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

Open and closed functions

  1. Sep 14, 2005 #1


    User Avatar
    Homework Helper

    I'm trying to understand open and closed functions, and right now I'm on the projection from R^2 to R, with f(x,y)=x. It seems this is both open and closed, but the wikipedia article on open and closed functions seems to disagree:

    I don't understand what exactly A is, and I can't think of any counterexamples myself. Are they talking about the same function as me? Can someone explain any of this?
  2. jcsd
  3. Sep 14, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    In their example, A is the hyperbola given by the equation xy = 1.
  4. Sep 14, 2005 #3


    User Avatar
    Homework Helper

    I see. So it's not closed. Thanks.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?