Do Products of L^2 Functions Converge in the Integral?

In summary, the conversation is discussing L^2 spaces and convergence in relation to a bounded set K\subset \mathbb{R}^2. It is mentioned that if g,h\in L^2, then gh\in L^1 by Holder inequality. There is a question about whether \lim_{n\rightarrow \infty} \int_{K} f_n g h = \int_{K} f g h is true and how it can be proven. The conversation also touches on the fact that L^2 is not closed under multiplication.
  • #1
NSAC
13
0
Hi i have a question about [itex]L^2[/itex] spaces and convergence.
Here it goes:
Let [itex]K\subset \mathbb{R}^2[/itex] be bounded.
Let [itex]g,h\in L^2(K)[/itex], and a sequence [itex]f_n\in L^2(K)[/itex] such that [itex]f_n[/itex] converges strongly to [itex]f\in L^2[/itex].
Is it true that [itex]\lim_{n\rightarrow \infty} \int_{K} f_n g h = \int_{K} f g h[/itex]? If it is how?
Thank you.
 
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  • #2
[itex]g,h \in L^2[/itex], then [itex]gh\in L^1[/itex] by Holder inequality.

and so I do not know the integral [itex]\int_K fgh[/itex] is well-defined?
 
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  • #3
zhangzujin said:
and so I do not know the integral \int_K fgh is well-defined?

I didn't get what you mean. Are you asking it as a question?
 
  • #4
zhangzujin said:
[itex]g,h \in L^2[/itex], then [itex]gh\in L^1[/itex] by Holder inequality.

and so I do not know the integral [itex]\int_K fgh[/itex] is well-defined?
Yes. [itex]L^2[/itex] consists of functions whose square is integrable. The product of any two such functions is integrable but the product of three of them may not be.
([itex]L^2[/itex] is not closed under multiplication.)
 

FAQ: Do Products of L^2 Functions Converge in the Integral?

What is the definition of a square integrable function?

A square integrable function is a function whose integral over its domain is finite. In other words, the area under the curve of the function is finite.

What is the significance of a function being square integrable?

A square integrable function is important in many areas of mathematics and science, as it allows for the calculation of certain properties, such as energy and probability, which are essential in understanding physical systems.

Can a function be square integrable on an infinite domain?

Yes, a function can be square integrable on an infinite domain. As long as the integral of the function is finite, it is considered square integrable.

How do you determine if a function is square integrable?

In order to determine if a function is square integrable, you need to calculate the integral of the function over its domain. If the integral is finite, then the function is square integrable.

Are all continuous functions square integrable?

No, not all continuous functions are square integrable. For a continuous function to be square integrable, the integral over its domain must be finite.

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