2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/104879We consider higher-rank versions of the standard numerical range for matrices. A central motivation for this investigation comes from quantum error correction. We develop the basic structure theory for the higher-rank numerical ranges, and give a complete description in the Hermitian case. We also consider associated projection compression problems.14 pages, 3 figures, to appear in Linear Algebra and its ApplicationsFunctional AnalysisOperator AlgebrasQuantum Physicstext