On Mon, 27 Oct 2008, Janis Voigtlaender wrote:
Henning Thielemann wrote:
On Mon, 27 Oct 2008, L.Guo wrote:
I think this is unresonable. then try it in GHC 6.8.3.
Prelude> round 3.5 4 Prelude> round 2.5 2
Is there any explanation about that ?
It's the definition we learnt in school ...
Hmm, Henning, this is strange. The two of us went to the very same school, but I know for a fact that I learnt 2.5 to round to 3, not 2 as above. ;-)
I meant the school before GCG! :-] So it seems to differ between schools and even teachers. (Much like the question whether zero should be counted as natural number or not.)
I think one reason is that repeated rounding should not be worse than rounding in one go. Consider the rule 'use ceiling when the first removed digit is 5'. Then
0.45 - (round to one place) -> 0.5 - (round to integer) -> 1
but
0.45 - (round to integer) -> 0
That is of course true (and was the topic of heated discussion with my fourth grade math teacher), but does not explain 2.5 -> 2.
Because doing otherwise would be odd rounding. ;-)