Inner Product Space/Hilbert Space Problem

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SUMMARY

The discussion centers on demonstrating that the mapping from an inner product space X to its dual space X' is surjective, which implies that X is a Hilbert space. The first part establishes that the functional f(x) = is a bounded linear functional with norm ||z||. The second part requires proving the surjectivity of the mapping z |--> f, necessitating a clear understanding of the properties of Hilbert spaces and surjective mappings.

PREREQUISITES
  • Understanding of inner product spaces and their properties
  • Knowledge of bounded linear functionals
  • Familiarity with the concept of surjective mappings
  • Comprehension of the definition and requirements of Hilbert spaces
NEXT STEPS
  • Study the properties of bounded linear functionals in inner product spaces
  • Learn about surjective mappings and their implications in functional analysis
  • Investigate the criteria that define a Hilbert space
  • Explore examples of inner product spaces that are not Hilbert spaces
USEFUL FOR

Mathematics students, particularly those studying functional analysis, and anyone interested in the properties of inner product spaces and Hilbert spaces.

mattos90
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Homework Statement


3. If z is any fixed element of an inner product space X, show that f(x) = <x,z> defines a bounded linear functional f on X, of norm ||z||.
4. Consider Prob. 3. If the mapping X --> X' (the space of continuous linear functionals) given by z |--> f is surjective, show that X must be a Hilbert space.

Homework Equations





The Attempt at a Solution


I solved question 3 without any difficulty, but I can't seem to make any progress on question 4.
 
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To start you off, write down explicitly what it means for a map to be surjective and write down the requirements for something to be a Hilbert space.

What are your ideas about showing that the map z |--> f is surjective?

How would you show each of the requirements for a Hilbert space?

Coto
 

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