Using synchronizing heuristics to construct homing sequences

Computing a shortest synchronizing sequence of an automaton is an NP-Hard problem. There are well-known heuristics to find short synchronizing sequences. Finding a shortest homing sequence is also an NP-Hard problem. Unlike existing heuristics to find synchronizing sequences, homing heuristics are not widely studied. In this paper, we discover a relation between synchronizing and homing sequences by creating an automaton called homing automaton. By applying synchronizing heuristics on this automaton we get short homing sequences. Furthermore, we adapt some of the synchronizing heuristics to construct homing sequences

Using Sat solvers for synchronization issues in partial deterministic automata

We approach the task of computing a carefully synchronizing word of minimum length for a given partial deterministic automaton, encoding the problem as an instance of SAT and invoking a SAT solver. Our experimental results demonstrate that this approach gives satisfactory results for automata with up to 100 states even if very modest computational resources are used.Comment: 15 pages, 3 figure

The upper bound for the length of the shortest homing sequences

Homing sequences are special input sequences that are used by various techniques of finite state machine based testing. Using a shorter homing sequence is typically preferred since it would yield a shorter test sequence. Finding a shortest homing sequence is known to be an NP–hard problem. The upper bound of shortest homing sequences is also a problem studied in the literature. A tight upper bound for the length of shortest homing sequence for a finite state machine with n states is known to be n(n−1)/2 . However, the known examples of finite state machines hitting to this upper bound also use n−1 input symbols, i.e. the size of the input alphabet also grows with the number of states. Is this upper bound reachable for a finite state machine with a constant number of inputs? In this work, we use an experimental analysis and we answer this question negatively. By exhaustively enumerating all finite state machines with two input symbols and two output symbols, we experimentally compute the upper bound for the length of the shortest homing sequence for finite state machines with 10 or less states. In order to make this computation feasible in practice, we apply several techniques to eliminate from our search those finite state machines which would not affect the result of the computatio

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

Polynomial Time Decidability of Weighted Synchronization under Partial Observability

We consider weighted automata with both positive and negative integer weights on edges and study the problem of synchronization using adaptive strategies that may only observe whether the current weight-level is negative or nonnegative. We show that the synchronization problem is decidable in polynomial time for deterministic weighted automata