Questions tagged [nondeterminism]

Questions about automata, formal grammars or other computation-models that specifically relate to the use of nondeterminism. Not to be confused with randomness or ambiguity!

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apply the method of conditional expectations

For a Randomized vertex cover problem Why there is not much hope of deriving an efficient, deterministic version using the method of conditional expectation? I can assume the problem is not ...
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Problem in NP: $EQ1 = \{(p_1,…,p_n): \exists x_1,…,x_m\in Z \ p_1(x_1,…,x_m)=…=p_n(x_1,…,x_m)=0. \}$

I have to following problem to show is in NP class. $EQ1 = \{(p_1,...,p_n): \exists x_1,...,x_m\in Z \ p_1(x_1,...,x_m)=...=p_n(x_1,...,x_m)=0. \}$ Here $p_1,...,p_n$ are polynomials in m ...
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Non-deterministic Turing machine for $L_1 = \{w\#0^n|w \text{ is a suffix of some $x$ in $L$ with } |x|=n\}$

Show if L is in NP, then also L1 is in NP $$L_1 = \{w\#0^n|w \text{ is a suffix of some $x$ in $L$ with } |x|=n\}$$ I know that if L is in NP, then there exists a NTM $M_L$ than accepts $x$, ...
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What is $f(n)$ in $NTIME(n)\subseteq DTIME(f(n))$ if $CIRCUITSAT$ is in $P$?

If $CIRCUITSAT$ in $n$ variables and $m$ gates has an $O((nm)^c)$ algorithm for a fixed $c>0$ then $NTIME(n)\subseteq DTIME(O(f(n)))$ for large enough $f(n)$. What is the smallest $f(n)$ in $NTIME(...
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Proving a problem is NP [duplicate]

I've seen in many textbooks if say we have a problem $Q$, we write a non-deterministic algorithm in polynomial time to solve problem $Q$, and then from that point it results that $Q\in NP$. Why is ...
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How to prove Shortest Common Superstring is NP-Hard

After some research and many youtube videos I have learnt that to prove a problem is NP-Hard; you would need to reduce that problem to known NP-Hard problems such as Subset Sum Problem, Halting ...
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Push Down Automatas: Is it still an accept state if stack is not empty?

I'm currently seeing if a PDA is in an accept state give an input string. After reading the entire input tape, I am currently in the accept state. However, in the stack, there are two items in it. So ...
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If A and B are NP-complete, then A ∪ B need not be NP-complete

I am studying the proof of this exercise (link) There exist N P-complete languages A and B such that A ∪ B is not N P-complete. Example: $A = \{1x : x ∈ SAT\} ∪ \{0x : x ∈ \{0, 1\}^∗\};$ $B =...
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Converting non-deterministic algorithm to deterministic

I was thinking about an non-deterministic algorithm to generate all the subsets of the $\{1..n\}$ set. ...
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How to prove Exact cover problem is NP Complete using Vertex Cover problem?

Using reduction theorem in NP, we want to prove that Exact cover is NPC by reducing it from Vertex Cover Problem. It is easy to derive it from SAT, but we can't find a solution yet to derive it from ...
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How to determine if a language is deterministic context-free language?

I have the following question to solve : DCFL means Deterministic Context-Free Language. Let $L$ be a DCFL over an alphabet $\Sigma$. For each of the following functions of $L$, determine whether $...
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motivation and idea of defining non-deterministic Turing machine

This is a very basic question but I spent some time reading and find no answer. I am not computer science majored but have read some basic algorithm stuff, for example, some basic sorting algorithms ...
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NFA for all strings not containing 1010

if I want to design a NFA (that's NOT A DFA) that accepts the set of all strings that do not contain the substring 1010, is this correct? because I can just accept 1010 by capturing it in the starting ...
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Minimal regular expression from minimal NFA for finite language in polynomial time?

Given a minimal NFA for a finite language, is there a polynomial-time algorithm to find a minimal regular expression for the same language? This question is based on a recent question regarding ...
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Why is it not possible to prove the equivalence of nondeterministic and deterministic Turing Machines the same way as for NFAs and DFAs?

I found en excercise asking this question. I know that for proving the equivalence of NFAs and DFAs we can use the conversion through subsets, and that for proving the equivalence of nondeterministic ...
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Like transitive reduction, but removing vertices rather than edges?

Suppose I have a directed graph $G = (V, E)$ (or, which is the same, a relation on the set $V$ as defined by the adjacency matrix) that may contain three vertices $x, y, z$, such that $xy, xz, yz \in ...
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How to make Turing machine deterministic?

My Turing machine starts with an empty tape. It writes a random word of the set $0^n1^n$ to the tape. Hopefully i made no mistakes. My question is about the productions coming out of state $q_0$: $δ(...
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What publication first introduced the concept of a non-deterministic Turing machine?

What publication first introduced the concept of a non-deterministic Turing machine? Turing did not define the concept in his 1936 paper.
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TQBF PSPACE-COMPLETE : Why this algorithm is exponential but Savitch's not?

So this is a question pertaining to the proof for $PSPACE-COMPLETE$ (for TQBF for example). The idea is to first prove the $L$ $is$ $PSPACE$(easy part) and next is to prove $PSPACE-COMPLETE$. The ...
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Why does NTM need to derive certificate to prove “If a language is in in NP iff it is decidable by some nondeterministic polynomial time TM”?

(Sipser's Chapter 7: Time COmplexity, Pgs 294-295) If we have to prove the forward direction, then we must have the certificate along with the verifier. I don't get why we are "guessing the ...
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Why is the run time of an $f(n)$ space decider bounded by $2^{O(f(n))}$?

In the proof of Savitch's theorem from the 3rd edition of Sipser's Intro to Theory of Computation, Sipser claims that the maximum time that an $ f(n) $ space nondeterministic Turing machine that halts ...
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Given an non-deterministic finite automaton, will its determinization always have unreachable states?

Given an NFA that accepts the regular language L, will its equivalent DFA which accepts the same language L always have unreachable states. If it does, why?
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How to adapt proof of the ND time hierarchy theorem for alternate definition of NDTM?

For reference, the version of the nondeterministic time hierarchy theorem in question is this one: The relevant portion of the proof in question (also from Arora-Barak) is here: Arora-Barak define a ...
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NL problem? $CONN$= {$〈G,k〉$ ∶$G$ is undirected graph with at least k connected components}

Consider the following decision problems: $CONN$= {$〈G,k〉$ ∶ $G$ is undirected graph with at least $k$ connected components} $E-CONN$= {$〈G,k〉$ ∶ $G$ is undirected graph with exactly $k$ connected ...
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Is the halting problem solvable for NPDAs?

After the total silence in response to my last question, I am rethinking my assumptions. DPDAs are, of course, solvable, and I believe that their loops can be found in the manner I described in my ...
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Non-deterministic Finite Automata | Sipser Example 1.16

I am working through the Sipser Book (2nd edition) and came across this example, which I do not understand. In the book it states that this NFA accepts the empty string, $\epsilon$. Could someone run ...
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Detecting loops in NPDAs

I'm aware that the halting problem is solvable for PDAs, but I have recently discovered that I am wrong about how to actually do it. I used to think that you could detect an infinite loop by meeting ...
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In what sense are dataflow architectures non-deterministic?

The Wikipedia article mentions non-determinism in the context of dataflow architectures. Arthur Veen's paper mentions non-determinism when it elaborates on MERGE nodes as conditional constructs. Are ...
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Why “Choice Points” introduce non-determinism in a program?

I'm studying the didactic programming language Oz, following the book "Concepts, Techniques, and Models of Computer Programming". In the book, the nondeterminism is introduced through the concept of ...
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What's the purpose of the non-deterministic Turing machine?

(*) Acronyms NTDM := non-deterministic Turing machine. TM := deterministic Turing machine. (*) Consider the following idea The NTDM is able to follow, in parallel, all paths of the tree of the ...
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Describe in words how a NTM can simulate a DTM

I have this assignment Describe in words how a DTM can simulate a NTM Describe in wordshow a NTM can simulate a DTM I'm working on this request and I'm crushing with the comparison. 1-I ...
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Characterization of NFA whose equivalent (minimal) DFA has exponential number of states

(I don't know if there are standard names for this, so) Let's say that a Nondeterministic Finite Automaton (NFA) is $n$-expansive if it has $n$ states and any Deterministic Finite Automaton (DFA) ...
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Proving the Complement of a DCFL is DCFL [duplicate]

If I Have a DCFL $L$ ( a CFL which can be recognised by a DPDA ), How do I prove that $\overline{L}$ is also a DCFL I checked my textbook for a proof but I wasn't able to understand the language. Can ...
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If NP is a subset of DTIME[n^O(log n)] then what happens?

If $\mathsf{NP}\subseteq \mathsf{DTIME}[n^{O(\log n)}]$ then what happens? Does it imply $\mathsf{NP}\neq \mathsf{EXP}$? Is there any other consequences such as $\mathsf{BPP}\neq \mathsf{EXP}$? Does ...
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Why cannot we enumerate all Turing machines that have no fixed point?

The language $$ L_1 = \{w \in \{0, 1\}^\ast \mid \exists x \in \{0, 1\}^\ast\colon M_w(x) = x\} $$ ($w$ is an encoding of a DTM, $M_w$ is the respective DTM.) is not decidable, according to Rice's ...
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Automata that is Turing complete if you add a nondeterminism

Pushdown automata have an interesting property: non-deterministic ones belong to a different computational class than deterministic ones. This is in contrast to finite state and turing machines, for ...
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How do I construct a NTM that accepts the language consisting of the coding of turing machines that halt on one input?

I currently have a problem with the following question: Let $L = \{ \langle M \rangle \mid \exists w: \text{$M$ halts for $w$ in at most $|w|^3$ steps} \}$. Construct an NTM (non-deterministic Turing ...
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The definition of weakest precondition for a non-deterministic language

In the classical IMP language, the definition of weakest precondition is: definition "wp c Q s ≡ ∃t. (c,s) ⇒ t ∧ Q t" This is stating that from state s, after ...
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The Law of Excluded Miracle in the language of guarded commands

The definition of weakest precondition is familiar (let me use Isabelle's syntax here): definition "wp c Q s ≡ ∃t. (c,s) ⇒ t ∧ Q t" the weakest precondition ...
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What to do with empty set during NFA to DFA conversion?

I am currently converting this NFA to a DFA I have come up with the following DFA: ...
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Understanding Hamiltonian Path, NP vs Co-NP

I am having difficulty understanding the distinction between NP and Co-NP. According to my textbook (Sipser), the HAMPATH problem is in NP. That is, for the language: HAMPATH = { (G,s,t) | G is a ...
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PDA of the language where the number of a's are NOT equal to the number of b's

I have this NPDA for language L = {w: num_a(w) == num_b(w)} all loops in q1 ...
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Given a NP Algorithm for SAT, do we expect to have Correct and Incorrect Solutions?

I am reading about Boolean Satisfiability Problem and Nondeterministic Algorithms, in the latter defination it says : In computational complexity theory, nondeterministic algorithms are ones that, ...
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What is the difference between the choice operator and nondeterminism in CSP?

I'm learning CSP now for my research. First time doing formal work in CS. I'm having a hard time understanding the difference between choice $\square$ operator and the nondeterminism $\sqcap$ operator....
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Why SAT Requires A Non-determinstic Algorithm?

I am getting started to understand the probelm of Satisfiability and i am reading (Computers and Intractability: A Guide to the Theory of NP-Completeness). I do understand the difference between a ...
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How to implement a maximal munch lexical analyzer by simulating NFA or running DFA?

I'm planning to implement a lexical analyzer by either simulating NFA or running DFA using the input text. The trouble is, the input may arrive in small chunks and the memory may not be enough to hold ...
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Understanding $\epsilon$ transitions on NFA

I can't understand why $\epsilon$ is accepted. I thought if $\epsilon$ is inputed then it would go from $q_1$ to $q_3$. $a$ is also accepted, but I though if $a$ is inputed then then the NFA would die,...
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How do non-deterministic algorithms work on current machines?

I have some questions regarding the exact nature of non-deterministic algorithms. Is it right that non-deterministic algorithms do not rely on any randomness whatsoever? In which case, this Wikipedia ...
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In certificate view of NL can we force the guesses to be in some format like $a^n b^n c^n d^n$?

In certificate view of NL the size of our guess can be polynomial.Can this guesses be like $a^n b^n c^n d^n$. Can we force the guesses to be in some format? I think it(the format) can be in regex ...
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Drawing a NFA for a string

I have these grammar rules defined as follows, FDL -> FDEF FDL | ε FDEF -> #feature #: FEXP FEXP -> #op #( FLIST #) FLIST -> FEXP #, FEXP | #feature ...