Creates a forecast with default parameters (alpha = 0.5, beta = 0.4, gamma = 0.6, number of forecasted values = length of period). You only need to specify the length of a season (number of values per season).

Creates a seasonal forecast. Set the following parameters:

• alpha: overall smoothing parameter (between 0 and 1)
• beta: seasonal smoothing parameter (between 0 and 1)
• gamma: trend smoothing parameter (between 0 and 1)
• m: number of values to forecast (between 0 and period)
• period: values per season (length of period) in the historical data
• data: list of float values with historical data