Beman Dawes <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> At 02:22 PM 7/7/2003, Rozental, Gennadiy wrote:
>
> >I could probably prohibit usage of CHECK_CLOSE with number of rounding
> >errors provided.
> >Is there any other general recommendations how to choose the tolerance
to
>
> >FP computation correctness checking?
>
> There has been some recent discussion on comp.lang.c++.moderated, subject
> "equality of two doubles". The last post was from Andrei Alexandrescu:
>
> >What's most of the time needed is relative precision.
> >
> >So, numerical gurus: how can one express "a equals b within 0.1%" over
> >the whole range of floating point numbers? If that can be done, it would
> >be a nice useful routine.
> >
> >bool approximately_equal(double lhs, double rhs, double relative_prec)
> >{
> > // fill in here please :o)
> >}
>
> But it really doesn't seem that a test library is the right home for such
> functions. I think all the fp stuff should be removed from Boost.Test, and
> passed on as a challenge to the numerics experts.
>
> After all, the user can always write:
>
> BOOST_CHECK( approximately_equal(...) );
>
> --Beman
>
A half-way solution is to have something like:
BOOST_CHECK_EQUAL_NUMBERS(x,y,IsEqual)
and let users specify their own Preciates.
By default, the Test library could provide
a straight-forward ABSOLUTE-ERROR comparator:
template<class N>
struct IsNearlyEqual
{
IsNearlyEqual ( N a_tol = N(1e-6) ) : m_tol(a_tol) {}
bool operator() ( N x, N y ) const
{
return x >= y ? ( x - y ) <= m_tol
: ( y - x ) <= m_tol ;
}
N m_tol ;
} ;
Which would be used as follows:
double n = ..., m = ... ;
BOOST_CHECK_EQUAL_NUMBERS(n,m,IsNearlyEqual<double>());
Fernando Cacciola
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