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: [email protected] [mailto:[email protected]] On Behalf > Of Josef Eisl > Sent: Tuesday, January 17, 2012 3:52 PM > To: [email protected] > Cc: [email protected] > 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 > [email protected] > https://www.gecode.org/mailman/listinfo/gecode-users > > _______________________________________________ Gecode users mailing list [email protected] https://www.gecode.org/mailman/listinfo/gecode-users
