© Production Planning and Control Dr.GENG Na Department of Industrial Engineering Logistics Management Shanghai Jiao Tong University
Production Planning and Control Dr. GENG Na Department of Industrial Engineering & Logistics Management Shanghai Jiao Tong University
© Chapter 2 Forecasting Contents 1.Introduction 2.The Time Horizon in Forecasting 3.Classification of Forecasts 4.Evaluating Forecast 5.Notation Conventions 6.Methods for Forecasting Stationary Series 7.Trend-Based Methods 8.Methods for Seasonal Series
Chapter 2 Forecasting Contents 1. Introduction 2. The Time Horizon in Forecasting 3. Classification of Forecasts 4. Evaluating Forecast 5. Notation Conventions 6. Methods for Forecasting Stationary Series 7. Trend-Based Methods 8. Methods for Seasonal Series
2.6.Methods of Forecasting Stationary Series Exponential Smoothing-the current forecast is weighted average of the last forecast and the last value of demand. new forecast a(current observation of demand)+(1-a)(Last forecast) E,=aD,-1+(1-a)E,-1 where 0<a1 is the smoothing constant,which determines the relative weight placed on the last observation of demand, while 1-a is weight placed on the last forecast. F=aD,-1+(1-a)F,-=F-1-a(F-1-D-i)=F-1-Ce-l
Exponential Smoothing -the current forecast is weighted average of the last forecast and the last value of demand. 1 1 ( ) (1 )(Last forecast) (1 ) tt t new forecast current observation of demand FD F where 0<1 is the smoothing constant, which determines the relative weight placed on the last observation of demand, while 1- is weight placed on the last forecast. 1 1 FD F tt t (1 ) 2.6. Methods of Forecasting Stationary Series 1 11 ( ) F FD t tt F e t t 1 1
2.6.Methods of Forecasting Stationary Series Exponential Smoothing F,=aD,-1+(1-a)F-1 F-1=aD-2+(1-ax)E-2 E=aD,-1+a(1-)D,-2+(1-a)2E-2 F=aD-+a(I-a)D-2+(1-a)F-2=...=>a(I-a)D- i=0
Exponential Smoothing 1 1 (1 ) FD F tt t 12 2 (1 ) FD F tt t 2 1 22 (1 ) (1 ) FD D F tt t t 2.6. Methods of Forecasting Stationary Series 2 1 22 1 0 (1 ) (1 ) ... (1 )i t t t t ti i FD D F D
2.6.Methods of Forecasting Stationary Series a) 0.1 The older of a past data,the =018 0.09 smaller of its contribution to 0.08 the forecast for a future 0.07 period. 0.06 0.05 0.04 0.03 0.02 0.01 0 0 12345678910111213141516171819 Fig.2-5 Weights in Exponential Smoothing
Fig.2-5 Weights in Exponential Smoothing The older of a past data, the smaller of its contribution to the forecast for a future period. (1 ) 0.1 i 2.6. Methods of Forecasting Stationary Series