Dear SAP expert,
We are assesing the use of forecast. I have read a lot about the formula for forecast and the result still not tally.
I create material with following data:
I have input consumption values like this:
and then run the forecast on period 01.2016
I got the following value (from table PROP):
The forecast result itself from table PROW
So, referring to formula for producing forecast in here:
and to check the accuracy in here:
Evaluating Forecast Accuracy - Consumption-Based Planning (MM-CBP) - SAP Library
My questions are:
1. Why after the forecast execution, my model shows blank? As I understand if originally is J (auto), after forecast execution, SAP will know already which model to be selected.
2. I understand how to calculate error total, as I have calculated manually in paralel using the formula (from link 'evaluating forecast accuracy'), by summing up the value of value difference of ex-forecast with its historical actual value, I got =18.169 which is totally the same (no question in here)
3. I dont understand how SAP come up with the MAD (table PROP) and how SAP can have MAD in previous period? I assume that it is by dividing the total of absolute difference of ex-forecast with its historical actual value divided by 12 (periods), I got 4.294 while SAP got 4.072 (not to mention dont know how SAP come up with 4.224 for MAD previous period, while this is the first time I execute forecast for this material.
4. I notice that trend is calculated in table PROP (trend = -0.320), and basic value (= 6.064) and each forecast value in table PROW also has its season index. Taking example of period 01.2016 (first date = 01/01/2016) from table PROW where season index is 0.61. From formula in link 'trend and seasonal' the forecast should be = (basic value + (forecast period * trend)) * season index.
= (6.064 + (12 * -0.32)) * 0.61
= 1.357
in which SAP calcualte for 01.2016 = 4
is my understanding of the formula not correct?
Best regards,
John