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# CHANGELOG – [Semigroups package][] for [GAP][]
Copyright © 2011-2025 [James D. Mitchell][] et al.
Licensing information can be found in the `LICENSE` file.
## Version 5.5.4 (released 29/08/2025)
This is a minor release that includes a technical change for compatibility with
Digraphs v1.11.0, and which removes the use of the SmallGroup package in the
Semigroups test suite.
## Version 5.5.3 (released 17/07/2025)
This is a minor release including some changes for compatibility with GAP by
@fingolfin.
## Version 5.5.2 (released 11/07/2025)
This is a minor release removing some extraneous files included in the release
archive for v5.5.1, and updating a test file due to some changes in a recent
version of GAP.
## Version 5.5.1 (released 19/06/2025)
This release containing one fix:
* Fix `TikzString` for bipartitions by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/1060
and updating the version of ``libsemigroups`` required to version 2.7.4 which
resolves:
https://github.com/semigroups/Semigroups/issues/1064
## Version 5.5.0 (released 19/02/2025)
## What's Changed
* Fix bug in gen pairs by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/1043
* Generalize `IsSelfDualSemigroup` declaration by @fingolfin in
https://github.com/semigroups/Semigroups/pull/1044
* Better inverses by @Tianrun-Y in
https://github.com/semigroups/Semigroups/pull/1021
* Use GAP kernel helper `IS_STRING_REP` to test for strings by @fingolfin in
https://github.com/semigroups/Semigroups/pull/1045
* Better Nambooripad by @Tianrun-Y in
https://github.com/semigroups/Semigroups/pull/1026
* Fix spelling by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/1050
* Avoid obsolete `C_NEW_STRING` macro by @fingolfin in
https://github.com/semigroups/Semigroups/pull/1051
**Full Changelog**: https://github.com/semigroups/Semigroups/compare/v5.4.0...v5.5.0
## Version 5.4.0 (released 19/10/2024)
## What's Changed
* Improved IsIsomorphicSemigroup Method by @awesometillman in https://github.com/semigroups/Semigroups/pull/1023
* fix typo in nambooripad partial order documentation by @Tianrun-Y in https://github.com/semigroups/Semigroups/pull/1030
* Better kernel module checking by @Joseph-Edwards in https://github.com/semigroups/Semigroups/pull/1032
* Fix ChooseHashFunction rank issue. by @reiniscirpons in https://github.com/semigroups/Semigroups/pull/1035
* kernel: Semigroups can be used in GAP on julia by @james-d-mitchell in https://github.com/semigroups/Semigroups/pull/1036
* Use LoadKernelExtension for gapbind_demo by @fingolfin in https://github.com/semigroups/Semigroups/pull/1039
## New Contributors
* @awesometillman made their first contribution in https://github.com/semigroups/Semigroups/pull/1023
* @Tianrun-Y made their first contribution in https://github.com/semigroups/Semigroups/pull/1030
**Full Changelog**: https://github.com/semigroups/Semigroups/compare/v5.3.7...v5.4.0
## Version 5.3.7 (released 11/03/2024)
This is a minor release with some changes for compatibility with GAP.
* Update Joe's info by @Joseph-Edwards in
https://github.com/semigroups/Semigroups/pull/1002
* Workaround for GAP 4.12 test failure due to new GAPDoc version by @fingolfin
in https://github.com/semigroups/Semigroups/pull/1004
* Use MarkAllButFirstSubBags for T_BIPART by @fingolfin in
https://github.com/semigroups/Semigroups/pull/1003
## Version 5.3.6 (released 19/02/2024)
This is a minor release with some changes related to forthcoming changes in
GAP. These changes were implemented by Fabian Zickgraf.
### Version 5.3.5 (released 14/02/2024)
This is a minor release fixing an issue in the kernel extension (reported by
Michael Orlitzky in Issue #996), with some further changes for compatibility
with GAP (by Max Horn), and fixing a bug in `IrredundantGeneratingSubset` which
gave an error for monogenic semigroups (by Reinis Cirpons).
### Version 5.3.4 (released 24/01/2024)
This is a minor release that fixes some issue in the build system, applies some
new linting rules, and perhaps most importantly re-enables the use of [HPCombi][]
in [libsemigroups][]. A number of different things were wrong which meant that:
* the correct configuration flags weren't set for building [Semigroups][] when
[HPCombi][] is enabled;
* [HPCombi][] was not detected properly because of a mistake in the path;
* the kernel module couldn't be built even when the last two items were
resolved, due to some missing functionality for [HPCombi][] types.
These issues arose because the main author no longer has access to any machines
running x86, and so the support for [HPCombi][] slowly eroded, unnoticed by me,
over time.
The other changes in this release are:
* some changes of PreImages... to NC versions (for compatibility with
forthcoming changes to GAP) by @cdwensley in
https://github.com/semigroups/Semigroups/pull/965
* buildsys: unify rpath handling by @fingolfin in
https://github.com/semigroups/Semigroups/pull/976
* Support GAP on Cygwin with libtool removed (for compatibility with
forthcoming changes to GAP) by @ChrisJefferson in
https://github.com/semigroups/Semigroups/pull/979
* Fix for [HPCombi][] by @james-d-mitchell (fixes the issues itemised above) in
https://github.com/semigroups/Semigroups/pull/978
* Linting by @james-d-mitchell in https://github.com/semigroups/Semigroups/pull/980
### New Contributors
* @cdwensley made their first contribution in
https://github.com/semigroups/Semigroups/pull/965
**Full Changelog**: https://github.com/semigroups/Semigroups/compare/v5.3.3...v5.3.4
### Version 5.3.3 (released 05/01/2024)
This is a minor release bumping the included+required versions of libsemigroups
to the latest version 2.7.2.
### Version 5.3.2 (released 07/10/2023)
This is a minor release with some bugfixes and minor improvements. Support
for GAP workspaces was broken in v5.3.0, and this issue has been resolved in
v5.3.2.
### Version 5.3.1 (released 19/09/2023)
This is a minor release fixing a minor issue in the build system.
### Version 5.3.0 (released 18/09/2023)
This release contains a fairly large number of changes, fixes, and
improvements. The biggest changes/new features in this release are:
* The build system has been completely updated by @fingolfin and @dimapase:
- Convert buildsystem to use Makefile.gappkg instead of automake by @fingolfin
in https://github.com/semigroups/Semigroups/pull/902
- Use the C++ compiler to link semigroups.so by @fingolfin in
https://github.com/semigroups/Semigroups/pull/942
- Work around autoconf 2.69 bugs by @fingolfin in
https://github.com/semigroups/Semigroups/pull/947
- set rpath for external libsemigroups by @dimpase in
https://github.com/semigroups/Semigroups/pull/954
- buildsystem: sane warning if not using gmake by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/955
* Some updates to improve the performance of `LatticeOfCongruences` and friends
by @james-d-mitchell in https://github.com/semigroups/Semigroups/pull/884
* Add `GreensLeftMultipliers` and related by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/925
The following bugs were fixed and/or issues resolved:
* Use same URL as in my other packages by @olexandr-konovalov in
https://github.com/semigroups/Semigroups/pull/907
* Fix a few typos inn the doc by @fingolfin in
https://github.com/semigroups/Semigroups/pull/913
* Increase required version of Digraphs and remove some redundant code by
@james-d-mitchell in https://github.com/semigroups/Semigroups/pull/921
* greens: fix `HClassReps(LClass)` for acting semigroups by @james-d-mitchell
in https://github.com/semigroups/Semigroups/pull/927
* greens: fix bug in `RightGreensMultiplier` for acting semigroups by
@james-d-mitchell in https://github.com/semigroups/Semigroups/pull/930
* congsemigraph: add `\=` method by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/933
* greens: fix `RhoOrbStabChain(DClass)` by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/932
* doc: remove empty xml files by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/934
* Fix a typo that breaks HPCombi support by @fingolfin in
https://github.com/semigroups/Semigroups/pull/941
* typo (ERNEL<-KERNEL) in configure.ac by @dimpase in
https://github.com/semigroups/Semigroups/pull/944
* fix the URL for libsemigroups in README.md by @dimpase in
https://github.com/semigroups/Semigroups/pull/945
* kernel: fix mem leaks by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/951
### Version 5.2.1 (released 05/03/2023)
This is a minor release with some changes for compatibility with upcoming
changes to GAP, and some updates to the build system.
### Version 5.2.0 (released 01/12/2022)
This release contains a number of fixes and improvements, and one new feature,
which is a method for `IsSelfDualSemigroup` and related functionality for
semigroups satisfying `CanUseFroidurePin`:
* m4/find_gap.m4: update by @fingolfin in
https://github.com/semigroups/Semigroups/pull/887
* Adds method for `IsSelfDualSemigroup` and related functionality by
@james-d-mitchell in https://github.com/semigroups/Semigroups/pull/890
* Fix some bugs by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/889
* Fix closure semigroup for non-libsemigroups types by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/891
* Add missing tests and doc for `IsSelfDualSemigroup` and friends by
@james-d-mitchell in https://github.com/semigroups/Semigroups/pull/892
* Change `-march=avx` -> `-mavx` by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/896
* Fix faulty usage of 0-simple RZMS translations code by @flsmith in
https://github.com/semigroups/Semigroups/pull/893
* build: replace `m4/ax_check_hpcombi` by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/897
### Version 5.1.0 (released 31/10/2022)
The following major new features have been added in this version:
* extensive support for translations by @flsmith in
https://github.com/semigroups/Semigroups/pull/720.
See Chapter 18 of the manual for details.
* support for `Sims1` in libsemigroups by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/873. This manifests in the new
functions:
* `IteratorOfRightCongruences`, `IteratorOfLeftCongruences`
* `NumberOfRightCongruences`, `NumberOfLeftCongruences`
* `SmalerDegreeTransformationRepresentation`
The following bugs were resolved:
* `IsDualSemigroupRep` is no longer a representation by @flsmith in
https://github.com/semigroups/Semigroups/pull/863
* fix an issue in `SemigroupIsomorphismByImages` by @james-d-mitchell
in https://github.com/semigroups/Semigroups/pull/866
* set `IsInjective` flag before calling `SetNiceMonomorphism` by @ThomasBreuer
in https://github.com/semigroups/Semigroups/pull/870
* Fix issue 869 (the multiplication table of fp semigroups/monoids was
sometimes incorrect) by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/871
* Resolve Issue #868 (there was recursion depth trap error when trying to
create an fp monoid from a small semigroup)by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/872
* semifp: add missing methods for fp monoids/semigroups by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/874
* Fix the README to use the correct version of GAP that's required by
@james-d-mitchell in https://github.com/semigroups/Semigroups/pull/876
* Replace gap implementation of `EqualInFreeBand` with C++ implementation from
libsemigroups by @reiniscirpons in
https://github.com/semigroups/Semigroups/pull/877
* Remove an obsolete comment by @fingolfin in
https://github.com/semigroups/Semigroups/pull/878
* Fix extreme tests by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/880
## New Contributors
* @ThomasBreuer made their first contribution in https://github.com/semigroups/Semigroups/pull/870
* @reiniscirpons made their first contribution in https://github.com/semigroups/Semigroups/pull/877
### Version 5.0.2 (released 12/08/2022)
This is a minor release hopefully resolving some crashes originating in
[libsemigroups][].
### Version 5.0.1 (released 11/08/2022)
This is a minor release resolving some issues in the kernel module and build
system [[Max Horn][]].
### Version 5.0.0 (released 05/08/2022)
This is a major release with several new features and some backwards
incompatible changes prompted by changes in GAP 4.12. Note that to use version
5.0.0 of [Semigroups][] GAP 4.12 is required. At the time of writing GAP 4.12
has not yet been released, and so the development version of GAP (in the
`master` branch of the git repo hosted on github) is required for
[Semigroups][] version 5.0.0.
The backwards incompatible changes in this release related to matrices over the
integers or over a finite field. In previous versions of [Semigroups][] there
was an implementation of matrices over the integers and over finite fields,
because at the time they were written it was not possible to use the matrices
in the GAP library. This is no longer the case, and some changes in the GAP
library for version 4.12, meant that the implementation in [Semigroups][] had
to be removed.
Previously, to create a matrix over the integers you could do:
Matrix(IsIntegerMatrix, [[0, 1], [1, 0]]);
The equivalent in version 5.0.0 of [Semigroups][] is:
Matrix(Integers, [[0, 1], [1, 0]]);
where `Integers` is the ring of integers. The changes for matrices over finite
fields are mostly internal, and it was, and still is, possible to create such
matrices using, for example,
Matrix(GF(4), Z(4) * [[0, 1], [1, 0]]);
In versions of [Semigroups][] before 5.0.0, the filter
`IsMatrixOverFiniteField` could also be used when constructing matrices, and
these features have been removed in version 5.0.0.
See: https://github.com/semigroups/Semigroups/pull/827
The new features introduced in version 5.0.0 are:
* Add support for partial orders of L/R-classes by [Wilf A. Wilson][] in
https://github.com/semigroups/Semigroups/pull/415
* Support for homomorphisms was introduced by Artemis Konstantinidi,
Chinmay Nagpal, and [James D. Mitchell][] in
https://github.com/semigroups/Semigroups/pull/797
and
https://github.com/semigroups/Semigroups/pull/828
### Version 4.0.3 (released 01/07/2022)
This is a minor release that includes a number of improvements and bug fixes:
* Update authors + mailmap by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/837
* Resolve issue #835 (implement `MultiplicationTable` for fp semigroups and
monoids) by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/838
* Improve ccache hit rate in CI by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/840
* Improve support for quotient semigroups by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/841
* semigrp: remove 2 unnec. methods after #841 by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/843
* congsemigraph: add meet method by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/842
* Remove superfluous strings from error messages by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/845
### Version 4.0.2 (released 05/06/2022)
This is a minor release that includes a number of minor fixes:
* conglatt: fix ordering issue by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/829
* Add support for partial orders of L/R-classes by @wilfwilson in
https://github.com/semigroups/Semigroups/pull/415
* conglatt: avoid recomputing principal congs by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/832
* semipperm: allow SmallerDegree for other types by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/833
* semipperm: resolve issue 817 by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/834
### Version 4.0.1 (released 21/04/2022)
This is a minor release that includes a number of changes:
* Avoid using `SIZEOF_VOID_P` by @wilfwilson in
https://github.com/semigroups/Semigroups/pull/803
* doc: allow manual compile without all deps by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/810
* Bump libsemigroups -> v2.1.4 by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/809
* Change http -> https by @fingolfin in
https://github.com/semigroups/Semigroups/pull/818
* Remove spurious dependency on libgmp by @fingolfin in
https://github.com/semigroups/Semigroups/pull/820
* Improve compatibility with GAP's MatrixObj project by @fingolfin in
https://github.com/semigroups/Semigroups/pull/819
* Better congruence lattices by @james-d-mitchell in
https://github.com/semigroups/Semigroups/pull/815
* Add more matrix generators by @flsmith in
https://github.com/semigroups/Semigroups/pull/822
### Version 4.0.0 (released 28/02/2022)
This is a major release which simplifies and improves many aspects of the
package. The kernel module has been simplified significantly, to make it easier
to incorporate future changes in [libsemigroups][], and some superfluous
functionality was withdrawn.
### Version 3.4.2 (released 07/02/2021)
This is a minor release resolving some issues in v3.4.1 [[James D. Mitchell][]],
with a number of improvements by [Wilf A. Wilson][].
### Version 3.4.1 (released 28/01/2021)
This is a minor release including some bugfixes and improvements. The required
minimum version of [libsemigroups][] is increased from v1.1.0 to v1.3.2. The
required version of `Digraphs` is increased to v1.2.0. The `datastructures`
package was implicitly required (via `Digraphs`), and now at least version
v0.2.5 is required explicitly. The version of GAP required was implicitly at
least v4.10.0, but was explicitly v4.9.0, it is now explicitly v4.10.0.
### Version 3.4.0 (released 28/08/2020)
This is a minor release with the following new features added to the package:
* `CanonicalReesMatrixSemigroup` and `CanonicalReesZeroMatrixSemigroup` written by Chris Russell.
* `ParseRelations` for finitely presented semigroups or monoids written by [Luke Elliott][].
* `TikzString` method was implemented for collections of PBRs by [Finn Smith][].
The following bugs/issues were resolved:
* [Issue #685](https://github.com/gap-packages/Semigroups/issues/685): after some somewhat recent changes in [libsemigroups][] some infinite finitely presented semigroups in GAP reported their size as being `-2`. Fixed by [James D. Mitchell][].
* [Issue #680](https://github.com/gap-packages/Semigroups/issues/680): Semigroups did not compile with recent git versions of [libsemigroups][]. Reported by [Wilf A. Wilson][] fixed by [James D. Mitchell][].
The required minimum version of [libsemigroups][] is now v1.1.0,
### Version 3.3.2 (released 28/06/2020)
This is a very minor release fixing the following issues.
* [Issue #676](https://github.com/gap-packages/Semigroups/issues/676) and
[Issue #677](https://github.com/gap-packages/Semigroups/issues/677) reported
by Reinis Cirpons, where for some congruences `NonTrivialCongruenceClasses`
failed to work, but `CongruenceClasses` did work. This was caused by an issue
in `EquivalenceRelationPartition`; resolved by [James D. Mitchell][].
* An issue in the equality, less than, and product methods for PBRs which
previously permitted PBRs of different degrees to be given as arguments,
resulting in unhelpful errors from within the implementations of these
methods; resolved by [James D. Mitchell][].
### Version 3.3.1 (released 28/05/2020)
This is a minor release fixing some issues in the build system [Max Horn][]
related to compatibility with future versions of GAP, and some other minor
fixes by [James D. Mitchell][] and [Wilf A. Wilson][].
### Version 3.3.0 (released 28/04/2020)
This is a minor release fixing some issues in the build system
[Chris Jefferson][], some improvements to the isomorphism capabilities of the
package [James D. Mitchell][], and the introduction of a rudimentary function
to compute the automorphism group of an arbitrary semigroup. From v3.3.0, the
Semigroups package requires the [images package][] version 1.3.0 or higher.
### Version 3.2.5 (released 28/03/2020)
This is a minor release to fixing some build issues for windows [Chris Jefferson][]
and fixing an issue in `IsRowTrimBooleanMat`, `IsColTrimBooleanMat`, and
`IsTrimBooleanMat` [Finn Smith][] see
[Issue #654](https://github.com/gap-packages/Semigroups/issues/654) for more details.
### Version 3.2.4 (released 28/02/2020)
This is a minor release to fix a memory leak and some other issues in the
kernel module.
### Version 3.2.3 (released 07/02/2020)
This is a minor release to make some changes for compatibility with the
[Digraphs package][] v1.1.1 and [GAP][], and to fix a memory leak in the kernel
module.
### Version 3.2.2 (released 17/01/2020)
This is a minor release to update the version of [libsemigroups][] to v1.0.5,
to include some changes for compatibility with [GAP][], and to fix the following issues
* [Issue #632](https://github.com/gap-packages/Semigroups/issues/632) where
file objects were not closed properly if an error was given;
* [Issue #636](https://github.com/gap-packages/Semigroups/issues/636) the
compiler flag `-march=native` is only added if it is supported by the compiler;
* [Issue #637](https://github.com/gap-packages/Semigroups/issues/637) where
`IsomorphismPermGroup` sometimes returned an incorrect answer.
The changes in this release were made by [Max Horn][] and [James D. Mitchell][].
### Version 3.2.1 (released 04/12/2019)
This is a minor release to update the version of [libsemigroups][] to v1.0.2,
and to include some changes for compatibility with [GAP][]. The changes in this
release were made by [James D. Mitchell][] and [Wilf A. Wilson][].
### Version 3.2.0 (released 04/10/2019)
This is a minor release including several cleanups, changes for compatibility
with [GAP][], and to update the required version of the [Digraphs package][] to
v1.0.0. The changes in this release were made by [James D. Mitchell][] and
[Wilf A. Wilson][].
### Version 3.1.5 (released 19/09/2019)
This is a minor release including several cleanups, changes for compatibility
with [GAP][], and to add the possibility to pass a `RandomSource` as a first
argument to some methods. All the changes in this release were made by
[Max Horn][].
### Version 3.1.4 (released 30/08/2019)
This is a minor release fixing some minor issues, mostly related to
compatibility with [GAP][] 4.11.
### Version 3.1.3 (released 07/06/2019)
This is a minor release of the Semigroups package, including some improvements
to `SmallestIdempotentPower` and `RepresentativeOfMinimalIdeal` by
[Wilf A. Wilson][] and some other minor modifications. Semigroups now requires
version 4.8.2 of the [orb package][], or newer.
### Version 3.1.2 (released 15/03/2019)
This is a minor release of the Semigroups package, including some changes to the
build system (by [D. V. Pasechnik][]), one issue was fixed
([Issue 581](https://github.com/gap-packages/Semigroups/issues/581) by Chris
Russell and [James D. Mitchell][]), and the version of [libsemigroups][]
required was increased to 0.6.7.
### Version 3.1.1 (released 15/02/2019)
This is a minor release of the Semigroups package, including some minor changes
in the kernel module (by [Max Horn][]) and the bibliography section of the
manual has been fixed and updated (by Murray Whyte).
### Version 3.1.0 (released 14/01/2019)
This is a major release of the Semigroups package, including several changes to
existing behaviour, new functionality, and bugfixes.
#### Changed functionality in this release
* Congruence posets are now digraph objects (in the sense of the
[Digraphs package][]) rather than lists of lists. This applies to
`LatticeOfCongruences`, `PosetOfCongruences`, and several other functions.
This change was made by [Michael Young][] in
[PR #385](https://github.com/gap-packages/Semigroups/pull/385).
* The attributes `LeftCayleyDigraph` and `RightCayleyDigraph` are introduced to
replace `LeftCayleyGraphSemigroup` and `RightCayleyGraphSemigroup`. These new
attributes return digraph objects (in the sense of the [Digraphs package][])
rather than lists of out-neighbours. There are also several new functions for
visualising Cayley digraphs, such as `TikzLeftCayleyDigraph`,
`DotLeftCayleyDigraph`, and `DotStringDigraph`. This functionality was all
added by [James D. Mitchell][] in
[PR #348](https://github.com/gap-packages/Semigroups/pull/348).
* `IteratorFromPickledFile` has been replaced by `IteratorFromGeneratorsFile`,
and `IteratorFromOldGeneratorsFile` has been removed. The behaviour of
`WriteGenerators` has also been modified slightly. This work was done by
[James D. Mitchell][] in
[PR #419](https://github.com/gap-packages/Semigroups/pull/419).
#### New functionality in this release
* Finn Smith added support for creating and representing dual semigroups in
[PR #470](https://github.com/gap-packages/Semigroups/pull/470),
via the new commands `DualSemigroup` and `AntiIsomorphismDualSemigroup`.
* Chris Russell added support for representing E-unitary inverse semigroups by
McAlister triple semigroups, via the command `McAlisterTripleSemigroup` and
others, in the PRs
[#271](https://github.com/gap-packages/Semigroups/pull/271) and
[#507](https://github.com/gap-packages/Semigroups/pull/507). Chris also
introduced the related functions `EUnitaryInverseCover`,
`IsFInverseSemigroup`, and `IsFInverseMonoid`.
* It is now possible to use the Semigroups package to construct direct products
of arbitrary finite semigroups with the command `DirectProduct`. Direct
products created in this way support the commands `Projection` and
`Embedding`. To enable the creation of direct products of arbitrary finite
semigroups, the related commands `NonTrivialFactorization`,
`IndecomposableElements`, and `IsSurjectiveSemigroup` were introduced. This
work was done by [Wilf A. Wilson][] in
PRs [#347](https://github.com/gap-packages/Semigroups/pull/347)
and [#558](https://github.com/gap-packages/Semigroups/pull/558).
* The functions `NambooripadPartialOrder` and `NambooripadLeqRegularSemigroup`
were added by Chris Russell in PRs
[#467](https://github.com/gap-packages/Semigroups/pull/467) and
[#479](https://github.com/gap-packages/Semigroups/pull/479).
* The option `numbers` is available when calling `DotString` on a congruence
poset (added by [Michael Young][] in
[PR #455](https://github.com/gap-packages/Semigroups/pull/455)).
* More `Info` statements can be produced, if desired, during computations of
congruence lattices (added by [Michael Young][] in
[PR #403](https://github.com/gap-packages/Semigroups/pull/403)).
* It is now possible to construct all non-empty two-sided ideals of a finite
semigroup with the command `Ideals` (added by [Michael Young][] in
[PR #500](https://github.com/gap-packages/Semigroups/pull/500)).
* `WriteMultiplicatiomTable`, `ReadMultiplicationTable`, and
`IteratorFromMultiplicationTableFile` were added by Chris Russell in
[PR #339](https://github.com/gap-packages/Digraphs/pull/339)
* A new constructor `BrandtSemigroup` was added by [James D. Mitchell][] in
[PR #411](https://github.com/gap-packages/Semigroups/pull/411).
* The command `WreathProduct` can be now applied to construct the wreath
producth of a transformation monoid or permutation group with a transformation
semigroup or permutation group. This work was done by Fernando Flores Brito in
[PR #262](https://github.com/gap-packages/Semigroups/pull/262).
* `SemigroupsTestAll` was introduced by [Michael Young][] in
PRs [#404](https://github.com/gap-packages/Semigroups/pull/404)
and [#446](https://github.com/gap-packages/Semigroups/pull/446).
* Some basic methods for `MinimalSemigroupGeneratingSet` were implemented by
[Wilf A. Wilson][] in
[PR #407](https://github.com/gap-packages/Semigroups/pull/407).
* It is now possible to write and read Rees matrix semigroups and Rees 0-matrix
semigroups to and from files with `WriteGenerators` and `ReadGenerators`
(added by [James D. Mitchell][] in
[PR #569](https://github.com/gap-packages/Semigroups/pull/569)).
* Special methods for `IsIdempotentGenerated` and
`IdempotentGeneratedSubsemigroup` for Rees matrix semigroups and Rees 0-matrix
semigroups were added by [Wilf A. Wilson][] in
[PR #325](https://github.com/gap-packages/Semigroups/pull/325).
* Special methods for `IsomorphismPartialPermSemigroup` for groups and
zero-groups were added by [Wilf A. Wilson][] in
[PR #406](https://github.com/gap-packages/Semigroups/pull/406).
* Semigroups in more kinds of families are now comparable via `\<`, including
pairs of semigroups of partial permutations, pairs of semigroups of
bipartitions, and pairs of semigroups of PBRs (added by
[James D. Mitchell][] in
[PR #568](https://github.com/gap-packages/Semigroups/pull/568)).
#### Issues resolved by this release
* The documentation now clarifies that only those subsemigroups of regular Rees
0-matrix semigroups defined over *permutation* groups are acting semigroups.
This problem was reported by [Wilf A. Wilson][] in
[Issue #336](https://github.com/gap-packages/Semigroups/issues/336) and fixed
by [James D. Mitchell][] in
[PR #337](https://github.com/gap-packages/Semigroups/pull/337).
* There was a bug in the kernel module that related to computing with
bipartitions, which would sometime cause an unexpected error. This was
reported by [Wilf A. Wilson][] and Finn Smith in
[Issue #444](https://github.com/gap-packages/Semigroups/issues/444), and fixed
by Finn Smith in
[PR #466](https://github.com/gap-packages/Semigroups/pull/466).
* The Semigroups package would sometimes automatically set the
`GeneratorsOfSemigroup` of a trivial group of partial permutations to be an
empty list. This was reported and fixed by [Wilf A. Wilson][] in
[PR #565](https://github.com/gap-packages/Semigroups/pull/565).
* The function `IsMonogenicSemigroup` incorrectly returned `true` for an empty
semigroup. This was reported and fixed by [Wilf A. Wilson][]
in [PR #567](https://github.com/gap-packages/Semigroups/pull/567).
There have also been many technical changes to the package and its kernel
module, including many by [Max Horn][], such as
those in PRs
[#490](https://github.com/gap-packages/Semigroups/pull/490),
[#491](https://github.com/gap-packages/Semigroups/pull/491),
[#493](https://github.com/gap-packages/Semigroups/pull/493),
[#501](https://github.com/gap-packages/Semigroups/pull/501),
[#553](https://github.com/gap-packages/Semigroups/pull/553), and
[#562](https://github.com/gap-packages/Semigroups/pull/562).
Semigroups now requires version 4.8.1 of the
[orb package](https://gap-packages.github.io/orb), or newer.
### Version 3.0.20 (released 01/10/2018)
This version contains some minor changes related to compatibility issues with
GAP, was updated to use [libsemigroups][] 0.6.4, and contains bugfixes for the
following issues:
* [Issue 530](https://github.com/gap-packages/Semigroups/issues/530): there was
a bug in the method for `IsFactorisableInverseMonoid` for an ideal of
semigroup. It only returned `true` if the parent semigroup was factorisable.
[[James D. Mitchell][]]
* [Issue 531](https://github.com/gap-packages/Semigroups/issues/531): there
were some issues with method selection for Green's classes, when the
[RCWA package][] was loaded at the same time as [Semigroups][].
[[Wilf A. Wilson][]]
* [Issue 532](https://github.com/gap-packages/Semigroups/issues/532): the
`Iterator` method for free inverse monoids used some implementational details
of the method for free group iterators in the GAP library. This caused an
error to be reported when [Semigroups][] and the [RCWA package][] were loaded
at the same time.
[[James D. Mitchell][]]
* [Issue 536](https://github.com/gap-packages/Semigroups/issues/536): the
`Iterator` method for free inverse monoids did not work as intended, because
some words could never be reached.
[[James D. Mitchell][]]
* [Issue 543](https://github.com/gap-packages/Semigroups/issues/543): the
[Semigroups][] tests failed when all packages were loaded.
[[Wilf A. Wilson][]]
### Version 3.0.19 (released 18/09/2018)
This version contains some minor changes related to compatibility issues with
GAP, and to resolve some incorrectly delegating methods for print/view/display.
([Wilf A. Wilson][])
### Version 3.0.18 (released 11/09/2018)
This version contains some minor changes related to compatibility issues with
GAP.
### Version 3.0.17 (released 23/08/2018)
This version contains some minor improvements and bugfixes.
### Version 3.0.16 (released 29/05/2018)
This version contains some minor improvements and bugfixes.
### Version 3.0.15 (released 24/03/2018)
This version contains some bugfixes, and some improved functionality:
* [Issue 444](https://github.com/gap-packages/Semigroups/issues/444): there was
a garbage collection error in the kernel module that sometimes resulted in a
GAP error `"\<func\> must return a value"`.
[Finn Smith]
* [Issue 459](https://github.com/gap-packages/Semigroups/issues/459): the method
for `IsTrivial` did not check if the number of generators was non-zero.
[[James D. Mitchell][]]
* [PR 457](https://github.com/gap-packages/Semigroups/pull/457): an improved
method for finding a set of generating pairs of a congruence over a Rees
0-matrix semigroup represented as a linked triple
[[Michael Young][]]
* [Issue 461](https://github.com/gap-packages/Semigroups/issues/461):
`NrCongruenceClasses` sometimes returned the wrong result for classes of
semigroups not defined in the [Semigroups][] package.
[[Michael Young][]]
* [Issue 463](https://github.com/gap-packages/Semigroups/pull/463): replaced use
of `EvalString` by `ValueGlobal`.
[[James D. Mitchell][]]
### Version 3.0.14 (released 15/02/2018)
This version contains a fix for the following issue, this was resolved by
updating the version of [libsemigroups][] to 0.6.3:
* [Issue 450](https://github.com/gap-packages/Semigroups/issues/450): There was
an intermittent error in some methods for congruences and finitely presented
semigroups arising from a bug in libsemigroups.
[[James D. Mitchell][]]
### Version 3.0.13 (released 08/02/2018)
This version contains some minor updates for compatibility with [GAP][] 4.9, and
some fixes for some minor issues.
### Version 3.0.12 (released 17/01/2018)
This version contains some minor updates for compatibility with [GAP][] 4.9, to
fix some bugs, to update the build system, and to update the kernel module for
[libsemigroups][] version 0.6.2.
The following improvements have been made:
* [PR 426](https://github.com/gap-packages/Semigroups/pull/426): a new faster
method for `IsomorphismFpSemigroup` for factorisable inverse monoids is added.
[Chris Russell]
* [PR 430](https://github.com/gap-packages/Semigroups/pull/430): the performance
of the maximal subsemigroups functionality has been improved.
[[Wilf A. Wilson][]]
The following issues are resolved:
* [Issue 424](https://github.com/gap-packages/Semigroups/issues/424): the
operation `MinimalFactorization` sometimes returned incorrect results.
[[James D. Mitchell][]]
* [Issue 435](https://github.com/gap-packages/Semigroups/issues/435): the
operation `ClosureInverseMonoid` sometimes returned incorrect results.
[[James D. Mitchell][]]
### Version 3.0.11 (released 18/12/2017)
This version contains some minor updates for compatibility with [GAP][] 4.9,
the build system has been modified slightly, the kernel module has been
updated for [libsemigroups][] version 0.6.1.
### Version 3.0.10 (released 04/12/2017)
This version contains some minor updates for compatibility with [GAP][] 4.9.
### Version 3.0.9 (released 24/11/2017)
This version contains some minor bugfixes, and updates for compatibility with
[GAP][] 4.9, [io][] 4.5.0, and [Digraphs][] 0.11.0.
### Version 3.0.8 (released 10/11/2017)
This version contains some minor bugfixes, and updates for compatibility with
[GAP][] 4.9 and [orb][] 4.8.0.
### Version 3.0.7 (released 02/10/2017)
This version contains some minor bugfixes, fixes some issues where some tests in
the main GAP repo returned different output when Semigroups was loaded than when
it was not, and updates the kernel module for version 0.5.2 of
[libsemigroups][]. The configuration option `--enable-debug` was added.
The following issues are resolved:
* [Issue 389](https://github.com/gap-packages/Semigroups/issues/389): the most
general method for `NaturalPartialOrder` sometimes returned incorrect results.
[[Wilf A. Wilson][]]
* [Issue 393](https://github.com/gap-packages/Semigroups/issues/393):
`StructureDescription` for finitely presented groups failed with an error when
Semigroups was loaded.
[[James D. Mitchell][]]
* [Issue 395](https://github.com/gap-packages/Semigroups/issues/395): GAP's test
`tst/testinstall/semigrp.tst` failed because of a missing method for
`NrEquivalenceClasses` for a generic semigroup congruence.
[[James D. Mitchell][] and [Wilf A. Wilson][]]
### Version 3.0.6 (released 27/09/2017)
This version contains some minor bugfixes, improves the compatibility of
Semigroups with other GAP packages, and updates the kernel
module for version 0.5.0 of [libsemigroups][]
The following issues are resolved:
* [Issue 371](https://github.com/gap-packages/Semigroups/issues/371): the
identity element of some types of monoids was not added to its
`GeneratorsOfSemigroup`. This meant that the semigroup generated by
`GeneratorsOfSemigroup(M)` was not equal to `M` in some rare cases.
[[Wilf A. Wilson][]]
* [Issue 377](https://github.com/gap-packages/Semigroups/issues/377): there was
a bug in the method for `IsInverseSemigroup` for non-acting semigroups that
sometimes returned a false positive.
[[Wilf A. Wilson][]]
### Version 3.0.5 (released 23/08/2017)
This version contains some minor tweaks and the following issue is resolved:
* [Issue 352](https://github.com/gap-packages/Semigroups/issues/352): There was
a name clash with some other GAP packages using `RandomMatrix` and
`IsTorsion`.
[[James D. Mitchell][]]
### Version 3.0.4 (released 16/07/2017)
Some minor issues are fixed in this release:
* [Issue 342](https://github.com/gap-packages/Semigroups/issues/342):
`DirectProduct` for transformation semigroups returned the wrong answer when
applied to semigroups satisfying `IsMonoidAsSemigroup`.
[[James D. Mitchell][]]
Some documentation and tests were added by [Michael Young][].
### Version 3.0.3 (released 21/06/2017)
Some minor issues are fixed in this release:
* [Issue 336](https://github.com/gap-packages/Semigroups/issues/336): Rees
(0-)matrix semigroups over non-permutation groups sometimes resulted in an
error.
[[James D. Mitchell][]]
* A method was added for `IsEUnitaryInverseSemigroup` for non-inverse
semigroups, which previously resulted in no method found.
[Chris Russell]
* Some error messages were improved in `ReadGenerators` and `WriteGenerators`.
[[James D. Mitchell][]]
### Version 3.0.2 (released 16/06/2017)
This is an minor release fixing some minor issues in the last release.
The following issues were resolved:
* [Issue 330](https://github.com/gap-packages/Semigroups/issues/330):
`InversesOfSemigroupElement` some times returned an incorrect value,
specifically when applied to the identity of a transformation monoid.
[[James D. Mitchell][]]
* [Issue 328](https://github.com/gap-packages/Semigroups/issues/328): when using
Linux the package compiled but failed to link pthreads and so the kernel
module failed to load in GAP.
[[James D. Mitchell][]]
There are improvements to the following:
* some missing documentation was added by [Michael Young][].
* the subsemigroup returned by `IdempotentGeneratedSubsemigroup` for Rees
(0-)matrix semigroup over a group has a smaller generating set than
previously, and can be found more quickly.
[[Wilf A. Wilson][]]
* `IsomorphismSemigroups` is extended so that it can be applied to arbitrary
simple, 0-simple, or monogenic semigroups.
[[Wilf A. Wilson][]]
### Version 3.0.1 (released 03/06/2017)
This is an extremely minor release fixing some minor issues in the last
release.
### Version 3.0.0 (released 02/06/2017)
This is a major release that dramatically expands the scope of the package. The
package now features a compiled C/C++ module which interfaces with the
[libsemigroups][] C++ library to allow high-speed computations for congruences
and certain categories of semigroup. There are also several new types of
semigroup and a variety of new methods which can be used with them.
### Version 2.8.2 (released 15/01/2018)
This is a minor release to correct the required version of [GAP][] in
`PackageInfo.g` (from GAP 4.9.0 to GAP 4.8.9).
### Version 2.8.1 (released 22/12/2017)
This is a minor release to update the output in some test file and manual
examples due to some changes in the GAP library code.
### Version 2.8.0 (released 26/05/2016)
In this release there are some new features and some bug fixes. In this
version, we welcome [Nick Ham][] to the contributors to the package.
#### New Features in Version 2.8.0
The new features in this release are contributed by [Nick Ham][]:
* `ApsisMonoid`
* `CrossedApsisMonoid`
* `ModularPartitionMonoid`
* `PlanarModularPartitionMonoid`
* `PlanarPartitionMonoid`
* `PlanarUniformBlockBijectionMonoid`
* `SingularApsisMonoid`
* `SingularCrossedApsisMonoid`
* `SingularModularPartitionMonoid`
* `SingularPlanarModularPartitionMonoid`
* `SingularPlanarPartitionMonoid`
* `SingularPlanarUniformBlockBijectionMonoid`
* `SingularUniformBlockBijectionMonoid`
* `UniformBlockBijectionMonoid`
#### Issues Resolved in Version 2.8.0
* [Issue 160](https://github.com/gap-packages/Semigroups/issues/160)
`IrreundantGeneratingSubset` behaved incorrectly when given a semigroup whose
generating set consisted of a single repeated element.
[[Wilf A. Wilson][]]
* [Issue 164](https://github.com/gap-packages/Semigroups/issues/164)
`MatrixEntries` gave an error for Rees 0-matrix semigroups whose matrices
contain `0`.
[[Wilf A. Wilson][]]
* Some tests failed when GAP was compiled in 32-bit mode.
[[Michael Young][]]
### Version 2.7.6 (released 19/04/2016)
This is a very minor release changing the name of the `README` (to `README.md`)
in the `PackageInfo.g` file.
### Version 2.7.5 (released 19/04/2016)
This is a minor release to fix
[Issue 151](https://github.com/gap-packages/Semigroups/issues/151), and to make
some changes for future compatibility with GAP. In
[Issue 151](https://github.com/gap-packages/Semigroups/issues/151) when the
method `IsomorphismPermGroup` was applied to a semigroups of non-permutation
transformations the returned mapping was not an isomorphism.
### Version 2.7.4 (released 02/03/2016)
This is a minor release to fix
[Issue 150](https://bitbucket.org/james-d-mitchell/semigroups/issue/150), and to
correct the required version of GAP (from 4.8.2 to 4.8.3).
In [Issue 150](https://bitbucket.org/james-d-mitchell/semigroups/issue/150) the
function `IsZeroSimpleSemigroup` entered an infinite loop for some examples of
semigroups of partial permutations.
### Version 2.7.3 (released 15/02/2016)
This is a minor release to fix some manual examples, to correct the package URL
in the `PackageInfo.g` file, and to fix some issues with semigroups of
bipartitions. It was formerly possible to create semigroups of bipartitions
where the generators had different degrees, but the created semigroups were
invalid; this is fixed in version 2.7.3.
### Version 2.7.2 (released 28/01/2016)
This is a minor release to fix to remove `ErrorMayQuit` which was renamed
`ErrorNoReturn` in GAP 4.8.2. This change was made by [Max Horn][].
### Version 2.7.1 (released 19/12/2015)
This is a minor release to fix
[Issue 144](https://bitbucket.org/james-d-mitchell/semigroups/issue/144). This
issue resulted in `IsInverseSemigroup` sometimes returning `true` for semigroups
which were not inverse. This occurred when the \\(\mathscr{D}\\)-classes of the
semigroup were computed before the method for `IsInverseSemigroup` was first
run.
### Version 2.7 (released 27/11/2015)
This is a minor release including some changes for compatibility with GAP 4.8,
and some bug fixes.
#### New Features in Version 2.7
* `IsomorphismReesZeroMatrixSemigroup` is introduced, and it is no longer
possible to apply `IsomorphismReesMatrixSemigroup` to a 0-simple semigroup.
This change was made for the sake of consistency, so that the `Range` of an
`IsomorphismReesMatrixSemigroup` is always a Rees matrix semigroup and not
sometimes a Rees 0-matrix semigroup as was formerly the case.
#### Changes for GAP 4.8
* several `ViewString` methods for semigroups and their elements were moved from
the `Semigroups` package to the GAP library. Some minor changes were made in
the method for `ViewString` for semigroups, and the tests, and manual examples
were updated accordingly.
* The meaning of `IsMonoidAsSemigroup` was changed to be consistent with the
meaning of `IsGroupAsSemigroup`. In earlier versions, `IsMonoidAsSemigroup`
was `false` for semigroups in the category `IsMonoid`. From Version 2.7,
`IsMonoidAsSemigroup` is `true` for monoids in the category `IsMonoid` and for
some further semigroups.
#### Issues Resolved in Version 2.7
* [Issue 136](https://bitbucket.org/james-d-mitchell/semigroups/issue/136):
`CyclesOfPartialPermSemigroup` sometimes resulted in an error due to using
`DegreeOfPartialPermSemigroup` instead of the maximum of the degree and the
codegree.
[James D. Mitchell][]
* [Issue 141](https://bitbucket.org/james-d-mitchell/semigroups/issue/141):
`PartialOrderOfDClasses` sometimes resulted in an error. This bug was
introduced in Semigroups 2.6 and did not effect any previous versions.
[James D. Mitchell][]
### Version 2.6 (released 22/09/2015)
This release includes some bugfixes, some minor new features, and one major new
feature (efficient methods for semigroups of matrices over a finite field).
#### New Features in Version 2.6
* extensive new features for computing with semigroups, monoids, and ideals, of
matrices with entries in a finite field. See Chapter 7 of the manual for more
details.
[[Markus Pfeiffer][]]
* The functions `RectangularBand`, `MonogenicSemigroup`, and `ZeroSemigroup` now
have an optional first argument to specify the category of the result; the
functions `LeftZeroSemigroup` and `RightZeroSemigroup` are introduced in a
similar sense.
[[Wilf A. Wilson][]]
* The new property `IsSemigroupWithAdjoinedZero` and attribute
`UnderlyingSemigroupOfSemigroupWithAdjoinedZero` are introduced.
[[Wilf A. Wilson][]]
* The operations `MotzkinMonoid` and `PartialJonesMonoid` were introduced.
[James D. Mitchell][]
#### Issues Resolved in Version 2.6
* [Issue 131](https://bitbucket.org/james-d-mitchell/semigroups/issue/131):
testing membership in a Rees 0-matrix semigroup that knows it is inverse
sometimes resulted in an error.
[[Michael Young][]]
* [Issue 132](https://bitbucket.org/james-d-mitchell/semigroups/issue/132): this
was a feature request to introduce the operations `MotzkinMonoid` and
`PartialJonesMonoid`.
[James D. Mitchell][]
* [Issue 134](https://bitbucket.org/james-d-mitchell/semigroups/issue/134): the
operation `PartialBrauerMonoid` returned the wrong answer when the argument
was `1`. The returned semigroup was not the partial brauer monoid of degree 1.
[James D. Mitchell][]
### Version 2.5 (released 01/06/2015)
This is a minor release including several bugfixes, lots of minor improvements
in the documentation, some improvements in performance, and some new features.
#### New Features in Version 2.5
* Semigroups of partial permutations now have a polynomial time (quadratic in
the degree) algorithm for computing the minimal ideal
[[Wilf A. Wilson][]]
* A more efficient `IsInverseSemigroup` method for Rees 0-matrix semigroups is
introduced, along with new methods for `Idempotents` and `NrIdempotents` for
inverse Rees 0-matrix semigroups
[[Wilf A. Wilson][]]
* The documentation for congruences has been improved and new tests have been
added.
[[Michael Young][]]
* A `UniversalSemigroupCongruence` now returns a much smaller set of generating
pairs.
[[Michael Young][]]
#### Issues Resolved in Version 2.5
Issue numbers refer to those on the [Bitbucket issue tracker][].
* [Issue 126](https://bitbucket.org/james-d-mitchell/semigroups/issue/126):
testing membership in a Rees 0-matrix semigroup that knows it is inverse
sometimes resulted in an error.
[James D. Mitchell][]
* [Issue 127](https://bitbucket.org/james-d-mitchell/semigroups/issue/127): the
main algorithm for computing with ideals of acting semigroups which know they
are regular contained a bug that resulted in incorrect results. In some
cases, some \\(\mathscr{D}\\)-classes were counted more than once, and the
returned value of `Size` was higher than the actual size of the ideal.
[James D. Mitchell][]
* [Issue 128](https://bitbucket.org/james-d-mitchell/semigroups/issue/128): in
some special cases `UnderlyingSemigroup`, `ViewObj`, `Size`, and related
methods, for Rees 0-matrix semigroups over non-groups returned an error.
[James D. Mitchell][]
* The universal congruence specified by generating pairs on a (0-)simple
semigroup no longer causes an error.
[[Michael Young][]]
### Version 2.4.1 (released 15/05/2015)
This is a extremely minor release to change 1 character in the PackageInfo.g
file (wrong package archive URL).
### Version 2.4 (released 02/04/2015)
This is a minor release including several bugfixes, and improvements in
performance, and some new features.
#### New Features in Version 2.4
* The function `RepresentativeOfMinimalIdeal` is introduced.
[[Wilf A. Wilson][]]
* Transformation semigroups now have a polynomial time (cubic in the degree)
algorithm for computing the minimal ideal
[[Wilf A. Wilson][]]
* The functions `RectangularBand`, `ZeroSemigroup`, and `MonogenicSemigroup` are
introduced.
[[Wilf A. Wilson][]]
* A method for choosing a random element of a semigroup has been introduced in
the case that the semigroup knows its set of elements. This new method choose
elements at random with uniform probability.
[[Wilf A. Wilson][]]
* The documentation and tests for congruences has been improved.
[Wilf A. Wilson][]] and [[Michael Young][]
* The functionality for Rees congruences has been rewritten and improved.
[[Michael Young][]]
* There is a new `Enumerator` method for congruence classes of a semigroup
congruence.
[[Michael Young][]]
#### Issues Resolved in Version 2.4
Issue numbers refer to those on the [Bitbucket issue tracker][].
* [Issue 88](https://bitbucket.org/james-d-mitchell/semigroups/issue/88):
an inefficiency in `JoinIrreducibleDClasses` of an inverse semigroup ideal
resulted in a call to `GeneratorsOfSemigroup`.
* [Issue 94](https://bitbucket.org/james-d-mitchell/semigroups/issue/94):
`EquivalenceClasses` of the trivial congruence (generated by 0 pairs of
elements) returned an error.
* [Issue 95](https://bitbucket.org/james-d-mitchell/semigroups/issue/95): The
class containing the zero element of a Rees 0-matrix semigroup was not
returned by `EquivalenceClasses` of a congruence over a Rees 0-matrix
semigroup.
* [Issue 108](https://bitbucket.org/james-d-mitchell/semigroups/issue/108):
`IsRegularSemigroup` with argument a Rees 0-matrix semigroup returned an
error.
* [Issue 119](https://bitbucket.org/james-d-mitchell/semigroups/issue/119):
`NrCongruencesClasses` and related methods did not work for Rees congruences.
* [Issue 121](https://bitbucket.org/james-d-mitchell/semigroups/issue/121):
`MultiplicativeZero` and `IsMultiplicativeZero` sometimes returned incorrect
results when applied to a non-acting semigroup (i.e. a semigroup not of
transformations, partial permutations, partitions, or subsemigroups of a Rees
0-matrix semigroup).
* [Issue 122](https://bitbucket.org/james-d-mitchell/semigroups/issue/122): A
bug in the creation of Green's classes of ideals of semigroups, which resulted
in an error.
* [Issue 123](https://bitbucket.org/james-d-mitchell/semigroups/issue/123):
`IsZeroSemigroup` sometimes returned a false positive when applied to a
non-acting semigroup.
### Version 2.3 (released 16/03/2015)
This is a minor release including some internal refactoring, and
subsequent bugfixes, and stability improvements.
* [Issue 116](https://bitbucket.org/james-d-mitchell/semigroups/issue/116) was
resolved. In some cases when the default length of hash tables in
[Semigroups][] was set to be very small, a segmentation fault occurred. This
is a bug in the [orb package][] (see
[Issue 10](https://github.com/gap-packages/orb/issues/10)), but we worked
around it to resolve this issue.
### Version 2.2 (released 20/01/2015)
This is a minor release including some bug fixes, performance
improvements, and additional functionality.
#### New Features in Version 2.2
* The functions `SmallestElementSemigroup`, `LargestElementSemigroup`,
and `GeneratorsSmallest`.
* Free bands are introduced.
* Error messages are more uniform.
* The function `RegularDClasses` was introduced to resolve
[Issue 102](https://bitbucket.org/james-d-mitchell/semigroups/issue/102).
* The documentation and code for semigroup congruences has been improved, and is
better integrated with the core [GAP][] system.
* The functions `ReadGenerators` and `WriteGenerators` were improved.
#### Issues Resolved in Version 2.2
* Some minor corrections were made to the methods for creating the ideals of
some semigroups in standard examples semigroups, such as
`SingularTransformationSemigroup`.
* [Issue 102](https://bitbucket.org/james-d-mitchell/semigroups/issue/102): we
introduced `RegularDClasses`.
* [Issue 104](https://bitbucket.org/james-d-mitchell/semigroups/issue/104): the
performance of `MaximalSubsemigroups` when applied to an inverse semigroup has
been improved.
* [Issue 105](https://bitbucket.org/james-d-mitchell/semigroups/issue/105):
`CyclesOfPartialPerm` is now documented and does not return nonsense.
* [Issue 106](https://bitbucket.org/james-d-mitchell/semigroups/issue/106):
`MaximalSubsemigroups` sometimes failed when the ResClasses package was
loaded. We refactored the code so that the method from ResClasses is no longer
applied.
* [Issue 107](https://bitbucket.org/james-d-mitchell/semigroups/issue/107): A
bug in the creation of Green's classes of an ideal of a semigroup, which
sometimes caused an error, has been resolved. This issue often caused
`MaximalSubsemigroups` to stop in an error.
* [Issue 110](https://bitbucket.org/james-d-mitchell/semigroups/issue/110):
`MaximalSubsemigroups` can be applied to any class of semigroup where it is
possible to find an isomorphism to a transformation semigroup.
* [Issue 111](https://bitbucket.org/james-d-mitchell/semigroups/issue/111):
`POPI(1)` returned the wrong semigroup. Similar issues existed in other corner
cases, and these have been resolved too.
### Version 2.1.1 (released 09/09/2014)
This is a very minor release to fix an issue caused by only loading the packages
needed (but not required) by [Semigroups][].
### Version 2.1 (released 04/09/2014)
This is a minor release including some bug fixes and performance improvements.
#### New Features in Version 2.1
* The functions:
- `AsTransformationSemigroup`,
- `AsPartialPermSemigroup`,
- `AsBipartitionSemigroup`,
- `AsBlockBijectionSemigroup`
which are shortcuts to `Range(IsomorphismXSemigroup(S))`.
* A method for `IsTransitive` for a transformation semigroup and, optionally, a
positive integer or list of positive integers. This method is based on Gabow's
algorithm for determining the strongly connected components of a directed
graph.
* The functions `MeetSemigroupCongruence` and `JoinSemigroupCongruences` for
finding the meet and join of a pair of congruences of a semigroup.
* There is a new method for `IsSynchronizingSemigroup`, suggested by Peter
Cameron, with better complexity than the previous method.
#### Issues Resolved in Version 2.1
Issue numbers refer to those on the [Bitbucket issue tracker][].
* There was a bug in `ReadGeneratorsFile`, which meant it sometimes returned
fail. The mode argument for `IO_FilteredFile` was not given.
* There was a bug in the `\in` method for a congruence of a Rees 0-matrix
semigroup, which sometimes returned the wrong answer for the zero of the
semigroup.
* There was a bug in `IteratorFromGeneratorsFile` that caused it to read only
every other line in the given file, and to crash if there were an odd number
of lines.
* There was no hash function for bipartitions.
* The documentation for `InverseSubsemigroupByProperty` did not specify the
arguments of the function.
* [Issue 82](https://bitbucket.org/james-d-mitchell/semigroups/issue/82): it is
now possible to take the quotient of a semigroup by an ideal using the `/`
operator.
* [Issue 96](https://bitbucket.org/james-d-mitchell/semigroups/issue/96):
`IsIsomorphicSemigroup` sometimes returned a false negative by incorrectly
comparing the output of `PartialOrderOfDClasses` (up to isomorphism) rather
than the transitive reflexive closure of `PartialOrderOfDClasses`.
* [Issue 97](https://bitbucket.org/james-d-mitchell/semigroups/issue/97): there
was a bug in the `Normalizer` method, which caused [GAP][] to crash when the
argument was a monoid with 0 generators.
* [Issue 98](https://bitbucket.org/james-d-mitchell/semigroups/issue/98):
`PartitionMonoid(1)` returned the wrong answer, it was missing the
non-identity element.
* [Issue 99](https://bitbucket.org/james-d-mitchell/semigroups/issue/99): the
documentation for `PartialOrderOfDClasses` was incorrect.
* [Issue 103](https://bitbucket.org/james-d-mitchell/semigroups/issue/103):
under certain circumstances an error was given when trying to compute with an
ideal of an inverse semigroup.
### Version 2.0 (released 17/04/2014)
This is a major release including many new features and several bug fixes.
#### New Features in Version 2.0
* extensive new features for computing with elements and
subsemigroups of the partition monoid. It is now possible to compute
with semigroups, monoids, inverse semigroups, inverse monoids, and
ideals consisting of elements of the partition monoid. Examples of
subsemigroups of this type are the Brauer monoids, Temperley-Lieb
monoids, and the dual symmetric inverse monoid. See Chapter 5 of the
manual for more details;
* support for ideals of transformation, partial permutation, and
bipartition semigroups, and subsemigroups of Rees 0-matrix
semigroups. It is now possible to compute anything about one of
these ideals that could formerly only be computed about a semigroup
defined by a generating set. Such ideals now use a data structure
similar to that used by semigroups defined by a generating set;
* the new operations `IsomorphismSemigroups`, `IsIsomorphicSemigroup`,
and `SmallestMultiplicationTable`. Some of the methods for this
operation require the Grape package to be fully installed;
* the new operation `MaximalSubsemigroups`, which returns the maximal
subsemigroups of an arbitrary semigroup. Some of the methods for
this operation require the Grape package to be fully installed;
* the operation `IsMaximalSubsemigroup`;
* the new operation `Normalizer` for computing a subgroup of a
permutation group consisting of those permutations that stabilise,
under conjugation, a transformation, partial perm, or bipartition
semigroup. The genss package is required for this operation in some
cases;
* the new operation `CharacterTableOfInverseSemigroup` for finding the
character table of an inverse semigroup of partial permutations;
* methods for defining and manipulating the congruences of a Rees
0-matrix semigroup;
* the properties `IsCongruenceFreeSemigroup`, `IsEUnitaryInverseSemigroup`;
* the attributes:
* `ComponentRepsOfTransformationSemigroup`
* `ComponentsOfTransformationSemigroup`
* `CyclesOfTransformationSemigroup`
* `ComponentRepsOfPartialPermSemigroup`
* `ComponentsOfPartialPermSemigroup`
* `CyclesOfPartialPermSemigroup`.
* the new function `IteratorFromGeneratorsFile` that returns an
iterator which reads semigroup elements from a file created using
`WriteGenerators`. This function is a convenient way of, for example,
looping over a collection of generators in a file without loading
every object in the file into memory. This might be useful if
the file contains more information than there is available memory;
* the operation `EndomorphismsPartition` that returns the monoid
of endomorphisms preserving a partition. This monoid is defined
using the minimum possible number of generators;
* a version of the function `Splash` that attempts to convert a string
containing a dot or tikz document into a pdf and opens this pdf.
Other file formats are also supported;
* the function `DotSemilatticeOfIdempotents` that produces a string
containing a dot document of the semilattice of idempotents of an
inverse semigroup grouped by \\(\mathscr{D}\\)-class;
* the operation `NaturalLeqInverseSemigroup`, which is an umbrella
operation for `NaturalLeqPartialPerm`, and other such functions.
#### Issues Resolved in Version 2.0
Issue numbers refer to those on the [Bitbucket issue tracker][].
* the main algorithm underlying many of the methods in [Semigroups][] has been
revised to avoid computing the same information more than once. Some further
internal rearranging and cleaning up was done.
* `MinimalIdeal` and `SingularTransformationSemigroup` now returns an ideal
rather than a semigroup defined by a generating set;
* to reduce the size of the package archive, the examples directory has been
removed. The content of the examples directory is available on
[this webpage](https://tinyurl.com/jdmitchell/data.php).
* several bugs in the setup for subsemigroups of Rees 0-matrix semigroups were
resolved. These issues would have caused [GAP][] to give an error in certain
circumstances.
* [Issue 33](https://bitbucket.org/james-d-mitchell/semigroups/issue/33): an
error was returned when trying to calculate the size, or multiply elements in
the quotient of a semigroup by an ideal.
* [Issue 36](https://bitbucket.org/james-d-mitchell/semigroups/issue/36),
[Issue 64](https://bitbucket.org/james-d-mitchell/semigroups/issue/64): the
function `SmallGeneratingSet` was ambiguous, in the sense that it was
sometimes unclear how to recreate a semigroup from its small generating set.
For example, `SmallGeneratingSet` of a monoid could return an empty list, but
this empty list could not be used to recreate the monoid in [GAP][]. This was
resolved by introducing the functions `SmallSemigroupGeneratingSet`,
`SmallMonoidGeneratingSet`, `SmallInverseSemigroupGeneratingSet`,
`SmallInverseMonoidGeneratingSet`. These functions can also now be applied to
collections of elements, i.e. not only to semigroups.
* [Issue 47](https://bitbucket.org/james-d-mitchell/semigroups/issue/47):
`ClosureSemigroup` had several bugs that could, in some cases, result in
incorrect results, or semigroups with invalid data structures.
* [Issue 50](https://bitbucket.org/james-d-mitchell/semigroups/issue/50) and
[Issue 59](https://bitbucket.org/james-d-mitchell/semigroups/issue/59):
`WriteGenerators` wrote nothing to a file in the case that it was not piping
through `xz` or `gzip`.
* [Issue 55](https://bitbucket.org/james-d-mitchell/semigroups/issue/55):
`DotDClasses` did not work when the argument was a Rees 0-matrix semigroup (it
worked as intended when the argument was a subsemigroup of such a semigroup
defined by a generating set).
* [Issue 56](https://bitbucket.org/james-d-mitchell/semigroups/issue/56): the
functions `Monoid` and `InverseMonoid` sometimes did not contain their
identity element.
* [Issue 57](https://bitbucket.org/james-d-mitchell/semigroups/issue/57): under
certain circumstances a bug in the [GAP][] kernel function `INV_KER_TRANS`,
that didn't handle kernels and transformations with different length and
degree properly, caused [GAP][] to give an error.
* [Issue 63](https://bitbucket.org/james-d-mitchell/semigroups/issue/63): there
was an error in the [GAP][] library functions `Monoid` and `InverseMonoid`,
when they were passed a monoid as an argument.
* [Issue 63](https://bitbucket.org/james-d-mitchell/semigroups/issue/63) (and
[Issue 4](https://github.com/gap-system/orb/issues) in the [orb package][]): a
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