[gecode-users] Reification

[Christian Schulte]

Actually, for 2. this is used: suppose you want express logical equivalence
by reification, say (x<y) ó (a < b). Then, one could express it by (x < y) ó
b0 = 1, (a < b) ó b1 = 1, and eqv(b0,b1,1). However it can be done more
efficiently by using just a single Boolean variable: (x < y) ó b=1 and (a <
b) ó 1. Only one Boolean variable, and no equivalence propagator.

 

Cheers

Christian

 

--

Christian Schulte, www.it.kth.se/~cschulte/

 

From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf
Of Joe Porter
Sent: Monday, April 27, 2009 7:16 PM
To: users at gecode.org
Subject: Re: [gecode-users] Reification

 

 

1.       It is really an equivalence: so what it actually says (your example
slightly simplified) is (x != y+c) ó b=1. If b=0 it will assert x == y+c,
and if b=1 it will assert x != y+c. I am not sure whether this answers your
question.


That's exactly what I wanted -- to use the boolean variables to record which
constraints could not be satisfied.
 

2.       Well depends on what you want to express, when you post xi == yi +
c ó b=1 for the same b for all i it means that if b=0, it must hold for all
i that  xi != yi +c and likewise if b=1, it must hold for all i that xi = yi
+ c. If you want to have Boolean control variables that make a statement
just for a particular i you have to create a new Boolean variable for each
i. 


So I guess that means that no one else has tried it ;-)

Thanks for all of your help,
-Joe

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.ps.uni-sb.de/pipermail/users/attachments/20090427/20451b92/attachment.htm>