Proving Boundedness of Operator T in L^p(-2,2)

In summary, the operator T maps from L^p(-2,2) to L^p(-2,2) is defined as (Tf)(x) = f(x)x. To show that the operator maps from L^p(-2,2) into the same space, we look at the integral \int\limits_{-2}^{2} |f(x)x|^pdx and use Holder's inequality and substitution to prove that the operator is bounded.
  • #1
dikmikkel
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Homework Statement


The operator T maps from [itex]L^p(-2,2)\rightarrow L^p(-2,2)[/itex] is defined [itex] (Tf)(x) = f(x) x[/itex]
Show that the operator maps from L^p(-2,2) into the same.

Homework Equations


p is a natural from 1 to infinity.
Holders inequality
Substitution integrals

The Attempt at a Solution


I look at the following integral
[itex] \int\limits_{-2}^{2} |f(x)x|^pdx = \int\limits_{-2}^{2}|f(x)x|^{p-1}|f(x)x|dx\leq
\int\limits_{-2}^{2} |f(x)x|^{p-1}\left[\left(\int\limits_{-2}^{2}|f(x)|^rdx\right)^{1/r}\left(\int\limits_{-2}^{2}|x|^qdx\right)^{1/q}\right] = \\
||f(x)||_p\int\limits_{-2}^{2} |f(x)x|^{p-1}\left[\left(\int\limits_{-2}^{2}|x|^qdx\right)^{1/q}\right][/itex]
And here I am stuck
Edit: maybe a substitution would do? I really need a hint.
 
Last edited:
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  • #2
I don't think you need anything fancy here: just notice that |x|<=2.
 
  • #3
You are right :) i made it. Tnx
 

1. What is a bounded operator?

A bounded operator is a mathematical concept used in functional analysis and linear algebra. It is a linear transformation between two normed vector spaces that preserves the distance between vectors, meaning the image of any vector is always within a finite distance from the origin.

2. How do you prove that an operator is bounded?

To prove that an operator is bounded, you need to show that it satisfies the definition of a bounded operator. This means that for any vector in the domain of the operator, the norm of the image of that vector is always less than or equal to the product of the norm of the vector and a constant. This constant is known as the operator norm, and it represents the maximum possible growth rate of the operator.

3. What is the significance of a bounded operator in mathematics?

Bounded operators are important in mathematics because they provide a way to analyze linear transformations between vector spaces in a more structured and controlled manner. They also have many applications in fields such as physics, engineering, and computer science.

4. How do you show that an operator is not bounded?

To show that an operator is not bounded, you would need to find a vector in the domain of the operator for which the norm of its image is not bounded by a constant multiple of its own norm. In other words, you would need to find a vector for which the operator norm does not exist.

5. Can a linear operator be bounded and unbounded at the same time?

No, a linear operator can only be either bounded or unbounded. If an operator is bounded, it is not possible for it to be unbounded, and vice versa. This is because the definition of a bounded operator requires the existence of an operator norm, which would not exist for an unbounded operator.

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