Re: Unexpected result with FD solver

[Jean Michel LECONTE]

try : 

ieq(LD1,LD2,Va):-
        LD1 = [X1,X2,X3,X4],
        LD2 = [D1,D2],
        fd_domain(LD1,0,20),
        fd_domain(LD2,1,12),
        Va #=<5,
        Va #>=0,
        X1 #=0,
        X2 #=< X1+4,
        X2 #>= X1+2,
        X3 #= X1+D1,
        X4 #= X2+D2,
        D1 #=< D2+Va,
        D1 #>= D2-Va,
        X4 #=< X3,
        fd_labeling(LD1),
        fd_labeling(LD2),
	fd_labeling(Va). 

read the note in the doc about fd_labeling, you have to do this operation if 
you want some answers cause when gprolog says
>         LD1 = [0,_#25(2..4),_#47(3..12),_#69(3..12)]
>         LD2 = [_#91(3..12),_#113(1..10)]
>         Va = _#134(0..5)

it just means that Va could be between 0 and 5 but thts not meaning that 
there's a solution...
gprolog tries to reduce the domain of possible values for each FD (i.e. 
constrained) variable but if you want a solution you have to 'label' each FD 
variable 

and the _#integer(a..b) means FD variable which has integer for internal 
system number (as an internal ID) is between a and b 


Jean Michel LECONTE
-----------------------------------------
address@hidden
address@hidden
----------------------------------------- 






Xiao-Hua Kong writes: 

> Hello, 
>
> I'm a beginer in Prolog, I want to use GNU Prolog for constraint sovling
> in FD. I have tried the solver with a set of in-equations. But for some of
> them, I did not get the result expected. 
>
> Here is an example: 
>
> I wrote a rule: 
>
> ieq(LD1,LD2,Va):-
> LD1 = [X1,X2,X3,X4],
> LD2 = [D1,D2],
> fd_domain(LD1,0,20),
> fd_domain(LD2,1,12),
> Va #=<5,
> Va #>=0,
> X1 #= 0,
> X2 #=< X1+4,
> X2 #>= X1+2,
> X3 #= X1+D1,
> X4 #= X2+D2,
> D1 #=< D2+Va,
> D1 #>= D2-Va,
> X4 #=< X3.
>  
> And asked for the possible assignment for these in-equations
> (constraints).
> However I got the follwing result: 
>
> 	| ?- ieq(LD1,LD2,Va). 
>
>         LD1 = [0,_#25(2..4),_#47(3..12),_#69(3..12)]
>         LD2 = [_#91(3..12),_#113(1..10)]
> 	Va = _#134(0..5) 
>
> In which the resulting domain of Va is larger than it should be. For
> example, ask 
> 	| ?- ieq(LD1,LD2,0).
> or	| ?- ieq(LD1,LD2,1). 
>
> will have an answer "no". 
>
> Is there any problem with the code? Or I should not use more than three
> variables in a constraint? How can I solve this problem. 
>
> BTW, what does _#integer mean in the result? 
>
> Thanks in advance.
> Xiaohua Kong 
>
>  
>
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