Scenarios where the Cauchy-Riemann equations aren't true?

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Discussion Overview

The discussion revolves around the Cauchy-Riemann equations and scenarios where they may not hold true. Participants explore the implications of these equations in different mathematical contexts, including the relationship between differentiability in C^1 and R^2, and the potential for defining metrics that could affect the validity of the equations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether there are scenarios where the Cauchy-Riemann equations do not hold, suggesting that the function f(z, z*) = z* z is useful despite not satisfying these equations.
  • Another participant states that an arbitrary continuously differentiable function from the plane into itself will not satisfy the Cauchy-Riemann equations, emphasizing the requirement for the Jacobian to be complex linear.
  • There is a discussion about the notation used for functions of two complex variables and the implications of differentiability between C^1 and R^2, with a participant noting that functions differentiable in one space are also differentiable in the other.
  • Concerns are raised about the expression of functions in terms of a single complex variable and the necessity for analytic functions to avoid terms containing the conjugate variable.
  • One participant proposes the idea of introducing a non-Euclidean metric to the x-y plane of a single complex coordinate z, questioning the implications for metrics in a space with two complex variables.

Areas of Agreement / Disagreement

Participants express differing views on the applicability and implications of the Cauchy-Riemann equations, with no consensus reached on the scenarios where they may not hold or the effects of introducing different metrics.

Contextual Notes

Participants discuss the implications of differentiability and the nature of complex functions, but there are unresolved assumptions regarding the definitions and conditions under which the Cauchy-Riemann equations apply.

thehangedman
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Are there any scenarios where the Cauchy-Riemann equations aren't true? And if so, would there really be any difference between C^1 and R^2 in those cases?

The function: f(z, z*) = z* z doesn't solve the Cauchy-Riemann equations yet I would think is quite useful.

Couldn't we add a metric within the C^1 dimension that would give us conditions where the Cauchy-Riemann equations wouldn't work?
 
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An arbitrary continuously differentiable function from the plane into itself will no satisfy the Cauchy Riemann equations.

One requirement is that the Jacobian is complex linear: that is, it is a rotation followed by a change of scale (scalar multiplication)

The coordinate functions of an analytic function can be shown to harmonic functions.
 
Last edited:
thehangedman said:
Are there any scenarios where the Cauchy-Riemann equations aren't true? And if so, would there really be any difference between C^1 and R^2 in those cases?

The function: f(z, z*) = z* z doesn't solve the Cauchy-Riemann equations yet I would think is quite useful.

Couldn't we add a metric within the C^1 dimension that would give us conditions where the Cauchy-Riemann equations wouldn't work?

I'm not sure I get your notation; is your f a function of 2 complex variables? Also,
what do you mean by a difference between C^1 and R^2 ? If you refer to differentiability,
any function differentiable in one is also (Real) differentiable in the other, since C^1 and R^2
are diffeomorphic as manifolds.

For

functions of a single complex variable, f(z)=z^ , with z^ conjugation, does not satisfy C-R
anywhere. A complex analytic function must be expressed without any terms containing z^.
This means, if your function f is expressed in terms of (x,y) , then, after the coordinate change
x= (z+z^)/2 and y=(z-z^)/2i , your function is analytic if , after cleaning up , the function
can be expressed in terms of z alone.
 
Bacle2 said:
I'm not sure I get your notation; is your f a function of 2 complex variables? Also,
what do you mean by a difference between C^1 and R^2 ? If you refer to differentiability,
any function differentiable in one is also (Real) differentiable in the other, since C^1 and R^2
are diffeomorphic as manifolds.

For

functions of a single complex variable, f(z)=z^ , with z^ conjugation, does not satisfy C-R
anywhere. A complex analytic function must be expressed without any terms containing z^.
This means, if your function f is expressed in terms of (x,y) , then, after the coordinate change
x= (z+z^)/2 and y=(z-z^)/2i , your function is analytic if , after cleaning up , the function
can be expressed in terms of z alone.

z and z* are the same single complex variable, one the conjugate of the other. I'm wondering what would happen if we gave the plane of the single complex coordinate z a metric? Essentially, break up z into it's component parts x and y and give the x-y plane a non-Euclidean metric. If we instead had 2 complex variables for our space (C^2), then would we possibly have 3 different metrics? One for between z0 and z1, and then one for each of the x-y planes of z0 and z1 respectively? Or could we somehow wrap all three metrics into just one?
 

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