HiGHS Changelog

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?)

  • 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

20231109

  • Updated to HiGHS 1.6.0

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.

  • Don’t return basis for MIPs. Caused trouble with older versions of AMPL with logical constraints (workaround: alg:basis=0.)

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

  • 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.

20230728

  • Option ‘tech:writesolution’

20230726

  • 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.

20230621

  • Fix quadratic objective with repeated subexpressions.

  • Fix Hessian API.

20230616

  • Imitate partial MIP start.

  • Changes in MP.

20230531

  • MIP start. HiGHS 1.5 supports complete MIP starts only.

  • Wrong solver options are gracefully reported via solve_message.

20230522

  • Fixed solution status reporting to AMPL

  • Fixed basis input with obj offset or missing data

  • Added warm start for LP problems

  • Reading column names from col file is present

20230424

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

20230227

  • Fixed a problem when retrieving basis status

  • Implemented retrieval of MIP gap so that if optimality is reached via presolving, the returned gap is 0

20230224

  • Updated to HiGHS 1.5.1; now returning number of LP iterations in a MIP solve

20230222

  • Fixed: now returning the correct dual values for the constraints

20230209

  • Updated to HiGHS 1.4.2

  • Fix for error encountered when passing variables status if variables with unknown basis status are present.

20230207

  • Changes in the MP library

20221228

  • Changes in MP

20221222

  • Updates for HiGHS 1.4.1

    • The run_crossover option has now values “on”, “off” and “choose”. The latter results in crossover being run if the result of IPM without crossover is imprecise

    • Bug fixes

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.

20221012

  • Piecewise-linear approximation of quadratics HiGHS accepts quadratic objectives. For nonconvex ones, set cvt:quadobj=0. Recognizing x^2 for stronger univariate approximation

20220928

  • Changes in MP: piecewise-linear approximations of nonlinear functions, default value of big-M

20220603

  • Fixed an issue with passing/retrieving basis information

20220524

  • First release of HiGHS for AMPL