[gecode-users] MinimizeScript: Beginners Question

[Christian Schulte]

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.

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
> 
> 


_______________________________________________
Gecode users mailing list
users at gecode.org
https://www.gecode.org/mailman/listinfo/gecode-users
-------------- next part --------------
A non-text attachment was scrubbed...
Name: print-last.patch
Type: application/octet-stream
Size: 6946 bytes
Desc: not available
URL: <http://www.gecode.org/pipermail/users/attachments/20120118/4c5056d2/attachment.obj>