English

A simplified formula for the matched projection of an idempotent

Functional Analysis 2025-12-10 v2

Abstract

Let L(H)\mathcal{L}(H) be the set of all adjointable operators on a Hilbert CC^*-module HH. For each TL(H)T\in\mathcal{L}(H), TT^* denotes its adjoint operator, and T|T^*| is the positive square root of TTTT^*. We establish a simplified formula for the matched projection m(Q)m(Q) of an idempotent QL(H)Q\in\mathcal{L}(H) as m(Q)=I+QIQ2,m(Q)=\frac{I+|Q^*|-|I-Q^*|}{2}, where II is the identity operator on HH. This explicit expression allows for the direct derivation of some basic properties of m(Q)m(Q).

Keywords

Cite

@article{arxiv.2512.05970,
  title  = {A simplified formula for the matched projection of an idempotent},
  author = {Qingxiang Xu},
  journal= {arXiv preprint arXiv:2512.05970},
  year   = {2025}
}