  The notion of defect of a finitely presented functor on a module category is
extended to arbitrary additive functors. The new defect and the contravariant
Yoneda embedding form a right adjoint pair. The main result identifies the
defect of the covariant Hom modulo projectives with the Bass torsion of the
fixed argument. When applied to a linear control systems, it shows that the
defect of the Malgrange functor of the system modulo projectives is isomorphic
to the autonomy of the system. Furthermore, the defect of the contravariant Hom
modulo injectives is shown to be isomorphic to the cotorsion coradical of the
fixed argument. Since the Auslander-Gruson-Jensen transform of cotorsion is
isomorphic to torsion, the above results raise two important questions: a) what
is a control-theoretic interpretation of the covariant Yoneda embedding of the
Malgrange module modulo injectives, and b) what is a control-theoretic
interpretation of the Auslander-Gruson-Jensen duality?
