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Questions tagged [automata]

In theoretical computer science, automata theory is the study of abstract 'mathematical' machines or systems and the computational problems that can be solved using these machines. These abstract machines are called automata. ("Automata", Wikipedia)

From Wikipedia,

Automata, or automata theory, is the study of mathematical objects called abstract machines or automata and the computational problems that can be solved using them. Automata comes from the Greek word αὐτόματα meaning "self-acting".

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Can I Determine the Set of First Chars Matched by Regex Pattern?

I would like to be able to compute the set of all characters which may be matched as the first character in a string by a given instance of java.util.regex.Pattern. More formally, given the DFA equivalent to a certain regular expression, I want the…
Daniel Spiewak
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Design DFA accepting decimal strings divisible by 7

I'm a student studying DFAs looking for a DFA that could find if a decimal number is divisible by 7. today I've solved divisibility problem for numbers 2,3,4,5,6,8,9 but I can't solve this problem for number 7. I've searched the web but I couldn't…
Peyman
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Difference between Transducer and NFA

Can someone tell me how a Transducer differs from a NFA?
samsamara
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Construct DFA for L = {(na(w)-nb(w)) mod 3>0}

As per the title: L = {(na(w)-nb(w)) mod 3>0} Alphabet = {a,b} I found two answers to this problem: In this solution, our language is accepted. However, w = b is accepted as well. In the next solution: Our problem of w = b is solved here but w…
Shubham
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How many languages does a DFA recognize?

According to Sipser's "Introduction to the Theory of Computation": If A is the set of all strings that machine M accepts, we say that A is the language of machine M and write L(M) = A. We say that M recognizes A ... A machine may accept several…
Paolo Mazza
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NFA recognizer in LISP

I have to define a function in lisp that, given a regular expression and an e-NFA as input, it returns true if the expression is accepted by the automata. For start, I've defined a function that generates an e-NFA (as a cons-cell) from a regular…
Fred_2
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How can I tell that a language is context-free from first sight?

My professor expects us to quickly tell if a given language is regular, context-free but not regular, or not context-free (in other words, without drawing a PDA, writing a context-free grammar, and using the pumping lemma for context-free…
John
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Syntax for Describing DFA or NFA

Do there exists any Standard Syntax for Describing the Transition Table for an NFA or DFA ?
Neel Basu
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OCaml: Combination of elements in Lists, functional reasoning

I am back to coding in OCaml and I missed it so much. I missed it so much I completely lost my reasoning in this language and I hit a wall today. What I want to do is the combination of elements between a set of n lists. I decomposed the problem by…
João Bastos
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Does a language compiler use a complex DFA to accept programs?

I am reading up on Theory of Computation. And I have no practical experience of programming compiler. So it occurred to me, does a C or Java compiler use a huge DFA to Validate a program (String in TOC parlance)? Are compilers practical…
Spandan
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Regular Expression to DFA

Can someone tell me if the attached DFA is correct ? I am suppose to give DFA for the language that has alphabet Σ ={a, b} I need DFA for this ----> A={ε, b, ab}
Jon Abraham
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Producing an automaton image of my Promela model

I'm using the SPIN model checker GUI - iSPIN. The GUI comes with a nice Automaton view generator, however in order to see the full automaton I need to zoom in/out. Also I would like to save that automaton in a nice image (avoid using print screen)…
Anton Belev
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concatenation & union - regular and context free languages

Given L1 context free non regular language. Given L2 regular language. Is it possible that L1 U L2 = regular language ? Also, is it possible that L1*L2 = regular language ? I think that the 2nd one is impossible. But I'm not sure. Would love to see…
Rouki
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Deciding if a given Language is Regular/Context-Free/Non Context-Free

I need some help with deciding if a given language is regular, context-free or not context-free. A brief, informal explanation is sufficient in the answer, hence no need to use pumping lemma. Lets say I have the following lanugages: L1 = { w ∈ {a,…
mrjasmin
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check if a string has four consecutive letters in ascending or descending order

Good day stack overflow. I'm a noob in using regex and here is my problem - I need to check a password if it contains 4 consecutive characters. so far what I have just covered is regarding the digits. Here is my regex: ascending digits -…
Oneb
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