  We investigate feedback forms for linear time-invariant systems described by
differential-algebraic equations. Feedback forms are representatives of certain
equivalence classes. For example state space transformations, invertible
transformations from the left, and proportional state feedback constitute an
equivalence relation. The representative of such an equivalence class, which we
call proportional feedback form for the above example, allows to read off
relevant system theoretic properties. Our main contribution is to derive a
quasi proportional feedback form. This form is advantageous since it provides
some geometric insight and is simple to compute, but still allows to read off
the relevant structural properties of the control system. We also derive a
quasi proportional and derivative feedback form. Similar advantages hold.
