Determine the norm of an operator Tf(t)

In summary, the conversation revolves around finding the bounded condition and norm for an operator on the space ##L^\infty(0,1)##. The participants discuss various approaches, such as finding a maximal norm and writing down the specific definition of the norm for the operator. They also mention the importance of including a square root and understanding the difference between the left and right side of the equation. The conversation ends with a request for recommendations on resources for similar examples.
  • #1
Frobenius21
12
0
Homework Statement
Hello,
I need to show that the operator
Tf(t) := g(t)f(t)

Where g is a function on
L^infinity(0,1)

-Is boundeed on the space L^2(0,1)

-and to calculate its norm.
Relevant Equations
Tf(t) = g(t)f(t)
I don't know how to start to find the bounded condition nor the norm. I thought about finding a maximal norm to show that it is bounded but I don't know how to continue.
 
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  • #2
What is the definition of the operator norm on ##L^\infty(0,1)##? Start from there.
 
  • #3
It sounds like f is in ##L^2## from the first part. Can you clarify what space all these objects live in?
 
  • #4
Yes, T is an operator on L^2(0,1).
I was able to show it is bounded by ||g|| in L^infinity(0,1). But I don't know how to find the norm.
 
  • #5
Why don't you start by writing down as specifically as possible how the norm is defined for T (don't just parrot the generic definition of a norm use what you know about the space and the definition of T)
 
  • #6
I am just not able to find a function, which maximazes the operator or a sequence of functions.

Can you give me a hint if you know?
 
  • #7
Can you write down the thing you are trying to maximize by finding a function? Once you've written down the thing you want to maximize working through it will be a lot easier.
 
  • #8
My understanding is that the norm for T has the form ||T||2 = int (|g (t) f (t)|^2) dt

Could you recommend books or resources with similar examples to the problem?
 
  • #9
I don't think that's right. The thing on the right depends on f, the thing on the left does not. Also there's a square root involved in the ##L^2## norm that you are missing
 
  • #10
Im sorry, I missed the square root.

What do you mean by the thing on the left/right? Do you mean the left hand side and the right hand side of the equation?
Or do you mean the left and right terms in the integral?
 
  • #11
Im starting to learn the subject so I am looking for resources and books with similar examples.
 
  • #12
Frobenius21 said:
Im sorry, I missed the square root.

What do you mean by the thing on the left/right? Do you mean the left hand side and the right hand side of the equation?
Or do you mean the left and right terms in the integral?
He means the left and right side of the equation. Your equation is not how the operator norm is defined so this is the first thing you need to find out.
 

Related to Determine the norm of an operator Tf(t)

1. What is the definition of the norm of an operator Tf(t)?

The norm of an operator Tf(t) is a measure of the size or magnitude of the operator. It is calculated by taking the supremum (least upper bound) of the operator's image under all possible inputs. In other words, it is the maximum amount by which the operator can magnify an input.

2. How is the norm of an operator Tf(t) different from the norm of a vector?

The norm of an operator Tf(t) is a measure of the operator's size or magnitude, while the norm of a vector is a measure of the vector's length. While the norm of a vector is a single number, the norm of an operator is a function that maps inputs to outputs.

3. What is the significance of the norm of an operator Tf(t) in mathematics?

The norm of an operator Tf(t) is an important concept in functional analysis and linear algebra. It is used to study the properties of operators and their behavior under various operations, such as composition and inversion. The norm also plays a crucial role in defining convergence and continuity of operators.

4. How is the norm of an operator Tf(t) calculated?

The norm of an operator Tf(t) is typically calculated using the operator norm formula, which involves taking the supremum of the operator's image under all possible inputs. In some cases, the norm can also be calculated using other methods, such as the spectral norm or the Frobenius norm.

5. Can the norm of an operator Tf(t) be negative?

No, the norm of an operator Tf(t) cannot be negative. By definition, the norm is always a non-negative number. It represents the magnitude of the operator and cannot have a negative value. If the norm of an operator is zero, it means that the operator is a zero operator, meaning it maps all inputs to the zero vector.

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