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

From: Dave Steffen (dgsteffen_at_[hidden])
Date: 2007-02-16 12:45:25

John Maddock writes:
 > 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

 Exactly.  I suspect the various grumblings that Gennadiy hears about
 this topic has much more to do with a mismatch between names and
 people's expectations than any fundamental problems.

 > 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.

 Right.  At least, that's true of people like me who do mathematical
 stuff.  Maybe there are vast herds of C++ programmers out there who
 think in terms of percentage tolerance, though.  I'm not saying it
 was necessarily a bad design problem.  It's a (mildly) bad design for
 what _I_ want, but then, I'm wrapping the whole unit test library up
 in my own interface anyway. :-)

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Dave Steffen, Ph.D.                Disobey this command!
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