Asymptotic Estimates for Solutions of Linear Systems of Ordinary Differential Equations Having Multiple Characteristic Roots Allen DevinatzJames Kaplan Indiana University Mathematics Journal 1973 text pdf 10.1512/iumj.1973.22.22029 10.1512/iumj.1973.22.22029 en Indiana Univ. Math. J. 22 (1973) 355 - 366 state-of-the-art mathematics http://iumj.org/access/