We study the inventory model with deteriorating items and time-varying demand and shortages created by Goyal et al. in 1992. Recently, Chang and Dye published a paper in the Journal of the Operational Research Society to extend this inventory model. However, their structure for the shortage cost and the opportunity cost due to lost sales had a problem. The purpose of this short note is threefold. First, we point out there is a necessary condition to run the algorithm of Chang and Dye. Second, we prove that for increasing demand the necessary condition is satisfied. Third, for the general time-varying demand, we offer an alternative to avoid the problem. A numerical example is provided to illustrate our procedure.
