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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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Regular expression 0*1*1+11*0*1 DFA

Will the expression "0*1*1+11*0*1" be accepted by the following automaton? As the expression generates strings ending with '1', I believe the automaton will accept it. However, I found the answer to be otherwise in one of the references. Can…
neotricks
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Reducing a DFA using the Pair Table method

I'm learning about reducing DFA's using the Pair Table Method (Systematic Reduction Method).Here is the DFA we are looking to reduce. The first step is to lay out the DFA in a table: 0 1 q0 …
Talen Kylon
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Why we can't reliably test for palindromes on one pass

I came across the concept of "palindrome". I try to understand by reading through wikipedia http://en.wikipedia.org/wiki/Palindrome#Computation_theory The paragraph caughts my attention This means that it is impossible for a computer with a finite…
Cheok Yan Cheng
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Superscript plus sign meaning

I have a quick question. What does the superscript plus sign mean here? = {w ∈ {0,1} : w ∈ (0^+)(1^+)} Been awhile since I've done these. This is for making a non-deterministic finite automata
Raslion
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Designing a Turing Machine's state table

Are they any helpful guidelines to describing what a Turing machine does if you already have the pseudo code for the algorithm? I'm taking a course on complexity theory and it takes me a while to describe a Turing machine that decides or accepts…
Firas Assaad
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Finiteness of Regular Language

We all know that (a + b)* is a regular language for containing only symbols a and b. But (a + b)* is a string of infinite length and it is regular as we can build a finite automata, so it should be finite. Can anyone please explain this?
Madhudeep Petwal
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Good resources to learn about models of computation?

Out of curiosity, I am trying to identify what model of computation a system I work with is functionally equivalent to, and prove the equivalence. The longer I spend on this problem the more I suspect the system isn't Turing-equivalent. My…
Chris
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How can I do automata/state machine coding in C++?

I have used it in another programming language and It's very usefull. I cannot find anything about this for C++. Let's for example take the following code: void change(); enum { end = 0, gmx } int gExitType; int main() { gExitType…
Gizmo
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From Parse Tree to NFA

I am looking for converting regular expression to NFA. I understand that we need to convert the regular expression to parse tree and then convert it to NFA. I am using java script. Are there any js tools for generating parse tree directly from the…
user567879
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Recognize A^n B^n language in Prolog with no arithmetics

How to recognize A^n B^n language in Prolog without arithmetics and for any A, B where A != B? With known A = a and B = b we could write % For each 'a' save 'b' in a list, then check % whether constructed list is equal to the rest of input…
Legat
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Why are there non-decidable languages? Can anyone explain me my book's solution?

In my book it is says that "there are non-decidable languages" And the proof is: Every algorithm is a word. Then there are only countable algorithms. But there are uncountable languages and therefore more than algorithms. Why is it said that…
Alfreda Zuñiga
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DFA to regular expression time complexity

I am looking at the time complexity analysis of converting DFAs to regular expressions in the "Introduction to the Automata Theory, Languages and Computation", 2nd edition, page 151, by Ullman et al. This method is sometimes referred to as the…
zpavlinovic
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Formal approach for text processing

During a coding interview I was asked the next question: Write a program which counts the number of words and lines in the input stream. Assume you have a reader with method nextChar(). At the first glance it looks simple. But then you…
Roman
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Can someone help me with this proof using the pumping lemma?

I just started reading about the pumping lemma and know how to perform a few proofs, mostly by contradiction. It is only this particular question which I don't seem to find an answer for. I have no idea on how to begin. I can assume that there has…
n00b1990
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"Untranslatable" Grammars to Regular Expression

Are there such things? Like for example, S -> aSb | ^ (possible words: ^, ab, aabb, aaabbb, aaaabbbb, ...) From what I've learned, the only regex that closely match the said grammar is: a*b* But the regex can produce words such as aab, abb, ...…
user1846682
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