Does there exist a function such that

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Discussion Overview

The discussion revolves around the existence of a function \( F: \mathbb{Z} \rightarrow \mathbb{Z} \) that satisfies the condition \( \Delta F(g_n) = \frac{\Delta g_n}{g_n} \) for some arbitrary function \( g \). The scope includes mathematical reasoning and exploration of function properties.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants define a finite difference operator and propose the existence of a function \( F \) under specific conditions.
  • There is a question about the quantifiers involved: whether it is \( \exists g \exists F \), \( \forall g \exists F \), or \( \exists F \forall g \).
  • One participant suggests \( \exists F \forall g \) as the correct interpretation.
  • A counterexample is provided where specific values for \( g \) lead to contradictions, suggesting that no such function \( F \) can exist for that particular \( g \).
  • Another participant questions the possibility of generalizing a non-piecewise function for the given values of \( g \) and suggests that a quadratic function could fit those points.
  • Concerns are raised about whether the range of \( F \) can truly be \( \mathbb{Z} \) due to the division by \( g_n \), indicating potential issues with the function's definition.

Areas of Agreement / Disagreement

Participants express differing views on the existence of the function \( F \) and the implications of specific values of \( g \). The discussion remains unresolved, with multiple competing perspectives on the conditions required for \( F \) to exist.

Contextual Notes

Limitations include the dependence on the specific values of \( g \) and the implications of division by \( g_n \), which may affect the validity of the proposed function \( F \).

epkid08
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If we define a finite difference operator as [tex]\Delta a_n = a_{n+1}-a_n[/tex]

Can we prove or disprove the existence of a function F, [tex]F:\mathbb{Z}\rightarrow\mathbb{Z}[/tex], such that [tex]\Delta F(g_n)=\frac{\Delta g_n}{ g_n}[/tex], where g is some arbitrary function?
Edit: fixed Big typo
 
Last edited:
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Is that [itex]\exists g\exists F[/itex], [itex]\forall g\exists F[/itex], or [itex]\exists F\forall g[/itex]?
 
[tex]\exists F\forall g[/tex]
 
Last edited:
suppose [itex]g_0 = 1, g_1 = 2[/itex] and [itex]g_2 = 1[/itex]

Then [tex]f(2) - f(1) = \frac {g_2 - g_1} {g_1} = 1[/tex] and

[tex]f(1) - f(2) = \frac {g_3 - g_2} {g_2} = -1/2[/tex]

so there can't be any F for this g
 
Can you generalize a non-piecewise function for g that has the values [itex]g_0 = 1, g_1 = 2[/itex], and [itex]g_2 = 1[/itex]?
 
epkid08 said:
Can you generalize a non-piecewise function for g that has the values [itex]g_0 = 1, g_1 = 2[/itex], and [itex]g_2 = 1[/itex]?

Why? Of course there is a quadratic going through these points.

Is the range of F really [itex]\mathbb{Z}[/itex]?. That is a problem with the division by [itex]g_n[/itex]
 
willem2 said:
Is the range of F really [itex]\mathbb{Z}[/itex]?. That is a problem with the division by [itex]g_n[/itex]
]

Now that I think about it, it shouldn't be.
 

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