This paper characterizes a general structure of complementary matrices invo
lved in the input-state-output inclusion principle for linear time invarian
t dynamic systems. Aggregations and restrictions are adopted as two practic
ally important classes within this scheme. Further, contractibility conditi
ons for feedback controllers are presented, including the decentralized con
trol design. The identified structure enables the formulation of conditions
on the complementary matrices which can be useful for analysis and synthes
is of control problems.