tdf94635 (FORECAST functions) and triple exponential smoothing

[Winfried Donkers]

Hi Eike,

> > To avoid double work, am I correct that the current LO codebase does not
> contain code that uses triple exponential smoothing?
> 
> I'm quite sure we don't have such. Not even double I guess ;-) The only
> place I ran across exponential smoothing was
> sc/source/ui/StatisticsDialogs/ExponentialSmoothingDialog.cxx
> ScExponentialSmoothingDialog::ApplyOutput()

OK, that means I have chosen my main winter task ;-)
 
> > I would also like to create a new source file,
> sc/source/core/tool/interpr8.cxx, as probably a lot of code lines will be
> added, all specifically for FORECAST.ETS functions. Any objections to
> that?
> 
> No, please go ahead. Would be good to have every new code related in one
> place and in a separate file.

OK, I will place all ETS code in interpr8.cxx (and leave the linear FORECAST code in interpr3.cxx).

> Btw, do you have access to Excel 2016 to compare results?

No, that will be the next challenge, finding someone with access to EXcel 2016. 
But it will take quite some time before my code will be forecasting with ETS, I must first get to some efficient algorithms to obtain smoothing constants alpha, beta and gamma and then I can really start coding the lot.

Winfried