Computational complexity, a part of theoretical computer science that deals with understanding how efficiently a problem can be solved.

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Can someone provide me a simplest way to calculate: [closed]

$42^{17} \pmod{3233}$ I know the answer is 2557 - But I need to know how to calculate this without help of a machine that generates the answer. Thank you!
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NP-complete impossible to solve in $O(n)$

NP-complete problems are likely to be unsolvable in polynomial time (although no one proved it yet). My question is, has anybody proved that they are unsolvable in $O(n^d)$ for some concrete small ...
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How to calculate a Modulo?

I really can't get my head around this "modulo" thing. Can someone show me a general step-by-step procedure on how I would be able to find out the 5 modulo 10, or 10 modulo 5. Also, what does this ...
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25 views

To prove a language is not recursive

Prove the language $$L_1=\{\sigma\in\{0,1\}^*|\sigma \text{ codes a TM which accepts at least one word }\}$$ is not recursive. I think it has something to do with $$L=\{\sigma\in\{0,1\}^*|\sigma ...
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Proof that **NP=P** implies **NP=NPC** [closed]

As the title says, I am not sure how the former implies the latter. Please someone sketch a few details. Many thanks
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Binary Search 2Log(n)+1 steps?

So this is probably a basic and slightly stupid question. So.....for a binary search to find a number it takes at most 2Log(n)+1 steps (or Log(2N) questions. Im not a math major or anything, but ...
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45 views

Cholesky of Matrix plus Identity

I have a positive definite matrix $A$ ($n \times n$ dimension) for which I have the Cholesky decomposition $A=LL^{'}$. I want to use this to compute a) The cholesky decomposition of $A+c^2\times I $ ...
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What do log-equivalent and log-complete mean?

I'm reading the paper The Complexity of Satisfiability Problems by Thomas Schaefer(1978). In the paper, he mentions the phrases "log-equivalent" and "log-complete." Searching through the Google ...
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Simplicial maps between simplicial 2-manifolds

Suppose I have two simplicial two-manifolds ("triangle meshes") $M_1$ and $M_2$. I want to compute a surjective simplicial map between $M_1$ and $M_2$, i.e. a surjective function $\phi$ between the ...
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Wouldn't each addition take time $O(n)$?

I am going over the asymptotic runtime of regular matrix multiplication. Here is a lecture slide I am referencing(too much to type out, shown below), from Algorithms Everything makes sense up ...
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Runtime Complexity | Recursive calculation using Master's Theorem

I have the following recurrence relation (arising from some kind of augmented merge sort): $$ T(n) = T\left({2n\over5}\right) + T\left({3n\over5}\right) + n$$ and I need to find the worst-case ...
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Proving a language $L$ is in $\mathrm{co\text{-}NP}$ if $| L \cap \{0,1\}^n | \in \operatorname{poly}(n)$ for all $n$

Let $L \in NP$ such that $|L \cap \{0,1\}^n|=\operatorname{poly}(n)$ for all $n$. Prove that $L \in \mathrm{co\text{-}NP}$. If I understand the problem correctly, in words this says that "for any ...
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Coppersmith-Winograd algorithm

I'm interested in algorithms to compute matrix multiplications. Is the Coppersmith-Winograd algorithm similar to the Strassen algorithm ? I have two other questions: 1) Are the multiplications done ...
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32 views

How to approximate a trigonometric to make less computation complexity

I having a trigonometric function such as $$ p_2(s) = \begin{cases} \frac {1}{(2 \pi)^2}(1-\cos (2 \pi s)), & \text{if $s \le1$ } \\ \frac {1}{2 }(s-1)^2, & \text{if $s >1$ } ...
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1answer
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Approximation of combination $ {n \choose k} = \Theta \left( n^k \right) $?

Is it a valid to say $$ {n \choose k} = \Theta \left( n^k \right) $$ for any $n$ and $k$? If so, how to prove it? Note: $k$ is not a function of $n$. Note: Observed it here (page 5): ...
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1answer
28 views

Why is $O(n^{km}+n^m)=O(n^{km})$?

I've seen this equation in one of my handouts $O(n^{km}+n^m)=O(n^{km})$, which doesn't seem obvious to me. This is what I got trying to work it out: $$\begin{align*}n^{km}+n^m &\leq C \cdot ...
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Recommended gentle introductory reading for computational complexity

I recently read this paper by Scott Aaronson titled: 'Why Philosophers Should Care About Computational Complexity'. I came across it via a link in Hacker News As somebody with a general interest in ...
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Is showing a graph is non-Hamiltonian NP-Complete?

Show that graph is not Hamiltonian. Is this an NP-complete problem? My guess is that this is not an NP-complete problem, because we can run DFS and check it. Like, if we have a Hamiltonian cycle ...
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Arithmetic circuit and complexity

Why scalar multiplications and additions can be considered free when looking at arithmetic circuits ? Thank you.
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An easy question about NP-hard

Consider an optimization problem includes two variables. If we fix the value of one variable, then the optimization problem over the other variable is NP-hard. Can it be concluded that the original ...
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51 views

Quick solution check for the TSP

Given a solution for the Boolean satisfiability or the Hamilton cycle problem it's obvious whether it's true or not, but how does one quickly check whether a solution for the TSP (travelling salesman ...
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1answer
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Given $L = L_1 \cap L_2$ where $L_1 \in NP$ and $L_2 \in coNP$, how do I express L as a symmetric difference of 2 sets in NP?

My ultimate goal is to show that $L \in PP$, but I need to figure out the title question first as an intermediary step. Any help is appreciated, thanks in advance.
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Computational Theory: Proof, Chomsky normal form

Prove or disprove: If $G$ is a CFG in Chomsky normal form, then for any string $w \in L(G)$ of length $n\geq 1$ then exactly $2n-1$ steps are required for any derivation of $w$. I'm stuck at where to ...
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Complexity of finding set of sets with maximum cardinality and constrained coverage.

Given a set of sets $S = \{S_1, S_2, \dots, S_n$}, let $S^{'} \subset S$ be the largest subset of S that obeys $\left| \bigcup_{S_i \in S^{'}}{S_i} \right| \leq k$. What is the complexity of finding ...
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Depths of top-level multiplication algorithms

I've seen that the depth of the Cantor/Kaltofen algorithm is in $O(\log n)$. Are the operations for this complexity undifferentiated ? Or this complexity is in terms of multiplications only ?
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BFS Modification For Total Shortest Paths

I was given the following problem as an assignment but it is really confusing me: Consider the BFS algorithm. Given a digraph G = (V, E) and a starting vertex s ∈ V, this algorithm computes for ...
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How to find a function that is the upper bound of this sum?

The Problem Consider the recurrence $ T(n) = \begin{cases} c & \text{if $n$ is 1} \\ T(\lfloor(n/2)\rfloor) + T(\lfloor(n/4)\rfloor) + 4n, & \text{if $n$ is > 1} \end{cases}$ A. Express ...
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65 views

Verifying whether a number is the determinant of a matrix

What is the (computationally) fastest way to determine whether a number is the determinant of a given real matrix? I am wondering if I have an upper bound on the absolute value of the determinant of ...
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20 views

Given inputs as positive integers $a$,$b$, and $c(i,j)$ where $i,j\leq a$, decide if there is a permutation $\tau$ such that

Given inputs as positive integers $a$,$b$, and $c(i,j)$ where $i,j\leq a$, decide if there is a permutation $\tau$ such that $$c(\tau(a),\tau(1))+\sum_{i=1}^{a-1} c(\tau(i),\tau(i+1))\leq b $$ Prove ...
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Is there an optimal algorithm to calculate $2^n - 1$ in $\theta(n^n)$

The sequence $(f_{n})_{n \in \mathbb{N}}$ is defined by $f_{0} := 0, f_{1} := 1$ and $f_{n} := 3f_{n-1}-2f_{n-2}$ for $n \in \mathbb{N}_{0} \setminus \{0,1\}$. Is there an algorithm that takes an $n ...
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Two non-negative functions $\,f,g$, such that $\,f \not\in \mathcal O(g)$ and $ g \not\in \mathcal O(\,f)$

Show that there exist two non-negative functions $\,f,g: \mathbb{N} \rightarrow \mathbb{R}$ such that $\,f \not\in \mathcal O(g)$ and $ g \not\in \mathcal O(\,f)$. It would be easy two find two such ...
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39 views

Directly Obtaining the $n$th Value of a Lucas Sequence

(As an aside: This question lies relatively upon the border between the realms of Computer Science and Mathematics, and thus may be appropriate for StackOverflow as well.) I am in need of a method of ...
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the sum of the reciprocals of the primes

The sum of the reciprocals of the primes is $\sum \limits_{p}\frac{1}{p} \approx N \ln\ln(N)$ what about this sum where $p_{3}=3,p_{5}=5,p_{n}=\sum \limits^{N}_{j=5}\frac{1}{p_{j}} \sum ...
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Time complexity of a recursive function on a given set

I am computing a function $fun$ which is defined as follows. $fun(m,s)=\sum_{\sigma_{p}\subset s;|\sigma_p|=m}\left [\prod_{i}i\in \sigma_p \sum_{j=1}^{|s-\sigma_p|}\sum_{\gamma_p\subset ...
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Is $L = \{0^{i}1^{i}0^{j}1^{i} | i, j > 0\}$ a context free language?

Is the following argument correct? $L = (A \circ B) \cap C$ where, $A = \{0^{i}1^{i}$ $|$ $i > 0\}$ $B = \{0^{j}1^{i}$ $|$ $i, j > 0\}$ $C = \{0^{i}1^{j}0^{k}1^{i}$ $|$ $i, j, k > 0\}$ We ...
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If $ f(n) = \sum_{i = 1}^{n} (n / i) \log(n / i) $ and $ g(n) = n ~ {\log^{2}}(n) $, then is $ O(f) = O(g) $?

I was trying to prove that if $$f(n) = \sum_{i=1}^{n}\frac{n}{i} \log\frac{n}{i} $$ $$g(n) = n \log^2n$$ then $O(f(n)) = O(g(n))$ I am not sure that it is the case, but based on my simulation ...
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Counting problem of combinations of symmetric matrix.

Given, a symmetric $n*n$ matrix $G$ with 0,1 entries. Each row of has same number of 1. $G$ is arranged in a certain order using a rule. The rule is described below- $G$ is partitioned in to two sub ...
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64 views

P vs NP and Countable vs Uncountable Decision Space

I have noticed that whenever the scope of a problem is pushed to infinity, problems in NP have an uncountably infinite decision space whereas problems in P seem to have a countably infinite decision ...
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Find all groups that meets the condition

I have $n$ elements, each of them have two unsigned int attributes $x$ and $y$. Now I'd like to find out all the groups that fit the following condition: $A.x \geq B.y$ and $B.x \geq A.y$. The ...
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the asymptotic approximation of a sum

$p_{n}$ and $p_{j}$ are two primes with $p_{n}<p_{j}$ where the $n$ and $j$ denotes the $n$th and the $j$th prime. I have this sum $$\sum \limits^{k=\frac{b-p^{2}_{n}p_{j}}{2p_{n}p_{j}} ...
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Formula to calculate password cracking time in years, taking into account Moore's law and known adversary guessing power [closed]

We know that the biggest human rights violators in human history are capable of one trillion password guesses per second as of approximately January 2013. Assume that the 1 trillion guesses per ...
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Approach for this Popular Algorithmic Problem

Given a matrix we have to select one value from each row so that the total value cost selected is minimum. Now the problem is we cannot select column "0" to "J" in "I"th row if we have selected ...
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Is “A New Kind of Science” a new kind of science?

A couple of years ago I was reading "New Kind of Science" (NKS) by S. Wolfram, and it presented lot of interesting ideas for a young Physics undergraduate. Now that I am studying Mathematics however, ...
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decidability of a given language

The language EGAL is $\{(A,B): A \text{ and } B \text{ are DFAs with } L(A) = L(B)\}$ How do I prove that such language is decidable by testing every word of $A$ and $B$ until a defined length ? i ...
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Why isn't NP=coNP? [duplicate]

My understanding is that if a problem is in NP, there is a nondeterministic polynomial-time Turing machine that decides it. That is to say, if an NP problem has a solution, the NP machine has a ...
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The meaning of 'worst case'

When giving bound on convergence rate, complexity and so on, people sometimes will specify it by 'worst case'. What is the meaning of 'worst case'?
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50 views

Exponential vs Polynomial running time

As per this article: http://stackoverflow.com/questions/4317414/polynomial-time-and-exponential-time we know that exponential is worse than polynomial in terms of running time. Is it safe to say that ...
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On the equidistant distribution of $n$ points on a sphere $S^2$ by algorithm and their “validity” measures by statistical methods

I have found an algorithm for distributing $n$ points $P_0, P_1, ..., P_n$ (approximately) equidstantly on a sphere where $$\varphi_i = \pi(\phi - 1)i \qquad \theta_i= \mathrm {asin} (2i/n - 1), ...
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Complexity of recurrence containing geometic series.

What is the complexity of the recurrence $T(n) = 3T(\frac n2) + O(n)$? So far I have: $ O(n) \le cn$ for some constant $c$ Hence: $$T(n) \le 3T(\frac{n}{2}) + cn$$ After a recursion: $$T(n) \le ...
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Complexity of recursive algorithm.

An algorithm solves problems of size $n$ by recursively solving two subproblems of size $n - 1$ and then combining the solutions in constant time. What is the algorithms running time? Assume $ ...