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Subject: |
rationalize not returning the simplest rational |
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Date: |
Fri, 19 Jul 2013 13:18:41 +0200 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.4 (gnu/linux) |
Hello schemers,
the procedure (rationalize x1 x2) from (rnrs) takes a number x1 and
returns the simplest rational that doesn't differ from x1 by more than
x2. The implementation in guile has this behavior:
scheme@(guile-user)> (rationalize #e-0.67 1/4)
$1 = -2/3
The problem here is that -1/2 is simpler than -2/3 (since 1<2 and 2<3)
and it also doesn't differ from #e-0.67 by more than 1/4 (even though
the difference is larger than for -2/3, it is still less than 1/4). So
the result from the expression above should be -1/2.
Tested with Guile 2.0.9.40-824b-dirty.
Regards,
--
Göran Weinholt <address@hidden>
"On your own and though you feel alone you are alive.
Don't you know it's just another day." -- You Are Alive, Fragma
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--- Begin Message ---
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Subject: |
Re: bug#14905: rationalize not returning the simplest rational |
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Date: |
Sun, 21 Jul 2013 06:56:03 -0400 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) |
Göran Weinholt <address@hidden> writes:
> the procedure (rationalize x1 x2) from (rnrs) takes a number x1 and
> returns the simplest rational that doesn't differ from x1 by more than
> x2. The implementation in guile has this behavior:
>
> scheme@(guile-user)> (rationalize #e-0.67 1/4)
> $1 = -2/3
>
> The problem here is that -1/2 is simpler than -2/3 (since 1<2 and 2<3)
> and it also doesn't differ from #e-0.67 by more than 1/4 (even though
> the difference is larger than for -2/3, it is still less than 1/4). So
> the result from the expression above should be -1/2.
Fixed in 620c13e8fc02060e0af8fa38398ee4de745d41e9.
Thanks!
Mark
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