Upper Bounds and Tight Upper Bounds

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SUMMARY

A Tight Upper Bound, denoted as $\Theta$, is a specific type of asymptotic bound that describes the growth rate of a function. For the function $f(n) = n^3 + 2n^2$, the tight upper bound is $\Theta(n^3)$, indicating that it grows asymptotically with $n^3$. This is distinct from the supremum or least upper bound, as the function approaches infinity without a definitive upper limit. In contrast, $O(n^4)$ serves as an asymptotic upper bound, while $\Omega(n)$ represents an asymptotic lower bound.

PREREQUISITES
  • Understanding of asymptotic notation, specifically $\Theta$, $O$, and $\Omega$.
  • Familiarity with polynomial functions and their growth rates.
  • Basic knowledge of limits and infinity in mathematical analysis.
  • Concept of upper and lower bounds in the context of algorithm analysis.
NEXT STEPS
  • Study the properties and applications of $\Theta$ notation in algorithm complexity analysis.
  • Learn how to derive tight bounds for various functions in algorithm design.
  • Explore the differences between asymptotic notations: $O$, $\Omega$, and $\Theta$.
  • Investigate examples of functions with different growth rates and their corresponding bounds.
USEFUL FOR

Mathematicians, computer scientists, and software engineers interested in algorithm analysis and performance optimization will benefit from this discussion.

Sudharaka
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Hi everyone, :)

What is a Tight Upper Bound? Is it the least upper bound? But then tight upper bound will be equivalent to the supremum. :confused:
 
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Sudharaka said:
Hi everyone, :)

What is a Tight Upper Bound? Is it the least upper bound? But then tight upper bound will be equivalent to the supremum. :confused:

Hi! :)

I think you are talking about the $\Theta$ bound.

It's a different type of bound.

Suppose we have the function $f(n) = n^3 + 2n^2$.
Its tight upper bound is $\Theta(n^3)$.
This is not a supremum (or least upper bound), since the function doesn't have one - it goes up to infinity.
The point it that it goes up asymptotically with $n^3$.

For instance $O(n^4)$ is an asymptotic upper bound, while $\Omega(n)$ is an asymptotic lower bound.
A tight bound is one that is both.
 
I like Serena said:
Hi! :)

I think you are talking about the $\Theta$ bound.

It's a different type of bound.

Suppose we have the function $f(n) = n^3 + 2n^2$.
Its tight upper bound is $\Theta(n^3)$.
This is not a supremum (or least upper bound), since the function doesn't have one - it goes up to infinity.
The point it that it goes up asymptotically with $n^3$.

For instance $O(n^4)$ is an asymptotic upper bound, while $\Omega(n)$ is an asymptotic lower bound.
A tight bound is one that is both.

Thanks much. That makes perfect sense now. :)
 

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