Why Generating Functions Work in Combinatorics

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Discussion Overview

The discussion revolves around the concept of generating functions in combinatorics, particularly their application in deriving closed form equations from recursive definitions, such as the Fibonacci sequence. Participants express curiosity about the underlying principles and the perceived complexity of the topic.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions the nature of generating functions, indicating that there are several types and expressing uncertainty about their connection to closed form equations derived from recursive definitions.
  • Another participant asserts that deriving a closed form for the Fibonacci sequence is a typical application of generating functions, seeking clarification on the type of generating functions being discussed.
  • Some participants express a feeling that the reasoning behind generating functions resembles calculus, suggesting that the underlying logic may not be fully transparent.
  • A participant shares a blog post about generating functions, indicating interest in additional resources on the topic.

Areas of Agreement / Disagreement

There appears to be some disagreement regarding the types of generating functions and their applications, with multiple viewpoints on their connection to recursive equations. The discussion remains unresolved as participants explore different aspects of the topic.

Contextual Notes

Participants mention a lack of clarity regarding the convergence of generating functions and the complexity of the reasoning involved, which may depend on specific definitions and assumptions about generating functions.

samspotting
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Why does generating functions work? In combinatorics we've accepted not to worry about convergence, and we saw how to get a function that returns the nth term of the fibonnaci sequence from the recursive definition, but there was so much magic in that.

The prof said not to worry about it until grad school.
 
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What kind of "generating function" are you talking about? I know several slightly different kinds of "generating functions" but none of them are connected with getting a closed form equation from a recursive equation.
 
Getting the closed form for the Fibonacci sequence seems like a typical application to me... You're thinking about Generating functions, right?
 
yes indeed.
 
Here is an interesting blogpost about generating functions by Foxmath.
 
Yeah, that is what we covered. It feels too much like calculus, the reasoning behind it all is rather hidden.
 

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