Re: [eclipse-clp-users] negate constraints

From: Oliver Shycle <oliver.shycle_at_...1...>
Date: Wed, 31 Mar 2010 14:27:35 +0200
Hello,

well I think the negation axample was not really good to express what i
want. Let me formulate the problem like this:
We stick to the variables and their domains as before. I need constraints
that express the following: "if any variable has a value greater than eight,
there must be at least one variable with a value smaller than eight."
-------------------------------
example :-
    OutputModel = [A, B, C, D],
    A #:: 1..100,
    B #:: 1..100,
    C #:: 1..100,
    D #:: 1..100,

% constraints

    labeling(OutputModel),
    writeln(OutputModel).
---------------------------------

I dont know how to express such kind of constraints.
Thanks for your help.

Oliver.

On 31 March 2010 11:02, Alexandre Saidi <Alexandre.Saidi@...37...> wrote:

> Hi Olivier,
> I’m not sur i understand what you want to do with the negation.
>
> Tell me what if :
> example :-
>
>     OutputModel = [A, B, C, D],
>     A #:: 1..100,
>     B #:: 1..100,
>     C #:: 1..100,
>     D #:: 1..100,
>
> #\+ (A #> 8 #\/ B#> 8 #\/  C #> 8 #\/ D#> 8),
>
>     labeling(OutputModel),
>     writeln(OutputModel).
>
> In both cases,  constraint propagation will restrict variable domaine.
> It’s better not to use Disjunction (like member).
>
> Alex
>
> Le 30 mars 2010 à 09:57, Oliver Shycle a écrit :
>
> Hi all,
>
> I have a problem to express negated constraints in ECLiPSe. In my programm,
> I want to express what value certain interval constraints may NOT have.
> Consider the following problem description: the program shall find values
> for four variables such that the values are NOT greater than 8.
>
> Here's the code:
> ------------------------------------------------------
> :- lib(ic).
>
> example :-
>
>     OutputModel = [A, B, C, D],
>     A #:: 1..100,
>     B #:: 1..100,
>     C #:: 1..100,
>     D #:: 1..100,
>
>     not(wrong_value(OutputModel)),
>     labeling(OutputModel),
>     writeln(OutputModel).
>
> wrong_value(Vars) :-
>     member(Var, Vars),
>     greater_eight(Var).
>
> greater_eight(X) :-
>     X #> 8.
> ------------------------------------------------------
>
> I know that I rather could limit the variable's domains to a maximum of 8,
> but I want to demonstrate my problem with this snippet. When ECLiPSe comes
> along the constraint "X #> 8" with the first variable of the list, the term
> evaluates to true. Therefore wrong_value evaluates to true without even
> setting up constraints for the other variables. The negation
> not(wrong_value(OutputModel)) thus becomes false and ECLiPSe sais it can't
> find a solution. If I test the code with a set of integers instead of
> variables everything works as expected.
> How can I tell ECLiPSe not to evaluate X #> 8 instantly, but keeping the
> constraint in mind for later instantiation during labeling/1?
>
> Many thanks for your help.
>
> Oliver.
>
>
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>  -------------------------------
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Received on Wed Mar 31 2010 - 12:27:42 CEST

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