A small update to the reported issue:
fun {SampleInts2 N}
Incr = 1.0 / {IntToFloat N-1}
in
for X in 0.0;X=<(1.0+1.0E~13);X+Incr
collect:C
do {C X}
end
end
IN the following call, the last value is displayed as 1.0:
{List.last {SampleInts2 10}}
However, it is slightly larger (actually 1.0+2.2204E~16) as the following
reveals
{List.last {SampleInts2 10}} - 1.0
Is the problem simply that there is no concise notation for 1.0+2.2204E~16?
So, therefore only 1.0 is printed (browsed, inspected, output to string)?
Thank you!
Best
Torsten
On Monday 25 June 2007 12:23:32 Torsten Anders wrote:
> Dear all,
>
> I came across some behaviour of floats in a C-style loop which I don't
> understand. In the following test function, I want to collect N floats
> between 0.0 and 1.0, including these boundaries.
>
> fun {SampleInts N}
> Incr = 1.0 / {IntToFloat N-1}
> in
> for X in 0.0;X=<1.0;X+Incr
> collect:C
> do {C X}
> end
> end
>
> {SampleInts 10}
> % -> [0.0, 0.11111 ... 0.88889]
>
> However, the last value (i.e., 1.0) is left out in the result. It appears
> that this last value is actually already slightly greater then 1.0 (due to
> the typical float problems I assume). So, I came up with the following
> hack, where I test against a number which is slightly larger than 1.0.
>
> fun {SampleInts2 N}
> Incr = 1.0 / {IntToFloat N-1}
> Max = 1.0+1.0E~13
> in
> for X in 0.0;X=<Max;X+Incr
> collect:C
> do {C X}
> end
> end
>
> {SampleInts2 10}
> % -> [0.0, 0.11111 ... 0.88889 1.0]
>
> Now, the surprising aspect for me is that with such a hack, the last
> element is indeed displayed as 1.0 and not anything slightly larger.
>
> I should perhaps mention that I am porting some Common Lisp program to Oz,
> where the equivalent of the first function works totally fine in Lisp. So,
> is there some magic at the Lisp side going on (Lisp supports ratios, not
> only floats), and the Oz behaviour is the usual thing to happen when you
> use floats? Any idea, how to write a version of SampleInts which works for
> an arbitrary high N?
>
> Thank you very much!
>
> Best
> Torsten
--
Torsten Anders
http://strasheela.sourceforge.net/
http://torsten-anders.de/
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