My Constraint Programming Blog

See Gecode version 3.4 released for a description of things that was changed in Gecode version 3.4.0.

One major change was replacement of tt, imp, eqv, ~ for logical implication, equivalence, and reification to a neater syntax, as well as post has been replaced with rel and expr.

For example, in alldifferent_except_0.cpp (decomposition of the global constraint all different except 0), this code segment

post(space,
     tt(imp(x[i] != c && x[j] != c, // =>
     x[i] != x[j])),
     icl
     );

is now written

rel(space,
   (x[i] != c && x[j] != c) >> (x[i] != x[j]),
   icl
);

This is a more direct syntax which I like very much. Since I'm a lazy person, I love this kind of syntactic sugar.

Another example is from who_killed_agatha2.cpp. This older code segment:

 post(*this, 
      tt(
        imp(hates_m2(i, agatha) == 1, 
            hates_m2(i, butler) == 1)), 
        opt.icl()
     ); 

is now written

 rel(*this, 
        (hates_m2(i, agatha) == 1) >> 
        (hates_m2(i, butler) == 1), 
        opt.icl()); 

Here are all the changed models, which are available at my Gecode page. Many of them required just a simple change of post() to rel(); then there is no special comment below.

A comment: I will very soon also blog about a couple (about 100) new Gecode models that also - as much as possible - use the new syntax.

• alldifferent_except_0.cpp. See above.
• assignment.cpp
• building_a_house.cpp
• bus_schedule.cpp
• calculs_d_enfer.cpp
• circuit_orbit.cpp
• clique.cpp
  Replaced

   post(*this, 
        tt(imp(
              x_bool[i] == 1 && x_bool[j] == 1, // ->
              b)),
  

  with rel(*this, (x_bool[i] == 1 && x_bool[j] == 1) >> b
• coins3.cpp
• coins_grid.cpp
• crossword.cpp I remove this model since it's using the obsolete matrix element trick, and is replaced with crossword2.cpp
• crossword2.cpp
• donald_gerald_robert.cpp
• furniture_moving.cpp
• global_contiguity.cpp
  Replaced:

  post(*this, tt(
     eqv(
        y[i] == 1, // <=>
        x[i] == 1)))
  

  with rel(*this, (y[i] == 1) == (x[i] == 1))
• hidato.cpp
• house2.cpp
• least_diff.cpp
• map.cpp
• nadel.cpp
• organize_day.cpp
• send_more_money_any_base.cpp
• seseman.cpp
• set_covering_deployment.cpp
• sonet.cpp
• stable_marriage.cpp
  Replaced reifications.

  BoolVar b1 = post(*this, ~(rankMen[m*n+w] < rankMen_res));
  BoolVar b2 = post(*this, ~(rankWomen_res < rankWomen[w*n+m]));
  post(*this, tt(imp(b1, b2)), opt.icl());
  

  with

  BoolVar b1 = expr(*this, (rankMen[m*n+w] < rankMen_res));
  BoolVar b2 = expr(*this, (rankWomen_res < rankWomen[w*n+m]));
  rel(*this, b1 >> b2, opt.icl());
  

  Note that post is here replaced with expr:
• traffic_lights.cpp
• who_killed_agatha.cpp
• who_killed_agatha2.cpp See above.
  Another change is the use of the expression element instead of the constraint element- I.e. instead of

  element(*this, hates_m2, the_victim, the_killer , IntVar(*this,1,1), opt.icl());
  

  we use

  rel(*this, element(hates,the_killer*n+the_victim) == 1, opt.icl());
  

• word_square.cpp has been removed since it used some obsolete construct and i replaced with a better model: word_square2.cpp
• young_tableaux.cpp
  Remodelled the constraints that the rows and columns should be increasing:

  for(int i = 0; i < n; i++) {
    rel(*this, m.row(i),IRT_LQ);
    rel(*this, m.col(i),IRT_LQ);
  }
  

• zebra.cpp
  Replaced

  post(space, abs(space, minus(space, x, y, icl), 
     icl) == 1, icl); 
  

  with rel(space, abs(x-y) == 1, icl);