Patch release v1.15.1 fixes:
Apache release binaries not including HiPO fixed in PR #3112.
Build for users with C++20 fixed in PR #3114.
OpenBLAS setup issue affecting performance fixed in PR #3122.
Values passed for string option values (except for file names) are converted to lower case PR #3108.
The highlights of v1.15 are the first variant of the parallel MIP solver and the addition of HiPO in Python.
Following PR #2886, our prototype multithreaded MIP solver is available, refactoring the worker/node-search logic of the branch-and-cut solver to run across multiple threads. This is the first release of the parallel MIP solver.
A fix to the parallel scheduler was merged in PR #3087.
Following PR #2994,
HiPO can now be used to solve LPs and QPs from highspy, with
documentation added in
PR #3024 and
PR #3060. HiPO
performance was further improved by faster handling of free variables
(PR #3013) and faster
triangular solves
(PR #3014).
Prompted by #2957,
square Hessians that are only slightly asymmetric are now accepted by
Highs::qFormatOk, rather than being rejected outright
(PR #2965,
PR #2984 and
PR #3003). Identification
of non-convexity in the QP solvers was also improved, with extended
documentation added in
PR #3056, and a further
bug affecting some QPs was fixed in
PR #3069. QP hot start
was added in PR #3089.
Following PR #2982,
several bugs in the computation of an Irreducible Infeasible Subsystem
(IIS) via Highs::getIis were fixed.
Following PR #3046,
zero-cost singleton columns are no longer fixed to an infinite bound
during HPresolve::dualFixing, and the size of shifts applied during
reduced-cost fixing was reduced in
PR #2986. Strengthened
variable bounds found during presolve are now retained
(PR #3010), a bug in
the computation of the fractional value of a variable with finite
lower and upper bounds was fixed
(PR #3005), and the
handling of infeasibilities for semi-continuous and semi-integer
variables was corrected
(PR #3018).
Following PR #3042, parallel simplex is no longer used when solving the LP relaxations that arise within the MIP solver, since it isn't safe to do so when the MIP solver is itself running in parallel.
Following PR #2971,
highspy now supports scalar division, and significant improvements
were made to highspy's static typing in
PR #2983. Context
manager support was added to highspy in
PR #3093.
Following PR #3039,
Highs::setBasis and Highs::setLogicalBasis have been implemented,
and additional methods were added to the C# wrapper in
PR #3041.
Prompted by #3044, a further bug was fixed in PR #3092, and PR #3091 corrects the re-checking of an implied bound, fixing #3090.
Following PR #2981, C-heap memory leaks in solver state cleanup were fixed, and PR #3081 fixes a bug in column stuffing.
Following PR #3016,
Highs::presolve() now logs and returns failure appropriately when
called inconsistently with the state of the incumbent model.
Prompted by #3007, a
potential typo in FactorHiGHSSolver::chooseNla() was corrected, and
several other minor fixes were collected in
PR #3017 and
PR #3004 (the latter
for HighsCliqueTable).
Following PR #3057, lines in HiGHS options files that contain only spaces are now ignored, and the text of the first line containing an error is printed in the resulting message.
The Python build has been updated and an additional python package is
available. The HiPO dependencies are linked via the optional
highspy-extras, e.g. Metis, for all platforms, and OpenBLAS, for
Windows and Linux. The highspy-extras package is automatically
consumed by highspy and does not need to be imported manually. Note,
that highspy-extras is distributed under the Apache 2.0 license, due
to the dependencies' licensing.
On Linux, libblas is no longer supported, in favour of OpenBLAS. MKL
support would be considered at a later stage.
Prompted by #3000,
PR #3027 fixes a
recent alpine:edge compilation issue.
Following PR #3025, all remaining thread sanitizer data race warnings are cleared.
GPU support was added for local Python pip installs in PR #3071 and the BLAS library used by HiPO is now checked at runtime (PR #3080).
The cibuildwheel workflow and pyproject configuration were updated
to cibuildwheel 4.0.0
(PR #3061), and the
NuGet publishing workflow now uses trusted publishing rather than an
API key
(PR #3062,
following PR #2959).
The macOS GitHub Actions build times were significantly improved in PR #3033, and the C# wrapper build was fixed to statically link the MSVC STL and correctly install on win32 (PR #3070).
Following PR #3001,
the install location of the readme and license files was corrected,
and explicit -fexceptions copts were added to the Bazel config
(PR #3072 and
PR #3075).