-- RadoslawSzymanek - 28 Jul 2008

* I (HakanK) am learning JaCoP and has some questions. Links below are to models at my JaCoP page http://www.hakank.org/JaCoP . (Explanation and links related to the problems are in the source files.)

- LeastDiff.java
The objective here is to minimize the difference ABCDE-FGHIJ, where A..J is 0..9 (all different).

I looked for the constraint XminusYeqZ? , but found none. Instead I had to use the following construct:

// diff = abcde - fghij
// ->
// diff + fghij = abcde
store.impose(new XplusYeqZ? (diff, value_fghij, value_abcde));

This works of course, but it would be nice with a constraint XminusYeqZ? (value_abcde, value_fghij, diff), though.
Is there are reason (other than that noone asked for it) why XminusYeqZ? is missing?

ANSWER : Implementing a constraint takes some time and coding (all functions from the interface must be implemented). In addition, if we find an improvement for a given constraint, we would have to change it in many places (XplusYeqZ? and XminusYeqZ? ) making it likely to introduce (efficiency) bugs. Here, for ease of maintenance, and small code footprint we force a user to transform his constraint like XminusYeqZ? into the XplusYeqZ? .

-This is not a question, just a note about modelling in JaCoP.

The more advanced models, DeBruijn? and Minesweeper , were surprisingly easy to model. Both are quite straightforward translations of my MiniZinc models, so there are probably better ways of modelling them in JaCoP. Please feel free to point out any suggestions.

- Are there any plans of supporting sets? There are some problem where modelling using sets helps much.

ANSWER : No immediate plans. Although, aware of that interest, we redesigned the domain abstract class to make it possible to write your own SetDomain? class and by providing functions specified by Domain you will be able to plugin SetDomain? into JaCoP withouth problems. SetDomain? by itself is of little use, the constraints must also be implemented. We concentrate mostly on CP(FD).

-- HakanK - 12 Aug 2008