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Xpress

What it is

FICO Xpress is a commercial linear, mixed-integer, and nonlinear programming solver. Its Python API uses a column-oriented loadproblem entry point, which polar-high's adapter feeds directly with the CSC arrays already produced by the engine. FlexTool dispatches through polar-high; it never imports xpress directly.

Official site: https://www.fico.com/en/products/fico-xpress-optimization

License options

  • Commercial. FICO sells perpetual and term licences directly and through partners.
  • Academic. Free academic licences for teaching and research; apply through the FICO Xpress academic partnership.
  • Community Edition. Free, no-registration size-limited build with a hard cap (historically 5000 variables / 5000 rows for LPs and MIPs; exact cap and small-print may change by release — confirm against the current FICO documentation). Useful for tutorials and small validation models, too small for typical FlexTool dispatch scenarios.

Licence and download portal: FICO's Xpress product page above.

Installation

Install the Python wrapper:

pip install xpress

The PyPI xpress wheel from FICO embeds the solver runtime, so no additional download is needed for the Community Edition.

For licensed users:

  1. Obtain xpauth.xpr from your FICO licence portal.
  2. Place it at one of the default locations searched by Xpress, or set the environment variable XPAUTH_PATH to point at it. Refer to the vendor's installation guide for the precise discovery order on your platform ([FIXME: confirm URL]).
  3. Floating-licence users point XPAUTH_PATH at the licence server's xpauth.xpr shim.

Unlike Gurobi/COPT, xpress.problem() does not currently accept a pre-constructed environment object, so the polar-high env= pass-through is accepted but unused for Xpress. Licence discovery is entirely vendor-side.

Verification

After installing the wrapper, run:

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

Expected: 'xpress' appears in the list.

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

To verify the licence works (this also prints the Xpress banner with the licence type):

python -c "import xpress; xpress.problem()"

Community Edition users see a banner stating the size cap. If the call raises an exception mentioning license, oem, or no token, see "Common errors" below.

Common errors

The error messages below are what FlexTool surfaces as FlexToolUserError. Xpress does not expose a stable numeric error code on its Python exceptions, so polar-high classifies licence errors by message text rather than code; the keyword set is license, licence, oem, expired, no token.

  • No xpauth.xpr found. Xpress raises with a message containing "license" or "no token". FlexTool shows: "Solver 'xpress' is installed but its license check failed. Details: ...". Fix by placing xpauth.xpr or setting XPAUTH_PATH.
  • Community-Edition size cap exceeded. Xpress raises with a message containing "oem" or "exceeds the size of an OEM problem". FlexTool surfaces this as the licence-error family. The fix is either to shrink the model or to upgrade to a full licence — Community Edition is unsuitable for production FlexTool scenarios.
  • Unknown Xpress control. Typing a wrong solver_arguments key raises a vendor exception from p.setControl(name, value); FlexTool shows "Solver 'xpress' returned an error: ...". The control names are in the Xpress reference manual ([FIXME: confirm URL]).

How to set it in FlexTool

On the solve entity:

solve_advanced.solver         = "xpress"
solve_advanced.solver_mip_gap = 0.005
solve_advanced.solver_arguments:
  defaultalg = 4
  presolve   = 1

flextool <input_db_url> --solver-time-limit 60 --highs-threads 8

The convenience knobs translate to Xpress's maxtime, miprelstop, and threads. Raw solver_arguments are passed verbatim to setControl and win on key collision.

Verified install on: [empty]