Probabilistic Inventory Designs
1 . CONTINUOUS REVIEW DESIGNS
1 . 1 " Probabilitized" EOQ Version
Some experts have searched for to adapt the deterministic EOQ style to echo the probabilistic nature of demand by utilizing an estimation that superimposes a constant buffer stock within the inventory level throughout the complete planning ecart. The size of the buffer is decided such that the probability of running out of stock during lead time (the period between placing and receiving an order) does not go beyond a prespecified value. Let
L = Lead time passed between placing and receiving an order
[pic] sama dengan Random varying representing require during business lead time [pic] = Average demand during lead period
[pic]= Common deviation of demand during lead time
B = Buffer share size
a = Maximum allowable probability of running low on stock during lead period The main supposition of the version is that the demand,[pic] пјЊduring lead time L is normally sent out with imply [pic] and standard change [pic]-that can be, N([pic], [pic]) FIGURE 14. one particular
Buffer share imposed for the classical EOQ model
Figure 13. 1 depicts the relationship between buffer inventory, B, as well as the parameters of the deterministic EOQ model including the lead time T, the average require during business lead time, [pic]#@@#@!!, and the EOQ, y*. Remember that L need to equal the effective lead time. The probability declaration used to identify B can be written because P [pic] [pic] B +[pic] [pic] [pic]
We can convert [pic] to a standard N (O, 1) random variable by using the following substitution [pic]
Thus, we have
Determine 14. 2 defines [pic] such that
Hence, the buffer size must meet
The need during the business lead time M usually is usually described with a probability thickness function per unit time (e. g., per day or perhaps week), from where the syndication of the require during D can be determined. Provided that the demand every unit time is normal with mean D and normal deviation [pic], the mean and standard deviation, [pic] and [pic], of require during business lead time, M, are calculated as [pic]
The method for [pic] requires D to be (rounded to) a great integer worth. [pic]
EOQ = 1000 models. If the daily demand is normal with suggest D sama dengan 100 lights and normal deviation [pic] = 12 lights-that can be, N (100, 10)-determine the buffer size so that the possibility of running out of stock is definitely below a =. 05. We know, the effective lead time is L sama dengan 2 times. Thus,
Given [pic]= 1 . 645, the buffer size is calculated as
W [pic] 13. 14 5. 1 . 645 [pic] 3 neon lamps
Thus, the perfect inventory insurance plan with buffer B necessitates ordering one thousand units when the inventory level drops to 223 (= B + [pic]sama dengan 23 + 2 * 100) models.
1 . two Probabilistic EOQ Model
There is not any reason to think that the " probabilitized" EOQ model can produce an optimal inventory policy. The fact that important information regarding the probabilistic mother nature of require is initially ignored, simply to be " revived" in a totally 3rd party manner for a later on stage from the calculations, is sufficient to refute optimality. To treat the situation, a far more accurate unit is offered in which the probabilistic nature from the demand is included directly inside the formulation of the model. In contrast to the case in Section 1 . 1, the newest model enables shortage of demand, as Physique 14. a few demonstrates. The policy requires ordering the amount y anytime the inventory drops to level R. As in the deterministic case, the reorder level L is a function of the business lead time between inserting and receiving an order. The optimal values of y and R are determined by minimizing the anticipated cost per unit period that includes the sum of the setup, holding, and scarcity costs. [pic]
The unit has 3 assumptions.
1 ) Unfilled require during business lead time can be backlogged.
installment payments on your No more than 1 outstanding buy is allowed.
3. The distribution of demand during lead time remains standing (unchanged) eventually.
To develop the total cost function per unit time, allow
f(x) sama dengan pdf of demand, times,...
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