Comments on “Polynomial Time Verification of Decentralized Diagnosability of Discrete Event Systems” versus “Decentralized Failure Diagnosis of Discrete Event Systems”: Complexity Clarification

An article on codiagnosability verification of discrete event systems was reported by Moreira et al, claiming an improvement in complexity over a paper by Qiu and Kumar. This note clarifies an oversight in the complexity analysis of Moreira et al's paper. Further the results of Moreira et al's paper were obtained in a more restricted setting of “projection masks”, in contrast to the more general “non-projection masks” allowed in Qiu and Kumar's paper, which was overlooked. Finally in the special case when the projection masks are used, the complexity of Qiu and Kumar's paper is lower compared to the non-projection masks case, and equals the corrected complexity of Moreira et al's paper.