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

Z (conjugate) not analytic?

  1. Oct 24, 2011 #1
    1. The problem statement, all variables and given/known data

    Show that f(z) = ¯z is not differentiable for any z ∈ C.

    2. Relevant equations

    3. The attempt at a solution

    Is it because the Cauchy-Reimann Equations don't hold?

    Z (conjugate) = x-iy


    Edit: Is there another approach? Because the CR Equations is something we learned later on.
  2. jcsd
  3. Oct 24, 2011 #2


    User Avatar
    Science Advisor
    Homework Helper

    Sure. Use the definition of f'(z)=lim h->0 (f(z+h)-f(z))/h. Show the limit is different if you pick h to be real from the limit if you pick h to be imaginary. That's really what the content of the CR equations is.
    Last edited: Oct 24, 2011
  4. Oct 24, 2011 #3
    I think I get it now.


    (conjugate((z+h)-z))/h = h(conjugate)/h

    If h=Δx, the ratio equals 1
    If h=Δiy, the ratio equals -1.

    Since the two approaches don't agree for any z, z(conj) is not analytic anywhere. Correct?
  5. Oct 24, 2011 #4


    User Avatar
    Science Advisor
    Homework Helper

    Yep, that's it. That's how you derive CR.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?