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2 Changes between GAP 4.9 and GAP 4.10
2.1 GAP 4.10.0 (November 2018)
2.1-1 New features and major changes
2.1-2 Improved and extended functionality
2.1-3 Changed documentation
2.1-4 Fixed bugs that could lead to crashes
2.1-5 Fixed bugs that could lead to incorrect results
2.1-6 Fixed bugs that could lead to break loops
2.1-7 Other fixed bugs
2.1-8 Removed or obsolete functionality
2.1-9 Packages
2.2 GAP 4.10.1 (February 2019)
2.2-1 Changes in the core GAP system introduced in GAP 4.10.1
2.2-2 New and updated packages since GAP 4.10.0
2.3 GAP 4.10.2 (June 2019)
2.3-1 Changes in the core GAP system introduced in GAP 4.10.21
2.3-2 New and updated packages since GAP 4.10.1

### 2 Changes between GAP 4.9 and GAP 4.10

This chapter contains an overview of the most important changes introduced in GAP 4.10.0 release (the first public release of GAP 4.10). Later it will also contain information about subsequent update releases for GAP 4.10.

These changes are also listed on the Wiki page https://github.com/gap-system/GAP/wiki/gap-4.10-release-notes.

#### 2.1 GAP 4.10.0 (November 2018)

##### 2.1-1 New features and major changes

Reduce impact of immediate methods

  GAP allows declaring so-called "immediate methods". The idea is that these are very simple and fast methods which are immediately called if information about an object becomes known, in order to perform some quick deduction. For example, if the order of a group is set, there might be immediate methods which update the filters `IsFinite` and `IsTrivial` of the group suitably.

  While this can be very elegant and useful in interactive GAP sessions, the overhead for running these immediate methods and applying their results can become a major factor in the runtime of complex computations that create thousands or millions of objects.

  To address this, various steps were taken:

  - some immediate methods were turned into regular methods;

  - a special handlers for `SetSize` was created that deduces properties which previously were taken care of by immediate methods;

  - some immediate methods were replaced by implications (set via `InstallTrueMethod`), a mechanism that essentially adds zero overhead, unlike immediate methods;

  - various group constructors were modified to precompute and preset properties of freshly created group objects, to avoid triggering immediate methods for these.

  As a result of these and other changes, consider the following example; with GAP 4.9, it takes about 130 seconds on one test system, while with GAP 4.10 it runs in about 22 seconds, i.e., more than six times faster.

      G:=PcGroupCode( 741231213963541373679312045151639276850536621925972119311,11664);;
      IsomorphismGroups(G,PcGroupCode(CodePcGroup(G),Size(G)))<>fail;

  Relevant pull requests and issues: #2386, #2387, #2522.

Change definition of `IsPGroup` to not require finiteness

  This is a small change in terms of amount of code changed, but we list it here as it has a potential (albeit rather unlikely) impact on the code written by GAP users: In the past, the GAP manual entry for `IsPGroup` defined p-groups as being finite groups, which differs from the most commonly used definition for p-groups. Note however that there was not actual implication installed from `IsPGroup` to `IsFinite`, so it always was possible to actually created infinite groups in the filter `IsPGroup`. In GAP 4.10, we adjusted (in #1545) the documentation for `IsPGroup` to the commonly accepted definition for p-groups. In addition, code in the GAP library and in packages using `IsPGroup` was audited and (in a very few cases) adjusted to explicitly check `IsFinite` (see e.g. #2866).

Experimental support for using the Julia garbage collector

  It is now possible to use the garbage collector of the Julia language instead of GAP's traditional GASMAN garbage collector. This is partly motivated by a desire to allow tight integration with GAP and Julia in the future. Warning: right now, this is slower, and also requires a patched version of Julia.

  Relevant pull requests: #2092, #2408, #2461, #2485, #2495, #2672, #2688, #2793, #2904, #2905, #2931.

libGAP (work in progress)

  We now provide a experimental way to allow 3rd party code to link GAP as a library; this is based on the libGAP code by SageMath, but different: while we aim to provide the same functionality, we do not rename any symbols, and we do not provide the same API. We hope that a future version of SageMath can drop its custom modifications for GAP and use this interface instead. Work is underway to achieve this goal. If you are interested in this kind of interface, please get in touch with us to help us improve it. See also this email.

  To get an idea how libGAP works, you can configure GAP as normal, and then execute `make testlibgap` which will build a small program that uses some of the existing API and links GAP. Relevant pull requests:

  - #1690 Add a callback to `FuncJUMP_TO_CATCH`

  - #2528 Add `IsLIBGAP` constant

  - #2702 Add GAP kernel API

  - #2723 Introduce command line options `--norepl` and `--nointeract`

##### 2.1-2 Improved and extended functionality

- #2041 Teach `FrattiniSubgroup` methods to check for solvability

- #2053 Faster computation of modular inverses of integers

- #2057 Various changes, including:

  - Improve computation of automorphism groups for fp groups (we still recommend to instead first convert the group to a computationally nice representation, such as a perm or pc group)

  - Add `MinimalFaithfulPermutationDegree` (Reference: MinimalFaithfulPermutationDegree) attribute for finite groups

  - Improve performance of `GQuotients(F,G)` when `F` is an fp group

  - Some other performance and documentation tweaks

- #2061, #2086, #2159, #2306 Speed up `GcdInt`, `LcmInt`, `PValuation`, `RootInt`, `SmallestRootInt`, `IsPrimePowerInt`

- #2063 Teach GAP that BPSW pseudo primes less than 2^64 are all known to be prime (the previous limit was 10^13)

- #2091 Refactor `DeclareAttribute` and `NewAttribute` (arguments are now verified stricter)

- #2115, #2204, #2272 Allow (optionally) passing a random source to many more `Random` methods than before, and also to `RandomList`

- #2136 Add `shortname` entry to record returned by `IsomorphismTypeInfoFiniteSimpleGroup`

- #2181 Implement `Union(X,Y)`, where `X` and `Y` are in `PositiveIntegers`, `NonnegativeIntegers`, `Integers`, `GaussianIntegers`, `Rationals`, `GaussianRationals`, `Cyclotomics`, at least where a suitable output object exists (we already provided `Intersection(X,Y)` for a long time)

- #2185 Implement `IsCentral(M,x)`, where `M` is a magma, monoid, group, ring, algebra, etc. and `x` an element of `M` (the documentation already claimed that these exist for a long time)

- #2199 Optimize true/false conditions when coding if-statements

- #2200 Add `StringFormatted` (Reference: StringFormatted), `PrintFormatted` (Reference: PrintFormatted), `PrintToFormatted` (Reference: PrintToFormatted)

- #2222 Turn hidden implications into actual implications

- #2223 Add operation `PositionsBound` (Reference: PositionsBound) which returns the set of all bound positions in a given list

- #2224, #2243, #2340 Improve `ShowImpliedFilters` output

- #2225 Improve `LocationFunc` for kernel function

- #2232 Make `ValueGlobal` faster

- #2242 Add global function `CycleFromList` (Reference: CycleFromList)

- #2244 Make `rank` argument to `InstallImmediateMethod` optional, similar to `InstallMethod`

- #2274 Ensure uniform printing of machine floats `nan`, `inf`, `-inf` across different operating systems

- #2287 Turn `IsInfiniteAbelianizationGroup` into a property and add some implications involving it

- #2293, #2602, #2718 Improved and documented various kernel and memory debugging facilities (requires recompiling GAP with `--enable-debug`, `--enable-valgrind` resp. `--enable-memory-checking`)

- #2308 Method selection code was rewritten from GAP to C

- #2326 Change `SimpleGroup` to perform better input validation and improve or correct error message for type 2E

- #2375 Make `last2` and `last3` available in break loops

- #2383 Speed improvements for automorphism groups

- #2393 Track location of `InstallMethod` and `InstallImmediateMethod`

- #2422 Improve tracking of `InstallMethod` and `DeclareOperation`

- #2426 Speed up `InverseMatMod` with integer modulus

- #2427 Fix and complete support for custom functions (i.e., objects which can be called like a function using `obj(arg)` syntax)

- #2456 Add `PrintString` and `ViewString` methods for character tables

- #2474 Change `IsConstantRationalFunction` and `IsUnivariateRationalFunction` to return `false` if input isn't a rational function (instead of an error)

- #2474 Add methods for multiplying rational functions over arbitrary rings by rationals

- #2496 Finite groups whose order is known and not divisible by 4 are immediately marked as solvable

- #2509 Rewrite support for `.gz` compressed files to use zlib, now works on Windows

- #2519, #2524, #2531 `Test` now rejects empty inputs and warns if the input contains no test

- #2574 When reporting syntax errors, GAP now "underlines" the complete last token, not just the position where it stopped parsing

- #2577, #2613 Add quadratic and bilinear add forms for `Omega(e,d,q)`

- #2598 Add `BannerFunction` to `PackageInfo.g`

- #2606 Improve `PageSource` to work on functions that were read from a file given by a relative path

- #2616 Speed up computation of quotients of associative words by using existing (but previously unused) kernel functions for that

- #2640 Work on `MatrixObj` and `VectorObj`

- #2654 Make `Sortex` stable

- #2666, #2686 Add `IsBiCoset` attribute for right cosets, which is true if the right coset is also a left coset

- #2684 Add `NormalSubgroups` methods for symmetric and alternating permutation groups

- #2726 Validate `PackageInfo.g` when loading packages

- #2733 Minor performance improvements, code cleanup and very local fixes

- #2750 Reject some invalid uses of `~`

- #2812 Reduce memory usage and improve performance the MTC (modified Todd-Coxeter) code that was rewritten in GAP 4.9, but which was much slower than the old (but buggy) code it replaced; the difference is now small, but the old code still is faster in some case.

- #2855, #2877 Add `IsPackageLoaded` (Reference: IsPackageLoaded)

- #2878 Speed up conjugacy tests for permutation by using random permutation of points when selecting base in centraliser

- #2899 `TestDirectory` reports number of failures and failed files

##### 2.1-3 Changed documentation

- #2192 Add an example for `PRump` (Reference: PRump)

- #2219 Add examples to the relations chapter (see Reference: Relations).

- #2360 Document `IdealDecompositionsOfPolynomial` (Reference: IdealDecompositionsOfPolynomial) (also accessible via its synonym `DecomPoly`) and `NormalizerViaRadical` (Reference: NormalizerViaRadical)

- #2366 Do not recommend avoiding `X` which is a synonym for `Indeterminate` (Reference: Indeterminate)

- #2432 Correct a claim about the index of `Omega(e,p,q)` in `SO(e,p,q)` (see `SO` (Reference: SO))

- #2549 Update documentation of the `-T` command line option (see Reference: Command Line Options)

- #2551 Add new command line option `--alwaystrace` which ensures error backtraces are printed even if break loops are disabled (see Reference: Command Line Options)

- #2681 Documented `ClassPositionsOfSolvableRadical` (Reference: ClassPositionsOfSolvableRadical) and `CharacterTableOfNormalSubgroup` (Reference: CharacterTableOfNormalSubgroup)

- #2834 Improve manual section about `Info` classes (see Reference: Info Functions)

##### 2.1-4 Fixed bugs that could lead to crashes

- #2154, #2242, #2294, #2344, #2353, #2736 Fix several potential (albeit rare) crashes related to garbage collection

- #2196 Fix crash in `HasKeyBag` on SPARC Solaris 11

- #2305 Fix crash in `PartialPerm([1,2,8],[3,4,1,2]);`

- #2477 Fix crash if `~` is used to modify list

- #2499 Fix crash in the kernel functions `{8,16,32}Bits_ExponentSums3`

- #2601 Fix crash in `MakeImmutable(rec(x:=~));`

- #2665 Fix crash when an empty filename is passed

- #2711 Fix crash when tracing buggy attribute/property methods that fail to return a value

- #2766 Fix obscure crashes by using `a!{l}` syntax inside a function (this syntax never was fully implemented and was unusable, and now has been removed)

##### 2.1-5 Fixed bugs that could lead to incorrect results

- #2085 Fix bugs in `JenningsLieAlgebra` and `PCentralLieAlgebra` that could e.g. lead to incorrect `LieLowerCentralSeries` results

- #2113 Fix `IsMonomial` for reducible characters and some related improvements

- #2183 Fix bug in `ValueMolienSeries` that could lead to `ValueMolienSeries(m,0)` not being 1

- #2198 Make multiplication of larger integers by tiny floats commutative (e.g. now 10.^-300 * 10^400 and 10^400 * 10.^-300 both give infinity, while before 10^400 * 10.^-300 gave 1.e+100); also ensure various strange inputs, like `rec()^1;`, produce an error (instead of setting `a^1 = a` and `1*a = a` for almost any kind of object)

- #2273 Fix `TypeOfOperation` for setters of and-filters

- #2275, #2280 Fix `IsFinitelyGeneratedGroup` and `IsFinitelyGeneratedMonoid` to not (incorrectly) assume that a given infinite generating set implies that there is no finite generating set

- #2311 Do not set `IsFinitelyGeneratedGroup` for finitely generated magmas which are not groups

- #2452 Fix bug that allowed creating empty magmas in the filters `IsTrivial` and `IsMagmaWithInverses`

- #2689 Fix `LogFFE` to not return negative results on 32 bit systems

- #2766 Fix a bug that allowed creating corrupt permutations

##### 2.1-6 Fixed bugs that could lead to break loops

- #2040 Raise error if eager float literal conversion fails (fixes #1105)

- #2582 Fix `ExtendedVectors` for trivial vector spaces

- #2617 Fix `HighestWeightModule` for Lie algebras in certain cases

- #2829 Fix `ShallowCopy` for `IteratorOfCartesianProduct`

##### 2.1-7 Other fixed bugs

- #2220 Do not set `IsSubsetLocallyFiniteGroup` filter for finite fields

- #2268 Handle spaces in filenames of gzipped filenames

- #2269, #2660 Fix some issues with the interface between GAP and XGAP (or other similar frontends for GAP)

- #2315 Prevent creation of groups of floats, just like we prevent creation of groups of cyclotomics

- #2350 Fix prompt after line continuation

- #2365 Fix tracing of mutable variants of `One`/`Zero`/`Inv`/`AInv`

- #2398 Fix `PositionStream` to report correct position

- #2467 Fix support for identifiers of length 1023 and more

- #2470 Do not display garbage after certain syntax error messages

- #2533 Fix composing a map with an identity map to not produce a range that is too big

- #2638 Fix result of `Random` on 64 bit big endian system to match those on little endian, and on 32 bit big endian

- #2672 Fix `MakeImmutable` for weak pointer objects, which previously failed to make subobjects immutable

- #2674 Fix `SaveWorkspace` to return `false` in case of an error, and `true` only if successful

- #2681 Fix `Display` for the character table of a trivial group

- #2716 When seeding a Mersenne twister from a string, the last few characters would not be used if the string length was not a multiple of 4. Fixing this may lead to different series of random numbers being generated.

- #2720 Reject workspaces made in a GAP with readline support in a GAP without, and vice versa, instead of crashing

- #2657 The subobjects of the mutable values of the attributes `ComputedClassFusions`, `ComputedIndicators`, `ComputedPowerMaps`, `ComputedPrimeBlockss` are now immutable. This makes sure that the values are not accidentally changed. This change may have side-effects in users' code, for example the object returned by `0 * ComputedPowerMaps( CharacterTable( "A5" ) )[2]` had been a mutable list before the change, and is an immutable list from now on.

##### 2.1-8 Removed or obsolete functionality

- Remove multiple undocumented internal functions. Nobody should have been using them, but if you were, you may extract it from a previous GAP release that still contained it. (#2670, #2781 and more)

- #2335 Remove several functions and variables that were deprecated for a long time: `DiagonalizeIntMatNormDriven`, `DeclarePackageDocumentation`, `KERNEL_VERSION`, `GAP_ROOT_PATHS`, `LOADED_PACKAGES`, `PACKAGES_VERSIONS`, `IsTuple`, `StateRandom`, `RestoreStateRandom`, `StatusRandom`, `FactorCosetOperation`, `ShrinkCoeffs`, `ExcludeFromAutoload`, `CharacterTableDisplayPrintLegendDefault`, `ConnectGroupAndCharacterTable`, `IsSemilatticeAsSemigroup`, `CreateCompletionFiles`, `PositionFirstComponent`, `ViewLength`

- #2502 Various kernel functions now validate their inputs more carefully (making it harder to produce bad effects by accidentally passing bad data to them)

- #2700 Forbid constructors with 0 arguments (they were never meaningful)

##### 2.1-9 Packages

GAP 4.10.0 distribution includes 140 packages.

Added to the distribution:

- The francy package by Manuel Martins, which provides an interface to draw graphics using objects. This interface allows creation of directed and undirected graphs, trees, line charts, bar charts and scatter charts. These graphical objects are drawn inside a canvas that includes a space for menus and to display informative messages. Within the canvas it is possible to interact with the graphical objects by clicking, selecting, dragging and zooming.

- The JupyterVis package by Nathan Carter, which is intended for use in Jupyter Notebooks running GAP kernels and adds visualization tools for use in such notebooks, such as charts and graphs.

No longer redistributed with GAP:

- The linboxing package has been unusable (it does not compile) for several years now, and is unmaintained. It was therefore dropped from the GAP package distribution. If anybody is willing to take over and fix the package, the latest sources are available at https://github.com/gap-packages/linboxing.

- The recogbase package has been merged into the `recog` package, and therefore is no longer distributed with GAP.

#### 2.2 GAP 4.10.1 (February 2019)

##### 2.2-1 Changes in the core GAP system introduced in GAP 4.10.1

Fixes in the experimental way to allow 3rd party code to link GAP as a library:

- Do not start a session when loading workspace if `--nointeract` command line option is used (#2840).

- Add prototype for `GAP_Enter` and `GAP_Leave` macros (#3096).

- Prevent infinite recursions in `echoandcheck` and `SyWriteandcheck` (#3102).

- Remove `environ` arguments and `sysenviron` (#3111).

Fixes in the experimental support for using the Julia garbage collector:

- Fix task scanning for the Julia GC (#2969).

- Fix stack marking for the Julia GC (#3199).

- Specify the Julia binary instead of the Julia prefix (#3243).

- Export Julia `CFLAGS`, `LDFLAGS`, and `LIBS` to `sysinfo.gap` (#3248).

- Change `MPtr` Julia type of GAP objects to be a subtype of the abstract Julia `GapObj` type provided by the Julia package `GAPTypes.jl` (#3497).

Improved and extended functionality:

- Always generate `sysinfo.gap` (previously, it was only generated if the "compatibility mode" of the build system was enabled) (#3042).

- Add support for writing to `ERROR_OUTPUT` from kernel code (#3043).

- Add `make check` (#3285).

Changed documentation:

- Fix documentation of `NumberFFVector` (Reference: NumberFFVector) and add an example (#3079).

Fixed bugs that could lead to crashes:

- Fix readline crash when using autocomplete with `colored-completion-prefix` turned on in Bash (#2991).

- Fix overlapping `memcpy` in `APPEND_LIST` (#3216).

Fixed bugs that could lead to incorrect results:

- Fix bugs in the code for partial permutations (#3220).

- Fix a bug in `Gcd` for polynomials not returning standard associates, introduced in GAP 4.10.0 (#3227).

Fixed bugs that could lead to break loops:

- Change `GroupWithGenerators` (Reference: GroupWithGenerators) to accept collections again (to avoid regressions in code that relied on this undocumented behavior) (#3095).

- Fix `ShallowCopy` (Reference: ShallowCopy) for for a Knuth-Bendix rewriting system (#3128). [Reported by Ignat Soroko]

- Fix `IsMonomialMatrix` (Reference: IsMonomialMatrix) to work with compressed matrices (#3149). [Reported by Dominik Bernhardt]

Removed or obsolete functionality:

- Disable `make install` (previously it displayed a warning which often got ignored) (#3005).

Other fixed bugs:

- Fix some errors which stopped triggering a break loop (#3013).

- Fix compiler error with GCC 4.4.7 (#3026).

- Fix string copying logic (#3071).

##### 2.2-2 New and updated packages since GAP 4.10.0

GAP 4.10.1 distribution contains 145 packages, including updated versions of 35 packages from GAP 4.10.0 distribution, and also the following five new packages:

- MajoranaAlgebras by Markus Pfeiffer and Madeleine Whybrow, which constructs Majorana representations of finite groups.

- PackageManager by Michael Torpey, providing a collection of functions for installing and removing GAP packages, with the eventual aim of becoming a full pip-style package manager for the GAP system.

- Thelma by Victor Bovdi and Vasyl Laver, implementing algorithms to deal with threshold elements.

- walrus by Markus Pfeiffer, providing methods for proving hyperbolicity of finitely presented groups in polynomial time.

- YangBaxter by Leandro Vendramin and Alexander Konovalov, which provides functionality to construct classical and skew braces, and also includes a database of classical and skew braces of small orders.

#### 2.3 GAP 4.10.2 (June 2019)

##### 2.3-1 Changes in the core GAP system introduced in GAP 4.10.21

Improvements in the experimental way to allow 3rd party code to link GAP as a library:

- Add `GAP_AssignGlobalVariable` and `GAP_IsNameOfWritableGlobalVariable` to the libGAP API (#3438).

Fixes in the experimental support for using the Julia garbage collector:

- Fix of a problem where the Julia GC during a partial sweep frees some, but not all objects of an unreachable data structure, and also may erroneously try to mark the deallocated objects (#3412).

- Fix stack scanning for the Julia GC when GAP is used as a library (#3432).

Fixed bugs that could lead to crashes:

- Fix a bug in `TransformationListList` (Reference: TransformationListList for a source and destination) which could cause a crash (#3463).

Fixed bugs that could lead to incorrect results:

- Fix a bug in `ClassPositionsOfLowerCentralSeries` (Reference: ClassPositionsOfLowerCentralSeries). [Reported by Frieder Ladisch] (#3321).

- Fix a dangerous bug in the comparison of large negative integers, introduced in GAP 4.10.1: if `x` and `y` were equal, but not identical, large negative numbers then `x < y` returned `true` instead of `false`. (#3478).

Fixed bugs that could lead to break loops:

- If the group has been obtained as subgroup from a Fitting free/solvable radical computation, the data is inherited and might not guarantee that the factor group really is Fitting free. Added a check and an assertion to catch this situation (#3154).

- Fix declaration of sparse action homomorphisms (#3281).

- `LatticeViaRadical` called `ClosureSubgroupNC` (Reference: ClosureSubgroupNC) assuming that the parent contained all generators. It now calls `ClosureSubgroup` (Reference: ClosureSubgroup) instead, since this can not be always guaranteed (this could happen, for example, in perfect subgroup computation). Also added an assertion to `ClosureSubgroupNC` (Reference: ClosureSubgroupNC) to catch this situation in other cases. [Reported by Serge Bouc] (#3397).

- Fix a "method not found" error in `SubdirectProduct` (Reference: SubdirectProduct) (#3485).

Other fixed bugs:

- Fix corner case in modified Todd-Coxeter algorithm when relator is trivial (#3311).

##### 2.3-2 New and updated packages since GAP 4.10.1

GAP 4.10.1 distribution contains 145 packages, including updated versions of 55 packages from GAP 4.10.1 distribution,

A new package MonoidalCategories by Mohamed Barakat, Sebastian Gutsche and Sebastian Posur have been added to the distribution. It is based on the CAP package and implements monoidal structures for CAP.

Unfortunately we had to withdraw the QaoS package from distribution of GAP, as the servers it crucially relies on for its functionality have been permanently retired some time ago and are not coming back (see https://github.com/gap-packages/qaos/issues/13 for details).

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