Contour integral with delta function

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Discussion Overview

The discussion revolves around the computation of a contour integral involving the delta function and a pole in the complex plane, specifically using Cauchy's integral theorem. The participants explore the implications of the delta function's properties and the nature of the contour used in the integral.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant queries how to compute the integral \(\oint _{C}dz D^{r} \delta (z) z^{-m}\) given that the delta function is not strictly analytic and there is a pole of order 'm'.
  • Another participant asks for clarification on the location of the pole and recalls Cauchy's integral theorem, suggesting a need for understanding its application.
  • A different participant challenges the notion of the delta function being "close to being analytic," asserting that it is not a function of a complex variable and proposes using a sequence of functions that converge to the delta distribution instead.
  • One participant inquires about the nature of the contour \(C\), questioning whether it intersects the origin and the implications for the integral's value based on this intersection. They also seek clarification on the meaning of \(D^r\), whether it represents a constant or a derivative operator.

Areas of Agreement / Disagreement

Participants express differing views on the properties of the delta function and its implications for the contour integral. There is no consensus on how to approach the computation or the nature of the integral based on the contour's characteristics.

Contextual Notes

Participants highlight limitations regarding the delta function's treatment as a non-analytic entity and the dependence on the contour's path, which remains unresolved.

mhill
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Using Cauchy's integral theorem how could we compute

[tex]\oint _{C}dz D^{r} \delta (z) z^{-m}[/tex]

since delta (z) is not strictly an analytic function and we have a pole of order 'm' here C is a closed contour in complex plane
 
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Can you find out for which z there is a pole?

If so, can you recall what Cauchy's integral theorem states?
 
When you write 'isn't strictly analytic' you are implying (to me at least) it is really close to being one. It isn't even a function of a complex variable.

Should you want to do this for any reason, then why not try the normal limit via a sequence of functions that converge to the delta distribution?
 
What kind of path is the C. Does it go through origo? If the integration path does not intersect the origo, isn't the integral zero because integrand is zero along the path? If the integration path intersects the origo, isn't it a divergent integral then?

What does [tex]D^r[/tex] mean? Is it a constant, or a derivative operator?
 

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