Clarifications regarding definitions of Taylor, Laurent etc. series

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Discussion Overview

The discussion focuses on clarifying the differences between Taylor, Laurent, and asymptotic series, including their definitions, applications, and convergence properties. Participants explore theoretical aspects and practical implications of these series in mathematical contexts.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant outlines their understanding of Taylor series, Laurent series, and asymptotic series, seeking confirmation on their accuracy.
  • Another participant emphasizes that a Laurent series converges on an annulus in the complex plane, while a Taylor series converges on a disk.
  • It is noted that every holomorphic function within a certain range has a unique, convergent Laurent series, which is claimed to be a stronger assertion than for Taylor series.
  • Participants mention that Laurent series can include terms with negative powers, contrasting with Taylor series.
  • A participant expresses confusion about the meaning of "around a point" in the context of series expansion, particularly for Laurent series.
  • Questions are raised about the appropriate series expansion to use for specific functions, such as e^(1/x), and whether asymptotic series are indeed expansions around infinity.

Areas of Agreement / Disagreement

Participants do not reach a consensus on all points, as there are varying interpretations and clarifications regarding the definitions and applications of the series discussed. Some points are reiterated, while others remain contested or unclear.

Contextual Notes

There are unresolved questions regarding the definitions of convergence for the series and the specific conditions under which each series is applicable. The discussion also highlights the potential for confusion in terminology and application.

Avichal
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I want to know the difference between various kinds of series like Taylor, Laurent and Asymptotic.

I have some understanding but I want some clarifications. Here is what I understand:-
1) Taylor series is just f(0) + x.f'(0) + x2.f''(0)/2! + ...
2) Laurent series is applied when taylor series cannot be applied like when f(0) is not defined.
3) Asymptotic series is around infinty point.

Am I correct? Correct me if I'm wrong
 
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Here are some crucial differences:
1. A Laurent series is convergent on an annulus in the complex plane, whereas the Taylor series is on a disk.

2. EVERY function that is holomorphic on r < | z - a | < R has a unique, convergent Laurent series (defined on this disk. The exact values of the coefficients depend on the annulus). This is a very strong claim, this is far from being true for a Taylor series. You might have R = infinity and r=0.

3. From a practical point of view: a Laurent series contains in general terms with negative powers, e.g. (z-a)^(-n) (when r > 0).
 
Here are some crucial differences:
1. A Laurent series is convergent on an annulus in the complex plane, whereas the Taylor series is on a disk.

2. EVERY function that is holomorphic on r < | z - a | < R has a unique, convergent Laurent series (defined on this disk. The exact values of the coefficients depend on the annulus). This is a very strong claim, this is far from being true for a Taylor series. You might have R = infinity and r=0.

3. From a practical point of view: a Laurent series contains in general terms with negative powers, e.g. (z-a)^(-n) (when r > 0).
 
Before that I have one more confusion. What does around a point mean when finding series of some function.
When finding taylor series, that means we use derivative at that point to approximate.

In case of laurent series, what does 'around some point' mean?
Also suppose I want a series expansion of e1/x what would I apply? Laurent or asymptotic?

Also am I write about asymptotic series i.e. it is series around point = infinity?
 

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