Introduction Let D be the demand for an item over a given period of time.We express it as the sum of two parts Dpet and Dran: D=DDet+DRam In many cases DDDet even DRam0: When the variance of the random component,Dram is small relative to the magnitude of Dpet: When the predictable variation is more important than random variation; When the problem is too complex to include an explicit representation of randomness in the modelIntroduction Let D be the demand for an item over a given period of time. We express it as the sum of two parts DDet and Dran: D=DDet+DRam In many cases DDDet even DRam0: • When the variance of the random component, DRam is small relative to the magnitude of DDet； • When the predictable variation is more important than random variation; • When the problem is too complex to include an explicit representation of randomness in the model