Proving The Hamming Metric: Open Subsets and Basis of X

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SUMMARY

The discussion revolves around proving properties of the Hamming metric in a metric space defined by sequences of binary values. Participants seek to demonstrate that the set U(d1,...,dp) is an open subset of X and that U serves as a basis for open sets in (X, d). Key points include identifying the structure of open balls in this space and understanding the implications of sequences summing to specific values. The conclusion emphasizes that the ball around (0,0,0,...) with radius 1 is everything except the sequence (1,1,1,...), and the ball around an arbitrary element can be described similarly.

PREREQUISITES
  • Understanding of metric spaces and the Hamming metric.
  • Familiarity with open sets and bases in topology.
  • Knowledge of infinite series and convergence.
  • Ability to work with sequences and their properties in mathematical analysis.
NEXT STEPS
  • Study the properties of metric spaces, focusing on completeness and convergence.
  • Learn about the concept of bases for topological spaces and their significance.
  • Explore the implications of the Hamming metric on sequence spaces.
  • Investigate examples of open and closed sets in different metric spaces.
USEFUL FOR

Mathematicians, students of topology, and anyone interested in understanding the properties of metric spaces, particularly those involving the Hamming metric and its applications in analysis.

  • #61
around an arbitrary element...wouldn't it be similar to before.

ie. (sum,k=1..infinity, (x_k-a_k)/2^k) < (1/2)^n

either x_k is with 1's starting in the kth position and 0's afterwards
and a_k is ..not sureOR 1's in the (K+1)st position

and a_k is not sure
 
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  • #62
Well, the balls around a with radius 1/2 are either:

1) elements which agree with a in it's first coordinate
2) elements which agree with a except possibly in it's first coordinate.

Can you see why?
Can you extend this to balls with radius (1/2)k??
 
  • #63
no...I don't follow
 
  • #64
Can you see why it is true for a=0?
 
  • #65
I think so?
 
  • #66
OK, npw apply the same reasoning to arbitrary a instead of 0...
 
  • #67
...I think I need a hint
 
  • #68
Well, when does

\sum_{k=1}^{+\infty}{\frac{|x_k-a_k|}{2^k}}=\frac{1}{2}

??
 
  • #69
x_k=(1,0,0,0,0...) and a_k=(0,0,0,...)

or

x_k=(0,1,0,0...) and a_k=(0,0,0,...)

or

a_k=(1,0,0,0,0...) and x_k=(0,0,0,...)

a_k=(0,1,0,0...) and x_k=(0,0,0,...)
 
  • #70
No, can you show my how you got that?

If

\sum_{k=1}^{+\infty}{\frac{|x_k-a_k|}{2^k}}=\frac{1}{2},

then what must hold for |x_k-a_k|.
 
  • #71
I have a new question.

How would I show that the metric space defined by the Hamming metric is complete?
 

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