Visually Representing Complex Derivatives

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    Complex Derivatives
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Discussion Overview

The discussion revolves around the visual representation of complex derivatives, exploring how the derivative of a complex function can be understood and depicted. Participants examine the implications of defining derivatives in the context of complex numbers compared to real functions, touching on theoretical and conceptual aspects.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions whether the expression f(z_{0} + Δz) represents a neighborhood around z_{0} and if the derivative retains the concept of instantaneous change as in real functions.
  • Another participant advises against the neighborhood picture, suggesting that a more general definition of the derivative is preferable, noting that the formula applies to various mathematical objects beyond complex functions.
  • A different viewpoint introduces the idea of representing Δz as a vector approaching zero to find the limit, while questioning the interpretation of z=x+iy as a point rather than a vector.
  • Further discussion references another thread to clarify the distinction between viewing z as a point and as a vector, emphasizing that complex calculus may be simpler due to the alignment of spaces in transformations.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of the neighborhood representation for complex derivatives, with no consensus reached on the best approach to visualize these concepts.

Contextual Notes

The discussion highlights the complexity of defining derivatives in different mathematical contexts and the potential limitations of using certain visual representations, but does not resolve these issues.

TheRainmaker
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I'm curious how the derivative of a complex function can be represented visually. It is defined as the limit of (f(z[itex]_{0}[/itex] + Δz) - f(z[itex]_{0}[/itex]) / Δz as Δz approaches 0. Is it right to say that f(z[itex]_{0}[/itex] + Δz) represents a neighborhood of radius Δz around z[itex]_{0}[/itex] in this case? Does the derivative still represent instantaneous change as in real functions?
 
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I do not recommend the neighbourhood 'picture', because you are moving on to a more general definition of the derivative.

Although the picture idea just about works for complex numbers it is better to work with the fundamental definition of the derivative.

That is because the formula you quote is pretty general and used for vectors, tensors and many other mathematical objects.

Many objects, such as vectors, do not reside in the same space as the independent variables, but in their own space. This is reflected in complex transformations from the xy to vu planes.
 
Then using a vector representation of the derivative definition, Δz is a vector that approaches zero to find the limit of the function. What if z=x+iy is viewed as a point rather than a vector?
 
You might like to revies this thread, it is a bit off topic but post#13 explains better what I mean.

https://www.physicsforums.com/showthread.php?t=640080&highlight=vector

What if z=x+iy is viewed as a point rather than a vector

That is exactly the point (pun intended).

z=x+iy is a point in one space but something else in another.

Complex calculus is simpler than vector calculus because the spaces in the transformation are the same, as with real analysis. That is xy and uv are both complex planes.
 

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