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

Name of Function

  1. Jan 31, 2004 #1
    The function defined over the real numbers as

    Code (Text):

    f(x) = {0, x rational
           {1, x irrational
    appears quite a lot in mathematics textbooks. Does anybody know if this function has a commonly accepted name?
  2. jcsd
  3. Jan 31, 2004 #2


    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    Well, it's the characteristc function of the set of irrationals, [tex]\chi (R - Q)[/tex].
  4. Jan 31, 2004 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I've heard it called the "salt and pepper" function.
  5. Jan 31, 2004 #4
  6. Jan 31, 2004 #5
    i've got a simple name and a mnemoic to remember it's name.

    name: the 0 if rational and 1 if irrational function.
    simple mnemoic: tziraoiif
  7. Feb 2, 2004 #6
    that doesn't sound simple
  8. Feb 3, 2004 #7
    What do you mean? I think it rolls right off the tounge.
  9. Feb 3, 2004 #8
    Probably Dirchlet Function(Check Spelling)
  10. Feb 3, 2004 #9
    Sure about that? The name Dirichlet has popped quite a number of time in my textbooks. I've never heard of Dirchlet.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook