Before revision: Farina and S. Rinaldi, Positive Linear Systems; Theory and Applications, J. Wiley, New York, 2000 constitute a class of systems that has the important property that its variables are never negative .
After revision: state, given a positive initial stateFarina and S. Rinaldi, Positive Linear Systems; Theory and Applications, J. Wiley, New York, 2000 constitute a class of systems that has the important property that its variables are never negative .