Complex Analysis Harmonic functions

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Discussion Overview

The discussion revolves around the properties of harmonic functions, specifically whether the linear combination of two harmonic functions remains harmonic. Participants explore the implications of the Laplace equation and the concept of differentiation as a linear operator.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant proposes to prove that u(x,y) + cv(x,y) is harmonic by using the Laplace equation, expressing uncertainty about the relationships involved.
  • Another participant suggests defining w(x,y) = u(x,y) + cv(x,y) and calculating wxx + wyy to demonstrate the harmonic property, indicating a potential method to resolve the initial query.
  • A third participant expresses appreciation for the suggestion, indicating a shift in focus from harmonic conjugates to this new approach.
  • A later reply questions the understanding of differentiation as a linear operator, implying a deeper conceptual discussion may be necessary.

Areas of Agreement / Disagreement

There is no clear consensus yet; participants are exploring different approaches and concepts related to the problem without resolving the initial query.

Contextual Notes

Participants have not fully articulated the relationships or properties needed to prove the harmonic nature of the linear combination, and there may be missing assumptions regarding the definitions of harmonic functions.

Alvis
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Suppose u(x,y) and v(x,y) are harmonic on G and c is an element of R. Prove u(x,y) + cv(x,y) is also harmonic.

I tried using the Laplace Equation of Uxx+Uyy=0

I have:
du/dx=Ux
d^2u/dx^2=Uxx

du/dy=Uy
d^2u/dy^2=Uyy

dv/dx=cVx
d^2v/dx^2=cVxx

dv/dy=cVy
d^2v/dy^2=cVyy
I'm not really sure how to prove these are harmonic...am I missing a relationship?
 
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Define w(x,y) = u(x,y) + cv(x,y) and calculate wxx + wyy. Basic properties of the partial derivative should give you the answer.
 
Wow, that's a really good idea. I was trying to do the harmonic conjugate but was getting nowhere. Thank you!
 
do you understand what it means to say that differentiation is a linear operator?
 
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