Hilbert Spaces

Author

John Robin Inston

Published

September 25, 2026

1 Hilbert Spaces

Recall that an Inner Product Space is a vector space with an inner product, which induces a norm and hence a metric (see Normed Space).

A Hilbert space is a complete inner product space, meaning that every Cauchy Sequence in the space converges to a limit within the space.

Standard examples are \(\mathbb{R}^n\) with the dot product, the sequence space \(\ell^2\), and \(L^2(\mu)\) for a measure space \((X,\mathcal{M},\mu)\).

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