Dear Robert,
On Feb 22, 2011 9:55pm, Robert Onslow <[email protected]> wrote:
> Alf Bert Charlie Douggie Ernie and Fred have their birthdays on consecutive
> days, but not necessarily in that order.
>
> Douggie’s birthday is as many days before Fred’s as Bert’s is after Fred’s.
> Charlie’s birthday is as many days before Fred’s as Bert’s is after Fred’s.
> This
> year, Ernie’s birthday is on a Saturday.
I think there is a problem with this description (identical
constraints for Douggie and Charlie?).
> I am thinking of a domain of 0#6 for each of A B C D E and F.
>
>
> I have
> got the constraints {FD.distinct Solution} and E :: 5 (even I can work that
> one
> out!)
>
> How would
> I combine propagators to model the other constraints? I can see that I will be
> working with {FD.modI .. 7} to wrap around the days of the week. I guess there
> may be some constrained variables M and N representing the number of days
> before
> and days after, but I am not sure how to combine the constraints in this
> problem.
I think I would split this problem into two problems.
(1) Find out the order of the birthdays.
(2) Calculate the weekdays from the relative order. (should be easy)
To solve (1), I would choose the domain 0#5 for the variables (to
represent 6 consecutive days, not the concrete weekdays)
and call FD.distinct as you proposed.
Then the first constraint can simply be written like this:
% D's birthday is before F's birthday:
D <: F
% D is as many days before F as B after F:
F - D =: B - F
The last constraint ("Ernie’s birthday is on a Saturday.") is not
encoded in the program, but you use it for subproblem (2).
Hope this helps,
Wolfgang
_________________________________________________________________________________
mozart-users mailing list
[email protected]
http://www.mozart-oz.org/mailman/listinfo/mozart-users
