WELCOME

You have successfully installed version 9.1.1 of the Gurobi Optimizer.

You'll find instructions for setting up your Gurobi license in this document, as well as a list of supported platforms, and Release Notes and guidelines for converting existing Gurobi code to run with this new version. Once you have finished browsing this document, you should refer to the Quick Start Guide, the Example Tour, the Reference Manual, or the Remote Services Reference Manual to get started using the Gurobi Optimizer.

Obtaining Your License

Gurobi Optimizer 9.1 uses the same licenses as version 9.0, so if you already have a Gurobi 9 license, there's no need to obtain a new one. If you don't already have a Gurobi 9 license, you will need to visit the Gurobi License Center. If you are a commercial user under maintenance, you should see your Gurobi 9 license under Current Gurobi Licenses. If you would like to request a free academic license, you can do so from the Free Academic License page. Once you have a license on the Gurobi web site, you will need to follow the instructions for installing a license in the Quick Start Guide.

Supported Platforms for Version 9.1

Platform	Operating System	Compiler	Notes
Windows 64-bit (win64)	Windows 10, Windows Server 2012 R2, Windows Server 2016, Windows Server 2019	Visual Studio 2015	Use gurobi_c++md2015.lib (e.g.) for C++
	Windows 10, Windows Server 2012 R2, Windows Server 2016, Windows Server 2019	Visual Studio 2017	Use gurobi_c++md2017.lib (e.g.) for C++
	Windows 10, Windows Server 2012 R2, Windows Server 2016, Windows Server 2019	Visual Studio 2019	Use gurobi_c++md2019.lib (e.g.) for C++
Linux® x86-64 64-bit (linux64)	Red Hat® Enterprise Linux 6.7-6.10, 7.3-7.7, 8.0-8.3 (and the corresponding CentOS distributions)	GCC 4.4/4.8
	SUSE® Enterprise Linux 12, 15	GCC 4.3/4.4/4.8
	Ubuntu® 16.04, 18.04, 20.04	GCC 4.6/4.8	Use libgurobi_g++5.2.a for newer C++ compilers
macOS 64-bit (mac64)	10.13 (High Sierra), 10.14 (Mojave), 10.15 (Catalina)	Xcode 7/8
AIX® 64-bit (power64)	AIX 7.1, 7.2	XL C/C++ 9	Due to limited Python support on AIX, this port does not include the Interactive Shell or the Python libraries.

Additional Supported Platform Information

Gurobi 9 supports the following language/platform versions:

Language	Version
Python	2.7, 3.6, 3.7, 3.8, 3.9
MATLAB	R2013a-R2020b
R	4.0
JDK	8, 11, 15
.NET core	2.1, 3.1

Release Notes for Version 9.1

In addition to performance enhancements, Gurobi 9.1 adds the following new features:

A New Heuristic For Models with Expensive Relaxations: Our new NoRel heuristic finds high-quality solutions in situations where the linear programming (LP) relaxation of a mixed-integer programming (MIP) problem is very expensive to solve. It is controlled by parameters NoRelHeurTime and NoRelHeurWork.
Integrality Focus: This new feature forces the solver to be much stricter about integrality constraints, thus avoiding many undesirable results (including trickle flows) that can come from small integrality violations. It is controlled by the IntegralityFocus parameter.
Further Python Matrix API Enhancements: Gurobi's Python interface - gurobipy - has been extended and improved to better support matrix-oriented modeling. Consult the documention for the new MConstr object for details.
Pip Install Support: Users can now utilize pip, the package installer for Python, to install gurobipy into their Python environment.
Releasing the GIL in Python API: When the optimize() method is called, gurobipy now releases the Global Interpreter Lock (GIL), which allows user programs to execute Python code in another Python thread while optimize() is running.
Tuning Tool Enhancements: We added a number of additional controls to our tuning tool. See the Parameter Tuning Tool documentation for more details.
Record/Replay for Compute Server and Cloud: We now support the record/replay feature for Gurobi Compute Server and Gurobi Instant Cloud. See Recording and Replay for more details.
Pre-specified User Cuts: By setting the Lazy linear constraint attribute to the new value -1, the user can declare a linear constraint to be a user cut. The constraint must be redundant with respect to the rest of the model. The solver can optionally add user cuts to the relaxation in order to cut off LP solutions that are encountered during the MIP solving process and potentially improve performance.
New Parameters and Attributes: In addition to the attributes and parameters directly tied to the new features above, there is one additional new parameter and one additional new attribute.
- PoolGapAbs New parameter to specify the maximum absolute gap allowed for stored solutions.
- FingerPrint New attribute to query the model fingerprint.

Code Conversion from Version 9.0

Programs that were originally written for version 9.0 of the Gurobi Optimizer generally won't require any code changes to use version 9.1. If you'd like to use the new features, some code changes are required.

Acknowledgements

We would like to thank Irv Lustig for several suggestions that helped to improve this release.

License Agreement

Note that this software is covered by the Gurobi End User License Agreement. By completing the Gurobi installation process and using the software, you are accepting the terms of this agreement.

Thank you for using Gurobi products!