## 2 Literature Review
### Centralization vs. Decentralization Strategies  
The effect of the number of warehouses on the stock levels in a distribution network has been the subject of research for many years. However, the literature on this problem is sparse. It is generally known that decreasing the amount of stock and, therefore, the implementation of a centralization strategy favors the reduction of inventory levels throughout the distribution network and improves the availability of stocks in the warehouses (better logistics customer service). At the same level of service, when the number of warehouses is reduced, the level of inventory in the entire network decreases. However, it should be borne in mind that this formula is only used to calculate the level of the safety margin, which is only a part of the total inventory [9; 10]. On the other hand reducing the number of warehouses results in higher transport costs-longer transport distances and possibly smaller batches of shipments to end customers, which is considered the most expensive part of transportation [11; 12]. There are a number of works that have dealt with a similar problem, e.g., [PERSON] and [PERSON] [13], who suggest a Lagrangian relaxation-based heuristics with the use of the subgradient method. [PERSON] et al. [14] took into consideration a supply chain with a production facility and multiple retailers. Another article that takes into consideration the costs of transportation is that of [PERSON] and [PERSON] [15]. They consider a semi-centralized inventory system with costs of transportation. The results of the studies concerning the centralization of stocks vary widely. The literature presents a wide range of recommendations for various external conditions [16]. [PERSON] et al. [17] suggest that decentralization may prove effective when a firm relies on the external suppliers and strategically manages inventory, while [PERSON] et al. [18] demonstrate that centralization strategy is conducive to the implementation of innovations in logistics services. On the other hand, [PERSON] and [PERSON] [19] show that centralized control is beneficial for supply chains with the unstable demand patterns, and also that centralized decision-making presents the best solution [20]. Moreover, there are some works that claim that production quantity, research and development level, and profit are highest if a centralized and decentralized supply chain exist in parallel [21]. The industry sector and type of business activity is a very important factor. The centralized stock method may be effective in businesses, in which inventory maintenance costs and their storage are extremely excessive, such as in the food business [22]. The literature rarely refers to the size of companies in relation to the benefits of centralization of warehousing. According to [PERSON] et al. [23] small and medium companies have a smaller number of resources, but also fewer skills, which translates into smaller benefits when using warehouse centralization. [PERSON] et al. [24] examined both a decentralized and a centralized storage system in the context of future costs and their changes. They showed that if there are supply disruptions and the demand is constant, decentralization of storage decreases the risk and should, therefore, also decrease the costs. The results of these studies contradict the classical views according to which, when demand is random and supply is constant, then using storage centralization is the best choice due to the risk-pooling effect. At the strategic level, the decentralization of storage can also provide a greater decision-making resilience. Also other problems were the subject of the conducted research. [PERSON] et al. [25] considered how the use of different numbers of suppliers is affected by supply disruptions. Articles by [PERSON] [26] and [PERSON] [27] address the topic of supplier selection under uncertainty.