Limit of limits of linear combinations of indicator functions

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Discussion Overview

The discussion revolves around the properties of a sequence of functions defined on ##\mathbb{R}^n##, specifically focusing on whether the limit function of a non-decreasing sequence of functions, each being a linear combination of indicator functions, can also be expressed as a limit of such "step" functions. The scope includes theoretical aspects of convergence and properties of functions in analysis.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant presents a sequence of functions ##0\leq f_1\leq f_2\leq ... \leq f_n \leq ...## converging to a function ##f## and questions if ##f## can also be represented as a limit of "step" functions.
  • Another participant suggests that while pointwise convergence may hold, there could be issues with other metrics, indicating potential complications in the proof.
  • A later reply clarifies that the pointwise convergence of ##f_n## to ##f## is considered, with the possibility of exceptions on a measure-zero set of ##\mathbb{R}^n##.

Areas of Agreement / Disagreement

Participants express differing views on the nature of convergence and the implications for the limit function. There is no consensus on the proof or the conditions under which ##f## can be represented as a limit of "step" functions.

Contextual Notes

The discussion highlights potential limitations regarding the types of convergence being considered and the implications of measure theory on the properties of the limit function.

Unconscious
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I have a sequence of functions ##0\leq f_1\leq f_2\leq ... \leq f_n \leq ...##, each one defined in ##\mathbb{R}^n## with values in ##\mathbb{R}##. I have also that ##f_n\uparrow f##.
Every ##f_i## is the limit (almost everywhere) of "step" functions, that is a linear combination of rectangles indicator functions.

Is there a way to prove that also ##f## is the limit of "step" functions?
 
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Unconscious said:
Is there a way to prove that also is the limit of "step" functions?
In what sense? You certainly will have \int \vert f-f_{n} \vert \rightarrow 0 but I think you will have problems with other metrics .
 
I mean pointwise convergence, optionally except on a measure-zero set of ##\mathbb{R}^n##.
 

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