Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Subsequential Limit of a Sequence

  1. Mar 11, 2013 #1
    I have a problem that asks for the subsequential limits, the limit superior, and the limit inferior for the sequence

    [itex]s_n = 4 ^{\frac {1} {n}}[/itex]

    I havent had trouble with my other problems, but I don't see any subsequences in the sequence (other than the sequence itself). Am I missing somthing?
  2. jcsd
  3. Mar 11, 2013 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    All sequences have subsequences. For example, isn't ##(s_{2n})## a subsequence of ##(s_n)##?
  4. Mar 12, 2013 #3


    User Avatar
    Science Advisor

    The "lim inf" of a sequence is the "infimum" (lower bound) of the set of all subsequential limits and the "lim sup" is the "supremum" (upper bound) of that same set. When you say you "can't find any subsequences" what you really mean is that you cannot find any subsequences that converge to different limits. That's not a problem. Because this sequence itself converges, it follows that all subsequences coverge to the same limit. "Limit inferior" and "limit superior" ("lim inf" and "lim sup") are both equal to that limit.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook