Questions tagged [asymptotics]

Questions about asymptotic notations and analysis

Filter by
Sorted by
Tagged with
3
votes
1answer
318 views

Why is this $f(n) \leq 6n^3 + n^2 \log n \in O(n^3)$ for all $n \geq 1$?

I'm currently studying for an algorithms midterm in about 2 days and am reading from the beginning of the course, and stumbled upon this when I actually looked at the examples. The question equation: ...
0
votes
1answer
93 views

Finding $c$ and $n_0$ for a big-O bound

A book I am reading demonstrates how $5n^3 + 2n^2 + 22n + 6 = O(n^3)$, which I believe is true. After all, there exists a value $c$ for which $cn^3$ is always greater than $5n^3 + 2n^2 + 22n + 6$ for ...
2
votes
2answers
161 views

Prove that $2^{(log(n)^{1/2})}$ is $O(n^a)$

Hopefully this is the right section. I need to prove that $2^{(log(n)^{1/2})}$ is $O(n^a)$. From the basic principle of Big-O notation, I know I need to find two numbers $c$ and $N$ so that $f(n) \le ...
5
votes
2answers
3k views

Confusion about big-O notation comparison of two functions

On page 16 of this algorithms book, it states: For example, suppose we are choosing between two algorithms for a particular computational task. One takes $f_1(n) = n^2$ steps, while the other takes ...
33
votes
2answers
1k views

How asymptotically bad is naive shuffling?

It's well-known that this 'naive' algorithm for shuffling an array by swapping each item with another randomly-chosen one doesn't work correctly: ...
1
vote
1answer
3k views

Big Omega of $n \log n$

While studying master method at recurrences topic I'm stacked at a point. It is written in the book as: $T(n) = 3T(n/4) + n \log n$, we have $a = 3, b = 4$, $f(n) = n \log n$, and $...
2
votes
2answers
167 views
1
vote
1answer
1k views

How to prove transitivity in small-o of asymptotic analysis?

Here is my proof, but I am not sure whether it is correct. We know: $\qquad \begin{array}{l} \forall {c_1},\exists {n_1},0 \le f\left( n \right) \le {c_1}g\left( n \right),\forall n \ge {n_1} \\ \...
2
votes
1answer
111 views

Recursive complexity with change of variable

I face a problem with computing a complexity. I have this equality : $P(u) = (\sqrt{u}+1)P(\sqrt{u}) + \theta(\sqrt{u})$ And I want to prove that $P(u) = O(u)$ This is how I process : I put $m = \...
15
votes
2answers
15k views

Why is there the regularity condition in the master theorem?

I have been reading Introduction to Algorithms by Cormen et al. and I'm reading the statement of the Master theorem starting on page 73. In case 3 there is also a regularity condition that needs to be ...
7
votes
2answers
1k views

Definition of $\Theta$ for negative functions

I'm working out of the 3rd edition CLRS Algorithms textbook and in Chapter 3 a discussion begins about asymptotic notation which starts with $\Theta$ notation. I understood the beginning definition of:...
0
votes
2answers
98 views

Why bound of linear function is same as that of quadratic equation

I am learning algorithms. So, I came along with something very interesting. The asymptotic bound of linear function $an+b$ is $O(n^2)$ for all $a>0$. This is same as for $an^2 + bn + c$. But ...
6
votes
1answer
2k views

Subtracting lower-order term to prove subtitution method works

Substation method fails to prove that $T(n)=\Theta(n^2) $ for the recursion $T(n)=4T(n/2) + n^2$, since you end up with $T(n) < cn^2 \leq cn^2 + n^2$. I don't understand how to subtract off lower-...
6
votes
1answer
282 views

what is the complexity of recurrence relation?

what is the complexity of below relation $ T(n) = 2*T(\sqrt n) + \log n$ and $T(2) = 1$ Is it $\Theta (\log n * \log \log n)$ ?
2
votes
1answer
2k views

Finding the number of leaves in a imbalanced recursion tree

I'm going through the MIT Online Course Videos on Intro. to Algorithms at here at around 38:00. So we have a recursion formula $\qquad T(n) = T(n/10) + T(9n/10) + O(n)$ If we build a recursion tree ...
14
votes
6answers
22k views

n*log n and n/log n against polynomial running time

I understand that $\Theta(n)$ is faster than $\Theta(n\log n)$ and slower than $\Theta(n/\log n)$. What is difficult for me to understand is how to actually compare $\Theta(n \log n)$ and $\Theta(n/\...
5
votes
3answers
299 views

Complexity inversely propotional to $n$

Is it possible an algorithm complexity decreases by input size? Simply $O(1/n)$ possible?
1
vote
3answers
767 views

Value of constants in Big Theta notation

In Big Theta notation used for defining the running time of an algorithm, are the constants $c_1$ and $c_2$ different for every value of $n$? Definition: $\qquad \displaystyle \Theta (g(n)) = \{ f(n)...
11
votes
2answers
277 views

Is $O$ contained in $\Theta$?

So I have this question to prove a statement: $O(n)\subset\Theta(n)$... I don't need to know how to prove it, just that in my mind this makes no sense and I think it should rather be that $\Theta(n)\...
5
votes
3answers
434 views

Asymptotic growth rate of $f(n)$ and $f(n+1)$

Let $f : \mathbb{R} \rightarrow \mathbb{R}$ be a continuous positive function, where $f(n)$ is integer for each integer $n$. Prove or disprove whether the following always holds: $\qquad f(n+1) = \...
45
votes
2answers
3k views

What is the meaning of $O(m+n)$?

This is a basic question, but I'm thinking that $O(m+n)$ is the same as $O(\max(m,n))$, since the larger term should dominate as we go to infinity? Also, that would be different from $O(\min(m,n))$. ...
7
votes
1answer
878 views

Solving the recurrence relation $T(n) = 2T(\lfloor n/2 \rfloor) + n$

Solving the recurrence relation $T(n) = 2T(\lfloor n/2 \rfloor) + n$. The book from which this example is, falsely claims that $T(n) = O(n)$ by guessing $T(n) \leq cn$ and then arguing $\qquad \...
13
votes
2answers
686 views

Do non-computable functions grow asymptotically larger?

I read about busy beaver numbers and how they grow asymptotically larger than any computable function. Why is this so? Is it because of the busy beaver function's non-computability? If so, then do all ...
1
vote
1answer
390 views

Recursion for runtime of divide and conquer algorithms

A divide and conquer algorithm's work at a specific level can be simplified into the equation: $\qquad \displaystyle O\left(n^d\right) \cdot \left(\frac{a}{b^d}\right)^k$ where $n$ is the size of ...
8
votes
2answers
472 views

$\log^*(n)$ runtime analysis

So I know that $\log^*$ means iterated logarithm, so $\log^*(3)$ = $(\log\log\log\log...)$ until $n \leq 1$. I'm trying to solve the following: is $\log^*(2^{2^n})$ little $o$, little $\omega$, ...
16
votes
1answer
331 views

Are asymptotic lower bounds relevant to cryptography?

An asymptotic lower bound such as exponential-hardness is generally thought to imply that a problem is "inherently difficult". Encryption that is "inherently difficult" to break is thought to be ...
10
votes
3answers
651 views

Error in the use of asymptotic notation

I'm trying to understand what is wrong with the following proof of the following recurrence $$ T(n) = 2\,T\!\left(\left\lfloor\frac{n}{2}\right\rfloor\right)+n $$ $$ T(n) \leq 2\left(c\left\...
14
votes
3answers
704 views

What goes wrong with sums of Landau terms?

I wrote $\qquad \displaystyle \sum\limits_{i=1}^n \frac{1}{i} = \sum\limits_{i=1}^n \cal{O}(1) = \cal{O}(n)$ but my friend says this is wrong. From the TCS cheat sheet I know that the sum is also ...

1
18 19 20 21
22