Functional differentiability: Frechet, but not Hadamard?

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SUMMARY

The discussion centers on the relationship between Frechet and Hadamard differentiability of functionals, specifically addressing cases where a functional T is Frechet differentiable with respect to one norm (\rho_2) but not Hadamard differentiable with respect to another norm (\rho_1). The infinity norm (\rho_1) and the L_1-norm (\rho_2) are highlighted as critical examples. The functional T is expressed as T(H)=s(\int x dH(x)), where s is a differentiable function. The user seeks a specific function s that meets these criteria, referencing R.M. Dudley's work from 1992 and 1994 for potential examples.

PREREQUISITES
  • Understanding of Frechet and Hadamard differentiability
  • Familiarity with norms, specifically infinity norm and L_1-norm
  • Knowledge of functional analysis and differentiable functions
  • Basic comprehension of measure theory and integration
NEXT STEPS
  • Research R.M. Dudley's examples of differentiable functions from 1992 and 1994
  • Study the implications of Frechet and Hadamard differentiability in functional analysis
  • Explore the properties of the infinity norm and L_1-norm in detail
  • Investigate additional resources on differentiable functions in the context of measure theory
USEFUL FOR

Mathematicians, functional analysts, and graduate students studying advanced calculus or functional analysis, particularly those interested in differentiability concepts and their applications in various norms.

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I have a question regarding functional differentiablility.

I understand that Frechet differntiability of a functional T with respect to a norm [itex]\rho_1[/itex] 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 [itex]\rho[/itex], but that the same functional is Frechet differentiable with respect to a different norm [itex]\rho_2[/itex]. Especially, this turn out to be the case for some functionals when [itex]\rho_1(\Delta)=sup_x |\Delta(x)|[/itex] is the infinity norm, and
[itex]\rho_2(\Delta)=\int |\Delta(x)|dx[/itex] is the L_1-norm.

According to a number of sources this should be the case for some functionals on the quite simple form [itex]T(H)=s(\int x dH(x) )=s(\int x h(x)dx),[/itex]
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.
 
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