On Tue, 12 Oct 2010 20:53:16 +0200, cej38 <junkerme...@gmail.com> wrote:
On Oct 12, 12:50 pm, David Sletten <da...@bosatsu.net> wrote:
This discussion may
help:http://www.gettingclojure.com/cookbook:numbers#comparing-floats
I originally tried something like float= described in the link, I give
the definition here
(defn float=
([x y] (float= x y 0.00001))
([x y epsilon]
(let [scale (if (or (zero? x) (zero? y)) 1 (Math/abs x))]
(<= (Math/abs (- x y)) (* scale epsilon)))) )
And the truth-table that was given with the function definition:
(float= 0.01 0.0) => false
(float= 0.001 0.0) => false
(float= 0.0001 0.0) => false
(float= 0.00001 0.0) => true
And this works for the problem that I discussed before
user=> (float= 0.0001 (- 12.305 12.3049))
true
But I can come up with a use case where it fails:
user=> (float= 12.3049 12.305)
true
The problem is that the IEEE specification does a great job of
comparing floats, but does a crap job of doing simple math on them.
and again it does exactly what it promises to do:
epsilon is maybe wrong-named here because it is not absolute value, but
amount of significant figures. it is multiplied by x to get precision. so
what you are asking is
|12.3049 - 12.305| <= 12.3049 * 0.00001 which holds true
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