Norm Retrieval by Projections on Infinite-Dimensional Hilbert Spaces

Abstract

We study the norm retrieval by projections on an infinite-dimensional Hilbert space $H.$ Let $\{e_i\}_{i∈I}$ be an orthonormal basis in $H$ and $W_i = \{e_i\}^⊥$ for all $i ∈ I.$ We show that $\{W_i\}_{i∈I}$ does norm retrieval if and only if $I$ is an infinite subset of $N.$ We also give some properties of norm retrieval by projections.