In the above mentioned articles, most researchers assumed that inventory holding cost is constant. But in
practice, holding cost may not always be constant. It may increase over time. Mishra et al. (2011) developed
deteriorating inventory model considering time dependent holding cost when demand is increasing with time.
In all the articles mentioned above, demand of product is either linearly or exponentially changing over time.
But for many products, during its decline phase, demand first decreases constantly, then declines at uniform rate