XPRESS Changelog

20240320

  • SOS constraints.

    • Fixed handling of SOS2 constraints created by AMPL as reformulations of PL expressions (option pl_linearize 1, default; set to 0 to use the solver’s native PL functions or MP linearization.)

    • Disallow repeated weights for SOS constraints (suffixes .sosno/.ref.)

  • Native handling of POW(x, INT).

    • Power expressions with positive integer exponent are passed natively to the solvers accepting them, vs previously quadratic or linear reformulation.

  • Option report_times.

  • Unused acc: options.

    • The constraint acceptance options acc:... for non-handled constraints are ignored (previously triggered error.)

20240312

  • Updated Xpress to 42.01.5

  • Xpress Global Solver

    • Native implementation of most supported non-linear functions. Not enabled by default.

20240306

  • Xpress Global Solver

    • Apply global (MI)NLP solver for non-convex non-linear models.

20240115

  • Solve result codes

    • List codes by running (solver) -!

    • [BREAKING] Standardized codes. Major changes:

      • 100-199 (solved?) means solution candidate provided, but can be suboptimal/infeasible

      • 300-349 means unbounded problem but feasible solution returned

      • 400-449 means limit/interrupt but feasible

    • [BREAKING] sol:chk:fail returns code 150 (solved?)

  • Improved translation of SOCP constraints.

    • Options cvt:socp, cvt:socp2qc.

  • Compact solution check warnings

  • Fixed presolve of the power function #226.

20231117

  • MP update: fixed graceful exit on Ctrl-C from AMPL in Linux and fixed issue with reading text-format NL files

20231103

  • Improved translation of logical constraints: inlining of nested disjunctions and conjunctions; fewer auxiliary binary variables.

20231017

  • Fixed a bug in NL reader on Windows.

20230919

  • mp_options. Receive mp_options from AMPL (for all MP solvers). They are parsed before (solvername)_options.

  • Solution checking: relative tolerance sol:chk:feastolrel; options sol:chk:round, sol:chk:prec.

20230831

  • Solution checking, options sol:chk:* (experimental).

  • Preprocess And/Or constraints.

20230817

  • Alternative solutions: solve status equal to that of the final solution.

  • Fixed a bug causing repeated names for auxiliary variables and constraints.

  • Option values can be assigned without ‘=’.

  • Fixed a bug where equivalent conditional comparisons were not unified.

20230808

  • Updates for Xpress 9.2 (42.01.01), which include many performance improvements in the MIP solver.

  • Non-convex quadratic problems are now solved to global optimality by default.

  • Added options ‘mip:heurshiftprop’, ‘tech:backgroundthreads’ and ‘tech:backgroundselect’.

  • The range of the control ‘mip:feasibilityjump’ was extended.

20230728

  • Option ‘tech:writesolution’.

20230727

  • Fixed a memory leak #217

  • Fixed quadratic constraints

20230726

  • MP: fixed inequalities of integer expressions with non-integer constants, see test_int_non_int.mod.

20230724

  • Option [solver_]auxfiles rc; transfers names of variables and linear constraints into the model; (solver)_options ‘cvt:names=0-3’ controls names.

20230714

  • Options barrier/primal/dual/network like in ASL.

20230621

  • Fix quadratic objective with repeated subexpressions.

  • Fix reformulation of ==> / else.

20230616

  • Changes in MP.

  • Eliminated spurious warnings

  • Fixed passing of quadratic objective

20230607

  • Amended detection and display of licensing errors

  • Licensing allows now usage of an XPRESS license from an AMPL-based deployment

20230603

  • Added option ‘tech:logfile’ to enable output to a log file

20230424

  • Changes in the MP library: added variable names support and removed spurious starting solution

20230227

  • Eliminated warning message when a non feasible solution is added as a starting point for the MIP search

20230207

  • Changes in the MP library

20221228

  • Changes in MP

20221222

  • Bug fixes in MP

20221211

  • Changes in MP: added the ==> else operator Implemented implication with ‘else’: constr1 ==> constr2 [else constr3]

  • Changes in MP: PLApproxRelTol, PLApproxDomain Parameters to control piecewise-linear approximation. cvt:plapprox:reltol default value changed from 1e-5 to 0.01.

20221208

  • First release of the MP-based driver for Xpress (solver version 9.0)

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