This is how round(x) is in the C library:
(http://www.gnu.org/s/libc/manual/html_node/Rounding-Functions.html)
Function: double round (double x)
— Function: float roundf (float x)
— Function: long double roundl (long double x)
These functions are similar to rint, but they round
halfway cases away from zero instead of to the nearest even integer.
I think they just compute round(x) as floor(x+0.5)
Perhaps rounding for rational numbers can be changed to floor(x+1/2),
accordingly.
On Sun, Nov 29, 2009 at 11:33 AM, mhampton <[email protected]> wrote:
> This is because in the code for rounding, an element's own round
> method is tried before converting to a float. The round function for
> rationals rounds up if its exactly halfway:
>
> else:
> q, r = self.numerator().quo_rem(self.denominator())
> if r < self.denominator() / 2:
> return q
> else:
> return q+1
>
> To get consistent results you could use round(N()) instead. But
> perhaps this should be considered a bug in the rational rounding. I'm
> not sure if there is a standard convention for that, its clearly a
> borderline case.
>
> -Marshall Hampton
>
> On Nov 29, 9:47 am, michel paul <[email protected]> wrote:
>> sage: round(4.5)
>> 5.0
>> sage: round(9/2)
>> 4.0
>>
>> I noticed some strange behavior in a graph and tried to narrow down the
>> issue. This was it.
>>
>> --
>> "Computer science is the new mathematics."
>>
>> -- Dr. Christos Papadimitriou
>
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L. Felipe Martins
Department of Mathematics
Cleveland State University
[email protected]
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