A formula for IRR

[salvomic]

I'm completing a program to calculate IRR, MIRR (modified IRR) and NPV for cash flows, both with list or matrix (editing them inside the program, L1 or M1), thanks to your help and good tips: stay tuned :-)

(I need only a reply about including some code of another user...)

I'm using solve() because it works better, also if in CAS it gives a warning in Terminal (for now I'm not be able to avoid that).