Re: [Quantlib-dev] [QuantLib-svn] SF.net SVN: quantlib: [13854] trunk/QuantLib/ql/interestrate.hpp

[Ferdinando A. <na...@am...>]

On Jan 2, 2008 3:59 PM, Luigi Ballabio <lui...@gm...> wrote:
> > It's quite a while that I've been considering to define the default
> > DayCounter in userconfig.hpp (and switch to ActualActual::ISDA in the
> > meantime): any objection if I do it?
>
> Yes--I don't like it :)  I'd rather have no default at all.

ok, I take your point: feel free to remove them as soon as you like or
wait for me to gradually remove them.
For what I'm mostly concerned it is enough to have defaults in the xml
specification of QuantLibXL, I don't need C++ defaults.

> I'm not sure that we should use a default day counter for the
> term structures that require one.  If anything, it _increases_ the
> inconsistency risk---if the user sets the day counter to one curve and
> not to the other, he'll (silently) get two curves with different day
> counters. It would be safer to have him specify both explicitly.

just to get the record straight: I think we shouldn't have a day
counter at all in term structure, as the way to calculate time might
be an implementation detail not available to end user tweaking.
On one hand a user selectable day counter might result in potential
mistakes, as it would happen if one uses 30/360, uses different day
counters for interacting term structures, etc. On the other hand it
does provide little benefit, namely it allows for a time-based public
interface where the user can decide how to measure time.
I don't feel that requiring ActualActual::ISDA as the only way to
measure time would harm anyone, and would remove all those possible
inconsistencies.
Just my 0.02=80

ciao -- Nando