RE: [boost] Re: Formal review: New Boost.Test Library

From: Fernando Cacciola (fcacciola_at_[hidden])
Date: 2001-12-06 13:50:10

----- Original Message -----
From: rogeeff <rogeeff_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Thursday, December 06, 2001 3:13 PM
Subject: [boost] Re: Formal review: New Boost.Test Library

> --- In boost_at_y..., "Fernando Cacciola" <fcacciola_at_g...> wrote:
>
> > > So, the system might
> > > provide functions to roughly estimate the expected error on the
> basis of
> > > the nature of the computation, the orders of magnitude of the
> numbers
> > > involved, and the properties of the current platform.
> > >
> > I agree that this would be *really* useful.
> > I'm not sure if there is any 'successful' research done in this
> area,
> > though.
> > Anyway, it's been quite some time since I last looked this up.
> > If I ever have the time, I would try to locate some recent reports
> about
> > this to see if an algorithm can be implemented.
>
> What about the algorithm implemented currently? It's documented on
> Floating-Point Numbers comperison tools page. Floating -point
> comparison tools could allows to omit a tolerance (macro does not
> allow this that is why number_of_rounding is not optional now).
>
I'm refering to an algorithm to find out the proper tolerance for a given
computation, which is what Ullrich was asking for.
Your implementations are of algorithms that 'scale' a given tolerance to
accomodate it to either the operands or the computation steps, but the
tolerance to be scaled must anyway be 'guessed' or fixed.

BTW: In your document you say:

 "is based on the reliable comparison algorithm"...

 I wouldn't say 'reliable'.
 Perhaps 'more confident'.

"The rounding error for a floating-point value should not exceed one half of
the std::numeric_limits<T>::epsilon(). "

Actually, the error is for the "operation", not the "value".
Besides, and more importantly, this rule holds only with respect to
*arithmetic* operations: + - * /
It doesn't hold, for instance, if you call 'sqrt()'.

Fernando Cacciola
Sierra s.r.l.
fcacciola_at_[hidden]
www.gosierra.com