Re: random number generators for calc

On Wed, Nov 28, 2012 at 5:07 PM, tino <ttk448@gmail.com> wrote:

> > > What is your opinion on implementing generators for other
> > > distributions like normal and all the ones listed under statistics
> > > (which calculate densities but don't generate)?
> >
> > Well, re-implementing the existing RAND and RANDBETWEEN with the new
> > generator is no brainer.  But I'm not sure if we really need to
> > provide multiple variants for different random number generators.
> > What we could do is to specify a run-time option for the algorithm
> > for the normal RAND and RANDBETWEEN functions rather than providing
> > multiple variants.  That would be my preference.  We already have
> > formula engine options in Tools - Options (in the Formula tab page),
> > so adding another one shouldn't be too difficult.
>
> Not sure I understand. My suggestion is that boost::mt19937 is the
> only underlying generator algorithm (generating int's) which is then
> transformed to get RAND() and RANDBETWEEN(i,j). Yet both are simple
> uniform distributions but the user might need Normal distributed
> random variables and then RAND() is of little use. So a function like
> RANDNORMAL() which generates N(0,1) (still using boost::mt19937)
> random numbers would be a useful addition, wouldn't it?

Ah ok. I think I mis-understood. Bear with me, as I'm not that versed with
random number generation algorithms at the moment.

Well, my position is that, since you know the subject matter very well, and
if you think it's a useful addition then I'm with you.

My only concern is that, we try to be compliant with ODF formula
specification, and I'm not sure how adding a custom function (that only we
understand) would affect that compliance and interoperability with other
ODF generators.  I still want to encourage adding new and useful functions;
I just want to know what sort of things we need to be aware of when adding
our own custom functions. Eike, do you have any insight on this?

Kohei