مريم جوشن

Modeling inventory systems and making decision about ordering policies is one of the important branches of Scientific and Industrial Researches, so that a large number of researchers have been checking and analyzing different models of inventory and production control, considering the importance of maintaining the inventory in production systems and their costs. In most of the existing models it is assumed that the items can be stored in unlimited time in order to fulfill the future demands and their quality as well as their quantity does not change over time. However, there are certain types of products that will be deteriorated or will become unusable over time (such as vegetables, meat, food, alcohol, photographic film, medicines, etc.), and there are some other types, the values and performances of which will be increased over time (such as handmade carpets, pickles, wine, etc.). As a result, if the rate of deterioration or amelioration is significantly high or is not low enough, its effect cannot be ignored. A few researchers have been engaged to simultaneous deterioration and amelioration. In fact, the quantity, value or performance of some of the products will be increased over time. These products are called ameliorating products. an‎d some of the products will deteriorate over time for some reasons such as corruption, evaporation, illness and deaths in animals. These products are called deteriorating products. In this study, some items such as young cattle, fish, chickens, ducks, pigs, etc. that are being ameliorated and deteriorated simultaneously are being discussed. In fact, the cattle grow faster at the beginning and later their growth will be slower. As a result, in this model, the rate of ameliorating is a decreasing function of time and the rate of deterioration is an increasing function of time.