Is F(x)=\sqrt{1+x^2} a Contraction Mapping on R?

In summary, The Contraction Mapping Theorem, also known as the Banach Fixed Point Theorem, is a fundamental result in mathematics that provides conditions for the existence and uniqueness of a fixed point for a contraction mapping on a complete metric space. A contraction mapping is a function on a metric space that decreases the distance between any two points in the space when those points are mapped by the function. For the Contraction Mapping Theorem to hold, the function must be defined on a complete metric space, it must be a contraction mapping, and the space must be a complete metric space. The Contraction Mapping Theorem has many applications in mathematics, including in the proof of the existence and uniqueness of solutions to differential equations, in the study of dynam
  • #1
flash
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If I take [tex]F(x)=\sqrt{1+x^2}[/tex], then the derivative is always less than one so this is a contraction mapping from R to R, right?

But there is no fixed point where [tex]F(x)=x[/tex], where the contraction mapping theorem says there should be.

So where have I gone wrong?

Cheers
 
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  • #2
The derivative is less than 1, true. But it approaches 1 as x->infinity. So there is no q<1 such that f'(x)<q. It's NOT a contraction mapping. Look again at the definition of 'contraction mapping'.
 
  • #3
Thanks :-)
 

What is the Contraction Mapping Theorem?

The Contraction Mapping Theorem, also known as the Banach Fixed Point Theorem, is a fundamental result in mathematics that provides conditions for the existence and uniqueness of a fixed point for a contraction mapping on a complete metric space.

What is a contraction mapping?

A contraction mapping is a function on a metric space that decreases the distance between any two points in the space when those points are mapped by the function. It is a type of function that brings points closer together.

What are the conditions for the Contraction Mapping Theorem to hold?

For the Contraction Mapping Theorem to hold, the function must be defined on a complete metric space, it must be a contraction mapping, and the space must be a complete metric space.

How is the Contraction Mapping Theorem used in mathematics?

The Contraction Mapping Theorem has many applications in mathematics, including in the proof of the existence and uniqueness of solutions to differential equations, in the study of dynamical systems, and in the analysis of iterative algorithms.

What are the practical implications of the Contraction Mapping Theorem?

The Contraction Mapping Theorem has practical implications in fields such as engineering, economics, and computer science, where it is used to prove the existence and uniqueness of solutions to problems that can be modeled as contraction mappings. It also provides a useful tool for analyzing and solving problems in these fields.

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