On the Synchronizing Probability Function and the Triple Rendezvous Time for Synchronizing Automata

Cerny's conjecture is a longstanding open problem in automata theory. We study two different concepts, which allow to approach it from a new angle. The first one is the triple rendezvous time, i.e., the length of the shortest word mapping three states onto a single one. The second one is the synchronizing probability function of an automaton, a recently introduced tool which reinterprets the synchronizing phenomenon as a two-player game, and allows to obtain optimal strategies through a Linear Program. Our contribution is twofold. First, by coupling two different novel approaches based on the synchronizing probability function and properties of linear programming, we obtain a new upper bound on the triple rendezvous time. Second, by exhibiting a family of counterexamples, we disprove a conjecture on the growth of the synchronizing probability function. We then suggest natural follow-ups towards Cernys conjecture.Comment: A preliminary version of the results has been presented at the conference LATA 2015. The current ArXiv version includes the most recent improvement on the triple rendezvous time upper bound as well as formal proofs of all the result

A linear bound on the k-rendezvous time for primitive sets of NZ matrices

A set of nonnegative matrices is called primitive if there exists a product of these matrices that is entrywise positive. Motivated by recent results relating synchronizing automata and primitive sets, we study the length of the shortest product of a primitive set having a column or a row with k positive entries, called its k-rendezvous time (k-RT}), in the case of sets of matrices having no zero rows and no zero columns. We prove that the k-RT is at most linear w.r.t. the matrix size n for small k, while the problem is still open for synchronizing automata. We provide two upper bounds on the k-RT: the second is an improvement of the first one, although the latter can be written in closed form. We then report numerical results comparing our upper bounds on the k-RT with heuristic approximation methods.Comment: 27 pages, 10 figur

A Note on a Recent Attempt to Improve the Pin-Frankl Bound

We provide a counterexample to a lemma used in a recent tentative improvement of the the Pin-Frankl bound for synchronizing automata. This example naturally leads us to formulate an open question, whose answer could fix the line of proof, and improve the bound.Comment: Short note presenting a counterexample and the resulting open questio

Synchronizing Times for kk-sets in Automata

An automaton is synchronizing if there is a word that maps all states onto the same state. \v{C}ern\'{y}'s conjecture on the length of the shortest such word is probably the most famous open problem in automata theory. We consider the closely related question of determining the minimum length of a word that maps $k$ states onto a single state. For synchronizing automata, we improve the upper bound on the minimum length of a word that sends some triple to a a single state from $0.5n^2$ to $\approx 0.19n^2$. We further extend this to an improved bound on the length of such a word for 4 states and 5 states. In the case of non-synchronizing automata, we give an example to show that the minimum length of a word that sends $k$ states to a single state can be as large as $\Theta\left(n^{k-1}\right)$.Comment: 19 pages, 4 figure

Reachability of Consensus and Synchronizing Automata

We consider the problem of determining the existence of a sequence of matrices driving a discrete-time consensus system to consensus. We transform this problem into one of the existence of a product of the transition (stochastic) matrices that has a positive column. We then generalize some results from automata theory to sets of stochastic matrices. We obtain as a main result a polynomial-time algorithm to decide the existence of a sequence of matrices achieving consensus.Comment: Update after revie

On the synchronization of finite state automata

Abstract: We study some problems related to the synchronization of finite state automata and the Cˇerny’s conjecture. We focus on the synchronization of small sets of states, and more specifically on the synchronization of triples. We argue that it is the most simple synchronization scenario that exhibits the intricacies of the original Cˇerny’s scenario (all states synchronization). Thus, we argue that it is complex enough to be interesting, and tractable enough to be studied via algo- rithmic tools. We use those tools to establish a long list of facts related to those issues. We observe that planar automata seems to be representative of the synchroniz- ing behavior of deterministic finite state automata. Moreover, we present strong evidence suggesting the importance of planar automata in the study of Cˇerny’s conjecture. We also study synchronization games played on planar automata. We prove that recognizing the planar games that can be won by the synchronizer is a co-NP hard problem. We prove some additional results indicating that pla- nar games are as hard as nonplanar games. Those results amount to show that planar automata are representative of the intricacies of automata synchronization.Doctorad

On the interplay between Babai and Cerny's conjectures

Motivated by the Babai conjecture and the Cerny conjecture, we study the reset thresholds of automata with the transition monoid equal to the full monoid of transformations of the state set. For automata with $n$ states in this class, we prove that the reset thresholds are upper-bounded by $2n^2-6n+5$ and can attain the value $\tfrac{n(n-1)}{2}$. In addition, we study diameters of the pair digraphs of permutation automata and construct $n$-state permutation automata with diameter $\tfrac{n^2}{4} + o(n^2)$.Comment: 21 pages version with full proof

Some remarks on synchronization, games and planar automata

Abstract—We study synchronization games on planar automata. We prove that recognizing the planar games that can be won by the synchronizer is a co-NP hard problem. We prove some additional results indicating that planar games are as hard as nonplanar games. Those results amount to show that planar automata are representative of the intricacies of automata synchronization.Sociedad Argentina de Informática e Investigación Operativa (SADIO

Some remarks on synchronization, games and planar automata

Abstract—We study synchronization games on planar automata. We prove that recognizing the planar games that can be won by the synchronizer is a co-NP hard problem. We prove some additional results indicating that planar games are as hard as nonplanar games. Those results amount to show that planar automata are representative of the intricacies of automata synchronization.Sociedad Argentina de Informática e Investigación Operativa (SADIO