Prove that f(n) = n * log (n) is O(n(1+sqrt(n))).

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In summary: Let me know if you need me to help.In summary, the student does not know how to solve for c in order to prove that f(n) is O(n(1+sqrt(n))). They are looking for help from the tutor and have asked for it.
  • #1
Logik
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Homework Statement



Prove that f(n) = n * log (n) is O(n(1+sqrt(n))).

Homework Equations


n/a


The Attempt at a Solution


I really don't know what to do else I wouldn't be here :? Some hints would be appreciated!
 
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  • #2
Definitions are usually a good place to start.
 
  • #3
f(n) is O(g(n)) if and only if there exists an n_0 part of natural numbers and a constant C that is part of rational numbers for which f(n) <= that c*g(n) for all n >= n_o

I know the def just don't know how to get g(n)...
 
  • #4
Logik said:
f(n) is O(g(n)) if and only if there exists an n_0 part of natural numbers and a constant C that is part of rational numbers for which f(n) <= that c*g(n) for all n >= n_o

I know the def just don't know how to get g(n)...
Well, you were given an f(n) and asked to prove
f(n) is O(n(1+sqrt(n))),​
weren't you? ...
 
  • #5
yes well I don't know how to go from f(n) to g(n)... the examples I have seen were just that you would multiply so part of f(n) until you could group everything together to get c* g(n) but this time I don't see how I can multiply anything to get anything that looks like g(n)...
 
  • #6
Logik said:
yes well I don't know how to go from f(n) to g(n)... the examples I have seen were just that you would multiply so part of f(n) until you could group everything together to get c* g(n) but this time I don't see how I can multiply anything to get anything that looks like g(n)...
I think I had misunderstood you -- your last post sounded like you said you didn't know what g(n) was.

Did you try solving for c? What did you get?
 
  • #7
I don't know where to start to solve for c.. that is my problem...

I don't understand where the 1 comes from... I know O(logn) < O(sqrt(n)) so I can get that but where is the (1+srt(n)) comes from?
 
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  • #8
Logik said:
I don't know where to start to solve for c.. that is my problem...

Well, assuming that the problem is correct, you have a known f(n) and g(n) in the inequality
f(n)< C g(n)

I think you can handle solving that for C.
 

FAQ: Prove that f(n) = n * log (n) is O(n(1+sqrt(n))).

What does "f(n) = n * log(n) is O(n(1+sqrt(n)))" mean?

This notation is known as Big O notation, which is a mathematical way to describe the limiting behavior of a function as its input grows. In this case, it means that the function f(n) grows no faster than n(1+sqrt(n)) as n increases.

How do you prove that f(n) = n * log(n) is O(n(1+sqrt(n)))?

To prove this, we need to show that there exists a positive constant c and a positive integer n0 such that f(n) <= c*n(1+sqrt(n)) for all n > n0. This can be done using mathematical induction or by using limits and derivatives.

How does the value of c and n0 affect the proof?

The value of c represents the slope of the function, while n0 represents the point at which the function begins to follow the growth rate of n(1+sqrt(n)). A smaller value of c and larger value of n0 make the proof stronger, as it shows that the function follows the growth rate at a lower input and with a smaller slope.

Can this proof be generalized for other functions?

Yes, this proof can be generalized for other functions by following the same logic and using the properties of Big O notation. However, the values of c and n0 may vary for different functions.

Why is proving Big O notation important in computer science?

Big O notation allows us to analyze the efficiency and performance of algorithms and functions as the input grows. By proving the Big O notation of a function, we can determine how much time and space it will require to run, and compare it to other functions to choose the most efficient one for a given task.

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