Smoothing Parameter Subcommands (EXSMOOTH command)

ALPHA, GAMMA, DELTA, and PHI specify the values that are used for the smoothing parameters.

• The specification on each subcommand is either a value within the valid range, or the keyword GRID followed by optional range values.
• If GAMMA, DELTA, or PHI are not specified but are required for the model, the default values are used.
• ALPHA is applied to all models. If it is not specified, the default value is used.

ALPHA. General smoothing parameter. This parameter is applied to all models. Alpha can be any value between and including 0 and 1. (For EM models, alpha must be greater than 0 and less than or equal to 1.) The default value is 0.1.

GAMMA. Trend smoothing parameter. Gamma is used only with models that have a trend component, excluding damped seasonal (DA, DM) models. It is ignored if it is specified with a damped seasonal or no-trend model. Gamma can be any value between and including 0 and 1. The default value is 0.1.

DELTA. Seasonal smoothing parameter. Delta is used only with models that have a seasonal component. It is ignored if it is specified with any of the nonseasonal models. Delta can be any value between and including 0 and 1. The default value is 0.1.

PHI. Trend modification parameter. Phi is used only with models that have a damped trend component. It is ignored if it is specified with models that do not have a damped trend. Phi can be any value greater than 0 and less than 1. The default value is 0.1.

The following table summarizes the parameters that are used with each EXSMOOTH model. An X indicates that the parameter is used for the model.