Show that a mapping is continuous

In summary: Essentially, you can use the definition of continuity to show that the inverse image of an open set in the range (T) is open in the domain (S). In summary, the conversation discusses the continuity theorems and how they can be used to prove that a mapping f carrying each point of E^{n+1}-0 onto a point in (\frac{x_{1}}{|x|^{2}},...,\frac{x_{n+1}}{|x|^{2}}) is continuous. The speaker is unsure of how to go about proving this and is seeking help. The responder suggests using the first continuity theorem and provides a specific example to illustrate how it can be applied.
  • #1
DeadOriginal
274
2

Homework Statement


Show that the mapping f carrying each point [itex](x_{1},x_{2},...,x_{n+1})[/itex] of [itex]E^{n+1}-0[/itex] onto the point [itex](\frac{x_{1}}{|x|^{2}},...,\frac{x_{n+1}}{|x|^{2}})[/itex] is continuous.

2. Continuity theorems I am given.
A transformation f:S->T is continuous provided that if p is a limit point of a subset X of S then f(p) is a limit point or a point of f(X).

Let f:S->T be a transformation of space S into space T. A necessary and sufficient condition that f be continuous is that if O is an open subset of T, then its inverse image [itex]f^{-1}(O)[/itex] is open in S.

A necessary an sufficient condition that the transformation f:S->T be continuous is that if x is a point of S, and V is an open subset of T containing f(x) then there is an open set U in S containing x and such that f(U) lies in V.

The Attempt at a Solution


I was thinking to prove this I would have to find an open set in the range of this function and show that its inverse image is also open in the domain but I am not sure how I would go about doing that.

Any help would be appreciated.
 
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  • #2
What is the definition of continuity you work with?
 
  • #3
I have three. They are

A transformation f:S->T is continuous provided that if p is a limit point of a subset X of S then f(p) is a limit point or a point of f(X).

Let f:S->T be a transformation of space S into space T. A necessary and sufficient condition that f be continuous is that if O is an open subset of T, then its inverse image f^(-1)(O) is open in S.

A necessary an sufficient condition that the transformation f:S->T be continuous is that if x is a point of S, and V is an open subset of T containing f(x) then there is an open set U in S containing x and such that f(U) lies in V.

I updated the original post to reflect this.
 
  • #4
I would use the first one. Given a sequence ## \mathbf{x}^{(n)} \rightarrow \mathbf{p} ##, prove that ## \frac {\mathbf{x}^{(n)}} {(x^{(n)})^2} \rightarrow \frac {\mathbf{p}} {p^2} ##.
 
  • #5
voko said:
I would use the first one. Given a sequence ## \mathbf{x}^{(n)} \rightarrow \mathbf{p} ##, prove that ## \frac {\mathbf{x}^{(n)}} {(x^{(n)})^2} \rightarrow \frac {\mathbf{p}} {p^2} ##.

I don't really understand. Can you elaborate a little bit? I don't know how I would show that a point [itex]x=(x_{1},x_{2},...,x_{n+1})[/itex] is a limit point.
 
  • #6
You don't have to prove ## \mathbf{x}^{(n)} \rightarrow \mathbf{p} ##, this is an assumption. Given that assumption, prove ## \frac {\mathbf{x}^{(n)}} {(x^{(n)})^2} \rightarrow \frac {\mathbf{p}} {p^2} ##.
 

Related to Show that a mapping is continuous

1. What is the definition of continuity in a mapping?

The continuity of a mapping refers to the property that small changes in the input of the mapping result in small changes in the output. In other words, as the input values approach each other, the output values also approach each other.

2. How is continuity mathematically expressed in a mapping?

A mapping is considered continuous if for any input value, the corresponding output value is within a certain distance or "delta" of the actual output value. This is expressed as: for all ε > 0, there exists a δ > 0 such that |x - x0| < δ implies |f(x) - f(x0)| < ε

3. What are some common methods for proving continuity in a mapping?

There are several methods for proving continuity in a mapping, including the epsilon-delta definition, the sequential criterion, and the limit definition. These methods involve showing that the mapping holds for all possible input values and that the output values approach each other as the input values get closer.

4. Can a mapping be continuous at some points and discontinuous at others?

Yes, a mapping can be continuous at some points and discontinuous at others. This is known as a piecewise continuous mapping. In this case, the mapping may have different definitions or behaviors at different points, but it is still considered continuous overall as long as it meets the criteria for continuity at each individual point.

5. What are some real-world applications of proving continuity in a mapping?

Proving continuity in a mapping is important in various fields such as physics, engineering, and economics. It allows us to understand how small changes in input variables affect the output in a predictable and stable manner. This is crucial for making accurate predictions, designing systems, and analyzing data in these fields.

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