Koelink, E.; Román, P.
(Symmetry, Integrability and Geometry: Methods and Applications, 2016)
A matrix-valued measure Θ reduces to measures of smaller size if there exists a constant invertible matrix M such that MΘM∗ is block diagonal. Equivalently, the real vector space A of all matrices T such that TΘ(X)=Θ(X)T∗ ...