Bounded Operators: Linearity & Inequality

In summary, a linear operator T: X -> Y is bounded if there exists M>0 such that ll Tv llY \leq M*ll v llX for all v in X. However, if this inequality is true, it does not necessarily mean that the function is linear. To show that something is a bounded linear operator from X to Y, one must demonstrate the inequality, prove linearity, and show that it is a mapping from X to Y. This is especially important in infinite-dimensional vector spaces, as linearity implies boundedness over finite dimensions.
  • #1
mathplease
26
0
a linear operator T: X -> Y is bounded if there exists M>0 such that:

ll Tv llY [tex]\leq[/tex] M*ll v llX for all v in X

conversely, if i know this inequality is true, is it always true that T: X ->Y and is linear?
 
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  • #2
No, if this inequality is true, then your function is not necessarily linear. For example:

[tex]|\sin(x)|\leq |x|[/tex]

But the sine function is not linear...

Was this what you meant?
 
  • #3
I think that it is automatically continuous. Is that what you wanted instead? As noted, this clearly doesn't imply linearity.
 
  • #4
Jamma said:
I think that it is automatically continuous. Is that what you wanted instead? As noted, this clearly doesn't imply linearity.

i see, yes. so in general, to show that something is a bounded linear operator from X to Y, you need to show the inequality, prove linearity and show that its a mapping from X to Y?
 
  • #5
mathplease said:
i see, yes. so in general, to show that something is a bounded linear operator from X to Y, you need to show the inequality, prove linearity and show that its a mapping from X to Y?

Yes, these are the things you need to show!
 
  • #6
micromass said:
Yes, these are the things you need to show!

haha, thanks guys. much clearer now.
 
  • #7
Note that linearity implies boundedness over finite dimensions- the linear maps are just the matrices. You only really need to take the boundedness into account when you are working over infinite-dimensional vector spaces.
 

FAQ: Bounded Operators: Linearity & Inequality

1. What is a bounded operator?

A bounded operator is a linear transformation between two normed vector spaces that preserves the structure of the vector space and satisfies a certain boundedness condition. This means that the operator does not "blow up" or become unbounded when applied to elements of the vector space.

2. What is linearity in the context of bounded operators?

Linearity refers to the property of a bounded operator to preserve the properties of addition and scalar multiplication. In other words, a bounded operator is linear if it satisfies the following conditions: f(x + y) = f(x) + f(y) and f(cx) = cf(x), where x and y are elements of the vector space and c is a scalar.

3. How is the boundedness of an operator determined?

A bounded operator is determined by its norm, which is the supremum (least upper bound) of the operator's values for all elements in the vector space. If the norm is finite, the operator is considered bounded. If the norm is infinite, the operator is considered unbounded.

4. What is the relationship between bounded operators and inequalities?

Inequalities are used to describe the boundedness of operators. An operator is considered bounded if its norm is less than or equal to a constant value. This constant value is referred to as the operator's bound. Inequalities are also used to compare the norms of different operators.

5. How are bounded operators used in mathematical analysis?

Bounded operators are fundamental in functional analysis and are used to study linear transformations between different vector spaces. They also play a key role in the study of differential equations and other areas of mathematics where linear operators are used to model real-world problems.

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