The OPTMILP Procedure

Node Log

The following information about the status of the branch-and-bound algorithm is printed in the node log:

Node

indicates the sequence number of the current node in the search tree.

Active

indicates the current number of active nodes in the branch-and-bound tree.

Sols

indicates the number of feasible solutions found so far.

BestInteger

indicates the best upper bound (assuming minimization) found so far.

BestBound

indicates the best lower bound (assuming minimization) found so far.

Gap

indicates the relative gap between BestInteger and BestBound, displayed as a percentage. If the relative gap is larger than 1,000, then the absolute gap is displayed. If no active nodes remain, the value of Gap is 0.

Time

indicates the elapsed real time.

The LOGFREQ= and LOGLEVEL= options can be used to control the amount of information printed in the node log. By default a new entry is included in the log at the first node, at the last node, and at 100-node intervals. A new entry is also included each time a better integer solution is found. The LOGFREQ= option enables you to change the interval between entries in the node log. Figure 11.4 shows a sample node log.

Figure 11.4: Sample Node Log

NOTE: The problem ex1data has 10 variables (0 binary, 10 integer, 0 free, 0     
      fixed).                                                                   
NOTE: The problem has 2 constraints (2 LE, 0 EQ, 0 GE, 0 range).                
NOTE: The problem has 20 constraint coefficients.                               
NOTE: The MILP presolver value AUTOMATIC is applied.                            
NOTE: The MILP presolver removed 0 variables and 0 constraints.                 
NOTE: The MILP presolver removed 0 constraint coefficients.                     
NOTE: The MILP presolver modified 0 constraint coefficients.                    
NOTE: The presolved problem has 10 variables, 2 constraints, and 20 constraint  
      coefficients.                                                             
NOTE: The MILP solver is called.                                                
          Node  Active    Sols    BestInteger      BestBound      Gap    Time   
             0       1       3     85.0000000    178.0000000   52.25%       0   
             0       1       3     85.0000000     88.0955497    3.51%       0   
             0       1       3     85.0000000     88.0626822    3.48%       0   
             0       1       3     85.0000000     87.9666563    3.37%       0   
             0       1       3     85.0000000     87.9661593    3.37%       0   
             0       1       3     85.0000000     87.8181818    3.21%       0   
NOTE: The MILP solver added 2 cuts with 13 cut coefficients at the root.        
             3       0       5     87.0000000     87.0000000    0.00%       0   
NOTE: Optimal.                                                                  
NOTE: Objective = 87.                                                           
NOTE: The data set WORK.EX1SOLN has 10 observations and 8 variables.