The calculation for characteristic multiplier of Hill's equation in case q(t) < 0

We have given the calculation for characteristic multiplier of Hill's equation x''+q(t)x=0 in case q(t)>0 in the work of Jinlin Shi et al. [Appl. Math. Comput., in press (AMC8559)]. In this paper, we consider the calculation for characteristic multiplier in case q(t)<0.