Partial impulse observability of linear descriptor systems

A research paper in this journal vol. 61, no. 3, pp. 427–434, 2012, by M. Darouach, provides a functional observer design for linear descriptor systems under the partial impulse observability condition. The is correct, but there was flaw algebraic criterion characterizing observability. In present paper, we derive novel characterization of terms simple rank condition involving system coefficient matrices and an alternative Wong sequences.