arXiv subjects
Publications and source records attributed to Mikhail N. Vyalyi.
We consider a problem of maximizing the product of the sizes of two uniform cross-$t$-intersecting families of sets. We show that the value of this maximum is at most polynomially larger (in the size of a ground set) than a quantity conjectured by Hirschorn in 2008. At the same time, we observe that it can be strictly bigger.
We consider a computational model which is known as set automata. The set automata are one-way finite automata with an additional storage---the set. There are two kinds of set automata---the deterministic and the nondeterministic ones. We denote them as DSA and NSA respectively. The model was introduced by M. Kutrib, A. Malcher, M. Wendlandt in 2014. It was shown that DSA-languages look similar to DCFL due to their closure properties and NSA-languages look similar to CFL due to their undecidability properties. In this paper we show that this similarity is natural: we prove that languages recognizable by NSA form a rational cone, so as CFL. The main topic of this paper is computational complexity: we prove that - languages recognizable by DSA belong to P and there are P-complete languages among them; - languages recognizable by NSA are in NP and there are NP-complete languages among them; - the word membership problem is P-complete for DSA without epsilon-loops and PSPACE-complete for general DSA; - the emptiness problem is in PSPACE for NSA and, moreover, it is PSPACE-complete for DSA.
We investigate regular realizability (RR) problems, which are the problems of verifying whether intersection of a regular language -- the input of the problem -- and fixed language called filter is non-empty. In this paper we focus on the case of context-free filters. Algorithmic complexity of the RR problem is a very coarse measure of context-free languages complexity. This characteristic is compatible with rational dominance. We present examples of P-complete RR problems as well as examples of RR problems in the class NL. Also we discuss RR problems with context-free filters that might have intermediate complexity. Possible candidates are the languages with polynomially bounded rational indices.
A regular realizability (RR) problem is testing nonemptiness of intersection of some fixed language (filter) with given regular language. We study here complexity of RR problems. It appears that for any language L there exists RR problem equivalent to L under disjunctive reductions on nondeterministic log space. It implies that for any level of polynomial hierarchy there exists complete RR problem under polynomial reductions.
A rational number can be naturally presented by an arithmetic computation (AC): a sequence of elementary arithmetic operations starting from a fixed constant, say 1. The asymptotic complexity issues of such a representation are studied e.g. in the framework of the algebraic complexity theory over arbitrary field. Here we study a related problem of the complexity of performing arithmetic operations and computing elementary predicates, e.g. ``='' or ``>'', on rational numbers given by AC. In the first place, we prove that AC can be efficiently simulated by the exact semidefinite programming (SDP). Secondly, we give a BPP-algorithm for the equality predicate. Thirdly, we put ``>''-predicate into the complexity class PSPACE. We conjecture that ``>''-predicate is hard to compute. This conjecture, if true, would clarify the complexity status of the exact SDP - a well known open problem in the field of mathematical programming.