Summary: This study is motivated by the paper of K. Skouri, I. Konstantaras, S. Papachristos
and I. Ganas
[Eur. J. Oper. Res. 192, No. 1, 79–92 (2009; Zbl 1171.90326
)]. We extend their inventory model from ramp type demand rate and Weibull deterioration rate to arbitrary demand rate and arbitrary deterioration rate in the consideration of partial backorder. We demonstrate that the optimal solution is actually independent of demand. That is, for a finite time horizon, any attempt at tackling targeted inventory models under ramp type or any other types of the demand becomes redundant. Our analytical approach dramatically simplifies the solution procedure.