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Gurobi

What it is

Gurobi is a commercial linear, mixed-integer, and quadratic programming solver used widely on large energy-system optimisation models. FlexTool writes each solve's model to an MPS file and runs Gurobi's command-line solver gurobi_cl on it in a separate process (found on PATH, or in ~/gurobi/bin), passing every parameter as a Name=value argument. FlexTool never inspects a licence: the licence-discovery path is Gurobi's own.

Official site: https://www.gurobi.com/

License options

  • Commercial. Named-user, floating, and machine licences via the Gurobi sales channel.
  • Academic. Free for students, faculty, and staff at recognised degree-granting institutions. Renewable annually from an academic IP.
  • Free trial. Time-limited evaluation licence available from the Gurobi website with vendor sign-off.
  • WLS (Web Licence Service). Cloud-friendly token-based licensing for containers, CI, and shared infrastructure.

Licence acquisition page: https://www.gurobi.com/solutions/licensing/

Installation

Install the Python wrapper:

pip install gurobipy

gurobipy lets FlexTool detect Gurobi at start ("Solvers:" line); the solve itself runs gurobi_cl, which comes with the Gurobi installation.

After installing the wrapper, set up a licence file. The simplest single-machine path:

  1. Sign in at https://www.gurobi.com/ and request a licence appropriate for your situation (commercial, academic, or trial).
  2. Use Gurobi's grbgetkey tool, or the equivalent web flow, to download a gurobi.lic file.
  3. Place gurobi.lic at either of:
  4. $HOME/gurobi.lic (user-scoped, the simplest), or
  5. /opt/gurobi/gurobi.lic (system-wide), or
  6. any path of your choice, then set the GRB_LICENSE_FILE environment variable to that path.

WLS and Compute Server users set up the licence the way gurobi_cl reads it (a gurobi.lic with the WLS credentials, or GRB_LICENSE_FILE). Server, cloud and licence parameters (ComputeServer, CS..., Cloud..., WLS..., TokenServer, ...) are taken from solver_config/gurobi.opt only: the input database's solver_arguments may not set them (see What the database may set).

Verification

After installing gurobipy, run:

python -c "from polar_high.solvers import available_solvers; print(available_solvers)"

Expected: 'gurobi' appears in the printed list:

['gurobi', 'cplex', 'xpress', 'copt', 'highs']

gurobi in the list confirms only that the wrapper is importable — licence discovery still happens at solve time. To check that the licence is also working, point FlexTool at any small Gurobi-targeted scenario and run it; or, outside FlexTool:

python -c "import gurobipy as gp; gp.Model().optimize()"

A clean exit (no GurobiError) means the licence is found.

Common errors

FlexTool runs Gurobi as the gurobi_cl command-line program. When it fails, FlexTool stops the run with a FlexToolUserError whose message includes gurobi_cl's own output (its stdout and stderr), so Gurobi's text is in the FlexTool log.

  • No licence, or the licence check failed. gurobi_cl exits with an error and prints, for example, "No Gurobi license found". FlexTool shows: "Solver 'gurobi' subprocess failed a license check. Details: 'gurobi' CLI for solve '' exited with returncode=... --- stdout --- ..." (see License options). Fix by placing the gurobi.lic file in your home folder (or /opt/gurobi/) or by setting GRB_LICENSE_FILE in the environment FlexTool runs in.
  • Licence expired. The same message, with Gurobi's text "License has expired". Renew the licence through the Gurobi web portal.
  • gurobi_cl not found. "Solver 'gurobi' CLI binary is not installed on this system." Install Gurobi and put gurobi_cl on the PATH.
  • Unknown Gurobi parameter. A misspelt name in solver_arguments (e.g. MIPGapp) stops the run before its first solve, with the closest name (MIPGap) in the message: the database may name only parameters in FlexTool's list (What the database may set). In gurobi.opt (or from solver_arguments where this computer allows unlisted names) FlexTool warns and passes it; Gurobi ignores it, prints Unknown parameter: 'MIPGapp' (ignored) and solves on, and FlexTool repeats that as a warning naming where the parameter was set. Fix the name. With console logging off (LogToConsole 0) Gurobi prints no such line, and there is no warning.
  • File parameters. Parameters that name a file or folder (LogFile, SolFiles, NodefileDir, InputFile, the .prm / .json file lists of tuning, concurrent and multi-objective runs) take a full path in gurobi.opt; in the database's solver_arguments they take only a plain file name, written in the solve's work folder, and a path is refused. See What the database may set. ResultFile is ignored everywhere (with a warning): FlexTool names its own result file and reads the solution from it.
  • Time or other limit reached. A MIP stopped at its time, node, solution or work limit, or at BestObjStop / BestBdStop, with a solution is kept with a warning that gives the gap reached; an LP, or a MIP without a solution, stops the run. See Time and other limits.
  • Objective values. BestObjStop, BestBdStop, Cutoff, MIPGapAbs and PoolGapAbs are written in unscaled currency; FlexTool scales them to the objective Gurobi sees (see Time and other limits).

How to set it in FlexTool

On the solve entity for the solve you want Gurobi to handle:

solve_advanced.solver         = "gurobi"
solve_advanced.solver_mip_gap = 0.005
solve_advanced.solver_arguments:
  Method     = 2
  Presolve   = 2
  MIPFocus   = 1

flextool <input_db_url> --solver-time-limit 60 --solver-mip-gap 0.001

--solver-time-limit 60 reaches Gurobi as TimeLimit=60 and --solver-mip-gap 0.001 as MIPGap=0.001, over the solve's solver_mip_gap (0.005) and any MIPGap in solver_arguments or gurobi.opt. Without the flags, solver_mip_gap gives MIPGap=0.005, and a MIPGap (or mipgap: names match without regard to case) in solver_arguments wins over it. --threads (Threads per run in the FlexTool window) sets Threads; without it, Threads in gurobi.opt or solver_arguments applies. --highs-threads does not change it. The run prints what Gurobi receives, for example:

Solver args (gurobi): Threads=1, MIPGap=0.001, LogToConsole=1, Method=2, Presolve=2, MIPFocus=1, TimeLimit=60

Verified install on: [empty]