Whats wrong with this prolog optimization solution?

Question

solve(Amounts) :-
    Total = 1505,
    Prices = [215, 275, 335, 355, 420, 580],

    length(Prices, N),
    length(Amounts, N),
    Amounts :: 0..Total//min(Prices),
    Amounts * Prices #= Total,

    labeling(Amounts).

That's not SWI-Prolog. Presumably it's [tag:eclipse-prolog] – false Mar 02 '16 at 10:40 — false, Mar 02 '16 at 10:40
Why do you say there's something wrong with it? – lurker Mar 06 '16 at 11:21 — lurker, Mar 06 '16 at 11:21

jschimpf · Answer 1 · 2016-03-08T21:45:30.297

5

There is nothing wrong with it. It is the example from http://eclipseclp.org/examples/xkcd287.ecl.txt, and if you hadn't omitted the line

:- lib(ic).

which loads the interval constraint solver, it would work just fine in ECLiPSe Prolog.

edited Mar 08 '16 at 21:45

answered Mar 03 '16 at 13:14

jschimpf

4,904
11
24

2

(cf. http://xkcd.com/287/) --- ... and `lib(ic)` is what, library for integer constraints? – Will Ness Mar 07 '16 at 20:18
2

`lib(ic)` stands for interval constraints. It implements constraints over integers and reals (represented as floating point intervals). I'll amend my answer. – jschimpf Mar 08 '16 at 21:42

score 2 · Answer 2 · 2016-03-11T22:01:53.130

Does also work in SWI-Prolog:

?- use_module(library(clpfd)).
?- [user].
solve(Amounts) :-
    Total = 1505,
    Prices = [215,275,335,355,420,580],
    length(Prices, N),
    length(Amounts, N),
    min_list(Prices, MinPrice),
    MaxAmount is Total//MinPrice,
    Amounts ins 0..MaxAmount,
    scalar_product(Prices, Amounts, #=, Total),
    label(Amounts).
^D
?- solve(X).
X = [1, 0, 0, 2, 0, 1] ;
X = [7, 0, 0, 0, 0, 0].

But I guess its not an optimization search problem,
the objective function is missing.

Bye

Whats wrong with this prolog optimization solution?

2 Answers2