Global constraints in SICStus CLPFD

From: Nick Lacey (nick.lacey_at_pobox.com)
Date: 02/08/05

  • Next message: Yereth Jansen: "Re: Another try" 
    Date: 07 Feb 2005 23:41:17 +0000

    Hello,

    I think I have a question about global constraints in CLP/FD in
    SICStus. I say 'I think', as if there was a solution without using
    global constraints, that would be just as good.

    Basically, what I want to do is be able to assert and retract
    constraints between an arbitrary number of different facts in the
    database. For example:

    fact_1(A):-
            A #< 9.

    fact_2(B):-
            B #= 8.

    fact_3(A):-
            A #= B.

    [I know there is no difference between A and B in this context - this
    is for illustration only]

    .. so A = 8. If fact_2 were changed so that B #=7, the value of A
    would change dynamically, and so on.

    This is very easy if we have local constraints, like:

    all_facts:-
            A #< 9,
            B #=8,
            A #= B.
    ---------------------------------
    | ?- all_facts(A,B).

    A = 8,
    B = 8 ? ;

    no
    | ?-
    ---------------------------------

    ... as we'd expect.

    But as the number of constraints will be arbitrary, I need to be able
    to assert and retract them at runtime, so I can't hard code them into
    one clause and make them all local constraints.

    I tried using FD sets, but found I had to do a lot of manipulation and
    consistency checking myself.

    I have a feeling I'm missing something obvious ... ? Do I need to use
    global constraints? I had a look through the SICStus manual, but I'm
    afraid I didn't find the entries concerning global constraints to be
    very helpful to me. (This is a failing of myself, not of the SICStus
    manual).

    If someone could give me a simple example and/or point me in the right
    direction, that would be wonderful.

    Many thanks,

    Nick

  • Next message: Yereth Jansen: "Re: Another try"

    Relevant Pages

    • Re: CLP(FD): what is necessary?
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    • Re: Global constraints in SICStus CLPFD
      ... Nick Lacey wrote: ... > global constraints, that would be just as good. ... > one clause and make them all local constraints. ... I had a look through the SICStus manual, ...
      (comp.lang.prolog)