RE: [boost] test_fp_comparisons and rounding errors

From: Beman Dawes (bdawes_at_[hidden])
Date: 2003-07-07 15:05:05

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