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Simple/trivial question on cauchy-riemann equations

  1. Aug 28, 2006 #1
    This is a simple question, but I don't have a complex analysis book handy to verify, and I'm by no means very familar with complex analysis at all. Are the statements:

    1. f(z) is analytic at a point z = z0 iff the cauchy-riemann equations hold in a neighborhood of z0
    2. f(z) is analytic at a point z = z0 iff the cauchy-riemann equations hold at z0, and f(z) has continuous partials at z0

    valid and equivalent? My gut says yes, but I have the feeling I'm missing something and that perhaps they're not equivalent. Wikipedia seems somewhat vague. Or are they not valid and I'm completely wrong? :)

    BTW, this is not a homework question, I am not taking a complex analysis course, this is entirely for myself. Thanks!
    Last edited: Aug 28, 2006
  2. jcsd
  3. Aug 28, 2006 #2


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    Yes, they are equivalent. It can be shown that if a function f(z) satisfies the Cauchy-Riemann equations hold in some neighborhood of z0 then f is in fact infinitely differentiable in that neighborhood. In fact, more: its Taylor series converges to the value of f(z) at every point in that neighborhood (which is the most basic definition of "analytic" on a neighborhood).
  4. Aug 28, 2006 #3


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    I though CR equations were only a necessary condition for differentiability; the sufficient condition being that the partials be continuous as well.

    Suppose though since I'm taking CA this fall, you can assign it as a homework problem and let me investigate it further . . . I mean, that's what the "A" stands for.:rolleyes:
    Last edited: Aug 28, 2006
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