HiGHS Changelog#

20241119#

  • Updated to HiGHS 1.8.1

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.

20240627#

  • Updated to HiGHS 1.7.1

  • Added calculation of primal and dual rays. See keyword alg:rays.

20240617#

  • Multi-objective emulator

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

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

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 MP linearization.)

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

  • Option report_times

  • Unused acc: options.

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

20240307#

  • Updated to HiGHS 1.7.0

  • Added solver pdlp (use option alg:method to specify it and alg:pdlpdgaptol, lim:pdlpnativetermination, pre:pdlpscaling and lim:pdlpiterationlimit).

  • Added optional pre centring steps (see options pre:centring, pre:maxcentringsteps and pre:centringratiotolerance).

  • Added options pre:userboundscale, pre:usercostscale, lim:objectivebound and lim:objectivetarget.

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