Extract constraint relaxation information from IloOplRelaxationIterator in OPL Script

Currently, the constraint relaxation information are stored as properties info, info2 and info3. Properties info and info2 store the original bounds and the relaxed bounds as strings. Property info3 stores the new bounds as numbers.

The below is an improved version of sample relaxationIterator that demonstrates how to extract the relaxation information from info, info2 and info3.

 
range r = 1..10;

dvar int+ x[r] in 1..10;

// Preferences are stated as data of the opl model.

// prefs[i] will be used to represent the preference of seeing cts[i] in the relaxation.

float prefs[i in r] = i;
 

minimize sum(i in r) x[i];

subject to {

   ct: sum(i in r) x[i] >= 10;

   forall(i in r) 

     cts: x[i] >= i+5;

} 

main {

   thisOplModel.generate();

   var def = thisOplModel.modelDefinition;   

   // Default behavior

   writeln("Default Behavior");

   var cons = new Array (); 

   var changeLB = new Array(); 

   var vals = new Array (); 

   var count = 0; 

   var iter = opl1.relaxationIterator; 

   for(var c in iter) 

   { 

     var ct=c.ct; 
 

     writeln(ct.name); 

     writeln("info = ",c.info); 

     writeln("info2 = ",c.info2); 

     writeln("info3 = ",c.info3); 
 

     var info_index=c.info.indexOf(","); 

     var info2_index=c.info2.indexOf(","); 

     if (c.info.substring(0, info_index)!=c.info2.substring(0, 

     info2_index)) { 

       writeln("Lower bound changed"); 

       //lower bound changed

       cons[count]=ct; 

       changeLB[count] = true; 

       vals[count]=c.info3; 

       count++; 

     } 

     else if 

     (c.info.substring(info_index)!=c.info2.substring(info2_index)) { 

       writeln("Upper bound changed"); 

       //upper bound changed

       cons[count]=ct; 

       changeLB[count] = false; 

       vals[count]=c.info3; 

       count++; 

     } 
 

   } 

   for (var i =0; i<cons.length; i++){ 

     if (changeLB[i]) { 

       cons[i].LB=vals[i]; 

     } else { 

       cons[i].UB=vals[i]; 

     } 

   } 
 

   cplex1.solve(); 

}

In the above codes, info and info2 are treated as strings. By checking whether the lower bound or the upper bound is changed, it determines whether the lower bound or the upper bound should be modified. Then the modification information (constraint, Upper bound or lower bound to be modified, and the new bound) will be stored in arrays first. Then all the modifications are applied together in the end.