Re: Derivates docs

+          "@volatility is the annualized volatility, in percent, of the
+          "asset for the period through to the exercise date.  "
+          "@days_to_maturity the number of days to exercise, and @rate
is "

Apologies if I'm way off-beam here - I couldn't work out if these
functional interfaces are intended to be compatible with something
that already exists.  Three points come to mind:

1) Wouldn't it be simpler if time-to-expiry is given in years,
to be consistent with the annualization of the vol and the risk-free
rate - saves the usual 365/365.25 tedium.  Also the docs don't appear
to state the compounding assumption of the risk-free rate (I assume
it's annualized as well).

2) These ten funcs are often collapsed into one by many financial
spreadsheet libraries - they take a parameter "C" or "P" for the
option type and a string argument to specify the requested output.
(If the output argument is an array one can return various values
for the price of a single calculation - not too important for BS
since it's quick but it's a helpful style for more heavyweight stuff)
Also when one is sceptical about say the gamma you can change an
input cell to see the delta, not edit the function call also risking
that the signature is different.

3) Spreadsheet gurus (wrong word, I really mean "nargs" but I suspect
it's a britishism) will often implement their own functions which
improve the builtin stuff.  The COUPNCD stuff I was just reading is
a prime example, and without disrespect to the B-S code referenced
here I might be doing the same.  I imagine this is quite common, so
that statistics nargs have their own regression functions
with extra bells and whisles and diagnostics and so on.  One issue
comes to mind: if I implement a function with the same name and
signature as a function in, can I have both
libraries loaded? I presume not?  If not, should I be able to,
calling derivatives::blaa or mylib::blaa explicitly? I'm
imagining the plugin manager could have a toggle to 'export' the
names into the unqualified namespace...

Hmm, I'm rambling. I'll try to be quick.  Spreadsheets would I
think benefit from this structure.  If I look at the number-theory
plugin I see both ithprime() and nt_phi().  Python has py_abs
which is a little odd even for an example - shouldn't it be able
to provide an alternative implementation of abs which can be
switched in?

Enough...  If anyone indulges in troll-feeding with me I'm happy
to keep ranting, but otherwise I should spare you.



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