Output regulation and tracking in linear multivariable systems

It is shown that the related questions of output tracking and output regulation (with and without input sensor measurement), all with associated internal stability, can be resolved via a single polynomial matrix formulation which employs the recently developed notion of skew prime polynomial matrices. In particular, the primary condition which must be satisfied in all cases is that R(s), the plant numerator matrix, and a matrix where zeros represent the modes of the exogenous system, be externally skew prime. This observation is then elucidated in light of a new internal model principle.