The Global Log
During the branch and bound tree search (see XPRSglobal (GLOBAL)), a summary log of nine columns of information is frequently printed. By default, the printing frequency increases over time. If MIPLOG is explicitly set to a negative value -n, a log line will be printed every n nodes. The nine columns consist of:
| Node | A sequential node number. |
| BestSoln | The value of the best integer solution found so far. |
| BestBound | A bound on the value of the optimal integer solution. |
| Sols | The number of integer solutions that have been found. |
| Active | The number of active (unsolved) nodes in the branch and bound tree search. |
| Depth | The depth of the current node in the branch and bound tree. |
| Gap | The percentage gap between the best solution and the best bound. |
| GInf | The number of global infeasibilities at the current node. |
| Time | The time taken. |
This log is also printed when an integer feasible solution is found. An asterisk (*) printed in front of the node number indicates that a solution has been found by an integral LP relaxation. Single characters indicate that a heuristic solution has been found. Lower case characters stand for different strategies of the Optimizer's diving heuristic: the letter a corresponds to strategy 1, the letter b to strategy 2, and so forth. Compare control HEURDIVESTRATEGY. By default, several strategies are applied. Upper case letters stand for special search heuristics. More precisely, R, L, M, C, U, and Z stand for the different modes of local search that can be selected by controls HEURSEARCHROOTSELECT and HEURSEARCHTREESELECT. For technical reasons, a U might also appear after a restart. The letter F represents the feasibility pump, T stands for a trivial heuristic. S, G, and B are reserved for special purpose heuristics for problems with set packing/partitioning constraints, GUBs, and branching on constraints, respectively. An I or an E indicate that a solution has been found while interdiction branching or the calculation of branching estimates.
During root node cutting, the column Node is replaced by two columns Its and Type, columns Active and Depth are replaced by Add and Del, respectively. These have the following meaning:
| Its | A counter for the number of cutting plane separation loops. |
| Type | The type of cuts that have been generated this round: G -- Gomory cuts, M -- model cuts, O -- outer approximation cuts (only for nonlinear problems), N -- network-based cuts, K -- any other type of cuts |
| Add | Number of cuts added to the LP relaxation in this iteration |
| Del | Number of cuts deleted from the LP relaxation in this iteration |
If MIPLOG is set to 3, a detailed log of eight columns of search information is printed for each node:
| Branch | A sequential node number. |
| Parent | The node number of the parent of the current node. A D or a U marks whether the current node is the down child or the up child, respectively, of its parent. |
| Solution | The optimal value of the LP relaxation at the current node. |
| Entity | The global entity on which the Optimizer will branch after this node. |
| Value | The current value of the entity chosen for branching. |
| Active | The number of active nodes in the tree search. |
| GInf | The number of global infeasibilities. |
| Time | The time taken. |
Not all the information described above is present for all nodes. If the LP relaxation is cut off, only Branch and Parent (and possibly Solution) are displayed. If the LP relaxation is infeasible, only Branch and Parent appear. The rest of the line will consist of a text message relaxation exceeds cutoff or relaxation infeasible. If an integer solution is discovered, this is highlighted before the log line is printed.
If MIPLOG is set to 2, the detailed log is printed at integer feasible solutions only. When MIPLOG is set to 1, the tree node logs are surpressed, but cutting loop logs will still be displayed. If MIPLOG is set to 0, neither cut nor node log wil be pritned. In any case, LP logs and intermediate status messages might still be printed.
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