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## Using a gurobi.env file

When you want to change the values of Gurobi parameters, you actually have several options. We've already discussed parameter changes through the command-line tool

and through interactive shellcommands

gurobi> m.setParam('Threads', 1)


Each of our language APIs also provides methods for setting parameters. The other option is through a gurobi.env file.

Whenever the Gurobi library starts, it will look for gurobi.env in the current working directory, and will apply any parameter changes contained therein. This is true whether the Gurobi library is invoked from the command-line tool, from the interactive shell, or from any of the Gurobi APIs. Parameter settings are stored one per line in this file, with the parameter name first, followed by at least one space, followed by the desired value. Lines beginning with the # sign are comments and are ignored. To give an example, the following (Linux) commands:

> echo "Threads 1" > gurobi.env
> gurobi_cl /opt/gurobi1000/linux64/examples/data/coins.lp
Using gurobi.env file
Set parameter Threads to value 1
Set parameter LogFile to value "gurobi.log"

Gurobi Optimizer version 10.0.0 build v10.0.0rc0 (linux64)
Copyright (c) 2022, Gurobi Optimization, LLC

Read LP format model from file /opt/gurobi1000/linux64/examples/data/coins.lp

Reading time = 0.00 seconds
: 4 rows, 9 columns, 16 nonzeros

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 1 threads

Optimize a model with 4 rows, 9 columns and 16 nonzeros
Model fingerprint: 0x06e334a4
Variable types: 4 continuous, 5 integer (0 binary)
Coefficient statistics:
Matrix range     [6e-02, 7e+00]
Objective range  [1e-02, 1e+00]
Bounds range     [5e+01, 1e+03]
RHS range        [0e+00, 0e+00]
Found heuristic solution: objective -0.0000000
Presolve removed 1 rows and 5 columns
Presolve time: 0.00s
Presolved: 3 rows, 4 columns, 9 nonzeros
Variable types: 0 continuous, 4 integer (0 binary)
Found heuristic solution: objective 26.1000000

Root relaxation: objective 1.134615e+02, 2 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  113.46153    0    1   26.10000  113.46153   335%     -    0s
H    0     0                     113.3000000  113.46153  0.14%     -    0s
H    0     0                     113.4500000  113.46153  0.01%     -    0s
0     0  113.46153    0    1  113.45000  113.46153  0.01%     -    0s

Explored 1 nodes (2 simplex iterations) in 0.00 seconds (0.00 work units)
Thread count was 1 (of 4 available processors)

Solution count 4: 113.45 113.3 26.1 -0

Optimal solution found (tolerance 1.00e-04)
Best objective 1.134500000000e+02, best bound 1.134500000000e+02, gap 0.0000%


would read the new value of the Threads parameter from gurobi.env and then optimize model coins.lp using one thread. Note that if the same parameter is changed in both gurobi.env and in your program (or through the Gurobi command-line tool), the value from gurobi.env will be overridden.

A few parameters can only be used from the Gurobi command-line tool, and thus can't be set through gurobi.env. These parameters are labeled 'Command-line only' in the Parameter section of the Gurobi Reference Manual.