ODFF: IRR

IRR
as documented by Excel returns an error in Excel under certain 
conditions (if the guess is wrong). ODFF needs to say if this is 
legitimate behaviour or not. Note that a less naive 
implementation could perhaps be designed, eg when solving for <5 
terms (or certainly for 2 terms as in the error example that 
Excel Help gives). Iteration is theoretically necessary for 6+ 
terms I think. The accuracy to be achieved needs at least a 
mention, even if it is not to be mandated.

David King