I have a problem in my code with turbo prolog which searches all paths and the shortest path in a graph between 2 nodes. The problem that i have is to test if the node is in the list or not (exactly in the clause of member)
1 ---- b ---- 3
--- | ---
--- | -----
a |5 d
--- | -----
--- | ---
2 --- | --- 4
-- c --
for example we have for b--->c
([b,c],5) , ([b,a,c],3) and ([b,d,c],7) : possible paths.
([b,a,c],3) : the shortest path.
and this is my code :
DOMAINS
list=Symbol *
PREDICATES
distance(Symbol, Symbol)
path1(Symbol, Symbol, list, integer)
path(Symbol, Symbol,list, list, integer)
distance(Symbol, list, integer)
member(Symbol, list)
shortest(Symbol, Symbol, list, integer)
CLAUSES
distance(a, b, 1).
distance(a, c, 2).
distance(b, d, 3).
distance(c, d, 4).
distance(b, c, 5).
distance(b, a, 1).
distance(c, a, 2).
distance(d, b, 3).
distance(d, c, 4).
distance(c, b, 5).
member(X, [X|T]).
member(X, [Y|T]) :- member(X, T).
absent(X, L) :-
member(X, L),
!,
fail.
absent(_, _).
/* find all paths */
path1(X, Y, L, C) :- path(X, Y, L, I, C).
path(X, X, [X], I, C) :- absent(X, I).
path(X, Y, [X|R], I, C) :-
distance(X, Z, A),
absent(Z, I),
path(Z, Y, R, [X|I], C1),
C = C1 + A
.
/* to find the shortest path */
shortest(X, Y, L, C) :-
path(X, Y, L, C),
path(X, Y, L1, C1),
C < C1.
This shows the shortest path and it's weight:
edge(a,b,6).
edge(a,c,1).
edge(b,d,5).
edge(c,e,4).
edge(c,f,1).
edge(d,h,3).
edge(e,h,7).
edge(f,g,2).
edge(g,h,1).
path(X,Y,M,[Y]) :- edge(X,Y,M).
path(X,Y,P,[Z|T]) :- edge(X,Z,M),path(Z,Y,N,T),
P is M+N.
pravilo(X,Y,Z) :- assert(min(100)),assert(minpath([])),!,
path(X,Y,K,PATH1),
(min(Z),K<Z,
retract(min(Z));assert(min(K))),
minpath(Q),retract(minpath(Q)),
assert(minpath([X|PATH1])),
fail.
?- pravilo(a,h,X);
write("Minimal Path:"),
minpath(PATH),
write(PATH),
nl,
write("Path weight:"),
min(Z),
write(Z).