# Using OR-Tools with .NET and GUROBI

We want to model our MILP problem with Google OR-Tools in .NET, and solve it using GUROBI (solver may change in the next 1-2 years). However, we couldn't find the correct syntax to call GUROBI.

https://developers.google.com/optimization says it is Solver solver = Solver.CreateSolver(solver_id);. There are examples of calling GLOP and SCIP, but not for GUROBI (or we failed to find). What we tried listed below, but solver returns null.

using Google.OrTools.LinearSolver;

Solver solver = Solver.CreateSolver("GUROBI");

Solver solver = Solver.CreateSolver("GUROBI_MIXED_INTEGER_PROGRAMMING");

Question 1: What is the correct way of calling GUROBI?

Question 2: Does OR-Tools allow using callbacks of GUROBI? If so, any source suggestions to refer? https://www.gurobi.com/documentation/9.1/refman/cb_codes.html

Thanks.

## 1 Answer

1. the library needs to find the gurobi shared library before you can create the solver. You can set GUROBI_HOME to help.
2. you can have callbacks, but only in c++. Look for or-tools/linear_solver/linear_solver.h. Search for callbacks.