On the necessity of looped-functionals arising in the analysis of   pseudo-periodic, sampled-data and hybrid systems
  Looped-functionals have been shown to be relevant for the analysis of a wide variety of systems. However, the conditions obtained in previous works on the analysis of sampled-data, impulsive and switched systems have only been shown to be sufficient for the characterization of their associated discrete-time stability conditions. We prove here that these conditions are also \necessary. This result is derived for a wider class of linear systems, referred to as impulsive pseudo-periodic systems, that encompass periodic, impulsive, sampled-data and switched systems as special cases. 
Corentin Briat and Alexandre Seuret
cs.SY math.CA math.DS math.OC