Non-Trivial Metric Spaces: Infinite Points by Convention?

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Discussion Overview

The discussion revolves around the nature of non-trivial metric spaces and whether they necessarily contain an infinite number of points. Participants explore definitions and examples, particularly in relation to sequences and common textbook cases.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions if all non-trivial metric spaces must have an infinite number of points, drawing a parallel to sequences.
  • Another participant seeks clarification on what is meant by "non-trivial."
  • A participant suggests that common textbook examples of sequences are infinite, prompting a question about metric spaces.
  • One reply notes that polynomial spaces can be finite metric spaces, implying that the term "non-trivial" may not strictly mean infinite.
  • A participant provides an example of a finite set with the discrete metric, questioning whether it would be considered trivial.
  • Another participant asks about the applications of finite sets with the discrete metric, highlighting that such sets can still be viewed as non-trivial despite having infinite points.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether non-trivial metric spaces must be infinite, with multiple competing views presented regarding the definitions and examples of metric spaces.

Contextual Notes

The discussion reflects varying interpretations of "non-trivial" and the implications of finite versus infinite metric spaces, with some assumptions about the relevance of examples from textbooks.

pivoxa15
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Is it by convention that all non trivial metric spaces have an infinite number of points?

Just like all non trivial sequences has an infinite number of points.
 
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What do you mean by "non-trivial"?
 
Good one. Probably what I mean is the examples that appear in any textbook. So all examples of sequences in textbooks have them as infinite sequences. Do all examples of metric spaces have infinite number of points?
 
Do all examples of metric spaces have infinite number of points?

Hmm. In algebra it is frequently used that polynomial spaces (sometimes finite) are metric spaces under a 'difference of degrees' type relation. No one calls it a metric space, but the three defining properties are invoked frequently.

But really my answer is yes, I have only seen metric space terminology in connection with topology and analysis, so non-trivial => infinite...
 
A finite set with the "discrete metric": d(u,v)= 0 if u= v, 1 otherwise is a finite metric space. Is that what you would consider "trivial"? I wouldn't.
 
Does a finite set with the discrete metric have any applications or anything else of importance?

A set like Q with the discrete metric is non trivial but there are an infinite number of points in it.
 

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