[eclipse-users] Channelling constraint

From: Patrick Pleass <pat_at_...82...>
Date: Wed, 24 Oct 2007 11:02:54 +1000
Hi All,

I have a simple student class allocation problem with disjoint resources. I
have modelled it in 2 different ways.

1) A list of class terms with fixed task ID, but variable Resource and Time,
i.e. class(1,R,T). class(2,R,T).
and
2) A matrix of class codes with rows and column positions indicating
Resource and Time

Each method works. However each model has characteristics that make it
desirable from the perspective of implementing hard constraints, soft
constraints and symmetry breaking strategies. What I would like to do is use
both models in a solution and join them.

I understand that this can be done (more or less) with a channelling
constraint or an implied constraint. What I would expect is that once in
place, these constraints would propagate changes between models. However,
examples of this are thin.

Can anyone please suggest a possible strategy?

One experiment I have tried (shown below) is to delay setting the matrix
class until the R and T for the task in the list method is set. This has
obvious propogation issues in that we are waiting for both to ground.

Code so far is below.

Cheers,

Pat

:- lib(ic).
:- lib(ic_global).

go:-
       	Time::1..2,
	Room::1..2,
       	findall(class(Class,Time,Room),class(Class,Time,Room),Classes), 

	dim(ClassMatrix, [2,2]),
	ClassMatrix[1..2,1..2]::1..4,

	( foreach(class(C,T,R),Classes),param(ClassMatrix) do
		channel(R,T,C,ClassMatrix)
	),
	ic_global:alldifferent(ClassMatrix),

	term_variables(Classes,ClassesV),
	
	search(ClassesV,0,input_order,indomain,complete,[]),
       	writeln(Classes).
       	
delay channel(R,T,C,M) if nonground((R,T)).
channel(R,T,C,Matrix) :-
   	subscript(Matrix,[R,T],C).

class(1,_,_).
class(2,_,_).
class(3,_,_).
class(4,_,_).
Received on Wed Oct 24 2007 - 02:02:55 CEST

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