Laurent expansion of principal root

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Discussion Overview

The discussion revolves around finding the Laurent expansion of a function that includes the principal branch cut of the nth root, specifically focusing on the function f(z)=-iz·√[4]{1-1/z^{4}}. Participants explore methods and challenges associated with this process, including the definition of the principal nth root and the conditions for expansion.

Discussion Character

  • Exploratory, Technical explanation, Homework-related

Main Points Raised

  • One participant inquires about the process for finding the Laurent expansion of a function with a principal branch cut.
  • Another participant suggests that the expansion can be approached like any other function and asks for clarification on the specific point of expansion.
  • A participant mentions the definition of the principal nth root and expresses uncertainty about how to expand √[n]{z} around a point where it is defined.
  • One participant asks if there is a common procedure for finding the Laurent expansion of any function.
  • Another participant notes that the Laurent series is essentially Taylor's series that includes negative powers.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on a specific method for finding the Laurent expansion, and multiple viewpoints and uncertainties remain regarding the process and definitions involved.

Contextual Notes

Some participants express confusion about the definitions and procedures related to Laurent expansions, indicating that the source material may lack clarity on these topics.

bernardbb
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How do I find the Laurent expansion of a function containing the principal branch cut of the nth root?

Example:
f(z)=-iz\cdot\sqrt[4]{1-\frac{1}{z^{4}}}
 
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In exactly the same way you would any other function. What's giving you trouble?

(p.s. about what point are you trying to find an expansion?)
 
Around any point a with |a|>1.

As far as I know, the principal nth root of z is defined as \sqrt[n]{|z|}e^{\frac{1}{n}i\mathrm{Arg}z}, which doesn't seem very helpful; how would you expand \sqrt{z} around a point where it is defined?

Perhaps these are silly questions; my book is very vague on Laurent expansions...

EDIT: I think I've got it... or maybe not...
 
Last edited:
is there any common and simple procedure to find the Laurent expansion of any function? If any then please reply me soon. Thanks
 
It's essential Taylor's series, allowing negative powers.
 

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