Almost-vector spaces in the intersection of translates of the frame space in finite dimension (2107.10103v4)

Abstract: We proved in a previous article a path-connectedness property of the intersection of translates of the space of finite-dimensional Hilbert space frames, which we formulated in the language of Stiefel manifolds $St(n,H)$. Yet, the notion of a Hilbert space frame has already been successfully extended to $C^*$-algebras and Hilbert modules. In this article, we prove a new property of the intersection of translates of the space of frames both in the finite-dimensional Hilbert space and finite-dimensional $C^*$-algebraic cases. This property expresses that there are many almost-vector spaces in these intersections, and it relies crucially on the hypothesis of finite dimension. When the translating $l$-tuple is made of frames, we see that the intersection almost contains the vector space spanned by these frames. We finally conjecture that the property and its consequence are true in a finite-dimensional left-Hilbert module because of the simple and related structure of the latter.