“…Our thesis work considers an additional problem that we frequently encounter in several dynamical systems: the nonnegativity of the states. (Benzaouia et al, 2006), (Benzaouia & Tadeo, 2010), , (Benzaouia et al, 2007), (Boukas & El Hajjaji, 2006), (El Hajjaji et al, 2006), (El Hajjaji & Chadli, 2008). The study of systems with nonnegative states is important in practice because many chemical, physical and biological processes involve quantities that have intrinsically constant and nonnegative signs: the concentration of substances, the levels of liquids, etc, are always nonnegative.…”