<Chapter Label="ChangesGAP47toGAP48"> 
<Heading>Changes between &GAP; 4.7 and &GAP; 4.8</Heading>

This chapter contains an overview of the most important changes
introduced in &GAP; 4.8.2 release (the 1st public 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
<URL>https://github.com/gap-system/gap</URL>, 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 
<URL>https://github.com/gap-system/gap/issues</URL>,
and you may use appropriate milestones from 
<URL>https://github.com/gap-system/gap/milestones</URL> to see all changes
that were introduced in corresponding &GAP; releases. An overview of the
most significant ones is provided below.

<Section Label="gap482">
<Heading>&GAP; 4.8.2 (February 2016)</Heading>

<Subsection Label="Changes in the core GAP48 system"> 
<Heading>Changes in the core &GAP; system introduced in &GAP; 4.8</Heading>

New features:
<List>
<Item>
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 <Ref Func="ProfileLineByLine" BookName="ref"/> and
<Ref Func="CoverageLineByLine" BookName="ref"/> for details on generating profiles,
and the <Package>Profiling</Package> package for transforming these profiles
into a human-readable form.
</Item>
<!-- https://github.com/gap-system/gap/pull/192 -->
<Item>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
<Log><![CDATA[
m[1,2];
m[1,2,3] := x;
IsBound(m["a","b",Z(7)]);
Unbind(m[1][2,3])
]]></Log>
</Item>
<Item>
<!-- https://github.com/gap-system/gap/pull/90 -->
Added support for partially variadic functions to allow function expressions
like
<Log><![CDATA[
function( a, b, c, x... ) ... end;
]]></Log>
which would require at least three arguments and assign the first three
to <A>a</A>, <A>b</A> and <A>c</A> and then a list containing any remaining
ones to <A>x</A>.
<P/>
The former special meaning of the argument <A>arg</A> is still supported
and is now equivalent to <C>function( arg... )</C>, so no changes in the
existing code are required.
</Item>
<Item>
Introduced <Ref Func="CallWithTimeout" BookName="ref"/> and
<Ref Func="CallWithTimeoutList" BookName="ref"/> 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 <C>GAPInfo.TimeoutsSupported</C>
before using this functionality.
</Item>
<Item>
&GAP; now displays the filename and line numbers of statements in backtraces
when entering the break loop.
</Item>
<Item>
Introduced <Ref Func="TestDirectory" BookName="ref"/> function to find
(recursively) all <F>.tst</F> files from a given directory or a list of
directories and run them using <Ref Func="Test" BookName="ref"/>.
</Item>
</List>

Improved and extended functionality:
<List>
<Item>
Method tracing shows the filename and line of function during tracing.
</Item>
<Item>
<Ref Func="TraceAllMethods" BookName="ref"/> and
<Ref Func="UntraceAllMethods" BookName="ref"/> to turn on and off tracing all
methods in &GAP;. Also, for the uniform approach
<Ref Func="UntraceImmediateMethods" BookName="ref"/> has been added as an
equivalent of <C>TraceImmediateMethods(false)</C>.
</Item>
<Item>
The most common cases of <Ref Oper="AddDictionary" BookName="ref"/> 
on three arguments now bypass method selection, avoiding the cost 
of determining homogeneity for plain lists of mutable objects.
</Item>
<Item>
Improved methods for symmetric and alternating groups in the "natural"
representations and removed some duplicated code.
</Item>
<Item> 
<!-- https://github.com/gap-system/gap/issues/7 -->
Package authors may optionally specify the source code repository,
issue tracker and support email address for their package using new
components in the <File>PackageInfo.g</File> file, which will be used
to create hyperlinks from the package overview page (see 
<File>PackageInfo.g</File> from the Example package which you may use
as a template).
</Item>
</List>

Changed functionality:
<List>  
<Item>
As a preparation for the future developments to support multithreading,
some language extensions from the <Package>HPC-GAP</Package> project were
backported to the &GAP; library to help to unify the codebase of both 
&GAP;&nbsp;4 and <Package>HPC-GAP</Package>. The only change which is not backwards
compatible is that <C>atomic</C>, <C>readonly</C> and <C>readwrite</C> 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.
</Item>
<Item>
There was inconsistent use of the following properties of semigroups:
<C>IsGroupAsSemigroup</C>, <C>IsMonoidAsSemigroup</C>, and
<C>IsSemilatticeAsSemigroup</C>. <C>IsGroupAsSemigroup</C> was true for
semigroups that mathematically defined a group, and for semigroups in the
category <Ref Filt="IsGroup" BookName="ref"/>; <C>IsMonoidAsSemigroup</C>
was only true for semigroups that mathematically defined monoids, but did
not belong to the category <Ref Filt="IsMonoid" BookName="ref"/>; and
<C>IsSemilatticeAsSemigroup</C> was simply a property of semigroups, as
there is no category <C>IsSemilattice</C>.
<P/>
From version 4.8 onwards, <C>IsSemilatticeAsSemigroup</C> is renamed to
<C>IsSemilattice</C>, and <C>IsMonoidAsSemigroup</C> returns true for
semigroups in the category <Ref Filt="IsMonoid" BookName="ref"/>.
<P/>
This way all of the properties of the type <C>IsXAsSemigroup</C> are consistent.
It should be noted that the only methods installed for <C>IsMonoidAsSemigroup</C>
belong to the <Package>Semigroups</Package> and <Package>Smallsemi</Package> packages.
</Item>
<Item>
<C>ReadTest</C> became obsolete and for backwards compatibility is replaced by
<Ref Func="Test" BookName="ref"/> with the option to compare the output up to
whitespaces.
</Item>
<Item>The function `ErrorMayQuit`, which differs from
<Ref Func="Error" BookName="ref"/> by not allowing execution to continue,
has been renamed to <Ref Func="ErrorNoReturn" BookName="ref"/>.
</Item>
</List>

Fixed bugs:

<List>
<Item>
A combination of two bugs could lead to a segfault. First off,
<Ref Func="NullMat" BookName="ref"/> (and various other &GAP; functions),
when asked to produce matrix over a small field, called 
<Ref Func="ConvertToMatrixRep" BookName="ref"/>. 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).
<P/>
Unfortunately, the C code catching this error had a bug and allowed
users to type <Q>return</Q> 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.
<P/>
This, too, has been fixed, by not allowing the user to ignore the error
by entering <Q>return</Q>.
</Item>
<Item>
The Fitting-free code and code inheriting PCGS is now using
<Ref Attr="IndicesEANormalSteps" BookName="ref"/> instead of
<Ref Attr="IndicesNormalSteps" BookName="ref"/>, as these indices are neither
guaranteed, nor required to be maximally refined when restricting to subgroups.
</Item>
<Item>
A bug that caused a break loop in the computation of the Hall subgroup for
groups having a trivial Fitting subgroup.
</Item>
<Item>
Including a <C>break</C> or <C>continue</C> statement in a function body
but not in a loop now gives a syntax error instead of failing at run time.
</Item>
<Item>
<Ref Oper="GroupGeneralMappingByImages" BookName="ref"/> now verifies that
that image of a mapping is contained in its range.
</Item>
<Item>
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.
</Item>
<Item>
Fixed the problem with using Windows default browser as a help viewer using
<C>SetHelpViewer("browser");</C>.
</Item>
</List>

</Subsection>

<Subsection Label="New and updated packages since GAP 4.7.8"> 
<Heading>New and updated packages since &GAP; 4.7.8</Heading>

<Index>Packages, new</Index>
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: 

<List>
<Item>
<Package>CAP</Package> (Categories, Algorithms, Programming) package
by Sebastian Gutsche, Sebastian Posur and Øystein Skartsæterhagen,
together with three associated packages
<Package>GeneralizedMorphismsForCAP</Package>,
<Package>LinearAlgebraForCAP</Package> and
<Package>ModulePresentationsForCAP</Package>
(all three - by Sebastian Gutsche and Sebastian Posur).
</Item>
<Item>
<Package>Digraphs</Package> package by Jan De Beule, Julius Jonušas,
James Mitchell, Michael Torpey and Wilf Wilson, which provides
functionality to work with graphs, digraphs, and multidigraphs.
</Item>
<Item>
<Package>FinInG</Package> package by John Bamberg, Anton Betten,
Philippe Cara, Jan De Beule, Michel Lavrauw and Max Neunhöffer
for computation in Finite Incidence Geometry.
</Item>
<Item>
<Package>HeLP</Package> package by Andreas Bächle and Leo Margolis,
which computes constraints on partial augmentations of torsion units
in integral group rings using a method developed by Luthar, Passi and
Hertweck.  The package can be employed to verify the Zassenhaus
Conjecture and the Prime Graph Question for finite groups, once
their characters are known. It uses an interface to the software
package <Package>4ti2</Package> to solve integral linear inequalities.
</Item>
<Item>
<Package>matgrp</Package> package by Alexander Hulpke, which provides
an interface to the solvable radical functionality for matrix groups,
building on constructive recognition.
</Item>
<Item>
<Package>NormalizInterface</Package> package by Sebastian Gutsche,
Max Horn and Christof Söger, which provides a GAP interface to
<Package>Normaliz</Package>, enabling direct access to the complete
functionality of <Package>Normaliz</Package>, such as computations
in affine monoids, vector configurations, lattice polytopes, and
rational cones.
</Item>
<Item>
<Package>profiling</Package> package by Christopher Jefferson for
transforming profiles produced by <Ref Func="ProfileLineByLine" BookName="ref"/>
and <Ref Func="CoverageLineByLine" BookName="ref"/> into a human-readable form.
</Item>
<Item>
<Package>Utils</Package> package by Sebastian Gutsche, Stefan Kohl and
Christopher Wensley, which provides a collection of utility functions
gleaned from many packages.
</Item>
<Item>
<Package>XModAlg</Package> package by Zekeriya Arvasi and Alper Odabas,
which provides a collection of functions for computing with crossed
modules and Cat1-algebras and morphisms of these structures.
</Item>
</List>

</Subsection>

</Section>


<Section Label="gap483">
<Heading>&GAP; 4.8.3 (March 2016)</Heading>

<Subsection Label="Changes in the core GAP system introduced in GAP 4.8.3">
<Heading>Changes in the core &GAP; system introduced in &GAP; 4.8.3</Heading>

New features:
<List>
<Item>
<!-- #647 -->
New function <Ref Func="TestPackage" BookName="ref"/> to run standard tests
(if available) for a single package in the current &GAP; session (also callable
via <C>make testpackage PKGNAME=pkgname</C> to run package tests in the same
settings that are used for testing &GAP; releases).
</Item>
</List>

Improved and extended functionality:
<List>
<Item>
<!-- #670 -->
<Ref Func="TestDirectory" BookName="ref"/> now prints a special status message
to indicate the outcome of the test (this is convenient for automated testing).
If necessary, this message may be suppressed by using the option
<C>suppressStatusMessage</C>
</Item>
<Item>
<!-- [#655] -->
Improved output of tracing methods (which may be invoked, for example, with
<Ref Func="TraceAllMethods" BookName="ref"/>) by displaying filename and line
number in some more cases.
</Item>
</List>

Changed functionality:
<List>
<Item>
<!-- #615 -->
Fixed some inconsistencies in the usage of
<Ref Prop="IsGeneratorsOfSemigroup" BookName="ref"/>.
</Item>
</List>

Fixed bugs that could lead to incorrect results:
<List>
<Item>
<!-- #626 -->
Fallback methods for conjugacy classes, that were never intended for infinite
groups, now use <Ref Prop="IsFinite" BookName="ref"/> filter to prevent them
being called for infinite groups. [Reported by Gabor Horvath]
</Item>
</List>

Fixed bugs that could lead to break loops:
<List>
<Item>
<!-- #665 -->
Calculating stabiliser for the alternating group caused a break loop in the
case when it defers to the corresponding symmetric group.
</Item>
<Item>
<!-- #663 -->
It was not possible to use <Ref Func="DotFileLatticeSubgroups" BookName="ref"/>
for a trivial group. [Reported by Sergio Siccha]
</Item>
<Item>
<!-- #648 -->
A break loop while computing <Ref Attr="AutomorphismGroup" BookName="ref"/> for
<C>TransitiveGroup(12,269)</C>. [Reported by Ignat Soroko]
</Item>
<Item>
<!-- #622 -->
A break loop while computing conjugacy classes of <C>PSL(6,4)</C>.
[Reported by Martin Macaj]
</Item>
</List>

Other fixed bugs:
<List>
<Item>
<!-- #654 -->
Fix for using Firefox as a default help viewer with
<Ref Func="SetHelpViewer" BookName="ref"/>. [Reported by Tom McDonough]
</Item>
</List>
</Subsection>
</Section>

</Chapter>


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