Prolog, find minimum in a list

Question

in short: How to find min value in a list? (thanks for the advise kaarel)

long story:

I have created a weighted graph in amzi prolog and given 2 nodes, I am

Answer 1

SWI-Prolog offers library(aggregate). Generalized and performance wise.

:- [library(aggregate)].
min(L, M) :- aggregate(min(E), member(E, L), M).

edit

A recent addition was library(solution_sequences). Now we can write

min(L,M) :- order_by([asc(M)], member(M,L)), !.
max(L,M) :- order_by([desc(M)], member(M,L)), !.

Now, ready for a surprise :) ?

?- test_performance([clpfd_max,slow_max,member_max,rel_max,agg_max]).
clpfd_max:99999996
% 1,500,000 inferences, 0.607 CPU in 0.607 seconds (100% CPU, 2470519 Lips)
slow_max:99999996
% 9,500,376 inferences, 2.564 CPU in 2.564 seconds (100% CPU, 3705655 Lips)
member_max:99999996
% 1,500,009 inferences, 1.004 CPU in 1.004 seconds (100% CPU, 1494329 Lips)
rel_max:99999996
% 1,000,054 inferences, 2.649 CPU in 2.648 seconds (100% CPU, 377588 Lips)
agg_max:99999996
% 2,500,028 inferences, 1.461 CPU in 1.462 seconds (100% CPU, 1710732 Lips)
true 

with these definitions:

```erlang
:- use_module(library(clpfd)).

clpfd_max([L|Ls], Max) :- foldl([X,Y,M]>>(M #= max(X, Y)), Ls, L, Max).

slow_max(L, Max) :-
   select(Max, L, Rest), \+ (member(E, Rest), E @> Max).

member_max([H|T],M) :-
    member_max(T,N), ( \+ H@ M=H ; M=N ).
member_max([M],M).

rel_max(L,M) :-
    order_by([desc(M)], member(M,L)), !.

agg_max(L,M) :-
    aggregate(max(E), member(E,L), M).

test_performance(Ps) :-
    test_performance(Ps,500 000,_).
test_performance(Ps,N_Ints,Result) :-
    list_of_random(N_Ints,1,100 000 000,Seq),
    maplist({Seq}/[P,N]>>time((call(P,Seq,N),write(P:N))),Ps,Ns),
    assertion(sort(Ns,[Result])).

list_of_random(N_Ints,L,U,RandomInts) :-
    length(RandomInts,N_Ints),
    maplist({L,U}/[Int]>>random_between(L,U,Int),RandomInts).

clpfd_max wins hands down, and to my surprise, slow_max/2 turns out to be not too bad...