On Wed, 10 Mar 2004, Raymond Hettinger wrote: > To these, the HP12C financial calculator adds: > * solve for missing variable in (n i% pv pmt fv) > * internal rate of return and net present value for a stream of cash > flows ... > By "pretty good" implementation, I mean that the implementations should > remain as straight-forward as possible and neither promise, nor get in a > snit about being accurate to the last place (i.e. a 9 place > approximation of gamma would be considered fine). Pretty good is not "good enough". One of the reasons the HP 12C is so popular is that every 12C gets *exactly* the same answer for the same inputs regardless of age, model, etc. The Python version would have to be a bit exact match to a 12C for that calculation. In addition, there are going to be requirements for directed rounding to ensure the stability of some functions over their domains. Directed rounding generally causes a machine wide pipeline drain and lots of ancillary machine wide FP effects. Having Python cause FP random FP bugs in other programs would not be good for its reputation. Personally, I would rather see extremely good and accurate, but possibly complex versions of these mathematical functions added into Python proper with the calculator module simply being a wrapper around the base library functions. That way, the calculator automatically benefits when the "state of the art" method in the main library advances or is corrected. -a
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