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Home > Archive > Prolog > August 2005 > How does ECLiPSe solve reified constraints?









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Author How does ECLiPSe solve reified constraints?
Linda

2005-08-23, 7:57 am

I know that ECLiPSe was implemented in Prolog and which and many other
constraint solvers can solve reified constraints.
In my mind, reified constraints are made up of both boolean and
numerical variables, then how to solve the constraints that mix them
together, namely how reified constraints are solved?

I will be very thankful if someone can give me some points.

Best regards!

Linda

Bart Demoen

2005-08-23, 7:57 am

Linda wrote:
> I know that ECLiPSe was implemented in Prolog and which and many other
> constraint solvers can solve reified constraints.
> In my mind, reified constraints are made up of both boolean and
> numerical variables, then how to solve the constraints that mix them
> together, namely how reified constraints are solved?
>
> I will be very thankful if someone can give me some points.


You seem to think that because there are booleans and numerics involved,
it should suddenly become much more difficult. It isn't - at least not
in principle. I will try to explain it with attributed variables -
syntax of no particular system intended - take:

X + Y = 1 <=> B

this could result in adding the following attributes to

X: if I get instantiated, check whether it can be decided that X+Y=1
and set B accordingly
Y: same
B: if I change to true, post the constraint X+Y = 1
if I change to false, post the constraint X+Y != 1

One more thing: one can implement booleans just as numeric values
with a domain [0,1].

Now, as to your original question "How does ECLiPSe solve it" - we'll have
to wait for ECLiPSe people of course :-)

Cheers

Bart Demoen
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