"vandenberg p" wrote:
Read my answer carefully: It says that there can be as many
answer as sign changes or "less." As long as there is an answer
and the guess rate (either the implicit one or the supplied one)
is in the right area an answer is provided.

And read my answers carefully -- both of them.

First, your original response did not allude to the fact that
proper choice of "guess" might find a solution. I did not
want other readers to be left with the (wrong) impression
that simply because there are a lot of cash flow sign changes,
there would be no solution or it would be difficult for IRR
to find a solution. As you point out in your second response,
it all depends on how close the (default) "guess" is to any
one of the solutions.

Second, and more significantly, I said that the number of sign
changes was not "necessarily" the answer -- as in "necessary
and sufficient" -- as you seemed to imply. In fact, as I indicated
in my other response, the real problem is that there is __no__
solution, at least to 2 of the 3 examples. It would not matter
how close a "guess" you make. It has little to do with the
number of sign changes (albeit we might need more than 2 or
3 for the situation to arise).