Functional differentiability: Frechet, but not Hadamard?

Click For Summary
The discussion centers on the relationship between Frechet and Hadamard differentiability of functionals, highlighting that while Frechet differentiability with respect to one norm implies Hadamard differentiability with the same norm, it is possible for a functional to be Frechet differentiable with one norm and not Hadamard differentiable with another. Specifically, examples are noted where the infinity norm leads to Frechet differentiability, while the L_1 norm does not. The functional T(H) = s(∫ x dH(x)) is mentioned as a case of interest, with the poster seeking a specific differentiable function s that demonstrates this property. A reference to R.M. Dudley's work is provided as a potential source for finding such a function. The discussion emphasizes the complexity of differentiability in functional analysis.
Testguy
Messages
5
Reaction score
0
I have a question regarding functional differentiablility.

I understand that Frechet differntiability of a functional T with respect to a norm \rho_1 implies Hadamard differentiability of the functional T with respect to the same norm.

However, it is no surprise that there would be cases where a functional T is not Hadamard differentiable with respect to a norm \rho, but that the same functional is Frechet differentiable with respect to a different norm \rho_2. Especially, this turn out to be the case for some functionals when \rho_1(\Delta)=sup_x |\Delta(x)| is the infinity norm, and
\rho_2(\Delta)=\int |\Delta(x)|dx is the L_1-norm.

According to a number of sources this should be the case for some functionals on the quite simple form T(H)=s(\int x dH(x) )=s(\int x h(x)dx),
where h(x) is the usual derivative of the function H(x), and s is some differentiable function.

I do however not find any s where this is the case.

Can anyone help me out with such a function s?

Any help is appreciated.
 
Physics news on Phys.org

Similar threads

  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 13 ·
Replies
13
Views
4K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
Replies
2
Views
1K
Replies
1
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K