Alex is spot on here: but let me expand a little.
You might have used the cost() member function for B&B. However the cost()
member function is just implemented in terms of the constrain() member
function. So what I would do is the following:
- Have a integer variable array cost containing the two cost variables you
have in mind.
- implement a constrain(const Space& _b) member function: _b refers to the
so-far best solution. Cast this to your script type, say b. Then this just
posts
rel(*this, cost, IRT_LQ, b.cost);
This enforces that this->cost is lexicographically smaller then the so
far best cost b.cost.
That's it. More on the constrain() function you can find in Chapter 2 of
MPG.
Cheers
Christian
--
Christian Schulte, www.gecode.org/~schulte
Professor of Computer Science, KTH, cschu...@kth.se
Expert Researcher, SICS, cschu...@sics.se
-----Original Message-----
From: users-boun...@gecode.org [mailto:users-boun...@gecode.org] On Behalf
Of Alexander Schiendorfer
Sent: Friday, January 29, 2016 12:06 PM
To: users@gecode.org
Subject: Re: [gecode-users] users Digest, Vol 124, Issue 6
Hi Juan,
it seems to me that you're searching for lexicographic branch-and-bound.
There is a global constraint lex_lesseq that you might want to consider for
posting in the constrain method of a Space.
Cheers,
Alex
On 29.01.2016 12:00, users-requ...@gecode.org wrote:
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> Today's Topics:
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> 1. Best way to implement multi-criterion optimization in Gecode?
> (Juan Carlos Hernandez)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 28 Jan 2016 12:30:54 +0100
> From: Juan Carlos Hernandez <jchernandez.mad...@gmail.com>
> To: users@gecode.org
> Subject: [gecode-users] Best way to implement multi-criterion
> optimization in Gecode?
> Message-ID:
> <CAFd=f3eau+xpqjo02kpt9swibpjxkifw-f2so-4me+x4kv7...@mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi everyone,
>
>
> I am trying to use Gecode to solve a multi-criterion problem
>
>
> minimize (F1(x,z), F2(x,z) )
>
> subject to constraints on x,z
>
>
> The objectives are ordered in order of importance, so I would like to
> first solve the problem P1
>
>
> minimize F1(x,z)
>
> subject to original constraints on x,z
>
>
> and then consider the modified problem P2
>
>
> minimize F2(x,z)
>
> subject to original constraints on x,z
>
> F1(x,z) = F1opt
>
>
> where F1opt is the optimal value of P1.
>
>
> What is the most efficient way to implement this in Gecode?
>
>
>
> I am now doing two completely separate searches, in the sense that I
> create a new Space and run BAB on it for each of the problems. I am
> sure that this cannot be the most efficient way of dealing with the
> problem, but am unable to figure out how to do it "the right way".
> Essentially, when solving P2 I should be able to make use of the work done
while solving P1...
>
>
> Any feedback is very much appreciated!
>
>
> Thanks,
>
> JC
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> End of users Digest, Vol 124, Issue 6
> *************************************
--
Alexander Schiendorfer, M.Sc.
Institute for Software & Systems Engineering Raum 3043, Gebäude N
Universität Augsburg
Web:
http://www.informatik.uni-augsburg.de/lehrstuehle/swt/se/staff/aschiendorfer
/
Tel.: +49 (821) 598 - 2196
E-Mail: alexander.schiendor...@informatik.uni-augsburg.de
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