A strange behavior when adding extra ASP constraints to pruning by `clause`

[yangdinglou]

I understand that the pruning may make the whole search slower in the DCC version, but here the issue is about a possible bug.
For example, in the examples/filter example, if I want to force the program contains 3 sub-clauses, adding

:-
    not clause(2).

to
https://github.com/logic-and-learning-lab/Popper/blob/8e132faa0f1a7554275f70b0bb7546cc79cce901/examples/filter/bias.pl
should prune the learned programs with less than 3 sub rules. However, a resource_error raises.

pyswip.prolog.PrologError: Caused by: 'pos_covered(Xs)'. Returned: 'error(resource_error(stack), Atom('27909')(stack_overflow, 3355306, choicepoints, 6710615, depth, 3355312, environments, 235922, globalused, 524267, localused, [Functor(565645,3,6710615,:(user, f([], [1])),[]), Functor(565645,3,6710614,:(user, f([1], [1])),[])], non_terminating, 1048576, stack_limit, 0, trailused))'.

One more strange thing is that, if adding

:-
    clause(2).

to the bias file, the learning is accelerated (with the correct result outputted).

I also test the same things in Popper 1.0, then expected pruning works.

% BEST PROG 4354:
f(A,B):-empty(A),empty(B).
f(A,B):-head(A,C),tail(A,D),odd(C),f(D,B).
f(A,B):-head(A,E),even(E),tail(A,C),f(C,D),prepend(E,D,B).
% Precision:1.00, Recall:1.00, TP:5, FN:0, TN:5, FP:0

vs

% BEST PROG 13759:
f(A,B):-empty(B),empty(A).
f(A,B):-tail(A,D),f(D,B),head(A,C),odd(C).
f(A,B):-tail(A,E),f(E,C),head(A,D),even(D),prepend(D,C,B).
% Precision:1.00, Recall:1.00, TP:5, FN:0, TN:5, FP:0

I failed to find the modification of clause's meaning in alan.pl. Could you please help?

[andrewcropper]

To check, what do you mean by the DCC version? Which branch are you using?

[yangdinglou]

The main branch of Popper. Maybe I'm misunderstanding, but I regard the Popper v2.0 as the DCC version (as mentioned in DCC repo).

[andrewcropper]

Thanks for the clarification. I tried adding that constraint and indeed Popper crashes. I had a quick look and it is unclear what causes this crash.

I will investigate more and get back to you.

[andrewcropper]

@yangdinglou I have fixed the issue. ce868ca

Popper was generating a non-terminating program that caused a stack overflow.

Regarding Popper, this code does not use the DCC approach. It uses a similar approach described in this paper: https://arxiv.org/pdf/2206.01614.pdf

[yangdinglou]

@andrewcropper Thank you, it works well. May I know why the solution is still there when

:-
    clause(2).

are given? I used to think it is a constraint to ignore solutions with more than 2 clauses. Should I use double negations?

[andrewcropper]

That constraint prohibits Popper from ‘generating’ a program with three rules/clauses. However, the newest version of Popper (https://arxiv.org/pdf/2206.01614.pdf) has an extra ‘combine’ stage where it tries to find a good combination of generated programs. These combinations do not (yet) need to obey the constraints in the bias file. In your use case, do you only want solutions with at most two rules? Kind regards, Andrew

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On 25 Jan 2023, at 07:39, yangdinglou ***@***.***> wrote: @andrewcropper Thank you, it works well. May I know why the solution is still there when :- clause(2). are given? I used to think it is a constraint to ignore solutions with more than 2 clauses. Should I use double negations? — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you were mentioned.Message ID: ***@***.***>