How to use Solver Gurobi while using python as the coding language

[arjun...@stellium.com]

Hi Team,

I want to use Gurobi solver to solve a MILP and MLQP problem with python as the coding language. I just wanted to understand if it is possible for me to do so. I want to know how would I call the Gurobi solver in python? I do not see Gurobi in any of the folders of OR-tools for python, how does the code interact with gurobi?

Do I need to buy a license for Gurobi?

Also does anybody have any information on the number of variables I can use in Gurobi?

PS: I am a novice to optimization tools.

[Jon Orwant]

Hi Arjun,

In addition to providing Google's solvers, OR-tools also provides wrappers around other solvers, including Gurobi for MILP (but not MLQP) problems. 

Gurobi is a commercial solver and you do need a license to use it. IIRC the license is free for educational use.

After you install Gurobi on your machine, you can use OR-tools to invoke it from Python as follows:

solver = pywraplp.Solver('SolveIntegerProblem',
                           pywraplp.Solver.GUROBI_MIXED_INTEGER_PROGRAMMING);

Jon

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[arjun...@stellium.com]

Thank you for the information Jon. :-)

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[Roman Istomin]

a follow-up question:

would C++ solver for the same purpose be constructed with the same solver name ("GUROBI_MIXED_INTEGER_PROGRAMMING")

and can Gurobi be used from under ORtools for other problems?
Especially this one:

operations_research::SimpleMinCostFlow()

if yes, what should I specify as solver for those problems?

On Wednesday, June 21, 2017 at 9:10:35 AM UTC-4, orwant wrote:

Hi Arjun,

In addition to providing Google's solvers, OR-tools also provides wrappers around other solvers, including Gurobi for MILP (but not MLQP) problems. 

Gurobi is a commercial solver and you do need a license to use it. IIRC the license is free for educational use.

After you install Gurobi on your machine, you can use OR-tools to invoke it from Python as follows:

solver = pywraplp.Solver('SolveIntegerProblem',
                           pywraplp.Solver.GUROBI_MIXED_INTEGER_PROGRAMMING);

Jon

On Wed, Jun 21, 2017 at 6:00 AM, <arju...@stellium.com> wrote:

Hi Team,

I want to use Gurobi solver to solve a MILP and MLQP problem with python as the coding language. I just wanted to understand if it is possible for me to do so. I want to know how would I call the Gurobi solver in python? I do not see Gurobi in any of the folders of OR-tools for python, how does the code interact with gurobi?

Do I need to buy a license for Gurobi?

Also does anybody have any information on the number of variables I can use in Gurobi?

PS: I am a novice to optimization tools.

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[Laurent Perron]

MinCostFlow is a polynomial algorithm. It does not use any MIP solver.

To use Gurobi in any language, you need to recompile from source or-tools with Gurobi installed 

See https://developers.google.com/optimization/install/python/source_linux (mac and windows are also available).

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[Roman Istomin]

Thanks,

So, do I understand correctly that Gurobi could only be used for Integer Programming problems?

Also, I did make third party with Gurobi installed, but to use Gurobi solver, do I need to explicitly tell ORtools to use it or does it use Gurobi by default when compiled with a thirdparty option?

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Best, Roman Istomin

[Laurent Perron]

Yes, and yes.

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[Henry]

Follow up question: I have a working version of gurobi and a license. I downloaded the or-tools source and did the following:

make third_party

Add the following to Makefile.local
UNIX_GUROBI_DIR = /Library/gurobi902/
GUROBI_LIB_VERSION = 90

Make python

However, when I try to create a solver using GUROBI_MIXED_INTEGER_PROGRAMMING, it says that this attribute doesn’t exist.

Best,

Henry

[Mizux Dev]

did you run `make clean_python` before ?

otherwise the enum should be generated in ortools/gen/ortools/linear_solver/pywraplp.py ~line100

can try to grep it:

```sh

grep -rn "GUROBI_" ortools/gen/ortools/linear_solver/pywraplp.py

```

[Henry Robbins]

At what point should I run make clean_python? Another person in my team has been able to successfully install on Windows. He said he had to use make install_python before everything worked. I have tried doing both and still get the error:

AttributeError: type object 'Solver' has no attribute ‘GUROBI_MIXED_INTEGER_PROGRAMMING'

What is the exact order I should preform these commands? Do you have any other ideas why this might not be working? By the way, I am using the master branch not the latest stable release.

Thanks!

Henry

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[Laurent Perron]

make third_party

edit Makefile.local

make clean

make python

make install_python

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[Henry Robbins]

Just tried this and received the same error. Here is some additional information that may be helpful in trouble shooting (attached). Thanks for the help! I really appreciate it!

Best,

Henry

[Xiang Chen]

How are you running your program?

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[Henry Robbins]

I have tried running both from command line and through my Jupyter Notebook

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[Henry Robbins]

If this helps, I tried running make test and this message was at the end:

makefiles/Makefile.dotnet.mk:36: Cannot find 'dotnet' command which is needed for build. Please make sure it is installed and in system path.

DOTNET_BIN =

Or-tools have been built and tested for C++ , Python3.6 , Java

Best,

Henry

On Jun 4, 2020, at 5:12 PM, Xiang Chen <xiang10...@gmail.com> wrote:

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[Laurent Perron]

If you are not compiling for dotnet, you can ignore this warning.

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[Henry Robbins]

Ok. Is there other information I can send to help troubleshoot? I followed the steps you outlined but am still receiving the same error.

Thanks again for the help!

Best,

Henry

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