Re: [boost] Boost Test Library: general floating point comparisons

From: John Maddock (john_at_[hidden])
Date: 2007-02-16 12:16:46

Gennadiy Rozental wrote:
> Which particular words/statements you are having difficulties with?

The problem for me is that it's too easy to forget that BOOST_CHECK_CLOSE 
refers to a persentage and not a relative error.  I've lost count of how 
many times I've made that mistake, even though I do understand what it does.

BOOST_CHECK_CLOSE_FRACTION is an improvement, but still doesn't spell out 
what it does.

Personally I would have liked these to have been really explicit:

BOOST_CHECK_PERSENTAGE_DIFFERENCE
BOOST_CHECK_RELATIVE_DIFFERENCE
BOOST_CHECK_EPSILON_DIFFERENCE

so that at double precision then I could use any of:

BOOST_CHECK_PERSENTAGE_DIFFERENCE(x, y, 4e-14);  // ~ 2 eps as a percent

BOOST_CHECK_RELATIVE_DIFFERENCE(x, y, 4e-16);  // ~ 2eps

BOOST_CHECK_EPSILON_DIFFERENCE(x, y, 2);  // 2eps

depending upon my mood :-)

The last option is by far the most readable to me.

To put things another way: how many people do you expect to thinking in 
terms of persentage differences between floating point numbers?  I'm afraid 
we (mostly) all think in terms of epsilon units, and once in that mind set, 
converting to persentages just doesn't come naturally.

HTH,

John.