Skip to content

Ordering Policies

deepbullwhip.policy.base.OrderingPolicy

Bases: ABC

Abstract ordering policy for a single echelon.

Source code in deepbullwhip/policy/base.py 
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
class OrderingPolicy(ABC):
    """Abstract ordering policy for a single echelon."""

    @abstractmethod
    def compute_order(
        self,
        inventory_position: float,
        forecast_mean: float,
        forecast_std: float,
    ) -> float:
        """Compute the non-negative order quantity for this period.

        Parameters
        ----------
        inventory_position : float
            On-hand inventory + pipeline - backorders.
        forecast_mean : float
            Point forecast of next-period demand.
        forecast_std : float
            Standard deviation of forecast error.

        Returns
        -------
        float
            Non-negative order quantity.
        """
        ...

compute_order(inventory_position, forecast_mean, forecast_std) abstractmethod

Compute the non-negative order quantity for this period.

Parameters:

Name Type Description Default
inventory_position float

On-hand inventory + pipeline - backorders.

 required
forecast_mean float

Point forecast of next-period demand.

 required
forecast_std float

Standard deviation of forecast error.

 required

Returns:

Type Description
float

Non-negative order quantity.
Source code in deepbullwhip/policy/base.py 
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
@abstractmethod
def compute_order(
    self,
    inventory_position: float,
    forecast_mean: float,
    forecast_std: float,
) -> float:
    """Compute the non-negative order quantity for this period.

    Parameters
    ----------
    inventory_position : float
        On-hand inventory + pipeline - backorders.
    forecast_mean : float
        Point forecast of next-period demand.
    forecast_std : float
        Standard deviation of forecast error.

    Returns
    -------
    float
        Non-negative order quantity.
    """
    ...

deepbullwhip.policy.order_up_to.OrderUpToPolicy

Bases: OrderingPolicy

Order-Up-To (OUT / base-stock) policy.

S = (L+1) * forecast_mean + z_alpha * forecast_std * sqrt(L+1) order = max(0, S - IP)

Parameters:

Name Type Description Default
lead_time int

Replenishment lead time in periods.

 required
service_level float

Target service level (e.g. 0.95). Used to set z_alpha.

 0.95
Source code in deepbullwhip/policy/order_up_to.py 
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
@register("policy", "order_up_to")
class OrderUpToPolicy(OrderingPolicy):
    """Order-Up-To (OUT / base-stock) policy.

    S = (L+1) * forecast_mean + z_alpha * forecast_std * sqrt(L+1)
    order = max(0, S - IP)

    Parameters
    ----------
    lead_time : int
        Replenishment lead time in periods.
    service_level : float
        Target service level (e.g. 0.95). Used to set z_alpha.
    """

    def __init__(self, lead_time: int, service_level: float = 0.95) -> None:
        self.lead_time = lead_time
        self.service_level = service_level
        self.z_alpha = stats.norm.ppf(service_level)

    def compute_order(
        self,
        inventory_position: float,
        forecast_mean: float,
        forecast_std: float,
    ) -> float:
        S = (self.lead_time + 1) * forecast_mean + (
            self.z_alpha * forecast_std * np.sqrt(self.lead_time + 1)
        )
        return max(0.0, S - inventory_position)