# FORECAST.ETS.SEASONALITY Function

Returns the number of samples in period as calculated by Calc in case of FORECAST.ETS functions when argument period_length equals 1.

Exponential Smoothing is a method to smooth real values in time series in order to forecast probable future values.

Exponential Triple Smoothing (ETS) is a set of algorithms in which both trend and periodical (seasonal) influences are processed. Exponential Double Smoothing (EDS) is an algorithm like ETS, but without the periodical influences. EDS produces linear forecasts. See the Wikipedia on Exponential smoothing algorithms for more information.

The same result is returned with FORECAST.ETS.STAT functions when argument stat_type equals 9 (and period_length equals 1). This function is available since LibreOffice 5.2.

#### Syntax

FORECAST.ETS.SEASONALITY (values, timeline, [data_completion], [aggregation])

values (mandatory): A numeric array or range. values are the historical values, for which you want to forecast the next points.

timeline (mandatory): A numeric array or range. The time line (x-value) range for the historical values. The time line doesn't have to to be sorted, the functions will sort it for calculations.
The time line values must have a consistent step between them.
If a constant step can't be identified in the sorted time line, the functions will return the #NUM! error.
If the ranges of the time line and historical values aren't of same size, the functions will return the #N/A error.
If the time line contains less than 2 periods of data, the functions will return the #VALUE! Error.

data_completion (optional): a logical value TRUE or FALSE, a numeric 1 or 0, default is 1 (TRUE). A value of 0 (FALSE) will add missing data points with zero as historical value. A value of 1 (TRUE) will add missing data points by interpolating between the neighboring data points. Although the time line requires a constant step between data points, the function support up to 30% missing data points, and will add these data points.

aggregation (optional): A numeric value from 1 to 7, with default 1. The aggregation parameter indicates which method will be used to aggregate identical time values:

 Aggregation ශ්‍රිත 1 AVERAGE 2 COUNT 3 COUNT 4 MAX 5 MEDIAN 6 MIN 7 එකතුව Although the time line requires a constant step between data points, the functions will aggregate multiple points which have the same time stamp.

#### Example

The table below contains a timeline and its associated values:

 A B 1 Timeline අගය 2 01/2013 112 3 02/2013 118 4 03/2013 132 5 04/2013 100 6 05/2013 121 7 06/2013 135 8 07/2013 148 9 08/2013 148 10 09/2013 136 11 10/2013 119 12 11/2013 104 13 12/2013 118

=FORECAST.ETS.SEASONALITY(Values;Timeline;TRUE();1)

Returns 6, the number of samples in period based on Values and Timeline named ranges above, no missing data, and AVERAGE as aggregation.

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