New FORECAST.ETS function in Calc
winfried.libreoffice at gmail.com
Thu Jan 7 07:44:59 PST 2016
As the making of the new FORECAST.ETS functions is nearing its
completion, I would like to discuss a naming issue.
Exponential Triple Smoothing has two types of calculation, the
difference being the way in which the periodical (seasonal) influence is
The first (and oldest) way is to define the periodical influence in
absolute values (i.e. in July 10 extra ice creams are sold as compared
to the average). This is called the additive method and is used by Excel
2016 in their FORECAST.ETS functions.
The second (newer and often more realistic) way is define the periodical
influence in relative terms (i.e. in July 5% extra is sold). This is
called the multiplicative method.
The method names indicate the way forecasts are calculated.
A sample document with the functions for various data sets and graphs is
attached to tdf#94635:
I have created both additive and multiplicative FORECAST.ETS (forecast),
FORECAST.ETS.STAT (statistical values like standard deviation) and
FORECAST.ETS.PI (prediction intervals, an indication of the accuracy of
the forecast) functions. That are 6 functions, with long names, e.g.
As an alternative I could add an optional argument to the function,
indicating whether (1) additive, (2) multiplicative or (3) the best of
the two is to be used for forecasts. IMHO the default value of the
argument should be 3.
On export/import to/from xlsx, this extra argument can be
removed/inserted with value 1.
Using this extra argument reduces the number of functions names, the
length of the function names and quite some lines of UI code.
Before making any changes, I would like to hear your thoughts about
this, as well as thoughts from others from a UI point of view.
BTW, I think these functions should be proposed to be added to the
OpenFormula standard, they have a lot of practical use cases.
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