Changing parameters
Rather than continuing optimization on a difficult model like
glass4, it is sometimes useful to try different parameter
settings. When the lower bound moves slowly, as it does on this
model, one potentially useful parameter is MIPFocus, which
adjusts the high-level MIP solution strategy. Let us now set this
parameter to value 1, which changes the focus of the MIP search to
finding good feasible solutions. There are two ways to change the
parameter value. You can either use method m.setParam():
gurobi> m.setParam('MIPFocus', 1)
Set parameter MIPFocus to value 1
...or you can use the m.Params class...
gurobi> m.Params.MIPFocus = 1 Set parameter MIPFocus to value 1Once the parameter has been changed, we call m.reset() to reset the optimization on our model and then m.optimize() to start a new optimization run:
gurobi> m.reset()
Discarded solution information
gurobi> m.optimize()
Gurobi Optimizer version 10.0.3 build v10.0.3rc0 (win64)
CPU model: 11th Gen Intel(R) Core(TM) i7-1185G7 @ 3.00GHz, instruction set [SSE2]
Thread count: 4 physical cores, 4 logical processors, using up to 4 threads
Optimize a model with 396 rows, 322 columns and 1815 nonzeros
Model fingerprint: 0x541d0ad3
Variable types: 20 continuous, 302 integer (0 binary)
Coefficient statistics:
Matrix range [1e+00, 8e+06]
Objective range [1e+00, 1e+06]
Bounds range [1e+00, 8e+02]
RHS range [1e+00, 8e+06]
Presolve removed 4 rows and 5 columns
Presolve time: 0.00s
Presolved: 392 rows, 317 columns, 1815 nonzeros
Variable types: 19 continuous, 298 integer (298 binary)
Found heuristic solution: objective 3.133356e+09
Root relaxation: objective 8.000024e+08, 72 iterations, 0.00 seconds (0.00 work units)
Nodes | Current Node | Objective Bounds | Work
Expl Unexpl | Obj Depth IntInf | Incumbent BestBd Gap | It/Node Time
0 0 8.0000e+08 0 72 3.1334e+09 8.0000e+08 74.5% - 0s
H 0 0 2.400019e+09 8.0000e+08 66.7% - 0s
H 0 0 2.220019e+09 8.0000e+08 64.0% - 0s
0 0 8.0000e+08 0 72 2.2200e+09 8.0000e+08 64.0% - 0s
H 0 0 2.166685e+09 8.0000e+08 63.1% - 0s
0 0 8.0000e+08 0 72 2.1667e+09 8.0000e+08 63.1% - 0s
0 0 8.0000e+08 0 77 2.1667e+09 8.0000e+08 63.1% - 0s
H 0 0 2.133351e+09 8.0000e+08 62.5% - 0s
0 0 8.0000e+08 0 80 2.1334e+09 8.0000e+08 62.5% - 0s
0 0 8.0000e+08 0 80 2.1334e+09 8.0000e+08 62.5% - 0s
0 0 8.0000e+08 0 83 2.1334e+09 8.0000e+08 62.5% - 0s
0 0 8.0000e+08 0 78 2.1334e+09 8.0000e+08 62.5% - 0s
0 0 8.0000e+08 0 83 2.1334e+09 8.0000e+08 62.5% - 0s
0 0 8.0000e+08 0 83 2.1334e+09 8.0000e+08 62.5% - 0s
0 0 8.0000e+08 0 88 2.1334e+09 8.0000e+08 62.5% - 0s
0 0 8.0000e+08 0 66 2.1334e+09 8.0000e+08 62.5% - 0s
H 0 0 2.050017e+09 8.0000e+08 61.0% - 0s
0 2 8.0000e+08 0 65 2.0500e+09 8.0000e+08 61.0% - 0s
H 1 4 2.050017e+09 8.0000e+08 61.0% 74.0 0s
H 6 8 2.000016e+09 8.0000e+08 60.0% 41.8 0s
H 130 128 1.700015e+09 8.0000e+08 52.9% 12.7 0s
H 199 203 1.644459e+09 8.0000e+08 51.4% 10.8 0s
H 213 213 1.644459e+09 8.0000e+08 51.4% 10.8 1s
H 244 269 1.633347e+09 8.0001e+08 51.0% 11.0 1s
1428 1027 1.5333e+09 40 44 1.6333e+09 8.0001e+08 51.0% 15.5 5s
3138 1602 1.3750e+09 58 22 1.6333e+09 8.0001e+08 51.0% 20.5 10s
* 4233 2185 66 1.600017e+09 8.0001e+08 50.0% 21.5 12s
* 4238 2082 67 1.550017e+09 8.0001e+08 48.4% 21.5 12s
H 4308 2026 1.500016e+09 8.0001e+08 46.7% 21.6 14s
4457 2226 1.1000e+09 36 65 1.5000e+09 8.0001e+08 46.7% 22.6 15s
H 4809 2136 1.450016e+09 8.0001e+08 44.8% 23.4 16s
H 4908 2043 1.400013e+09 8.0001e+08 42.9% 23.9 17s
H 5098 2027 1.350013e+09 8.0001e+08 40.7% 24.8 18s
H 5282 1752 1.200013e+09 8.0001e+08 33.3% 25.7 18s
Interrupt request received
Cutting planes:
Gomory: 37
Cover: 9
Implied bound: 41
MIR: 51
Flow cover: 266
RLT: 107
Relax-and-lift: 99
Explored 5332 nodes (140122 simplex iterations) in 19.00 seconds (18.72 work units)
Thread count was 4 (of 4 available processors)
Solution count 10: 1.20001e+09 1.35001e+09 1.40001e+09 ... 1.64446e+09
Solve interrupted
Best objective 1.200012600000e+09, best bound 8.000066838804e+08, gap 33.3335%
Results are consistent with our expectations. We find a better
solution sooner by shifting the focus towards finding feasible
solutions (objective value 1.2e9 versus 1.5e9).
The setParam() method is designed to be quite flexible and forgiving. It accepts wildcards as arguments, and it ignores character case. Thus, the following commands are all equivalent:
gurobi> m.setParam('NODELIMIT', 100)
gurobi> m.setParam('NodeLimit', 100)
gurobi> m.setParam('Node*', 100)
gurobi> m.setParam('N???Limit', 100)
You can use wildcards to get a list of matching parameters:
gurobi> m.setParam('*Cuts', 2)
Matching parameters: ['Cuts', 'CliqueCuts', 'CoverCuts', 'FlowCoverCuts',
'FlowPathCuts', 'GUBCoverCuts', 'ImpliedCuts', 'MIPSepCuts', 'MIRCuts', 'ModKCuts',
'NetworkCuts', 'SubMIPCuts', 'ZeroHalfCuts']
Note that Model.Params is a bit less forgiving than
setParam(). In particular, wildcards are not allowed
with this approach. You don't have to worry about capitalization of
parameter names in either approach, though, so
m.Params.Heuristics and m.Params.heuristics are
equivalent.
The full set of available parameters can be browsed using the
paramHelp() command. You can obtain further information on a
specific parameter (e.g., MIPGap) by typing
paramHelp('MIPGap').
