Proving Existence of Min. Distance in ##S## from ##p_0##

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Homework Help Overview

The problem involves proving the existence of a minimum distance from a point ##p_0## to a nonempty closed subset ##S## of ##E^n##. The discussion centers around the properties of closed sets and the behavior of distance functions.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the implications of ##p_0## being in ##S## and question how this affects the minimum distance. There is a discussion about the difference between minimum and infimum, particularly in relation to open and closed sets.

Discussion Status

The discussion is ongoing, with participants raising questions about the definitions and properties of minimum distances in relation to closed sets. Some guidance has been offered regarding the nature of the distance set being non-empty and bounded below.

Contextual Notes

Participants note the distinction between closed and open sets, particularly in the context of the existence of minimum values, and question the implications of these properties on the problem at hand.

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Homework Statement



Prove that if ##S## is a nonempty closed subset of ##E^n## and ##p_0\in E^n## then ##\min\{d(p_0,p):p\in S\}## exists.

2. The attempt at a solution

If ##p_0## was in ##S## why would ##\min\{d(p_0,p):p\in S\} = 0?## Is it just because it is the minimum? How about if ##p_0 \in S## then what will ##\max\{d(p_0,p):p\in S\}## be?
 
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Lee33 said:

Homework Statement



Prove that if ##S## is a nonempty closed subset of ##E^n## and ##p_0\in E^n## then ##\min\{d(p_0,p):p\in S\}## exists.

2. The attempt at a solution

If ##p_0## was in ##S## why would ##\min\{d(p_0,p):p\in S\} = 0?## Is it just because it is the minimum? How about if ##p_0 \in S## then what will ##\max\{d(p_0,p):p\in S\}## be?

max is not really the issue. The minimum of a set of numbers is the smallest number in the set. If you take the open interval (0,1) it doesn't have a minimum. It does have an infimum which is 0 but that's not in the set. So it doesn't have a minimum. So if you put S to be the open interval (0,1) and ##p_0=0##, then the minimum does not exist. If S were closed why is the situation different?
 
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Lee33 said:

Homework Statement



Prove that if ##S## is a nonempty closed subset of ##E^n## and ##p_0\in E^n## then ##\min\{d(p_0,p):p\in S\}## exists.

Don't forget that {d(p_0,p):p\in S\} is a non-empty subset of IR bounded below (by 0).
 
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Thank you Dick and PeroK! I think I understand now.
 

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