[gecode-users] CP example for Scheduling and assignment

Mon Feb 13 09:32:13 CET 2012

Hi,

I am one of the beginner users of CP and Gecode.

I am doing a problem model on allocation, binding and scheduling and the
closest example I could find on Gecode is the open-shop scheduling problem.
I was hoping that you could guide me to a better example that also involves
binding (assigning tasks to resources) in addition to scheduling just to
get an idea. I have been trying hard but have not managed to do the binding
in parallel with scheduling so far.

Thank you in advance.

Best regards,
Wajid

On Sun, Feb 12, 2012 at 8:05 PM, Wajid Hassan <wajidhassan at gmail.com> wrote:

>
>
>
>
> On Wed, Jan 18, 2012 at 1:15 PM, Josef Eisl <zapster at zapster.cc> wrote:
>
>> On 01/18/2012 12:01 PM, Christian Schulte wrote:
>> > Hi,
>> >
>> > I added the command line switch -print-last to the trunk. In case you
>> build
>> > Gecode yourself from source you can use the attached patch to get the
>> > behaviour.
>>
>> Works like a charm, thanks!
>>
>> br
>> Josef
>>
>>
>> >
>> > Christian
>> >
>> > --
>> > Christian Schulte, www.ict.kth.se/~cschulte/
>> >
>> >
>> > -----Original Message-----
>> > From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On
>> Behalf
>> > Of Josef Eisl
>> > Sent: Tuesday, January 17, 2012 7:02 PM
>> > To: cschulte at kth.se
>> > Cc: users at gecode.org
>> > Subject: Re: [gecode-users] MinimizeScript: Beginners Question
>> >
>> > On 01/17/2012 04:59 PM, Christian Schulte wrote:
>> >> Hi Josef,
>> >>
>> >> Thanks for your observations as far as MPG is concerned. I'll think
>> >> them through and look how to improve. The information being spread out
>> >> can't really be helped much as each location takes a different angle
>> >> and different depth. But I promise I'll think...
>> >>
>> >> Then printing each solution is actually what you want (I guess):
>> >> normally, finding a best solution takes so long that you will have to
>> >> settle for the solution that has been found last after the time is up.
>> >> But maybe there could be an additional switch which would only make
>> >> sense in a best solution search scenario: -print-last where only the
>> >> last solution found is printed, and if a time out is encountered then
>> >> also the last and not necessarily best solution is printed. Would that
>> > make you happy?
>> >
>> > Yes, such an option would be great :).
>> >
>> > Thanks again for your time!
>> >
>> > br
>> > Josef
>> >
>> >>
>> >> Christian
>> >>
>> >> --
>> >> Christian Schulte, www.ict.kth.se/~cschulte/
>> >>
>> >>
>> >> -----Original Message-----
>> >> From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On
>> >> Behalf Of Josef Eisl
>> >> Sent: Tuesday, January 17, 2012 3:52 PM
>> >> To: cschulte at kth.se
>> >> Cc: users at gecode.org
>> >> Subject: Re: [gecode-users] MinimizeScript: Beginners Question
>> >>
>> >> Hello!
>> >>
>> >> On 01/17/2012 02:31 PM, Christian Schulte wrote:
>> >>> Hi,
>> >>>
>> >>> Please let me take your questions in turn.
>> >>>
>> >>> 1. Changing the relation from strict (that is, "<") to a non-strict
>> >>> (that is, "<=") will typically not work. It would entail that you do
>> >>> not only find all _optimal_ solutions but all solution for each and
>> >>> every cost value! So normally that will be way too many solutions!
>> >>> Try it out with Gist on a small example and you will see that this
>> >>> will make
>> >> things break down.
>> >>
>> >> Ups, my bad. Clearly adding a non strict constraint does not make much
>> >> sense.
>> >>
>> >>> Should I add a tip in MPG that the order must be strict for things to
>> >> work?
>> >>
>> >> Maybe, but I my eyes it is more confusing that
>> >> MinimizeSpace/MinimizeScript return non-optimal solutions, at least
>> >> for a new user. Some other things about MPG and optimization that are
>> not
>> > straight forward in my opinion:
>> >>
>> >> 1. Information is spread over several chapters:
>> >>    - 2.5 Best solution search
>> >>    - 3.2 Using a cost function
>> >>    - 6.3 Support for cost-based optimization
>> >>    - 7.4 Search engines
>> >>
>> >> 2. Best Solution Search engine
>> >> It is mentioned in 2.5 and 7.4 but not 3.2 and 6.3 and there are no
>> >> links to the other sections. Maybe it should be stated more clearly
>> >> that BAB or Restart must be used for best solution search.
>> >>
>> >> 3. constrain()
>> >> In 2.5: "Note that every space defines a default constrain() member
>> >> function (to keep the design of models simple). If a model does not
>> >> re-define the
>> >> constrain() member function, the default function will be called which
>> >> throws an exception of type SpaceConstrainUndefined (as this is a
>> >> modeling error)".
>> >> In my eyes the second sentence is not true as OptimizeSpace provides a
>> >> valid constrain().
>> >>
>> >> These are rather beginner problems than problems of MPG. Gecode is one
>> >> of the best documented free software I've seen. I just want to share
>> >> my experience.
>> >>
>> >>> 2. To find all optimal solutions, I would first find _one_ optimal
>> >>> solution as normal. Then I would find all solutions (starting a new
>> >>> search) where the cost value is equal to the optimal const value.
>> >>
>> >> I see. That makes sense.
>> >>
>> >>> 3. You see that printing "all" optimal solutions with respect to 1.
>> and
>> > 2.
>> >>> does not really make much sense.
>> >>
>> >> Ok using -solutions for optimal solutions does not work. But how about
>> >> printing only the last (optimal if -solutions 0) solution with
>> >> MinimizeScript?
>> >>
>> >>> I hope that helps
>> >>
>> >> Thank you very much for your quick and detailed answers!
>> >>
>> >> Josef
>> >>
>> >> _______________________________________________
>> >> Gecode users mailing list
>> >> users at gecode.org
>> >> https://www.gecode.org/mailman/listinfo/gecode-users
>> >>
>> >>
>> >
>> >
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>>
>>
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