  In this paper we investigate when a parameterized controller, designed for a
plant depending on unknown parameters, admits a realization which is
independent of the parameters. It is argued that adaptation is unnecessary for
this class of parameterized controllers. We prove that standard model reference
controllers (state and output--feedback) for linear time invariant systems with
a filter at the plant input admit a parameter independent realization. Although
the addition of such a filter is of questionable interest, our result formally,
and unquestionably, establishes the deleterious effect of such a modification,
which has been widely publicized in the control literature under the name
L1-adaptive control.
