Writing a function of x and y as a function of z

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Discussion Overview

The discussion revolves around the challenge of expressing a function of two real variables, x and y, as a function of a complex variable z, specifically for the purpose of integration with respect to z. Participants explore methods and implications of such transformations, particularly in the context of complex analysis.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about a general method for converting a complex function into a function of z, expressing a specific function involving x and y.
  • Another participant seeks clarification on whether "z" refers to the third coordinate in a Cartesian system or the complex variable defined as z = x + iy.
  • A participant confirms that "z" refers to the complex variable z = x + iy.
  • One participant acknowledges recognizing a specific form of the function but requests a more general method for such transformations.
  • Another participant suggests a method for expressing x and y in terms of z and its conjugate, indicating that these expressions derive from the definition of z.
  • A later reply cautions that not all functions f(x,y) can be expressed solely as a function of z, noting that the complex conjugate z* may not cancel out unless the function is analytic in the complex plane.

Areas of Agreement / Disagreement

Participants express differing views on the generalizability of expressing functions of x and y as functions of z, with some acknowledging limitations based on the analyticity of the function in question.

Contextual Notes

Limitations include the dependence on the analyticity of the function and the potential presence of the complex conjugate in the expressions, which may affect the ability to express the function solely in terms of z.

ericm1234
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Is there a general method for this?
I remember in complex analysis going the other direction; that is, a function of z becoming a function of x and y.
But I need to turn a complex function in a function of just z, for the purpose of integrating with respect to z.
In particular, the function is
x^2/2-cx-y^2/2+ i(x-c)y where c is a constant.
 
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When you say z, are you referring to z, as in the third coordinate of an x,y,z system or the complex variable z, as in z= x + iy?
 
complex variable z, as in z=x+iy.
 
In fact I now see how to write this in terms of z but it is from recognizing the form. Is there a more general method?
Please no one reply with "well if you recognize the form in this particular equation.", because again, I already see it.
General method please?
 
Hi, try:

x= (z+ z^)/2 , where z^ is the conjugate, i.e. if z=x+iy, then z^= x-iy

y=( z- z^)/2i

It comes from z=x+iy
 
Thanks
 
Be aware that you cannot necessarily write a function f(x,y) solely as a function of ##z = x + i y##. You may find that the complex conjugate ##z^\ast = x - iy## does not cancel out of your expression.

You will only be left with a function of z (and not z*) if your function is analytic in the complex plane.
 

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