The complexity of quantified constraints using the algebraic formulation

Carvalho, Catarina; Martin, Barnaby; Zhuk, Dmitry; Larsen, Kim G.; Bodlaender, Hans L.; Raskin, Jean-Francois

Abstract

Let A be an idempotent algebra on a finite domain. We combine results of Chen, Zhuk and Carvalho et al. to argue that if A satisfies the polynomially generated powers property (PGP), then QCSP(Inv(A)) is in NP. We then use the result of Zhuk to prove a converse, that if Inv(A) satisfies the exponentially generated powers property (EGP), then QCSP(Inv(A)) is co-NP-hard. Since Zhuk proved that only PGP and EGP are possible, we derive a full dichotomy for the QCSP, justifying the moral correctness of what we term the Chen Conjecture. We examine in closer detail the situation for domains of size three. Over any finite domain, the only type of PGP that can occur is switchability. Switchability was introduced by Chen as a generalisation of the already-known Collapsibility. For three-element domain algebras A that are Switchable, we prove that for every finite subset Delta of Inv(A), Pol(Delta) is Collapsible. The significance of this is that, for QCSP on finite structures (over three-element domain), all QCSP tractability explained by Switchability is already explained by Collapsibility. Finally, we present a three-element domain complexity classification vignette, using known as well as derived results.

Citation

Carvalho, C., Martin, B., Zhuk, D., Larsen, K. G., Bodlaender, H. L., & Raskin, J. (2017). The complexity of quantified constraints using the algebraic formulation. In 42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017) : August 21-25, 2017, Aalborg (Denmark) ; proceedings. https://doi.org/10.4230/lipics.mfcs.2017.27

• Presentation Conference Type: Conference Paper (Published)
• Conference Name: Mathematical Foundation of Computer Science
• Acceptance Date: Sep 8, 2017
• Online Publication Date: Aug 25, 2017
• Publication Date: Dec 1, 2017
• Deposit Date: Sep 8, 2017
• Publicly Available Date: Sep 14, 2017
• Series Title: Leibniz International Proceedings in Informatics (LIPIcs)
• Series Number: 83
• Series ISSN: 1868-8969
• Book Title: 42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017) : August 21-25, 2017, Aalborg (Denmark) ; proceedings.
• DOI: https://doi.org/10.4230/lipics.mfcs.2017.27
• Public URL: https://durham-repository.worktribe.com/output/1145651
• Additional Information: Conference dates: August 21–25, 2017