2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/188657Matrix quasi exactly solvable operators are considered and new conditions are determined to test whether a matrix differential operator possesses one or several finite dimensional invariant vector spaces. New examples of $2\times 2$-matrix quasi exactly solvable operators are constructed with the emphasis set on PT-symmetric Hamiltonians.14 pages, 1 figure, one equation corrected, results addedQuantum PhysicsHigh Energy Physics - Theorytext