title: What is difference between different asymptotic notations?
body: <p>I am really very confused in asymptotic notations. As far as I know, Big-O notation is for worst cast, omega is for best case and theta is for average case. However, I have always seen Big O being used everywhere, even for best case. For e.g. in the following link, see the table where time complexities of different sorting algorithms are mentioned-</p>
  
  <p><a href="https://en.wikipedia.org/wiki/Best,_worst_and_average_case" rel="nofollow">https://en.wikipedia.org/wiki/Best,_worst_and_average_case</a></p>
  
  <p>Everywhere in the table, big O notation is used irrespective of whether it is best case, worst case or average case. Then what is the use of other two notations and where do we use it?</p>