Re: Strange difference in FD between E*E and E**2

[Daniel Diaz]

Thank you for this bug report.

I check this ASAP.

My first idea: the behavior of strangePower1/2 is due to the fact that FD vars 
can only take positive values. Anyway the behavior is incorrect. I'll try to 
fix this.

Daniel

Le 16 déc. 2011 à 15:17, Fred Bapst a écrit :

> Hello,
> 
> With the following code, strangePower1(A,B) gives one solution, where the 
> other versions give two:
> 
> strangePower1(A,B) :-
>       fd_domain([A,B],0,5),
>       (A-B)**2 #> 16,          % <-------
>       fd_labeling([A,B]).
> 
> strangePower2(A,B) :-
>       fd_domain([A,B],0,5),
>       (A-B)*(A-B) #> 16,       % <-------
>       fd_labeling([A,B]).
> 
> strangePower3(A,B) :-
>       fd_domain([A,B],0,5),
>       A**2 -2*A*B +B**2 #> 16, % <-------
>       fd_labeling([A,B]).
> 
> | ?- strangePower2(A,B).
>  A = 0  B = 5 ? a
>  A = 5  B = 0
>  (15 ms) no
> | ?- strangePower1(A,B).
>  A = 5 B = 0
>  yes
> 
> Can you explain why? Do you think this difference is reasonable from the 
> programmer's point of view?
> 
> Observed in gprolog-1.4.0, both in Win32 and Linux32.
> 
> Best regards.
> 
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