Show L^p(E) is separable for any measurable E.

In summary, the conversation discusses the search for a countable, dense subset in a given set E. The suggestion is to use step functions over intervals with rational endpoints, but the issue arises that E can be any L-msb set, leading to uncertainty about whether all intervals will be included. The conversation also mentions the possibility of embedding L^p(E) into L^p(R) and the idea of using simple functions with rational coefficients to solve the problem. It is noted that this approach does not work for p = infinity.
  • #1
jpriori
2
0
I have a sense that the countable, dense subset I'm looking for is the step functions, maybe over intervals with rational endpoints, but I'm not sure how to deal with the fact that E is any L-msb set, so there's no guarantee all the intervals are in there.
 
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  • #2
You could find an embedding from ##L^p(E)## into ##L^p(\mathbb{R})##.
 
  • #3
jpriori said:
I have a sense that the countable, dense subset I'm looking for is the step functions, maybe over intervals with rational endpoints, but I'm not sure how to deal with the fact that E is any L-msb set, so there's no guarantee all the intervals are in there.

Don't you mean the simple functions?
 
  • #4
Though it isn't true if p = infinity, is it?
 
  • #5
Robert1986 said:
Though it isn't true if p = infinity, is it?

You're right, L^oo is not separable.

Edit: I think there is an argument using simple functions with rational coefficients. It should
be in most graduate Analysis books.
 
Last edited:

Related to Show L^p(E) is separable for any measurable E.

What is L^p(E)?

L^p(E) is a function space that contains all measurable functions on a measurable space E that satisfy a certain norm condition. This space is commonly used in the study of functional analysis and measure theory.

What does it mean for L^p(E) to be separable?

A function space is considered separable if it contains a countable dense subset. In other words, there exists a sequence of functions that can approximate any function in the space with arbitrary precision.

Why is it important to show that L^p(E) is separable?

Showing that L^p(E) is separable is important because it allows for the use of certain approximation techniques and simplifies mathematical proofs. It also helps in the study of various properties of the space, such as the existence of solutions to certain equations.

How can we prove that L^p(E) is separable for any measurable E?

There are several approaches to proving the separability of L^p(E). One method is to construct a countable set of simple functions that are dense in the space. Another method is to use the Rademacher functions, which are known to be dense in L^p(E) for any measurable E.

Does the separability of L^p(E) hold for all values of p?

Yes, the separability of L^p(E) holds for all values of p. This is because the techniques used to prove separability are independent of the value of p and only rely on the properties of measurable functions on a measurable space E.

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