Prove the function is continuous (topology)

In summary, the conversation discusses the continuity of a function ##I## from a set of continuous functions ##X## to itself, where the distance between two functions is defined as the integral of the absolute value of their difference. The goal is to prove that ##I## is continuous using the given definition of continuity. A possible strategy is to show that for any ##\varepsilon > 0##, there exists a ##\delta > 0## such that if the distance between two functions is less than ##\delta##, then the distance between their integrals is less than ##\varepsilon##. However, this may not always be true and a counterexample needs to be found.
  • #1
DotKite
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Homework Statement


Let X be the set of continuous functions ## f:\left [ a,b \right ] \rightarrow \mathbb{R} ##.
Let d*(f,g) = ## \int_{a}^{b}\left | f(t) - g(t) \right | dt ## for f,g in X. For each f in X set,

## I(f) = \int_{a}^{b}f(t)dt ##

Prove that the function ## I ##: (X,d*) → (X,d) is continuous

Homework Equations



The definition of d is given as d(## a_{i},b_{i} ##) = max ## \left \{ \left | a_{i} - b_{i} \right | \right \} ##

Here is the definition of continuity I am working with

Let (X,d) and (Y,d') be metric spaces, and let a be in X. A function f : X→Y is said to be continuous at the point a in X if ## \varepsilon > 0 ## and there exists a ## \delta > 0 ## such that

d'(f(x),f(a)) < ## \varepsilon ##

whenever x is in X and

d(x,a) < ## \delta ##


The Attempt at a Solution



Let ## \varepsilon > 0 ##, there exists a ## \delta > 0 ## such that if d*(f,g) < ## \delta ##

then

d(I(f), I(g)) = max {|I(f) - I(g)|} = max ## \left \{ \left | I(f)-I(g) \right | \right \} ## = max ## \left \{ \left | \int_{a}^{b} f(t)dt - \int_{a}^{b}g(t) dt \right | \right \} ## = max ## \left \{ \left | \int_{a}^{b} f(t) - g(t) dt \right | \right \} ##...


So I was thinking that i should let ## \delta = \varepsilon ## and somehow show

max ## \left \{ \left | \int_{a}^{b} f(t) - g(t) dt \right | \right \} ## < ## \delta ##

I could show that by showing max ## \left \{ \left | \int_{a}^{b} f(t) - g(t) dt \right | \right \} ## < ## \int_{a}^{b}\left | f(t)-g(t) \right |dt ## because d(f,g) < ## \delta ##

But I don't think that inequality is true, and this is where I am stuck
 
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  • #2
Find a counterexample if you think it is untrue.
 

FAQ: Prove the function is continuous (topology)

What does it mean for a function to be continuous in topology?

In topology, a function is considered continuous if small changes in the input result in small changes in the output. This means that points close to each other in the domain should be mapped to points that are also close to each other in the range.

How do you prove that a function is continuous in topology?

To prove that a function is continuous in topology, you need to show that the preimage of every open set in the range is an open set in the domain. This means that any open set in the output has an open set in the input that maps to it.

What is the definition of a continuous function in topology?

A continuous function in topology is defined as a function between two topological spaces that preserves the topological structure. This means that the open sets in the domain are mapped to open sets in the range.

Why is proving continuity important in topology?

Proving continuity is important in topology because it allows for the study of topological spaces and their properties. It also helps to determine which functions are suitable for certain types of analysis and can provide insights into the structure of a given space.

What are some common techniques used to prove continuity in topology?

Some common techniques used to prove continuity in topology include using the definition of continuity, using the concept of open sets, and using the epsilon-delta method. Other techniques may include using the properties of continuous functions, such as the composition of continuous functions being continuous.

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