Questions tagged [computation-models]

The definition of the set of allowable operations used for computation and their respective costs. Some examples of models include Turing machines, recursive functions, lambda calculus, and production systems.

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Turing Completeness of System Which Randomly Fails to Complete Calculations

If one were to create a variant of a turing complete language which upon completing a calculation randomly changes the answer by one, would it be Turing complete? For example, say I had a Python ...
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ORAM: Is it generic?

Recently, plenty of researchers are looking at designing efficient data-oblivious algorithms. Roughly speaking, an algorithm is said to be data-oblivious if its data access patterns are independent of ...
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CFG Equivalent of regular expressions

So I was wondering something about the Chomsky hierarchy. DFAs (and NFAs) accept regular languages, while NPDAs accept context-free languages. Right-regular or left-regular grammars produce regular ...
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Context-free and context-sensitive grammars in FSM with counters

Consider an extension of finite-state machines that utilizes a finite set $C$ of counters. Let's call them counter automata. Before execution, each counter $c\in C$ is set to zero. Every transition, ...
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Turing machine states, lost in the jungle

There is a lengthy discussion going on at the English Language & Usage StackExchange site suggesting various synonyms for dead code, and it got me wondering about an angle that wasn't covered -- ...
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How do nondeterministic Turing machines compute general function problems?

(Hope this hasn't been asked before, but I didn't find anything.) In my understanding, nondeterminism applies to decision problems only, due to the requirement of the existence of an accepting path. ...
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runtime of problems vs algorithms

I know that a solving a specific problem can have different runtimes on different models of computation. But can a specific algorithm have different runtimes on different models of computation? Also, ...
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Is there a broader class of total functions than $PR$? [duplicate]

In total functional programming programs are restricted to total computable functions. A well-known class of total functions are the primitive recursive functions ($PR$). However the Ackermann ...
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Primitive Recursion equipped with an evaluator function

The wikipedia article for primitive recursion mentions a limitation that primitive recursive function can't compute the function $ ev(i,j) $ which computes the $ i $th primitive recursive function on ...
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Theoretical justification of "halting problem avoidance"

The wikipedia page for the Halting problem mentioned practical solutions to avoiding the halting problem such as avoiding infinite loops. And there is a mention that "by restricting the capabilities ...
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Turing Machine with additional finite memory of size $n$

The question itself: Let us define a generalization of Turing Machines to include a finite memory of >size $n$. We denote such a Turing Machine formally as: $M_{mem} = (Q, Σ, γ, δ_{mem}, n, q_0, ...
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Generate a graph to exact size using Kronecker product graph model

In network science, we can take sample a complex system and derive from this sampling a representative network (or graph) that describes the system to some extent. A model of a network, is a powerful ...
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Are QR codes Turing-complete under the rules of Conway's Game of Life?

This is a bit of a weird question, but I was wondering earlier if QR codes are Turing-complete when interpreted as initial states for Conway's Game of Life. My intuition is "yes", as there are ...
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Is there any count-preserving cellular automata which tends do "10101010..."?

Suppose that I have a bit string of finite length. Is there any bit rewriting rule rewrire :: (Bit,Bit,Bit) -> (Bit,Bit,Bit), that doesn't change the total count ...
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Construct DFA given oracle access to the language

I was given the following question. Given a minimal DFA $A$ with $m$ states over some alphabet $\Sigma$ which is a "black box" (you can only run words to it and it tells you if it accepts ...
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How can a Turing machine accept infinite number of inputs? [closed]

How it is possible for a turing machine to process an infinitely long input ?
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Pi Calculus: Restriction necessary for molecular (atomic) action?

In "A Calculus of Mobile Processes, Part 1" [1], Milner et al. give an example for transmitting a pair of values $(u,v)$ from the process $P$ to either $R$ or $Q$ (see page 13). All three processes ...
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A linear code, what is that?

I have been trying to understand the polytope model used for loop nest optimizations. Now while going through some of the thesis written on this, i came across the term/phrase "linear code" a number ...
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What theorem are these? (from Scott Aaronson's blog)

Browsing Scott Anderson's blog, I found this list of theorem. Among them are: If every second or so your computer’s memory were wiped completely clean, except for the input data; the clock; a static, ...
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Why does using an encoding trick like Gödel numbers make a register machine universal?

Here the author describes the Random Access Stored Program machine and the problem of indirect addressing. The author states: But this does not solve the problem (unless one resorts to Gödel numbers)....
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Can one consider living (biological) cell to be Turing Complete?

Universal Turing Machine can be boiled down to two components. Infinite tape of input and an action table, a finite state machine that moves read/write head along the tape and writes to it depending ...
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Why classification represents all computations?

I'm a computer science student taking a theory of computation class. Recently we were taught about what is computable and what is not and about the Turing machine. As I understood (please correct me ...
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Prove that the Kolmogorov complexity function cannot be approached from below

How would one go about proving that Kolmogorov function $K(x)$ cannot be approached from below by any computable function? After some research it seems I must show the function $K(x)$ is not lower ...
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Maximal class for which function equivalence is decidable

I previously asked if it's decidable whether two primitive recursive functions are equivalent: "primitive recursive functional equivalence". The answer was no. Here is my followup. What is the most ...
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Relation of deterministic push down automata and lower elementary recursion

Deterministic context free languages are the context free languages that can be accepted by a deterministic push down automata. Deterministic context free languages can be recognized by a ...
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Is there anything that MUST be done on a multi-core CPU?

When considering how multi-thread-friendly our program must be, my team puzzled about whether there's anything that absolutely cannot be done on a single-core CPU. I posited that graphics processing ...
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About the SOS degree of a function and optimization algorithms for the function

Given a non-negative function on the hypercube $f : \{0,1\}^n \rightarrow \mathbb{R}_{\geq 0}$ one says that it is of "SOS-degree" of $d$ (denoted as $deg_{SOS}(f) =d$) if $d$ is the minimum ...
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Turing machine that can tell if it ends in standard position?

Suppose we have a TM $M$ with alphabet $\{0, 1 \}$ with n states. Say $M$ halts in standard position if it is scanning the left-most $1$ of a non-broken string of $1$s (and everything else on the tape ...
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Why is universal turing machine considered with only one head?

While defining the following time hierarchy theorem (for deterministic case ) : If $f(n)\log{f(n)}=o(g(n))$ then there are languages decidable in $O(g(n))$ which cannot be decided in $O(f(n))$ The ...
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How to convert a Turing Machine program to a tiling using Wang Tiles?

This is a cross-post from a post on MathSE due to lack of answers. To illustrate my question I provide the following example. The website Online Turing Machine provides a Turing Machine simulator. ...
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Is a LBA with stack more powerful than a LBA without?

Even so a linear bounded automata (LBA) is strictly more powerful than a pushdown automata (PDA), adding a stack to a LBA might make it more powerful. A LBA with stack should not be Turing complete, ...
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Smallest class of automata model whose corresponding language class contains CFL and is closed against (dis)allowing nondeterminism in the model

From a comment, an interesting question popped up. The class of CFLs (the languages recognized by PDAs) are obviously not closed under nondeterminism - what I mean by this is that deterministic PDAs ...
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Is integer sorting possible in O(n) in the transdichotomous model?

To my knowledge there doesn't exist a $O(n)$ worst-case algorithm that solves the following problem: Given a sequence of length $n$ consisting of finite integers, find the permutation where every ...
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Turing machine - infinite tape - does that thing exist?

Can we use a Turing machine with infinite tape as a basis to prove anything disregarding the fact that such a thing can never exist? Do we have the right to regard a machine (a construct) in the same ...
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Quantum lambda calculus

Classically, there are 3 popular ways to think about computation: Turing machine, circuits, and lambda-calculus (I use this as a catch all for most functional views). All 3 have been fruitful ways to ...
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Simplest Turing-complete ruleset for Markov algorithm

Is there an example of a particular ruleset for a Markov algorithm that is Turing-complete? If so, what is the simplest example of such a ruleset?
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What can be said about the Halting Problem if we can include the halting status to the input?

I was reading about Turing Machines and the Halting Problem, i understand that you need an oracle to decide whether given input will halt or loop forever. But why do we need an oracle if we can ...
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Computational power of Actor Model

In the question below, let TM be Turing machine, NTM be nondeterministic Turing machine and PTM be probabilistic Turing machine. In his paper "Actor Model of Computation: Scalable Robust Information ...
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Can computation models be categorized in terms of efficiency?

It is widely accepted that turing-complete systems are equivalent in terms of computability - i.e., whatever a turing-machine can do, can be emulated by automatas, the lambda calculus and other ...
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Can a Turing Machine have infinite accept states?

I'm still fairly new to Turing Machines, but I've been doing some research. I know that a Turing Machine can have an infinite tape and that it requires a finite number of states, but does it ...
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What does it mean to be "independent of machine model"?

I have often heard people mention off-hand that the class $\mathsf{P}$ is "machine-independent", or "independent of machine model", or "invariant under change of machine model" - something to do with ...
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Expressing classic automata in modern terms

This semester I was introduced to finite automata (FSM), then pushdown automata (PDA), and now the Turing machine (TM). Granted that there're many possible implementations of these abstractions (...
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Can a Turing machine have infinite states?

Does it make sense for a Turing machine to have infinite number of states ? I had previously asked a question Can Turing machines have infinite length input. From which I came to know about Type-2 ...
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A model of computation vs an abstract machine

Wikipedia says A model of computation is a formal description of a particular type of computational process. The description often takes the form of an abstract machine that is meant to perform ...
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Programming language where every expression makes sense

Per recommendation I am reposting this from Stack Overflow. Recently I have been thinking about following issue. Consider the code for a standard "Hello world!" program: ...
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Is modulus capable of universal computation?

I heard once that you could translate any digital circuit into a modulus operation, perhaps modulusing against different numbers? It was a long while ago though and don't remember where I heard it. ...
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Is infinitely fast computer fundamentally impossible even theoretically?

This may get slightly philosophical, but consider the following program: ...
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Classical Computation without NOT

Is it possible to do universal classical computation using bits and 2-bit gates when you cannot perform a NOT operation on a single bit (hence cant do CNOT and so on). If yes, what are the possible ...
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Are Cellular Automata always computers?

I was reading on Complex Systems journal and found a paper where the author states that a cellular automaton can be viewed as a computer. In the introduction part: Cellular automata can be viewed as ...
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In principle, what is the relation between Artifical Intelligence and Turing machine?

I am working on my cs project about AI & Turing machines, so i know that Artifical Intelligence is meant to implement different algorithms into the machine {the computer} to solve a problem or a ...

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