1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Order symbol

  1. Nov 27, 2012 #1
    Hi, I noticed in mathematics the O symbol is used in the following way:

    A term T is in O(x^p), if lim x->0 T/x^p=c, for a constant c.

    While in computer science the O symbol is used is this way:

    A term T is in O(x^p), if lim x->∞ T/x^p is a constant.

    What gives, these two notations seem to be the complete opposite of each other?
  2. jcsd
  3. Nov 27, 2012 #2


    User Avatar
    Science Advisor

    The O symbol is valid in both cases. It is up to you to define what the x limit is.
  4. Nov 28, 2012 #3
    But don't they contradict each other?

    For example, in the first case x^7 is in O(x^5), but in the second case it is not.
  5. Nov 28, 2012 #4


    User Avatar
    Science Advisor

    No, they are just two distinct cases of a general concept. We should aways say "f(x)= O(g(x)) as x-> a and specify a. They are using two different values of a and so getting two different results.
  6. Nov 28, 2012 #5
    Aha, thanks!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook