hi Joachim and Kish, thanks a lot, that was very helpful! I tried learning from examples but didn't bother to read the tutorial far enough - my bad! Best, Misha On 02/28/2013 11:14 PM, Joachim Schimpf wrote: > On 27/02/2013 19:30, Misha Aizatulin wrote: >> hi all, >> >> I'm having trouble understanding how to use minimize(). Attached is a >> simple example that tries to find an allocation of dance lessons to >> dance couples (satisfying requests), and then choose the one with the >> minimal cost. Unfortunately, minimize() does not find the globally >> minimal solution. What is the correct way to use that? > > A constraint program has to follow a certain structure, in order to > make sense (http://www.eclipseclp.org/doc/tutorial/tutorial055.html) > > solve(Variables) :- > read_data(Data), > setup_constraints(Data, Variables), > labeling(Variables). > > An essential point is that the constraint setup code must not contain > "choices" or "alternatives", except in the form of alternative values > for variables (i.e. their domain). In your code, the cost/3 predicate > represents such choices, and must be replaced. In the following, I > have used element/3 constraints to do that: > > > :- lib(ic). > :- lib(branch_and_bound). > > %------- the data --------- > > ncouples(2). > > % request(Couple, PossibleLessons) > request(1, [0,1,2]). > request(2, [0,2,3]). > > % Lesson 0 1 2 3 > cost(1, [1,0,0,0]). % Couple 1 > cost(2, [0,0,1,1]). % Couple 2 > > % ----- the constraint model --------- > > schedule(Allocation) :- > ncouples(NCouples), > ( > for(I, 1, NCouples), > foreach(Lesson, Allocation), > foreach(Cost, Costs) > do > request(I, PossibleLessons), % get data > Lesson :: PossibleLessons, % create variable > cost(I, LessonCostsForI), % get data > Lesson1 #=Lesson+1, % create constraints > element(Lesson1, LessonCostsForI, Cost) > ), > alldifferent(Allocation), % more constraints > TotalCost #= sum(Costs), > > % ---- the search ---- > minimize(labeling(Allocation), TotalCost). > > > > -- Joachim > > ------------------------------------------------------------------------------ > Everyone hates slow websites. So do we. > Make your web apps faster with AppDynamics > Download AppDynamics Lite for free today: > http://p.sf.net/sfu/appdyn_d2d_feb > _______________________________________________ > ECLiPSe-CLP-Users mailing list > ECLiPSe-CLP-Users_at_lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/eclipse-clp-users >Received on Tue Mar 05 2013 - 14:32:00 CET
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