Hi Reuben,
Thanks for your contribution. I didn't know the Apache POI Libraries and much less the fgl interface to it.
In any case, the corresponding Excel function for what I am doing is XIRR, which is not an Excel standard function but an Add-in. The difference is that in IRR you pass a list of values and in XIRR you pass a list of values and dates. To use IRR instead, in a 4 year loan for example, I'll have to pass around 1400 values, 95% of the being 0.
I could not find it i POI docs, I supposed because it is an Add-in.
Regards
Luis