# Re: [eclipse-clp-users] ECLiPSe - Real variables domain propagation problem

From: Solly Brown <sollyb_at_...25...>
Date: Mon, 27 Jul 2009 21:54:02 +1000
```Mark Wallace wrote:
> Hi Wayne,
> It's a bit late at night here, but I confess I'm puzzled by the
> following (inspired by your query):
> ?- [B, C] :: 0.0 .. 1.0, D \$= C * (1.0 - B).
> B = B{0.0 .. 1.0}
> C = C{0.0 .. 1.0}
> D = D{-1.0 .. 1.0}
> It seems to me D ought to be constrained to be non-negative.
>     Cheers
>         Mark
Eclipse treats this situation as D \$= C - C*B and the allowed bounds of
these two terms are calculated independently before being combined. So
the first term has bounds 0 < C < 1 and the second term has bounds 0 <
C*B < 1. When the second term is subtracted from the first the lowest
possible bound is 0 - 1 = -1, whilst the upper bound is 1 - 0 = 1.

Cheers, Solly

>>
>> ?- A :: 0.0 .. 0.5, [B, C] :: 0.0 .. 1.0, A \$= eval(B + C).
>> A = A{0.0 .. 0.5}
>> B = B{0.0 .. 0.5}
>> C = C{0.0 .. 0.5}
>> There is 1 delayed goal.
>> Yes (0.00s cpu)
>
>
> --
> Professor Mark Wallace
> Room 6.43
> Faculty of Information Technology
> Building H
> Monash University
> Caulfield
>
> Tel: 34276
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```
Received on Mon Jul 27 2009 - 11:54:19 CEST

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