# Tagged Questions

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### Integer programming feasibility is NP-what

What is the complexity class of the general problem of integer programming feasibility? The sources I've looked at are, in my opinion, very confusing. Some say NP-hard, some say NP-complete. Some ...
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### Basic questions about descriptive complexity

I'm trying to learn descriptive complexity, and I'm having trouble on a basic level wrapping my head around what it means for a logical formula to define a computational language. I've tried and ...
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### Proof of theorem about connection between nondeterministic and deterministic Turing machines complexity classes

I need source for proof of this theorem: Every $T(n)$ time nondeterministic Turing machine has an equivalent $2^{O(T(n))}$ deterministic Turing machine. I have book by Michel Sipser, ...
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### What are the current lower bounds for $NTIME$ vs $DTIME$?

Trivially, we have $DTIME(f(n)) \subset NTIME(f(n))$. Is it known whether or not this inclusion is strict? Do we know if $DTIME(f^c(n)) \subset NTIME(f(n))$ for any $c$? Is there any $c$ for which ...
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### Reference for problems without efficient algorithm (in polynomial time)

I'm writing paper and need your help in finding some famous (or not so famous) problems without efficient algorithm, but from logic or computer science. So far, I have: -Boolean satisfiability ...
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### Complexity of the algorithms for Singular Value Decomposition

As said in the title, I would like to find out something on the numerical algorithms for computing the SVD decomposition of a rectangular matrix, with particular regard to their the computational ...
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### Why is positional number system natural?

In the theory of computation, one mainly deals with maps $\Sigma^*\rightarrow\Sigma^*$. To discuss computation on other sets $X$ than $\Sigma^*$, one fixes a representation ...
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### efficient summation of $\sum_{i=1}^{n}\sum_{j=1}^{n}\sum_{k=1}^{n}\sum_{l=1}^{n}A_{ij}A_{ik}A_{il}A_{jk}A_{jl}A_{kl}$

I want to find an efficient algorithm for calculating a sum of products with entangled indices. For example, $\sum_{i=1}^{n}\sum_{j=1}^{n}\sum_{k=1}^{n} A_{ij}A_{jk}A_{ki}$, where $A_{ij}$ is the a ...
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### Books on computational complexity

Can anyone recommend a good book on the subjects of computability and computational complexity? What are the de facto standard texts (say, for graduate students) in this area? I've heard a thing or ...
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### Is there a function that only generates primes?

The title sums it up: does there exist a "nice" injective function $f(n)$ such that $f(n)\in\mathbb P$ for all $n\in\mathbb N$? I'm having difficulty specifying exactly what I want "nice" to mean, ...
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### Is there a winning strategy for Scrabble?

I am sure many of us are addicted to the popular Facebook app: Words with Friends, which is basically an online version of Scrabble. In Playing Games with Algorithms:Algorithmic Combinatorial Game ...
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### Proving NP-completeness (hardness) exercises

I am looking for a list of exercises that can be done to practice polynomial time reductions to prove NP-hardness of problems. I know there are hundreds (thousands?) of problems proven to be NP-hard. ...
Is there an algorithm to test divisibility in space $O(\log n)$, or even in space $O(\log(n)^k)$ for some $k$? Given a pair of integers $(a, b)$, the algorithm should return TRUE if $b$ is divisible ...