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In a base-stock system inventory position is given by on-hand inventory-backorders+orders and since inventory never goes negative, inventory position=r+1. Once an order is placed the base stock level is r+1 and if X≤r+1 there won't be a backorder. The probability that an order does not result in back-order is therefore:
We have available a forecast of product demand d t over a relevant time horizon t=1,2,...,N (for example we might know how many widgets will be needed each week for the next 52 weeks). There is a setup cost s t incurred for each order and there is an inventory holding cost i t per item per period ( s t and i t can also vary with time if desired).
– the product quantity in the inventory. The decision of the inventory control policy concerns the product quantity in the inventory after the product decision. This parameter includes the initial inventory as well. If nothing is produced, then this quantity is equal to the initial quantity, i.e. concerning the existing inventory.
The average inventory is the average of inventory levels at the beginning and end of an accounting period, and COGS/day is calculated by dividing the total cost of goods sold per year by the number of days in the accounting period, generally 365 days. [3] This is equivalent to the 'average days to sell the inventory' which is calculated as: [4]
Modeling multiple stages allows other types of inventory, including cycle stock and prebuild along with safety stock due to time phased demands, to be more accurately predicted. [18] As part of inventory optimization, supplier performance, customer service and internal asset metrics should be continuously monitored to enable continuous improvement.
Higher WIP inventory levels are advantageous in that they can support a surge in demand, as well as improve cycle time since there is more material in production. However, this can also increase storage costs and obsolescence risk, as well as lead to waste if demand is lower than expected. [ 13 ]
In materials management, ABC analysis is an inventory categorisation technique which divides inventory into three categories: 'A' items, with very tight control and accurate records, 'B' items, less tightly controlled and with moderate records, and 'C' items, with the simplest controls possible and minimal records.
The average response time or sojourn time (total time a customer spends in the system) does not depend on scheduling discipline and can be computed using Little's law as 1/(μ − λ). The average time spent waiting is 1/(μ − λ) − 1/μ = ρ/(μ − λ). The distribution of response times experienced does depend on scheduling discipline.