- ABC analysis
- Backorders
- Container shipments
- Economic order quantity
- Fill Rate
- Financial impact of accuracy
- Inventory accuracy
- Inventory control
- Inventory costs (carrying costs)
- Inventory turnover
- Lead time
- Lead demand
- Min/Max Planning
- Minimal Order Quantities (MOQ)
- Multichannel Order Management
- Optimal service level formula
- Perpetual Inventory
- Phantom Inventory
- Prioritized Ordering
- Product life-cycle
- Reorder point
- Replenishment
- Safety stock
- Service level
- Stock-keeping unit (SKU)

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MOQ (Minimal Order Quantities) are a ubiquitous form of ordering constraint in supply chain. An MOQ constraint indicates that a supplier won't accept a purchase order below a specified threshold typically expressed in units or in dollars. Frequently, multiple MOQ constraints coexist and must be satisfied together. The general MOQ problem consists of computing the (near) optimal purchase orders that both satisfy all the MOQ constraints while maximizing the economic returns associated to the units purchased.

The general MOQ problem is formalized as a

`moqsolv`

, the advanced numeric solver provided by Lokad to address the general MOQ problem.- a minimal quantity expressed in units per SKU, which typically reflects items that are too cheap to be sold individually.
- a minimal quantity expressed in dollars for the purchase order as a whole, which is frequently encountered when the supplier does not charge for the delivery.
- a minimal quantity expressed in units per
*category*of items, which is frequently found for products that are*made to order*with minimal size on production batches.

Dealing with one constraint at a time is usually reasonably straightforward in practice. However, as soon as multiple MOQ constraints need to be taken into account together at the same time, composing a purchase order that satisfies all those constraints becomes a lot harder.

- the
**items**which represent what can actually be purchased. Item quantities are frequently integral numbers; although there is no restriction here for them to be. - the
**ordered quantities**for every item (possibly zero) which represent a potential solution to the MOQ problem. - the
**rewards**associated to each extra unit for each item - basically what is obtained through the stockrwd function (stock reward), although using this function is not a requirement. - the
**costs**associated to the units to be acquired. The goal is indeed to maximize the reward for a given spending budget expressed in*costs*. Costs are typically expected to be flat per unit, but here we don't make assumptions; thus, price breaks may be taken into account. - the
**targets**which represent a way of specifying a stopping criteria which may not be the actual costs. This one is quite subtle, and covered in greater detail below.

The canonical stopping criteria while purchasing according to a

The concept of the

Ex: Frank the supply chain manager puts a target at 90% fill rate. The solving the MOQ problem consists of computing the smallest order - in costs - while *maximizing the rewards* that delivers a 90% fill rate. This order is NOT the smallest order possible to achieve the 90% fill rate - as this would be a pure fill-rate prioritization. Instead, it's the smallest order that, while prioritizing the rewards, is large enough to deliver a 90% fill rate. A pure fill-rate prioritization would have been a mistake because, unlike the stock reward, it does not take into account the cost associated to the generation of dead stock.

Let $I$ be the set of items being considered for ordering. Let $q_i$ with $i \in I$ the quantity to be ordered for the item $i$.

Then, we define a series of functions.

- Let $r_i(q)$ be the
*reward*when holding $q$ units of the item $i$. - Let $c_i(q)$ be the
*cost*when buying $q$ units of the item $i$. - Let $t_i(q)$ be the
*target*when holding $q$ units of the item $i$.

The reward function can return positive or negative values, however both the cost and target functions are strictly positive: $$\forall i, \forall q, c_i(q) > 0 \text{ and } t_i(q) >0$$ Let $M$ be the set of MOQ constraints. For each $m \in M$, we have $I_m$ the list of items that belongs to the constraint $m$ and $Q_m$ the minimal quantity that should be reached to satisfy the constraint. Let $m_i(q)$ the function that defines the contribution of the item $i$ to the MOQ constraint $m$ when $q$ units are purchased. The constraint $m$ is said to be satisfied if: $$\forall i \in I_m, q_i = 0 \text{ or } \sum_{i \in I_m}m_i(q_i) \geq Q_m$$ Thus, all MOQ constraints can be satisfied in two ways: either by reaching the MOQ threshold, or by having all item's quantities at zero.

Then, let $C$ be the maximal cost that can be afforded for the purchase order. We define $\textbf{q}_C=(q_i)_i$ the best purchase order as: $$\textbf{q}_C = \underset{q}{\operatorname{argmax}} \left\{ \sum_i r_i(q_i) \text{ with $m$ satisfied } \forall m\in M \right\}$$ The purchase order is the "best" in the sense that is maximizes the reward for a given budget. The solution $\textbf{q}_C$ is not unique, however, this consideration is rather theoretical because the MOQ problem is too hard for an exact resolution anyway. For the sake of simplicity, we proceed as if the solution was unique in the following.

Finally, let $T$ be a target minimum, we define $\textbf{q}^T$ with $$C^T = \underset{C}{\operatorname{min}} \left\{ \left(\sum_{q_i \in \textbf{q}_C} t_i(q_i) \right) \geq T \right\}$$ and $$\mathbf{q}^T = \textbf{q}_{C^T}$$ The solution $\mathbf{q}^T$ is built on top of $\textbf{q}_C$, that is, it's the smallest optimal (budget-wise) ROI-maximizing solution that is good enough to fulfill the target.