Re: [eclipse-clp-users] How to extend lib(ic) to get stronger propagation?

Ulrich,

there are two possibilities there:

a) you can use something like CHR to detect combinations of constraints from
which you can detect new constraints. This is expressed as rules that you
can write yourself, very easy to do in ECLiPSe.

b) You can treat a set of inequalities as a global constraint, set up a
graph and then detect properties (e.g. cycles) in that graph. This can be
more powerful, but you will have to write the constraint yourself. There
have been some publications on this, I don't have a reference handy. Perhaps
somebody else can help?

Helmut

-----Original Message-----
From: Ulrich Scholz [mailto:Ulrich.Scholz_at_eml-d.villa-bosch.de] 
Sent: 17 November 2009 12:25
To: eclipse-clp-users_at_lists.sourceforge.net
Subject: [eclipse-clp-users] How to extend lib(ic) to get stronger
propagation?

Hi again,

It is clear that a constraint package cannot detect and propagate all
possible simplifications.  But sometimes, a specific simplification can be
of great help.

Consider the following constraint program.

  [eclipse 3]: lib(ic), [A, B] :: [0, 100], A #=< B, B #=< A.

  A = A{[0, 100]}
  B = B{[0, 100]}


  Delayed goals:
          -(B{[0, 100]}) + A{[0, 100]} #=< 0
          B{[0, 100]} - A{[0, 100]} #=< 0
  Yes (0.00s cpu)


It would really help me if (an extended) ic would simplify this case to
A#=B.  Labeling is no option for me, I need to detect this case early.

Could you suggest an approach?  Maybe checking some conditions on every
posting of #=<?  Depending on the outcome, I could thenpost one of #=, #<,
or #=<.

Thanks,

Ulrich



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