How Can We Map the Open Interval (0,1) to the Real Line R Using a Homeomorphism?

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SUMMARY

The forum discussion focuses on finding an explicit homeomorphism from the open interval (0,1) to the real line ℝ. A proposed solution is the function f(x) = (2x - 1) / (1 - (2x - 1)²), which establishes a bijection and is confirmed as a homeomorphism. The discussion also references the function f(x) = tan(πx/2) as a known homeomorphism from (-1,1) to ℝ, highlighting the relationship between these mappings. Additionally, participants explore the possibility of defining a metric on (0,1) that maintains the same topology as the standard absolute value metric.

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  • Understanding of homeomorphisms in topology
  • Familiarity with bijections and their properties
  • Knowledge of trigonometric functions and their transformations
  • Basic concepts of metric spaces and topology
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  • Study the function f(x) = tan(πx/2) and its implications in mapping intervals
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  • Investigate other potential homeomorphisms from (0,1) to ℝ
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Homework Statement


Find an explicit homeomorphism from (0,1) to R.


Homework Equations


A homeomorphism from (-1,1) to R is f(x)=tan(pi*x/2).


The Attempt at a Solution


I'm horrible a modifying trig functions. Obviously, to shift by b you add b to (x) and you can change the frequency by including a scalar to pi. I tried f(x)=tax(2pi*(x+1)/2), but this doesn't do the trick.
 
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You are close, you just need to change a few things. Also Do you have to use a trig function? What about x/1-x2, that maps (-1,1) -> ℝ, could you modify that?
 
Last edited:
6.28318531 said:
You are close, you just need to change a few things. Also Do you have to use a trig function? What about x/1-x2, that maps (-1,1) -> ℝ, could you modify that?

Consider: ##f: (0,1) → \mathbb{R} \\
\ \ x → \frac{2x-1}{1-(2x-1)^2} ##

This mapping is a Homeomorphism. meaning a Bijection.
could someone specify a metric on (0,1) that defines (the same topology) as the abs. value (i.e. the usual) metric and makes this open interval into a complete set?
 

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