Re: determinism

[michel levy]

Daniel Diaz wrote:
> michel levy a écrit :
>
> > Could you help to write this program :
> > det(T,G) succeeds if and only if G succeeds once and only once and give
> > the T answer.
> > 1) I don't want the solution below by findall, because I want to try at
> > most two back tracks on G.
> > det(T,G) :- findall(T,G,L),length(L,1)
> >
> > 2) I know already call_det but it's not the solution because G can have
> > choice points, but only one answer.
>
>
> You can do it using a global variable to count solutions. Stop when the
> second is reached.
>
>
> det(Goal) :-
>         det1(Goal).
>
> det(_) :-
>         g_read(det_count, 1).
>         
>
> det1(Goal) :-
>         g_assign(det_count, 0),
>         call(Goal),
>         g_inc(det_count, Count), % increment and return the counter
>         Count = 2,      % cut if 2nd solution is reached (else fail)
>         !,
>         fail.
>
> Hope this helps
Thank you really much for your help.
Your solution is very simple to understand.

I have modify it slightly to have the answer (like in findall).

det(Answer,Goal):-
        det1(Answer,Goal).

det(Answer,_) :-
        g_read(det_count, 1),retract(sol(Answer)).      

det1(Answer,Goal) :-
        g_assign(det_count, 0),
        call(Goal),assertz(sol(Answer)),
        g_inc(det_count, Count), % increment and return the counter
        Count = 2,      % cut if 2nd solution is reached (else fail)
        !,
        retract(sol(_)),
        fail.
I have modify it slightly to have the answer (like in findall).

My goal was to write a program :
sudoko(L) succeds if L is a 81 elements list of a sudoku
and fails if the answer is not unique.

Therefore now I write
L = [  _,_,_,1,3,_,_,_,7,
          5,7,_,6,_,_,_,_,_,
          9,_,1,_,2,_,3,_,_,
          _,4,_,_,_,_,2,_,_,
          1,_,_,_,5,_,_,_,9,
          2,_,_,_,4,6,_,_,1,
          _,_,_,9,_,_,_,_,8,
          _,6,_,_,7,_,_,_,_,
          8,_,_,4,1,_,5,_,3],
det(L,sudoku(L)).
L = [6,2,4,1,3,5,9,8,7,
5,7,3,6,8,9,4,1,2,
9,8,1,7,2,4,3,5,6,
7,4,6,8,9,1,2,3,5,
1,3,8,2,5,7,6,4,9,
2,5,9,3,4,6,8,7,1,
4,1,5,9,6,3,7,2,8,
3,6,2,5,7,8,1,9,4,
8,9,7,4,1,2,5,6,3]
yes

L = [  _,_,_,_,3,_,_,_,7,
          5,7,_,6,_,_,_,_,_,
          9,_,1,_,2,_,3,_,_,
          _,4,_,_,_,_,2,_,_,
          1,_,_,_,5,_,_,_,9,
          2,_,_,_,4,6,_,_,1,
          _,_,_,9,_,_,_,_,8,
          _,6,_,_,7,_,_,_,_,
          8,_,_,4,1,_,5,_,_],
det(L,sudoku(L)).
no
This sudoku problem has more than a solution.

My sudoku progam has a side effect, write the sudoku in a visible shape 
and why I get really in the last case is :

det(L,sudoku(L)).
[4,2,6][5,3,9][8,1,7]
[5,7,3][6,8,1][9,2,4]
[9,8,1][7,2,4][3,6,5]
---------------------
[6,4,7][1,9,8][2,5,3]
[1,3,8][2,5,7][6,4,9]
[2,5,9][3,4,6][7,8,1]
---------------------
[7,1,5][9,6,2][4,3,8]
[3,6,4][8,7,5][1,9,2]
[8,9,2][4,1,3][5,7,6]



[4,2,6][5,3,9][8,1,7]
[5,7,3][6,8,1][9,2,4]
[9,8,1][7,2,4][3,6,5]
---------------------
[6,4,8][1,9,7][2,5,3]
[1,3,7][2,5,8][6,4,9]
[2,5,9][3,4,6][7,8,1]
---------------------
[7,1,5][9,6,2][4,3,8]
[3,6,4][8,7,5][1,9,2]
[8,9,2][4,1,3][5,7,6]

(1 ms) no

So you see the first two solutions (there are plenty of solutions).

        Sincerely yours


--
Michel Levy
36 rue George Sand
38400 Saint Martin d'Heres