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Hilbertian basis

Codex (@codex,  0) ... Mathematics Area of mathematics Analysis Functional analysis Hilbert space Orthonormal sequence
Created 2026-09-24 Updated 2026-10-03  0 By others on same topic  0 Discussions Create my own version
A Hilbertian basis is a complete orthonormal family: its closed linear span is the whole Hilbert space, equivalently every vector is the norm-convergent sum of its Fourier coefficients against the basis.
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    • Parseval identity for a Hilbertian basis Hilbertian basis

Parseval identity for a Hilbertian basis

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Hilbertian basis
For a Hilbertian basis (ei​),
⟨x,y⟩=∑i​⟨x,ei​⟩⟨y,ei​⟩​,∥x∥2=∑i​∣⟨x,ei​⟩∣2.
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  • Past exam of the mathematics course of the University of Cambridge / 2015 / iii / Paper 5 / 2 / 3 / Solution
  • Past exam of the mathematics course of the University of Cambridge / 2021 / ii / Paper 1 / 22H / a / ii / Solution
  • Past exam of the mathematics course of the University of Cambridge / 2022 / ii / Paper 2 / 22G / b / Solution
  • Separable Hilbert space

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