Complete second order linear differential equations with almost periodic solutions (Q1191844)

The author considers equations of the type \(u''(t)+Bu'(t)+Au(t)=0\) \((t\geq 0)\) in a complex Banach space, where \(A\) and \(B\) are densely defined closed linear operators. He characterizes equations having almost periodic solutions using results of \textit{H. O. Fattorini} [Second order linear differential equations in Banach spaces, Amsterdam (1985; Zbl 0564.34063)] and of the authors [Pac. J. Math. 142, 175-195 (1990; Zbl 0731.34070)].