XPRESS Changelog#

20250617#

  • Changes in MP

    • Multi-objective emulator: added support for objective-specific options via objective suffixes beginning with option_

    • Option cvt:unnest: bits 2 and 4 switch on inlining of linear and quadratic subexpressions produced during reformulations (by default on).

    • Options cvt:pre:ctx2ineq, cvt:pre:ctx2count to control context propagation into conditional comparisons #267.

20250531#

  • Updated to Xpress 45.01.01 (9.6) that includes:

    • Pre root parallel heuristics phase.

    • New deterministic measure of algorithmic work.

    • Performance improvements.

  • Option lp:opttol (opttol), synonym for previous lp:optimalitytolerance.

  • Added keywords lim:work, lim:prerootwork and mip:prerooteffort.

  • Added value 3 to pre:domcol.

20250429#

  • Fix a bug in parsing of quadratic expressions, which could wrongly parse products of unequal linear expressions, such as (x-3)*(x-z-5).

20250426#

  • Relinked with XPRESS 44.01.04.

  • Non-linear constraints are now passed via the expression API, that can improve performance.

  • Changes in MP

    • Option cvt:qp2pass (default even faster parsing of quadratics)

20250329#

  • Changes in MP:

    • Option cvt:multoutcard to limit the size of out-multiplied QP expressions. Can improve speed on large models.

    • Improved parsing of quadratic expressions.

  • Renamed option poolnbest to sol:poollimit. Old name kept as synonym.

20250308#

  • Fix several option descriptions.

  • Default to natively accept nonlinear expressions since they seem to perform well in v9.5. Full XPRESS license required.

20241227#

  • Fix acceptance options for nonlinear formulas (still disabled by default.)

  • Option pre:solve_nlp

  • Updated to Xpress 9.5 (44.01.01):

    • Performance improvements in the Global optimization engine and in the MIP solver

    • New column-based presolve eliminations to reduce model size when free variables are present in the model instance.

    • In models with big-M coefficients, additional tightening of coefficients is performed.

    • Knapsack cover inequalities are now strengthened by using superadditive lifting.

20240823#

  • Updated to Xpress 43.01.03

  • Added hybrid gradient algorithm (set bar:alg to 4)

  • Option bar:cpuplatform defaults to -2. To replicate the previous versions behaviour, set to -1.

20240724#

  • Option acc:_all

    • Useful to disable all reformulations (acc:_all=2), or force linearization (acc:_all=0).

  • Option cvt:prod

    • Controls reformulation of binary products into logical constraints.

  • Faster input of quadratic expressions.

20240617#

  • Multi-objective emulator

    • obj:multi=2 forces emulation, even if MO natively supported.

    • Fixed a bug in the objective degradation suffixes .objasbtol, .objreltol.

20240606#

  • Fix mip:basis (post-solving as fixed MIP), although fix + resolve from AMPL can be faster.

  • Fix reporting infeasibility with obj:multi=1.

20240604#

  • Presolve division by constant, resulting in fewer constraints

  • Fix no-solution case in multi-objective emulator

20240529#

  • Multi-objective emulator

    • All flat MP solvers support multi-objective mode (obj:multi=1), either natively, or via emulation.

    • Suffixes .objpriority, .objweight, .objabstol, .objreltol.

    • [BREAKING] Default intuitive handling of .objweight, see option obj:multi:weight, even when natively supported.

20240429#

  • [BREAKING] Merged report_times and timing; they are now aliases, set the value to 1 to have basic info, to 2 to have more detailed info.

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)