How to show a function is analytic?

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Discussion Overview

The discussion revolves around methods to demonstrate that a function, specifically log(z-i), is analytic. Participants explore various approaches related to complex analysis, including differentiability, the Cauchy-Riemann equations, and integration techniques.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant suggests that to show a function is analytic, it must be proven differentiable, specifically questioning how to apply this to log(z-i).
  • Another participant mentions the Cauchy-Riemann equations as a necessary condition for a function to be analytic, detailing the requirements for the partial derivatives of the real and imaginary components.
  • A participant expresses uncertainty about how to separate log(z-i) into its real and imaginary parts, u + iv.
  • One participant proposes differentiating log(z-i) and showing that the derivative exists in a region surrounding a point, noting that the derivative is \(\frac{1}{z-i}\) and exists everywhere except at z=i.
  • Another participant suggests an alternative method of integrating the function over a closed line to demonstrate that the integral is zero.
  • A participant introduces the expression for log(z) in terms of its modulus and argument, indicating a potential approach to the problem.

Areas of Agreement / Disagreement

Participants present multiple competing views on how to show that log(z-i) is analytic, with no consensus on a single method being preferred or universally applicable.

Contextual Notes

Some participants express uncertainty about the separation of the logarithmic function into its real and imaginary components, and there are unresolved questions regarding the applicability of different methods in various contexts.

numberthree
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how to show a function is analytic??

I know that to show a function is analytic I need to prove its differentiable, but for a fuction like log(z-i), how could i show it is analytic?
 
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Use the "Cauchy-Riemann equations which should be mentioned early in any book on "functions of a complex variable". A function f(x+ iy)= u(x,y)+ iv(x,y) is analytic at z_0= x_0+ iy_0 if and only if the partial derivatives, \partial u/\partial x, \partial u/\partial y, \partial v/\partial x, and \partial v/\partial y are continuous at the point and
\frac{\partial u}{\partial x}= \frac{\partial v}{\partial y}
and
\frac{\partial u}{\partial y}= -\frac{\partial v}{\partial x}
 


yes, i know wat u mean, but i don't know how to separate log(z-i) into u + iv form
 


numberthree said:
I know that to show a function is analytic I need to prove its differentiable, but for a fuction like log(z-i), how could i show it is analytic?

Why not just differentiate it and then show the derivative exists in a region surrounding a point then it is analytic in that region so:

\frac{d}{dz} \log(z-i)=\frac{1}{z-i}

and that derivative exists everywhere except at z=i.
 


Or you could integrate the function over a closed line and show the integral is zero.
 


use log(z) = log(|z|) + i (arg(z))
 

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