Re: [boost] [Test] BOOST_CHECK_CLOSE Feature request

From: Bjørn Roald (bjorn_at_[hidden])
Date: 2005-11-12 07:24:47

On Thursday 10 November 2005 18:33, Gennadiy Rozental wrote:
> "John Maddock" <john_at_[hidden]> wrote in message
> news:005301c5e616$7a3cef90$5c410352_at_fuji...
>
> >I have a couple of feature requests for Boost.Test:
> >
> > 1) Can BOOST_CHECK_CLOSE please print the actual difference between the
> > values (as a percent to match the tolerance) as well as the values
> > themselves?  The reason this is important, is that it's not always easy
> > to get this value from the input values - because the precision of the
> > machine
> > on which the test is run far outstrips that of the author's machine, so
> > his
> > calculator isn't any use :-(
>
> This is doable. The message would sould like this:
>
> difference between var1 {<value>} and var2 {<value>} is x% and exceeds e%
>

Why are we using percentage and not and not the epsilon value?  Percentage 
just causes you to have to move the point 2 digits in your head. 

> > 2) Can we please have a  that uses a whole number of
> > epsilon as the tolerance?  IMO BOOST_CHECK_CLOSE should have been written
> > this way to begin with, but it's too late now
>
> Actually it was this way originally. It was causing constant confusion with
> absolute comparison. I thought persents will bring better message.
> Unfortunately many users since then indicated that original version (for
> those who knew how to use it) was better. If there is a general consensus I
> am willing to rollback. Or we could introduce a new tool.

I see, I also read the docs on this.  Maybe using percent give unitroduced 
users a better hint that it is the difference between the two values as a 
percentage of their distance to zero that is tested -- not a maximum value 
for the absolute difference between the two.  I guess this is because it is 
hard to understand how to express an absolute value as a percentage.  Hence, 
you kind of force them to study what to put in as parameter, make them read 
the documentation.  If you just throw "the value of epsilon" at them, they 
may be more likely to be confused. 

I support having BOOST_CHECK_EPSILON as suggested as an alternative, its name 
suggest a clear meaning to those that have studied the concepts described in 

http://www.boost.org/libs/test/doc/components/test_tools/floating_point_comparison.html

maybe a better name would be BOOST_CHECK_CLOSE_EPSILON as it suggest
the strong relationship to BOOST_CHECK_CLOSE.  After all their functionallity 
is the same, just different expectations on one parameter.

> > Again it should print out
> > the actual relative error as a multiple of epsilon as well as the input
> > values. 

agree

I also read the docs, and spotted some problems:

copy/paste error in top of 
libs/test/doc/components/test_tools/reference/BOOST_CHECK_SMALL.html
I suspect:

BOOST_WARN_SMALL( val, tolerance )
BOOST_CHECK_CLOSE( val, tolerance )
BOOST_REQUIRE_CLOSE( val, tolerance )

should have been:

BOOST_WARN_SMALL( val, tolerance )
BOOST_CHECK_SMALL( val, tolerance )
BOOST_REQUIRE_SMALL( val, tolerance )

and
file:///dsk1/src/boost_1_33_0/libs/test/doc/components/test_tools/floating_point_comparison.html
 unreasonable to use an operator=(...) f
                                                 ^^^^^
should be operator equal not asignment

below that in same file I read: (firefox)
 u - v | <= e * |u| and | u - v | <= e * |v|
^^^
missing |

caused by:

 <P style="text-indent: -20"> |<I> u </I>-<I> v </I>| &lt;= <I>e * |u|</I> and 
                ^^^^^^^^^^^^^^
in the html souce.            

regards,
Bjørn Roald