Never minimal automata and the rainbow bipartite subgraph problem

  • Authors:
  • Emanuele Rodaro;Pedro V. Silva

  • Affiliations:
  • Departamento de Matemática, Faculdade de Ciências, Universidade do Porto, Porto, Portugal;Departamento de Matemática, Faculdade de Ciências, Universidade do Porto, Porto, Portugal

  • Venue:
  • DLT'11 Proceedings of the 15th international conference on Developments in language theory
  • Year:
  • 2011

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Abstract

Never minimal automata, introduced in [4], are strongly connected automata which are not minimal for any choice of their final states. In [4] the authors raise the question whether recognizing such automata is a polynomial time task or not. In this paper, we show that the complement of this problem is equivalent to the problem of checking whether or not in an edge-colored graph there is a bipartite subgraph whose edges are colored using all the colors. We prove that this graph theoretic problem is NP-complete, showing that checking the property of never-minimality is unlikely a polynomial time task.