This chapter contains an overview of the most important changes introduced in GAP 4.8.1 release (the 2nd beta release of GAP 4.8). Later it will also contain information about subsequent update releases for GAP 4.8. First of all, the GAP development repository is now hosted on GitHub at https://github.com/gap-system/gap, and GAP 4.8 is the first major GAP release made from this repository. The public issue tracker for the core GAP system is located at https://github.com/gap-system/gap/issues, and you may use appropriate milestones from https://github.com/gap-system/gap/milestones to see all changes that were introduced in corresponding GAP releases. An overview of the most significant ones is provided below.
New features:
Added support for profiling which tracks how much time in spent on each line of GAP code. This can be used to show where code is spending a long time and also check which lines of code are even executed. See the documentation for ProfileLineByLine
(Reference: ProfileLineByLine) and CoverageLineByLine
(Reference: CoverageLineByLine) for details on generating profiles, and the Profiling package for transforming these profiles into a human-readable form.
Added ability to install (in the library or packages) methods for accessing lists using multiple indices and indexing into lists using indices other than positive small integers. Such methods could allow, for example, to support expressions like
m[1,2]; m[1,2,3] := x; IsBound(m["a","b",Z(7)]); Unbind(m[1][2,3])
Added support for partially variadic functions to allow function expressions like
function( a, b, c, x... ) ... end;
which would require at least three arguments and assign the first three to a, b and c and then a list containing any remaining ones to x.
The former special meaning of the argument arg is still supported and is now equivalent to function( arg... )
, so no changes in the existing code are required.
Introduced CallWithTimeout
(Reference: CallWithTimeout) and CallWithTimeoutList
(Reference: CallWithTimeoutList) to call a function with a limit on the CPU time it can consume. This functionality may not be available on all systems and you should check GAPInfo.TimeoutsSupported
before using this functionality.
GAP now displays the filename and line numbers of statements in backtraces when entering the break loop.
Introduced TestDirectory
(Reference: TestDirectory) function to find (recursively) all .tst
files from a given directory or a list of directories and run them using Test
(Reference: Test).
Improved and extended functionality:
Method tracing shows the filename and line of function during tracing.
TraceAllMethods
(Reference: TraceAllMethods) and UntraceAllMethods
(Reference: UntraceAllMethods) to turn on and off tracing all methods in GAP. Also, for the uniform approach UntraceImmediateMethods
(Reference: UntraceImmediateMethods) has been added as an equivalent of TraceImmediateMethods(false)
.
The most common cases of AddDictionary
(Reference: AddDictionary) on three arguments now bypass method selection, avoiding the cost of determining homogeneity for plain lists of mutable objects.
Improved methods for symmetric and alternating groups in the "natural" representations and removed some duplicated code.
Package authors may optionally specify the source code repository, issue tracker and support email address for their package using new components in the PackageInfo.g
file, which will be used to create hyperlinks from the package overview page (see PackageInfo.g
from the Example package which you may use as a template).
Changed functionality:
As a preparation for the future developments to support multithreading, some language extensions from the HPC-GAP project were backported to the GAP library to help to unify the codebase of both GAP 4 and HPC-GAP. The only change which is not backwards compatible is that atomic
, readonly
and readwrite
are now keywords, and thus are no longer valid identifiers. So if you have any variables or functions using that name, you will have to change it in GAP 4.8.
There was inconsistent use of the following properties of semigroups: IsGroupAsSemigroup
, IsMonoidAsSemigroup
, and IsSemilatticeAsSemigroup
. IsGroupAsSemigroup
was true for semigroups that mathematically defined a group, and for semigroups in the category IsGroup
(Reference: IsGroup); IsMonoidAsSemigroup
was only true for semigroups that mathematically defined monoids, but did not belong to the category IsMonoid
(Reference: IsMonoid); and IsSemilatticeAsSemigroup
was simply a property of semigroups, as there is no category IsSemilattice
.
From version 4.8 onwards, IsSemilatticeAsSemigroup
is renamed to IsSemilattice
, and IsMonoidAsSemigroup
returns true for semigroups in the category IsMonoid
(Reference: IsMonoid).
This way all of the properties of the type IsXAsSemigroup
are consistent. It should be noted that the only methods installed for IsMonoidAsSemigroup
belong to the Semigroups and Smallsemi packages.
ReadTest
became obsolete and for backwards compatibility is replaced by Test
(Reference: Test) with the option to compare the output up to whitespaces.
Fixed bugs:
A combination of two bugs could lead to a segfault. First off, NullMat
(Reference: NullMat) (and various other GAP functions), when asked to produce matrix over a small field, called ConvertToMatrixRep
(Reference: ConvertToMatrixRep (for a list (and a field))). After this, if the user tried to change one of the entries to a value from a larger extension field, this resulted in an error. (This is now fixed).
Unfortunately, the C code catching this error had a bug and allowed users to type "return" to continue while ignoring the conversion error. This was a bad idea, as the C code would be in an inconsistent state at this point, subsequently leading to a crash.
This, too, has been fixed, by not allowing the user to ignore the error by entering "return".
The Fitting-free code and code inheriting PCGS is now using IndicesEANormalSteps
(Reference: IndicesEANormalSteps) instead of IndicesNormalSteps
(Reference: IndicesNormalSteps), as these indices are neither guaranteed, nor required to be maximally refined when restricting to subgroups.
A bug that caused a break loop in the computation of the Hall subgroup for groups having a trivial Fitting subgroup.
Including a break
or continue
statement in a function body but not in a loop now gives a syntax error instead of failing at run time.
Fixed a bug in caching the degree of transformation that could lead to a non-identity transformation accidentally changing its value to the identity transformation.
At the time of the release of GAP 4.7.8 there were 119 packages redistributed with GAP. New packages that have been added to the redistribution since the release of GAP 4.7.8 are:
CAP (Categories, Algorithms, Programming) package by Sebastian Gutsche, Sebastian Posur and Øystein Skartsæterhagen, together with three associated packages GeneralizedMorphismsForCAP, LinearAlgebraForCAP and ModulePresentationsForCAP (all three - by Sebastian Gutsche and Sebastian Posur).
FinInG package by John Bamberg, Anton Betten, Philippe Cara, Jan De Beule, Michel Lavrauw and Max Neunhöffer for computation in Finite Incidence Geometry.
matgrp package by Alexander Hulpke, which provides an interface to the solvable radical functionality for matrix groups, building on constructive recognition.
profiling package by Christopher Jefferson for transforming profiles produced by ProfileLineByLine
(Reference: ProfileLineByLine) and CoverageLineByLine
(Reference: CoverageLineByLine) into a human-readable form.
generated by GAPDoc2HTML