Re: xirr implementation

[Morten Welinder <mortenw gnome org>]

Gnumeric gets -80.59% too, at least for me.  Jean: typo?

Note, that the input isn't particular reasonable: a loan of $15M being
repaid with three payments of $1.3M.  That clearly requires a large
negative interest rate.

Xirr is based on finding roots of a high-degree polynomial.  That is a
bit of an art form and there can be more than one solution.  Finding
the roots is an iterative process -- no closed-form formula can exist
for degree of 5 or more.

In your 577 day example there could have been that many roots
and thus different answers.  I mention this because in order to
get the result that the users wants, one really has to constrain
the roots to a range. Gnumeric uses a lower limit of -100% in
the search and an upper limit here of 57700%.

Maybe OO uses a different lower limit and thus cannot find the root.

Morten