Questions tagged [computability]
83 questions
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Disjunctive Normal Form and satisfiable is in P (DNFSAT)
I am reading that a language that is in Disjunctive Normal Form and is satisfiable is a language in P, but there is no explanation, could anyone tell me why?
ili
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proving that a language is part of a grammar and vice versa
so here a grammar R and a Langauge L, I want to prove that from R comes out L.
R={S→abS|ε} , L={(ab)n|n≥0}
so I thought I would prove that L(G) ⊆ L and L(G) ⊇ L are right.
for L (G) ⊆ L: I show by induction on the number i of derivative steps…
rem208
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How do you prove whether a simple unmeaningful code is computable or not?
The characteristics of a computable problem are:
Complete means that it covers all the cases;
Mechanistic means that it is precise;
Deterministic means that the same output will be provided if the same input is entered.
Correct me if I'm wrong, I…
Lorale
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REGEX L(r) = {a^n b^m : n + m is even}, r =?
So I did a problem earlier that said:
L(r) = {w in {a,b}* : w contains at least 2 a's}
For that one I said {a^2n , b} because that guarantees a string like aab or aabaab etc. Not sure how to approach the one I posted about in the title. Possibly a…
solnay
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What does it mean to pass the machine and it's description as the input in the halting problem?
In the proof of the halting problem, why do we have to pass the machine and its description as an input?
For example, I could have passed the description of the machine and some other input(not the machine itself) and still the proof by…
sayantan dasgupta
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Why is it assumpted that the time-complexity of multiplication by n is constant?
Regardless of how the multiplication(or division) operation is implemented(i.e. whether it is a software function or a hardware instruction), it won't be solvable in time O(1). for big n values, the processor cannot even compute it by one…
Mehran Ghofrani
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Going from a language to a context free grammar
Given the language K = {e^h f^i | 2h > i > h} I need to generate a context free grammar
Some production rules I came up with are: S -> eeTfff and T -> eTff | ϵ
They only work when n = m + 1, but I don't know how to generate any rules for every…
sunnybool
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How to construct this turing machine?
How can we construct TMs such that it accepts(Give description only):
a + b = c
a . b = c
Input is of the form a#b#c.
a,b and c belongs to {0,1}* and are positive binary unsigned integers.
I know that we can construct TMs if the input has unary…
chelsea
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Computability of a probability theory problem
This is a problem I solved for a course and I was wondering if my solution is correct. I wouldn't normally post a pure mathematics problem, except that I believe that is is incomputable, and hence a computer science problem.
You are given:
P(S) =…
Panayiotis Karabassis
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Reducibility Etm undecideable
I want to ask about reduction.
In the proof that Etm is undecideable in the definition of M1 is
1.if x!=w,reject
2.if x==w,run M on input w and accept if M does
In many proofs that I meet I see that bold line but i can not understand how can I do…
A.Shoob
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Prove that a specific language is not semidecidable
I have to prove that the language L = {< M >: |L(M)| <= 2016} is NOT semi-decidable. Now I thought of doing it like this:
Take a random alfabet E. Now there are an infinite number of words in E. We can only conclude that |L(M)| <= 2016 by passing…
user4424299
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Emulating numerical operations in software
The numerical operations we do in our programs are limited by the number of bytes that a language specifies for a given datatype (or maybe hardware supports). Say I can use integer to do calculations on my paycheck (even "short" is more than enough…
Microkernel
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Is the Reduction function a correspondence?
I'm studying Computability and Complexity and i came out with a doubt.
The Function that reduce a problem to another one is Turing-Computable. I was wondering if its even a one-to-one function ( a correspondence) since looking,for example, to the…
doze
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Turing Degree and Local Contest Questions?
I ran into a olympiad question on Practical Computer Knowledge.
For A ⊆ ℕ we have a = degT(A) = {B | B ≡T A} and D = {degT(A) | A ⊆ ℕ}. For (D, ≤) that has A ≤T B iff a ≤ b. Which of the following is false:
(D,≤) is a distributive lattice
(D,≤)…
user4733521
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Where can I find good explanations of Computability and Complexity?
I have a repeat coming up in Computability and Complexity and I was wondering if anybody has good resources for this sort of study.
Things like regular languages, context free and context sensitive languages and all that sort of stuff.
For…
Ayohaych
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