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From: Dave Steffen (dgsteffen_at_[hidden])
Date: 2007-02-16 12:47:58


Please don't top post. Rearranged:

Glenn Schrader writes:
>
> Hugo Duncan wrote:
> > Hi,
> >
> > Just to chime in with my problems using BOOST_CHECK_CLOSE ...
> >
> > I always have problems when checking for small numbers or zero.
> > I write something like BOOST_CHECK_CLOSE(0,x,1e-5) and start
> > wondering why it fails, then rewrite the test using an epsilon
> > value.
> >
> > When I know the value is going to be near zero this is ok, but
> > sometimes tests are written for computed values. A possible
> > solution would be to have a check that uses the maximum of a
> > relative and an absolute tolerance.
> >
> Hmmm.
>
> An absolute difference is:
>
> BOOST_CHECK_CLOSE( x, y, 1e-5 );
>
> True??

 Uh, no, I don't think so. IIRC BOOST_CHECK_CLOSE does a relative
 error check.

> so wouldn't a relative difference be:
>
> BOOST_CHECK_CLOSE( x / y, 1, 1e-5);
> or equivalently
> BOOST_CHECK_CLOSE( x, y, abs(y) * 1e-5);
> or maybe even
> BOOST_CHECK_CLOSE( x, y, max(abs(x),abs(y)) * 1e-5);

 No, that's not what BOOST_CHECK_CLOSE does, unless it's changed since
 1.33.1 (which is what I'm looking at). The discussion here is, very
 approximately, that since it's not immediately obvious _what_ kind of
 test is being done in BOOST_CHECK_CLOSE because of the name, and that
 this causes confusion.

----------------------------------------------------------------------
Dave Steffen, Ph.D. Fools ignore complexity.
Software Engineer IV Pragmatists suffer it.
Numerica Corporation Some can avoid it.
ph (970) 461-2000 x227 Geniuses remove it.
dgsteffen_at_[hidden] -- Alan Perlis
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