From: Benoit Hoessen <b.hoessen_at_gmail.com>

Date: Fri, 26 Feb 2010 08:57:24 +0100

Date: Fri, 26 Feb 2010 08:57:24 +0100

Hello, First, thank you for your response. I will try to explain better the problem I'm trying to solve and the problem I'm facing to model it using ECLiPSe. My problem is the following: we have a list of N boxes of different sizes but same height. We must create J stacks with those boxes. A stack may contain up to 12 boxes. In a stack, the box B can be put on box A if the width of A is greater or equals the width of B and if the length of A is also greater or equals the length of B. My problem is that I don't know how I can model this. I tried to following way, but I don't think it's a good way to model it. Data: * A box is represented with a term: box(Length,Width). The N boxes are in a list. * A number is associated with the boxes by using a dynamic predicate (boxIndex(+I, +B) : is true if B is a box and I is a number) where one box is associated with 1 and only 1 number. * The J stacks are represented by a list LStacks of length J * A stack is represented by a list of length 12 * A box in a stack is represented by it's number Constraints: * To model the constraint "up to 12 boxes in a stack", J*12 - N boxes of width=length=0 are created. The constraint is now that there will always be 12 boxes in a stack My problem is to model the constraint on 2 boxes in a stack. I could use the suspend library to wait that the 2 variables are instantiated to check the satisfaction on the constraint, but I don't like this approach as it won't use any domain consistency method. For me, in a "ideal world" I would'n use the number associated with the boxes and the stacks would be represented by variables defined on a domain D such that it is the set of the possible boxes. The constraint on 2 boxes would be a kind of primitive constraint and as it uses only 2 variable, an arc-consistency method could be used. The problem is that -as far as I know- symbolic domains in ECLiPSe don't accept terms. Is there a way to get closer to my "ideal world" ? Benoit Hoessen 2010/2/25 Kish Shen <kisshen_at_cisco.com>: > Benoit Hoessen wrote: >> >> Hello, >> >> I am currently learning to use eclipse and I'm facing a problem. I >> have a list of couples that needs to be ordered according some >> constraints. I tried the following model: >> >> ArrayCouples is the array of my couples [Couple0, Couple1, ... ] >> NbCouples is the number of couples >> OrderedList is a list of integers where each integer represent the >> index of a Couple in ArrayCouples. Those integers are the variables of >> my problem and their domain is [0..NbCouples - 1] >> >> And the constraints should be (with a c-like syntax) >> for (i = 0 ; i < NbCouples-2; i++){ >> CoupleA = ArrayCouples[i]; >> CoupleB = ArrayCouples[i+1]; >> //constraint on the element of CoupleA & CoupleB >> } >> >> But it seems that I can't model this with eclipse with my current >> knowledge or it's not the way I should model my problem. >> >> Can somebody tell me what my error is? > > Hi Benoit, > > It is difficult to give any specific answer, as it is not clear what your > exact difficult is. You may indeed want to learn more about programming in > ECLiPSe. Another general comment I can say is that it is probably not a very > good idea to try and specify the program you want to write in C and then try > to translate this to ECLiPSe. C does not map very well to ECLiPSe (or Prolog > in general), and in any case you should be thinking about modelling your > problem at a higher level... > > One possible issue is the data structures you are using: you mention lists > -- these do not map well to C arrays. ECLiPSe (and Prolog) does provide > something similar to C arrays -- structures, which allows random access to > its elements. In addition, ECLiPSe provides syntax that is > more convenient to use (than what is standard in Prolog), and which also > looks more like traditional array syntax that you find in C. This array > notation is described in the manual: > > http://www.eclipse-clp.org/doc/userman/umsroot024.html > > One issue you should be aware of is the index starts from 1, rather than 0. > > On the other hand, for the specific example you show in C, it is not clear > that you do need random access to the elements, so a list may be the right > data structure to use. Your example can be dnne in ECLiPSe using a do-loop > (which is simply a different way of writing recursion, the standard way in > Prolog to write "loops"): > > (fromto(NbCouples, [CoupleA,CoupleB|Rest],[CoupleB|Rest], [_]) do > /* constraint on CoupleA and B */ > ) > > If you also need the index, you can add another iteration specifier like > count(I,Min,Max). > > Cheers, > > Kish > > > > -- > This e-mail may contain confidential and privileged material for the > sole use of the intended recipient. Any review, use, distribution or > disclosure by others is strictly prohibited. If you are not the intended > recipient (or authorized to receive for the recipient), please contact > the sender by reply e-mail and delete all copies of this message. > Cisco Systems Limited (Company Number: 02558939), is registered in > England and Wales with its registered office at 1 Callaghan Square, > Cardiff, South Glamorgan CF10 5BT. >Received on Fri Feb 26 2010 - 07:57:32 CET

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