Is there an inverse of Summation?

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    Inverse Summation
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Discussion Overview

The discussion revolves around the concept of finding an inverse of summation, particularly in the context of infinite series and functions. Participants explore the relationship between the zeroes of a function and the zeroes of its summation, as well as the implications of different choices for summation indices and function definitions.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether there is a way to find the zeroes of the summation of a function g(x) defined as the infinite series of f(x).
  • Another participant critiques the initial formulation, noting that the choice of summation index as x is unusual and suggests that it may lead to confusion.
  • A participant proposes redefining g(x) to G(x) with a different summation index N, raising questions about the independence of f(x) from N.
  • There is a suggestion to consider a function of the form f(nx) and whether this changes the nature of the summation.
  • One participant presents a specific function f(x) = x^3/(1-n)^x and inquires about finding the zeroes of the summation, expressing uncertainty about the appropriateness of their questions.
  • Another participant reflects on the variability of methods for finding zeroes, suggesting that different functions may require different approaches.

Areas of Agreement / Disagreement

Participants express differing views on the formulation and implications of summation indices and functions. There is no consensus on a universal method for finding zeroes of the summation, and the discussion remains unresolved regarding the best approach.

Contextual Notes

Participants highlight potential limitations in their assumptions about summation indices and the independence of functions, but these remain unresolved within the discussion.

cmcraes
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Say for some general function f(x), and g(x) = ∑x=0 f(x) (assuming function is defined)
Is there a way to find the zeroes of g(x)? Is there any relationship between the zeroes of f(x) and g(x)? Sorry if this question is poorly asked, i just began learning about summations and infinite series.
Thanks
 
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cmcraes said:
Say for some general function f(x), and g(x) = ∑x=0 f(x)

This makes no sense.

First a minor point, but your summation index is ##x##, which is an unusual choice. So I assume you sum over the naturals?

Second, your summation index is ##x## so it shouldn't be used outside the summation. Setting ##g(x)## equal to this makes little sense to me.

Indeed, by definition we can write

\sum_{x=0}^{+\infty} f(x) = f(0) + f(1) + f(2) + f(3) + ...

So your equality

g(x) = \sum_{x=0}^{+\infty} f(x)

means

g(x) = f(0) + f(1) + f(2) + f(3) + ...

which is probably not what you want.
 
What if we assume N is being used in the function f(x)
And we reset g(x) (I'm on mobile right now so I can't use symbols) to equal

G(x) = Summation from N=0 to +Infinity of f(x)?
 
cmcraes said:
What if we assume N is being used in the function f(x)
And we reset g(x) (I'm on mobile right now so I can't use symbols) to equal

G(x) = Summation from N=0 to +Infinity of f(x)?

Now ##f(x)## is independent from ##N##. So you're just adding a bunch of constants. Is this your intention?
 
How about a function f(nx)?
(Maybe I just need to go learn more about Infinite series and Functions)
 
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cmcraes said:
How about a function f(nx)?
(Maybe I just need to go learn more about Infinite series and Functions)

So you're considering

g(x) = \sum_{n=0}^{+\infty} f(nx)

?
 
Say the function f(x) is (off the top of my head): x^3/(1-n)^x

How would we go about finding the zeroes g(x) of the sum of From n=0 to +infinity? Or am I asking all the wrong questions?
 
cmcraes said:
Say the function f(x) is (off the top of my head): x^3/(1-n)^x

How would we go about finding the zeroes g(x) of the sum of From n=0 to +infinity? Or am I asking all the wrong questions?

I don't really think there is one universal method. Some things work in one occasion but not in the other. I think the best you can do is to consider a specific function and try to work it out for that.
 
OKay, Thanks!
 

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