Re: [eclipse-clp-users] Propagation question for IC

There is already a solution for this on the ECLiPSe web site
http://eclipseclp.org/examples/dmc_challenge_2019_sep.ecl.txt

It does not solve by propagation alone either, probably for
the reason you have discovered yourself.

Regards,
Joachim


On 01/04/2020 10:34, Panagiotis Stamatopoulos wrote:
> Thank you very much for your reply, Joachim!
> 
> Actually, the origin of my question is a puzzle I was trying to solve:
> https://alexis.lindaikejisblog.com/photos/shares/5d56b650ce177.jpg
> 
> I wanted to stick to IC, as I intended to use it for a course I teach.
> In addition, I wanted to get the answer just by propagation, without
> any labeling, as the puzzle can be solved just by logical inferences.
> Following your suggestion to use the reified form of #::, I ended with
> the program that follows. Do you believe that there could be a better
> solution, as far as readability is concerned (and advertisement of the
> advantages of CLP)? Anyway, this program works fine.
> Thank you very much, again.
> 
>       Takis
> 
> -------------------------------------------------------------------------
> 
> :- lib(ic).
> 
> code(X1, X2, X3) :-
>     [X1, X2, X3] #:: 0..9,
>     corcor(X1, X2, X3, 6, 8, 2, 1),
>     corwro(X1, X2, X3, 6, 1, 4, 1),
>     corwro(X1, X2, X3, 2, 0, 6, 2),
>     corcor(X1, X2, X3, 7, 3, 8, 0),
>     corwro(X1, X2, X3, 7, 3, 8, 0),
>     corwro(X1, X2, X3, 7, 8, 0, 1).
> 
> /* corcor/7: N is the number of correct and well placed
>   * digits of code X1/X2/X3 compared to N1/N2/N3 */
> 
> corcor(X1, X2, X3, N1, N2, N3, N) :-
>     #::(X1, N1, B1),
>     #::(X2, N2, B2),
>     #::(X3, N3, B3),
>     N #= B1 + B2 + B3.
> 
> /* corwro/7: N is the number of correct but wrongly placed
>   * digits of code X1/X2/X3 compared to N1/N2/N3 */
> 
> corwro(X1, X2, X3, N1, N2, N3, N) :-
>     #::(X1, [N2, N3], B1),
>     #::(X2, [N1, N3], B2),
>     #::(X3, [N1, N2], B3),
>     N #= B1 + B2 + B3.
> 
> -------------------------------------------------------------------------
> 
> On 01-Apr-20 11:20 AM, Joachim Schimpf wrote:
>> On 31/03/2020 19:22, Panagiotis Stamatopoulos wrote:
>>> Hello All,
>>>
>>> I hope you are healthy and safe. May I ask a (maybe trivial) question
>>> in the context of the IC library? Why the query
>>>
>>> ?- X #:: [1, 3], B #= (X #= 2).
>>> X = X{[1, 3]}
>>> B = B{[0, 1]}
>>> There is 1 delayed goal.
>>>
>>> does not enforce Β to be equal to 0?
>>
>>
>> IC's arithmetic equality and inequality constraints generally
>> enforce bounds-consistency, that's why the hole in the domain
>> of X is not taken into account.
>>
>> On could argue that for simple cases like X #= Y+Const stronger
>> domain-consistency should be enforced, this is the reason for
>> having http://eclipseclp.org/doc/bips/lib/ic/ac_eq-3.html .
>> Unfortunately, a reified version of ac_eq/3 is missing!
>>
>> If, as in your example, the equation contains only one variable,
>> you could use the reified form of #::, i.e.
>>
>> ?- X #:: [1, 3], #::(X, 2, B).
>> X = X{[1, 3]}
>> B = 0
>>
>>
>> By the way, lib(gfd) also does what you expect:
>>
>> ?- lib(gfd).
>>
>> ?- X #:: [1, 3], B #= (X #= 2).
>> X = X{[1, 3]}
>> B = 0
>>
>>
>> Cheers,
>> Joachim