[gecode-users] question about lexical ordering constraint and others

[Christian Schulte]

Hi Kish,

1) Hmmm, never thought about that. You could emulate this behavior by
extending one array as you suggested. Do you know any application that
relies on this behavior?  

2) Just ICL_DEF which is as the algorithm by Paul Shaw, see the referenced
paper.

3) Gecode always chooses the best propagator, cumulative is a good example:
if all the variables for the use are assigned it'll choose the special case.
If it is clear that cumulative is not needed (for example, all tasks require
more than half of the resource), a disjunctive scheduling propagator is
posted. This is true for all constraints: you ask which constraint you want
to have and Gecode posts the best propagator(s) it can for the constraint.

Cheers
Christian

--
Christian Schulte, KTH, web.it.kth.se/~cschulte/

-----Original Message-----
From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf
Of Kish Shen
Sent: Tuesday, May 10, 2011 6:35 PM
To: users at gecode.org
Subject: [gecode-users] question about lexical ordering constraint and
others

Hi,

I have a few (more) question about various Gecode constraints that I am
interfacing to ECLiPSe:

1) the constraint for lexical ordering

rel(Home, IntVarArgs, IntRelType, IntVarArgs)

requires the two arrays to be the same size. It seems the same restriction
applies in the global constraint catalog for the lexical ordering
constraints as well. However, the existing ECLiPSe lexical ordering
constraints does not have this restriction -- i.e. the two sequences of
numbers being compared can be different lengths. What is the reason for the
same length restriction?

The lexical ordering for sequences of different length used in ECLiPSe seems
to be the natural one, where missing numbers in the shorter sequence are
replaced by 'bottom', i.e. a value smaller than any number.
So (using . to separate numbers in a sequence)

1.3 > 1.2.5

1.2.5 > 1.2

etc.

Could such a definition of ordering be used in the Gecode version as well?

2. What IntConLevel is supported in the binpacking constraint? I can't find
a specification for this in the reference documentation (in
doc-latest) [beyond the default of ICL_DEF]

3. For various versions of the same constraint (e.g. cumulative), some
arguments can be IntArgs or IntVarArgs. In general, does it make a
difference if I always use the version with IntVarArgs, even if all the
IntVar has only one element in their domain (i.e. they are integers)?
I guess what I am asking is if (in general) Gecode does a check of its
IntVarArgs argument to see if they are all integers and calls a more
efficient implementation for the constraint if there is one? [I was
specifically looking at the cumulative constraint, but there are obviously
others].

The reaosn I ask is that in interfacing such constraints to ECLiPSe, I
currently don't check if such arguments are all integers or if they contain
some domain variables (IntVar). I can do this check, but if it is done in
Gecode already, there is no reason for me to do so.


Thanks in advance for any help and information!

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.

_______________________________________________
Gecode users mailing list
users at gecode.org
https://www.gecode.org/mailman/listinfo/gecode-users