approxEqual() has fooled me for a long time...

[Andrei Alexandrescu]

On 10/20/10 5:32 CDT, Lars T. Kyllingstad wrote:
> (This message was originally meant for the Phobos mailing list, but for
> some reason I am currently unable to send messages to it*.  Anyway, it's
> probably worth making others aware of this as well.)
>
> In my code, and in unittests in particular, I use std.math.approxEqual()
> a lot to check the results of various computations.  If I expect my
> result to be correct to within ten significant digits, say, I'd write
>
>    assert (approxEqual(result, expected, 1e-10));
>
> Since results often span several orders of magnitude, I usually don't
> care about the absolute error, so I just leave it unspecified.  So far,
> so good, right?
>
> NO!
>
> I just discovered today that the default value for approxEqual's default
> absolute tolerance is 1e-5, and not zero as one would expect.  This
> means that the following, quite unexpectedly, succeeds:
>
>    assert (approxEqual(1e-10, 1e-20, 0.1));
>
> This seems completely illogical to me, and I think it should be fixed
> ASAP.  Any objections?

I wonder what would be a sensible default. If the default for absolute 
error is zero, then you'd have an equally odd behavior for very small 
numbers (and most notably zero). Essentially nothing would be 
approximately zero.

Andrei