Saturday, 13 January 2007

mg.metric geometry - Metric on one-point compactification

Is there a standard construction of a metric on one-point compactification of a proper metric space?



Comments:



  • A metric space is proper if all bounded closed sets are compact.

  • Standard means found in literature.

From the answers and comments:



Here is a simplification of the construction given here (thanks to Jonas for ref).
Let d be the original metric. Fix a point p and set h(x)=1/(1+d(p,x)).
Then take the metric
hatd(x,y)=mind(x,y),,h(x)+h(y),hatd(infty,x)=h(x).



A more complicated construction is given here (thanks to LK for ref), some call it "sphericalization".
One takes
bard(x,y)=d(x,y)cdoth(x)cdoth(y),bard(infty,x)=h(x).
The function bard does not satisfies triangle inequality, but one can show that there is a metric rho such that tfrac14cdotbardlerholebard.

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