Question

Me and a friend are writing a program which is supposed to solve a CLP problem. We want to use minimize to optimize the solution but it won’t work, because it keeps saying that the number we get from sum(P,#=,S) is between two numbers (for example 5..7). We haven’t been able to find a good way to extract any number from this or manipulate it in any way and are therefore looking for your help.

The problem seems to arise from our gen_var method which says that each element of a list must be between 0 and 1, so some numbers come out as “0..1” instead of being set properly.

Is there any way to use minimize even though we get a number like “5..7” or any way to manipulate that number so that we only get 5? S (the sum of the elements in a list) is what we’re trying to minimize.

gen_var(0, []).
gen_var(N, [X|Xs]) :-
        N > 0,
        M is N-1,
        gen_var(M, Xs),
    domain([X],0,1).

find([],_).
find([H|T],P):- match(H,P),find(T,P).

match(pri(_,L),P):-member(X,L), nth1(X,P,1).

main(N,L,P,S) :- gen_var(N,P), minimize(findsum(L,P,S),S).
findsum(L,P,S):- find(L,P), sum(P,#=,S).

Answer 1

I’ve slightly modified your code, to adapt to SWI-Prolog CLP(FD), and it seems to work (kind of). But I think the minimum it’s always 0!

:- use_module(library(clpfd)).

gen_var(0, []).
gen_var(N, [X|Xs]) :-
    N > 0,
    M is N-1,
    gen_var(M, Xs),
    X in 0..1 .

find([], _).
find([H|T], P):-
    match(H, P),
    find(T, P).

match(pri(_,L),P):-
    member(X, L),
    nth1(X, P, 1).

findsum(L,P,S) :-
    find(L, P),
    sum(P, #=, S).

main(N, L, P, S) :-
    gen_var(N, P),
    findsum(L, P, S),
    labeling([min(S)], P).

Is this output sample a correct subset of the expected outcome?

?- main(3,A,B,C).
A = [],
B = [0, 0, 0],
C = 0 ;
A = [],
B = [0, 0, 1],
C = 1 ;