Possible to evaluate the gamma function analytically?

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Discussion Overview

The discussion centers on the possibility of evaluating the gamma function analytically for non-integer values. Participants explore various methods and representations, including integral forms and specific cases like half values and integers.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about the analytical evaluation of the gamma function beyond integers and half values, mentioning attempts with Taylor expansion and residue integration.
  • Another participant references a well-known integral representation of the gamma function: \(\Gamma (z) = \int_{0}^\infty t^{z-1} e^{-t} dt\).
  • A different participant expresses interest in finding a non-numerical solution for specific values of \(z\), such as \(\pi\), and questions the feasibility of evaluating the integral in closed form.
  • One participant notes that closed form values for the gamma function appear to be limited to integer or half-integer values of \(z\).

Areas of Agreement / Disagreement

Participants do not reach a consensus on the possibility of evaluating the gamma function analytically for non-integer values, and multiple competing views remain regarding the methods and representations discussed.

Contextual Notes

Participants acknowledge limitations in finding closed form solutions for certain values of \(z\) and the challenges associated with evaluating the integral representation.

LeBrad
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Does anybody know if it's possible to evaluate the gamma function analytically? I know it becomes a factorial for integers, and there's a trick involving a switch to polar coordinates for half values, but what about any other number? I have tried using a Taylor expansion and residue integration, but neither seems to work. Just curious if it's possible.
 
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Yes, let me PM this to Ed Witten.
 
There are several representations. The best known is in terms of an integral
[tex] \Gamma (z) = \int_{0}^\infty t^{z-1} e^{-t} dt[/tex]
 
I understand that, but I'm looking for a non-numerical solution to that integral for a value of z such as Pi. The integral is impossible to evaluate in closed form, but is there some other way?
 
I can't claim expertize on the gamma function, but from what I have able to find, the only closed form values are for integer or half integer values of z.
 

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