# Tag Info

Accepted

### Can we efficiently enumerate the words accepted by a DFA by order of increasing weight?

EDIT: Added Lemma 2 which covers all cases asked about. Lemma 1. Given a DFA with alphabet $\{0,1\}$ and an integer $n$, it is possible to enumerate all length-$n$ words in the language of the DFA, ...
Accepted

### Is DFA language inclusion decidable in quasi-linear time?

EDIT: the question has an answer by Michael Wehar. A better than quadratic running time contradicts the strong exponential time hypothesis. https://cstheory.stackexchange.com/a/29166/2367 ORIGINAL ...

### Error in Robson's proof about separating strings?

Thanks Tassle. I was about to give the same answer. J.M. Robson.
Accepted

### Number of minimal DFAs of size at most $m$?

According to Ishigami Y., Tani S. (1993) The VC-dimension of finite automata with $n$ states, http://link.springer.com/chapter/10.1007/3-540-57370-4_58 , the VC-dimension of the concept class of $n$-...

### Is there a well-defined division operation on finite automata?

Take a look at this MFCS 2013 paper, which studies compositionality in automata. Perhaps it will help.
Accepted

### Is it decidable whether the output length of a transducer is bounded by the input length?

The other contributor deleted his answer, maybe to let me extend my above comment, so here it is. Let $T$ be a possibly nondeterministic transducer, and $L$ be a regular language. Modify $T$ into a ...
Accepted

### Complexity of DFA intersection in this specific case?

The precise bound is $2^n$. The lower bound was given in the comments: the state complexity of $A^*a_1A^* \cap \dotsm \cap A^*a_nA^*$ is $2^n$. For the upper bound, it suffices to observe that if $B$ ...
Accepted

### Error in Robson's proof about separating strings?

Converting my comment to an answer: This is taken care of in the paragraph just before Theorem 1. If the accepting state is reached at some $v_j$, then we necessarily have $j>i$, and we can compose ...
Accepted

### Bounds on this Strategy for Separating Words

The second section of Robson's "Separating strings with small automata" proves $F(n) = O((n \log n)^{1/2})$. The string sequence $(10^n)^n$ gives a lower bound of $\Omega(n^{1/2})$. If the ...
Accepted

### Separating words with random DFAs

It appears, via code, that if you take a random string $x$ and then form $y$ by flipping only the first bit of $x$, then a random DFA on $n/5$ states fails to separate $x,y$ with high probability. So, ...

### NFA to 2DFA: what are the upper and lower bounds?

The recent survey Two-Way Finite Automata: Old and Recent Results by Pighizzini states in the introduction: The costs of the simulations of 1NFAs by 2DFAs and of 2NFAs by 2DFAs are still unknown. ...
Accepted

### NFA to DFA Powerset Construction : A Partial determinization algorithm with trade-off between running time and size for the resulting automata?

The paper [HP06] is in the spirit of your idea, although in a different direction, in the context of infinite words. It can be adapted more easily to finite words. In the powerset construction, we ...
Accepted

### Automata : Language Containment, Minimality & Graph Homomorphism

For inclusion, using your condition that non-final states can be mapped to final states does not work. Consider for instance that $A$ is a rejecting sink $p_0$, and $B$ is the minimal automaton for ...
Accepted

### Finite Automata with succinct representation of chains of states

This is a very partial answer, but I have some ideas: Clearly the union of NSAs can be taken without any blowup - just use the nondeterministic union of the initial states. As for determinization, ...

### 2DFA to 1DFA - Converting two way deterministic finite automata to one way deterministic finite automata

Kozen presents a constructive proof of the equivalence of 1dfa and 2dfa in a chapter of his book titled "Automata and Computability". If I recall correctly, it is a standard argument and the ...
Accepted

### Oncina-Garcia RPNI algorithm for learning DFAs

The algorithm is named RPNI, not RNPI. Given that the language generating the inputs is regular and that enough examples are given (the characteristic set), the algorithm returns the canonical (i.e., ...

### Random Cerny Conjecture

I think this problem has little to do with Cerny's conjecture. There the problem is to find a word that works for every pair of states. Here it is enough to show that the word will work whp. for any ...
Accepted

### 2DFA to 1DFA - Converting two way deterministic finite automata to one way deterministic finite automata

First, a warning: this will involve exponential $(2^{n \log n})$ blowup in the number of states (see here). However, if your application is fine with computing the states of the DFA "on the fly" then ...

### Is there a well-defined division operation on finite automata?

Lets give some obvious way to recover one "factor" of the product automaton. If $\mathcal A_i = (Q_i, \delta_i, q_{0i}, F_i), i = 1,2$ and $\mathcal A = \mathcal A_1 \times \mathcal A_2$ denotes the ...

### Number of minimal DFAs of size at most $m$?

(NB: the upper bound given in the accepted answer is better or equal to the one given here) An upper bound is proposed in this paper given in one of the previous comments: “On the number of distinct ...
Accepted

### FSM transducer sequential composition decidability

The problem seems undecidable: consider a transducer $F$ that parses and "executes" a single step of a Turing machine $M$ with the head $H$ on symbol $a$, in state $S$ and with tape content $x[a]by$ ...

### What is the enlightenment I'm supposed to attain after studying finite automata?

Actually, my students sometimes ask precisely this -- after spending a large chunk of the semester on finite automata and finally arriving at Turing machines. Why spend so much time on a weaker ...
Accepted

### How to check if a the language represented by a DFA is finite

The language accepted by a deterministic finite automata is infinite if and only if there exists some cycle on some path from which a final state is reachable. If you minimize your automaton, then ...
Accepted

### How to constrain a finite automaton (NFA and DFA) to a tree?

I think the easiest way of enforcing tree shape is the set of conditions $q_0$ is not in the image of $\delta$, $\delta$ is injective, and $M$ is connected (to avoid isolated cycles). Note that this ...

### Finite Automata with succinct representation of chains of states

A model that seems somewhat relevant is capacitated automata: http://www.cs.huji.ac.il/~ornak/publications/fsttcs14b.pdf
Accepted

### Is Bayes optimal RL of a finite set of DFAs feasible?

Even determining whether there is a policy which always succeeds is NP-complete, by a reduction from constructing optimal decision trees (Hyafil and Rivest, Constructing Optimal Binary Decision Trees ...

### Can we efficiently enumerate the words accepted by a DFA by order of increasing weight?

After discussing it further with a3nm, I propose an algorithm that is different than Neal's algorithm and works in a more general setting. The approach gives polynomial delay algorithm but it uses ...

### Separating words and graph isomorphism

I hadn't thought about the Separating Words problem before, but based on looking at the Robson paper referenced in the linked answer, I don't immediately see how techniques from GI would apply. At a ...
1 vote

### A conjecture related to the Cerny conjecture - counterexample/reference request

I found a partial answer to question 2. The same idea is discussed in the last 10 minutes of this lecture.
1 vote

### When designing a DFA, am I allowed to design two separate Machines and perform an Intersection on them?

Thanks to the hint given by @Micheal Wehar, I looked into Cartesian Product constructions and Intersections and I came across this answer: https://stackoverflow.com/questions/7780521/how-to-use-the-...

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