“…where the matrices E k , A k ∈ R n×n , B k ∈ R n×m , C k ∈ R p×n are periodic with period K ≥ 1, i.e., E k = E k+K , A k = A k+K , B k = B k+K , C k = C k+K , and the matrices E k are allowed to be singular for all k. Recently, this class of periodic descriptor systems (1.1) is discussed and studied extensively in the problem of solvability and conditionability [36], the computation of H ∞ -norm and system zeros [35,50], and the compensating and regularization problems for periodic descriptor systems [9,23].…”