analytical formula which compute the Chebyshev distance $$\Delta = \inf_{c \in \mathcal{C}} \Vert b - c \Vert$$ associated to the inconsistent $\max-T$ system, where $\mathcal{C}$ is the set of second members of consistent systems defined with the same matrix $A$. Based on the same analytical formula, we give, for an inconsistent $\max-\min$ system, an efficient method to obtain all its consistent subsystems, and we show how to iteratively get all its maximal consistent subsystems.