and
. The pencils
and
are assumed to be regular. If
is singular,these Gramians do not, in general, satisfy the "expected" Lyapunov-like (Sylvester) equations (for example,
if
is the continuous-time teachability Gramian). This is shown by expressing the solution of the descriptor system in terms of the parameters of the Laurent expansion of
or
. We derive the Lyapunov-like equations which these Gramians do satisfy.