<!-- %W  introduc.xml    GAP 4 package AtlasRep             Thomas Breuer -->


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<Chapter Label="chap:introduc">
<Heading>Introduction to the &AtlasRep; Package</Heading>

The aim of the &GAP;&nbsp;4 package &AtlasRep; is
to provide a link between &GAP; and databases such as the
&ATLAS; of Group Representations <Cite Key="AGRv3"/>,
which comprises generating permutations and matrices
for many almost simple groups,
and information about their maximal subgroups.
This database is available independent of &GAP; at

<P/>
<URL>&ATLASSERVER;</URL>.
<P/>

The &AtlasRep; package consists of this database
(see Section&nbsp;<Ref Sect="sect:An Atlas of Group Representations"/>)
and a &GAP; interface
(see Section&nbsp;<Ref Sect="sect:The GAP Interface to the Atlas of Group Representations"/>);
the latter is extended by further information available via the internet
(see Section&nbsp;<Ref Sect="sect:Web Contents for the AtlasRep Package"/>).

<P/>

This package manual has the following parts.

<List>
<Mark>A tutorial</Mark>
<Item>
    gives an overview how the functions of the package
    can be used, see Chapter&nbsp;<Ref Chap="chap:tutorial"/>.
</Item>
<Mark>User interface functions</Mark>
<Item>
    are described in
    Chapter&nbsp;<Ref Chap="chap:The User Interface of the AtlasRep Package"/>.
</Item>
<Mark>Customizations of the package</Mark>
<Item>
    are described in Chapter&nbsp;<Ref Chap="chap:atlasrep"/>.
</Item>
<Mark>Information how to extend the database</Mark>
<Item>
    can be found in Chapter&nbsp;<Ref Chap="chap:Private Extensions"/>.
</Item>
<Mark>More technical information</Mark>
<Item>
    can be found in the chapters&nbsp;<Ref Chap="chap:utilities"/>
    (concerning &GAP; objects that are introduced by the package)
    and&nbsp;<Ref Chap="chap:Technicalities of the AtlasRep Package"/>
    (concerning global variables and sanity checks).
</Item>
</List>


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<Section Label="sect:An Atlas of Group Representations">
<Heading>The &ATLAS; of Group Representations</Heading>

The &ATLAS; of Group Representations &nbsp;<Cite Key="AGRv3"/>
consists of matrices over various rings,
permutations, and shell scripts encoding so-called black box programs
<Index>black box program</Index>
(see <Cite Key="Nic06"/>
and Section&nbsp;<Ref Sect="sect:Black Box Programs"/>).
Many of these scripts are straight line programs
<Index>straight line program</Index>
(see&nbsp;<Cite Key="BSW01"/>, <Cite Key="SWW00"/>,
and&nbsp;<Ref Sect="Straight Line Programs" BookName="ref"/>)
and straight line decisions
(see Section&nbsp;<Ref Sect="sect:Straight Line Decisions"/>).
These programs can be used to compute certain elements in a group <M>G</M>
from its standard generators
(see&nbsp;<Cite Key="Wil96"/>
and Section&nbsp;<Ref Sect="sect:Standard Generators Used in AtlasRep"/>)
for example generators of maximal subgroups of <M>G</M>
or representatives of conjugacy classes of <M>G</M>.

<P/>

The &ATLAS; of Group Representations has been prepared by Robert Wilson,
Peter Walsh, Jonathan Tripp, Ibrahim Suleiman, Richard Parker,
Simon Norton, Simon Nickerson, Steve Linton, John Bray, and Rachel Abbott
(in reverse alphabetical order).

<P/>

The information was computed and composed using computer algebra systems
such as &MeatAxe; (see&nbsp;<Cite Key="CMeatAxe"/>),
Magma (see&nbsp;<Cite Key="CP96"/>), and &GAP;
(in reverse alphabetical order).
<Index Key="MeatAxe">&MeatAxe;</Index>
<Index Key="Magma"><Package>Magma</Package></Index>
Part of the constructions have been documented in the literature on
almost simple groups, or the results have been used in such publications,
see for example the bibliographies in&nbsp;<Cite Key="CCN85"/>
and&nbsp;<Cite Key="BN95"/>
which are available online at
<URL>http://www.math.rwth-aachen.de/~Thomas.Breuer/atlasrep/bibl</URL>.

<P/>

If you use the &ATLAS; of Group Representations to solve a problem then
please send a short email to&nbsp;&WILSONMAIL; about it.
The &ATLAS; of Group Representations database should be referenced
with the entry&nbsp;<Cite Key="AGRv3"/> in the bibliography of this manual.

<P/>

If your work made use of functions of the &GAP; interface
(see Section&nbsp;<Ref Sect="sect:The GAP Interface to the Atlas of Group Representations"/>)
then you should also reference this interface,
using the information printed by the &GAP; function
<Ref Func="Cite" BookName="ref"/>.

<P/>

For referencing the &GAP; system in general,
use the entry&nbsp;<Cite Key="GAP"/> in the bibliography of this manual,
see also <URL>http://www.gap-system.org</URL>.

</Section>


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<Section Label="sect:The GAP Interface to the Atlas of Group Representations">
<Heading>The GAP Interface to the &ATLAS; of Group Representations</Heading>

<Index Key="C-MeatAxe"><C>C</C>-&MeatAxe;</Index>
The &GAP; interface to the &ATLAS; of Group Representations consists of
essentially two parts.

<List>
<Item>
  First, there is the <E>user interface</E>
  which allows the user to get an overview of the contents of the database,
  and to access the data in &GAP; format;
  this is described in
  Chapter&nbsp;<Ref Chap="chap:The User Interface of the AtlasRep Package"/>.
  Advanced users may add their own data to the database,
  this is described in Chapter&nbsp;<Ref Chap="chap:Private Extensions"/>.
</Item>
<Item>
  Second, there is <E>administrational information</E>,
  which covers also the declaration of &GAP; objects
  such as straight line decisions and black box programs.
  This is important mainly for users interested in the actual implementation
  (e.&nbsp;g., for modifying the package) or in using it together with the
  <C>C</C>-&MeatAxe; standalone (see&nbsp;<Cite Key="CMeatAxe"/>);
  this is described in
  Chapter&nbsp;<Ref Chap="chap:Technicalities of the AtlasRep Package"/>.
</Item>
</List>

Information concerning the <C>C</C>-&MeatAxe;,
including the manual&nbsp;<Cite Key="CMeatAxe"/>,
can be found at

<P/>
<URL>http://www.math.rwth-aachen.de/~MTX</URL>
<P/>

The interface and this manual have been provided by Thomas Breuer,
except for the interpreter for black box programs
(see Section&nbsp;<Ref Sect="sect:Black Box Programs"/>),
which is due to Simon Nickerson.
Comments, bug reports, and hints for improving the interface
can be sent to&nbsp;<Email>sam@math.rwth-aachen.de</Email>.
<!-- There is a reference to this statement in Chapter
     ``chap:The User Interface of the AtlasRep Package''. -->

</Section>


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<Section Label="sect:What's New in AtlasRep?">
<Heading>What's New in &AtlasRep;, Compared to Older Versions?</Heading>

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<Subsection Label="sect:What's New in Version 2.1.9?">
<Heading>What's New in Version &VERSIONNUMBER;?
(&RELEASEMONTH; &RELEASEYEAR;)</Heading>

<List>
<Item>
  Now prescribing a ring in <Ref Func="AllAtlasGeneratingSetInfos"/>
  and related functions automatically prescribes its characteristic.
  Up to now, one had to specify also the characteristic,
  otherwise characteristic zero was erroneously assumed.
</Item>
<Item>
  Up to now, <Ref Func="AllAtlasGeneratingSetInfos"/>
  and related functions, when called only with a prescribed ring
  in positive characteristic, could erroneously return also entries about
  representations in characteristic zero.
</Item>
<Item>
  The default for the user preference <C>"AtlasRepDataDirectory"</C>
  (see Section <Ref Subsect="subsect:AtlasRepDataDirectory"/>)
  has been improved in the situation where the package directory is not
  writable <E>and</E> the &GAP; session runs inside a &Julia; session;
  if this is the case then a &Julia; scratchspace is used as the default.
</Item>
<Item>
  The star <C>*</C> that may appear in some lines of the output of
  <Ref Func="DisplayAtlasInfo"/> is now documented.
  Thanks to Will Chen for reporting that an explanation for it was missing.
</Item>
</List>

</Subsection>


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<Subsection Label="sect:What's New in Version 2.1.8?">
<Heading>What's New in Version 2.1.8? (January 2024)</Heading>

An example in Section <Ref Subsect="sect:tutmaxes"/> of the Tutorial
had to be adjusted because the results of the function
<Ref Func="SmallerDegreePermutationRepresentation" BookName="ref"/>
depend on random computations,
in particular the implementation in &GAP; 4.13 may yield a nicer
representation than had been shown before.

</Subsection>


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<Subsection Label="sect:What's New in Version 2.1.7?">
<Heading>What's New in Version 2.1.7? (August 2023)</Heading>

<List>
<Item>
  Requesting certain matrix groups in characteristic zero had caused
  an error in version 2.1.6,
  provided that the feature to store downloaded files was disabled,
  that is, the value of the user preference <C>"AtlasRepDataDirectory"</C>
  (see Section <Ref Subsect="subsect:AtlasRepDataDirectory"/>) was an empty
  string.
  This bug is now fixed.
  Thanks to Lixin Zheng for reporting this problem.
</Item>
<Item>
  The name of a maximal subgroup of the group <M>M_{12}.2</M> had to be
  changed from <C>"D8.(S4x2)"</C> to <C>"2^3.(S4×2)"</C> because the old name
  suggested a wrong group structure.
  This bug had been announced in
  <URL><LinkText>a StackExchange discussion</LinkText>
  <Link>https://math.stackexchange.com/questions/4577016/group-names-in-gap-character-table-library</Link></URL>.
</Item>
<Item>
  A typo in the documentation of <C>AGR.MXS</C>
  (see Section <Ref Sect="sect:The Tables of Contents of the AGR"/>)
  was fixed.
  Thanks to Max Horn for spotting this.
</Item>
<Item>
  &GAP; 4.13 will provide the new <Q>package extension</Q> feature,
  which allows a package to execute &GAP; code <E>after</E> the package
  and some other required packages have been loaded.
  In &AtlasRep;, this feature is now used for example in order to achieve
  that those functions which depend on the <Package>Browse</Package>
  package can be used also if this package gets (installed and) loaded
  after &AtlasRep; has been loaded.
</Item>
<Item>
  The code for building the documentation of the package has been adjusted to
  <URL><LinkText>a change in &GAP; 4.13</LinkText>
  <Link>https://github.com/gap-system/gap/pull/5178</Link></URL>.
  This does not affect most users of the package because the package archive
  contains a ready documentation.
  <!-- The point is to get correct cross-references to other packages
       in more situations. -->
</Item>
</List>

</Subsection>


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<Subsection Label="sect:What's New in Version 2.1.6?">
<Heading>What's New in Version 2.1.6? (October 2022)</Heading>

The package now requires the <Package>utils</Package> package
<Cite Key="utils"/>,
and uses its <Ref Func="Download" BookName="utils"/> function
for downloading remote files.
The former user preference <C>FileTransferTool</C> of the &AtlasRep; package
is no longer supported;
it had been used in older versions to distinguish between different
download tools.

<P/>

A method for <Ref Attr="ConjugacyClasses" BookName="ref"/> has been added
that uses a straight line program for computing class representatives
of a group that has been created with
<Ref Func="AtlasGroup" Label="for various arguments"/>,
provided such a program is available.
Thanks to Frank Lübeck for suggesting this.

</Subsection>


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<Subsection Label="sect:What's New in Version 2.1.5?">
<Heading>What's New in Version 2.1.5? (August 2022)</Heading>

Two bugs concerning local file permissions and the handling of
download failures were fixed.
Thanks to Frank Lübeck and Fabian Zickgraf for reporting these problems.

</Subsection>


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<Subsection Label="sect:What's New in Version 2.1.4?">
<Heading>What's New in Version 2.1.4? (August 2022)</Heading>

A few changes in the code for downloading files were needed
in order to make some CI tests happy.

</Subsection>


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<Subsection Label="sect:What's New in Version 2.1.3?">
<Heading>What's New in Version 2.1.3? (August 2022)</Heading>

The server address for the core part of the database has changed.

<P/>

Additional table of contents files are now available,
which contain checksums in SHA256 format instead of the checksums
computed by <Ref Func="CrcFile" BookName="ref"/> and
<Ref Func="CrcString" BookName="ref"/>.
Note that the latter values can be interpreted only by &GAP;.

<P/>

For <M>364</M> representations, the corresponding characters have been
identified and can thus be used for accessing these representations
with <Ref Func="OneAtlasGeneratingSetInfo"/>,
see <Ref Func="DisplayAtlasInfo"/>.

</Subsection>


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<Subsection Label="sect:What's New in Version 2.1.2?">
<Heading>What's New in Version 2.1.2? (March 2022)</Heading>

Not much.

<P/>

The release of Version&nbsp;2.1.2 was necessary for technical reasons:
Now the testfile mentioned in <F>PackageInfo.g</F> exits &GAP; in the end,
and the external links in the package documentation were corrected
(the links in version&nbsp;2.1.1 pointed to a wrong directory).

</Subsection>


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<Subsection Label="sect:What's New in Version 2.1.1?">
<Heading>What's New in Version 2.1.1? (February 2022)</Heading>

<List>
<Item>
  The new function <Ref Oper="EvaluatePresentation"
  Label="for a group, a group name (and a number)"/> computes
  the images of the relators of a presentation
  (see Section <Ref Subsect="Semi-Presentations and Presentations"/>).
</Item>
<Item>
  The new function <Ref Oper="StandardGeneratorsData"
  Label="for a group, a group name (and a number)"/> allows one
  to compute standard generators from given generators,
  provided a recipe for that task (a <Q>find</Q> straight line program)
  for the group in question is available.
</Item>
<Item>
  The function <Ref Oper="AtlasGroup" Label="for various arguments"/>
  sets known information about the group and the representation,
  such as <Ref BookName="ref" Prop="IsPrimitive"/>.
  <P/>
  (Thanks to Steve Linton for suggesting this feature.)
</Item>
<Item>
  The function <Ref Func="ResultOfBBoxProgram"/> now admits an optional
  argument,
  which is used as options record in calls to <Ref Func="RunBBoxProgram"/>.
</Item>
<Item>
  The new user preference <C>"AtlasRepJsonFilesAddresses"</C>
  (see Section <Ref Subsect="subsect:AtlasRepJsonFilesAddresses"/>)
  allows one to use Json format data files for matrix representations
  in characteristic zero,
  which in turn makes it possible to create the matrices over
  prescribed fields, for example fields returned by
  <Ref Func="AlgebraicExtension" BookName="ref"/>.
  The information stored in the table of contents file about the field of
  entries of the matrix representations has been extended by
  a &GAP; independent description of this field and the defining polynomial
  used in the Json format data files.
</Item>
<Item>
  When the value of the user preference <C>"AtlasRepDataDirectory"</C>
  is an empty string then data files that are fetched from remote servers
  are read into the &GAP; session without storing the files.
  (An advantage is that one need not care about where one has permissions
  for storing files. A disadvantage is of course that one has to fetch
  a file again whenever it is needed.)
</Item>
</List>

</Subsection>


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<Subsection Label="sect:What's New in Version 2.1.0?">
<Heading>What's New in Version 2.1.0? (May 2019)</Heading>

The main differences to earlier versions concern extensions of the
available data.
Up to now, such extensions were possible only in the sense that one could
notify certain <E>locally available files</E> to the package's functions.
With this version,
it becomes possible to notify also <E>remote data files</E>,
i. e., data files which have to be downloaded before they can be read
into &GAP;,
in the same way as the data from the &ATLAS; of Group Representations.
Two extensions of this kind become automatically available
with this package version,
see Section <Ref Sect="sect:Adding a Private Data Directory"/> for details.

<P/>

Thus the focus of the package has changed.
In earlier versions, it provided a &GAP; interface to the data in the
&ATLAS; of Group Representations,
whereas now this database is regarded as one collection (the <Q>core part</Q>)
among others.
Where applicable,
the package manual tries to distinguish between general data available to
the &AtlasRep; functions and the data from the
&ATLAS; of Group Representations.

<P/>

In order to provide this new functionality,
the following changes have been implemented.
Note that some are <E>incompatible changes</E>,
compared with earlier versions of the package.

<P/>

<List>
<Item>
  The format of the <C>identifier</C> components of the records returned by
  <Ref Func="AtlasGenerators"/>, <Ref Func="AtlasProgram"/>, etc.,
  has been changed for those data that belong to extensions,
  see <Ref Sect="sect:identifier component"/>.
  In the new format, the name of the extension is not added to the
  group name but to the individual filenames;
  this allows for example the combination of files from the core database
  and from extensions in one identifier.
  Functions for converting between the old and the new format are available,
  see <Ref Func="AtlasRepIdentifier"
  Label="convert an old type identifier to a new type one"/>.
</Item>
<Item>
  The records returned by <Ref Func="AtlasGenerators"/> etc.
  contain also a component <C>contents</C>,
  with value the identifier of the part of the database to shich the
  generators belong.
</Item>
<Item>
  The tables of contents of the &ATLAS; of Group Representations and
  of extensions are no longer stored in the form of sequences of
  calls to &GAP; functions.
  Instead, each table of contents is defined via a JSON format file,
  see <Ref Sect="sect:JSON"/>.
  In particular, the file <F>atlasprm.json</F> replaces the former
  <F>gap/atlasprm.g</F>.
  <P/>
  Two advantages of this change are that there is no danger to call
  unwanted &GAP; functions when such files (which are expected to be
  available in the world wide web) get evaluated,
  and that the information is independent of &GAP;
  &ndash;note that &MeatAxe; format files and straight line programs
  can be used by other program systems as well.
</Item>
<Item>
  The functions <C>ReloadAtlasTableOfContents</C>,
  <C>StoreAtlasTableOfContents</C>, and
  <C>ReplaceAtlasTableOfContents</C> are no longer available.
  They had been intended for updating the table of contents of the
  &ATLAS; of Group Representations, but it has turned out that this was
  in fact not useful.
</Item>
</List>

The second major change concerns the handling of user parameters.

<List>
<Item>
  &GAP;'s general <E>user preferences</E> mechanism
  (see <Ref Func="SetUserPreference" BookName="ref"/>)
  has been used since version 1.5.1 of the package for dealing with certain
  customizations of &AtlasRep;'s behaviour,
  concerning the paths of data directories and two issues with 
  &MeatAxe; format files.
  <P/>
  Now this mechanism is used in more cases,
  see Section <Ref Sect="sect:atlasrep user preferences"/> for an overview.
  The new user preferences replace certain components of the record
  <Ref Var="AtlasOfGroupRepresentationsInfo"/>
  that were recommended in earlier versions of the package.
  These components are currently still available but are no longer used
  by the package's functions.
  Also the global variable <C>ATLASREP_TOCFILE</C> is no longer supported,
  use the user preference <C>AtlasRepTOCData</C> instead,
  see Section <Ref Subsect="subsect:AtlasRepTOCData"/>.
  Analogously, use the user preference <C>HowToReadMeatAxeTextFiles</C>
  instead of the no longer available <C>CMeatAxe.FastRead</C>.
  <P/>
  The switch to user preferences is an <E>incompatible change</E> if you
  are used to change the values of these components in your code,
  for example in your <F>gaprc</F> file,
  see&nbsp;<Ref Sect="The gap.ini and gaprc files" BookName="ref"/>.
  All assignments to these components should be changed to calls of
  <Ref Func="SetUserPreference" BookName="ref"/>.
  <P/>
  Another consequence of this change is that the former
  function <C>AtlasOfGroupRepresentationsUserParameters</C> of the package
  is no longer supported,
  use <Ref Func="ShowUserPreferences" BookName="ref"/>
  or <Ref Func="BrowseUserPreferences" BookName="Browse"/>
  with argument <C>"AtlasRep"</C> instead.
</Item>
</List>

Finally, the following improvements have been added.

<List>
<Item>
  Straight line programs for computing generators of normal subgroups
  can now be fetched with <Ref Func="AtlasProgram"/>,
  using the argument <C>"kernel"</C>.
  The available programs of this type are shown in the
  <Ref Func="DisplayAtlasInfo"/> overview for a group.
  More than <M>200</M> such programs are available in a new data directory
  <F>datapkg</F> of the package.
  If fact, this collection of files is part of an extension of the
  database that is distributed together with the package.
  <P/>
  In earlier versions of the package, this kind of information had been
  available only implicitly; it had been stored via <C>AGR.KERPRG</C>,
  which is not supported anymore.
</Item>
<Item>
  <Ref Func="AtlasProgram"/> supports more variants of arguments:
  <C>"contents"</C> can be used to list the available data extensions,
  <C>"contents"</C> and <C>"version"</C> can be used to restrict the
  data under consideration,
  and one can request a program for computing <E>standard</E> generators
  of some maximal subgroup, not just generators (provided that this
  information is available).
  <P/>
  The information about the version of straight line programs is shown by
  <Ref Func="DisplayAtlasInfo"/>, as well as the availability of straight
  line programs for computing standard generators of maximal subgroups.
  <P/>
  Making this information more explicit has the side-effect that the
  access to the &AtlasRep; data with
  <Ref Func="BrowseAtlasInfo" BookName="Browse"/> is both safer and simpler,
  if at least version&nbsp;1.8.6 of the <Package>Browse</Package> package
  is available.
  (For that, the function <C>AGR.InfoPrgs</C> has been extended
  such that also the <C>identifier</C> records are included in the result.)
</Item>
<Item>
  Straight line programs for computing <E>standard</E> generators
  of a maximal subgroup, if available,
  can now be fetched with <Ref Func="AtlasProgram"/>,
  using the argument <C>"maxstd"</C>.
</Item>
<Item>
  The function <Ref Attr="AtlasRepInfoRecord" Label="for a string"/>
  now admits a group name as its argument, and then returns information
  about the group and its maximal subgroups;
  this information had been used before by <Ref Func="DisplayAtlasInfo"/>,
  but it had not been programmatically accessible.
</Item>
<Item>
  The sanity checks for the data
  (see Section&nbsp;<Ref Sect="sect:AGR Sanity Checks"/>)
  have been extended, in particular they can be applied also to
  data extensions.
  To some extent, these checks can be used also to derive new information;
  the code for that should be regarded as heuristic and experimental,
  runtimes and space requirements may be large,
  depending on the new data to be examined.
</Item>
<Item>
  Different header formats are now supported when reading and writing
  &MeatAxe; format files,
  see Section <Ref Subsect="subsect:WriteHeaderFormatOfMeatAxeFiles"/>,
  and one can set a global default for the creation of mode 2 &MeatAxe; files,
  see Section <Ref Subsect="subsect:WriteMeatAxeFilesOfMode2"/>.
</Item>
<Item>
  The function <Ref Func="MeatAxeString"/> admits also an integer matrix
  as argument.
</Item>
<Item>
  The function <Ref Func="CMtxBinaryFFMatOrPerm"/> admits an optional
  argument <A>base</A>, in order to write &MeatAxe; format files that
  contain either zero based or one based permutations.
</Item>
<Item>
  The meaningless lines about <M>p</M>-modular representations of
  groups with nontrivial <M>p</M>-core have been removed from the file
  <F>gap/mindeg.g</F>.
</Item>
</List>

</Subsection>


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<Subsection Label="sect:What's New in Version 1.5.1?">
<Heading>What's New in Version 1.5.1? (March 2016)</Heading>

<List>
<Item>
  The paths of the directories where downloaded data files get stored
  are now customizable,
  see Section <Ref Subsect="subsect:AtlasRepDataDirectory"/>.
  Up to now, the data were stored in subdirectories of the package directory,
  which might cause problems with write permissions, depending on the
  installation of the package.
  (Note that choosing other data directories can be useful also in order to
  keep existing local data files when a new version of &GAP;
  or of the &AtlasRep; package gets installed.)
  Thanks to Bill Allombert for pointing out this problem.
</Item>
<Item>
  The information about data files from the &ATLAS; of Group Representations
  has been extended by <Ref Func="CrcFile" BookName="ref"/> values.
  These values are checked whenever data from such a file are read,
  and an error is signalled if the checksum does not fit to the expected one.
  Note that several users may access the same data files,
  and a user should not suffer from perhaps corrupted files that have been
  downloaded by other users.
  Thanks to Frank Lübeck for the idea to introduce this consistency test.
</Item>
<Item>
  Whenever <Ref Func="StringFile" BookName="gapdoc"/> is called by functions
  of the package, this happens in the wrapper function <C>AGR.StringFile</C>,
  in order to replace occasional line breaks of the form <C>"\r\n"</C>
  by <C>"\n"</C>.
  Apparently it may happen that the <C>"\r"</C> is silently smuggled in
  when data files get copied to the local computer.
  Thanks to Marek Mitros for help with detecting and fixing this problem.
</Item>
<Item>
  The function <Ref Func="FFMatOrPermCMtxBinary"/> can now read also
  permutations stored in binary files that have been created with
  version 2.4 of the C-&MeatAxe;;
  note that this format is different from the one that is written by
  version 2.3.
  Conversely, <Ref Func="CMtxBinaryFFMatOrPerm"/> has been generalized
  such that both formats can be written.
  The reference to the C-&MeatAxe; documentation now points to that
  of version 2.4.
  Thanks to Jürgen Müller for pointing out this problem.
</Item>
<Item>
  The function <Ref Func="MeatAxeString"/> can now encode
  permutation matrices in different ways.
  The mode (the first header entry) can be either 2 (then the positions of
  the nonzero entries are listed) or 1 or 6 (then all entries of the matrix
  are listed).
  In previous versions, the function produced a matrix of mode 2
  whenever this was possible, but this behaviour is not useful if the result
  is not processed by the C-&MeatAxe;.
  Thanks to Klaus Lux for pointing out this problem.
</Item>
<Item>
  Depending on the terminal capabilities and the user preference
  <C>DisplayFunction</C> (see <Ref Subsect="subsect:DisplayFunction"/>),
  some non-ASCII characters may appear in the output shown by
  <Ref Func="DisplayAtlasInfo"/>.
</Item>
</List>

</Subsection>


<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
<Subsection Label="sect:What's New in Version 1.5?">
<Heading>What's New in Version 1.5? (July 2011)</Heading>

<List>
<Item>
  The function
  <Ref Func="AtlasSubgroup"
   Label="for a group name (and various arguments) and a number"/>
  now admits also the return value
  of <Ref Func="OneAtlasGeneratingSetInfo"/> or the return value of
  <Ref Func="AtlasGroup" Label="for various arguments"/> as its first
  argument.
  The latter is implemented via the new attribute
  <Ref Attr="AtlasRepInfoRecord" Label="for a group"/>,
  which is set in the groups constructed
  by <Ref Func="AtlasGroup" Label="for various arguments"/>.
</Item>
<Item>
  Information about transitivity, rank, primitivity, and point stabilizers
  of many permutation representations is now available.
  If applicable then this information appears in the records returned by
  <Ref Func="OneAtlasGeneratingSetInfo"/>,
  it is part of the overview shown by <Ref Func="DisplayAtlasInfo"/>,
  and it is shown also in the data overview in the web,
  see Section <Ref Sect="sect:Web Contents for the AtlasRep Package"/>.
  <P/>
  Two new manual sections about point stabilizers have been added,
  see the sections
  <Ref Subsect="subsect:Example: Index 770 Subgroups in M22"/>
  and <Ref Subsect="subsect:Example: Index 462 Subgroups in M22"/>.
</Item>
<Item>
  Information about the characters afforded by many matrix and permutation
  representations is now available.
  If applicable then this information appears in the records returned by
  <Ref Func="OneAtlasGeneratingSetInfo"/>,
  for matrix representations it is part of the overview shown by
  <Ref Func="DisplayAtlasInfo"/>,
  and it is shown also in the data overview in the web,
  see Section <Ref Sect="sect:Web Contents for the AtlasRep Package"/>.
</Item>
<Item>
  The functions <Ref Func="Character"
  Label="for a character table and a list" BookName="ref"/>,
  <Ref Func="Identifier" Label="for character tables" BookName="ref"/>,
  <Ref Func="IsPrimitive" BookName="ref"/>,
  <Ref Func="IsTransitive" BookName="ref"/>,
  <Ref Func="Transitivity" BookName="ref"/>, and
  <Ref Func="RankAction" BookName="ref"/>
  are now supported as input conditions in
  <Ref Func="DisplayAtlasInfo"/> and
  <Ref Func="OneAtlasGeneratingSetInfo"/>.
</Item>
<Item>
  It is now possible to restrict the data shown by
  <Ref Func="DisplayAtlasInfo"/> or returned by
  <Ref Func="OneAtlasGeneratingSetInfo"/> to private or non-private data.
</Item>
<Item>
  A tutorial for beginners was added to the manual,
  see Chapter <Ref Chap="chap:tutorial"/>,
  and the manual was restructured.
</Item>
<Item>
  In the overview shown by <Ref Func="DisplayAtlasInfo"/>
  and in the data overview in the web
  (see Section <Ref Sect="sect:Web Contents for the AtlasRep Package"/>),
  the ordering of groups was improved such that, e.g.,
  <C>"A9"</C> precedes <C>"A10"</C>.
</Item>
<Item>
  The function <Ref Func="AtlasClassNames"/> now admits also a Brauer table
  as its argument, and works also for character tables of bicyclic extensions
  of simple groups.
</Item>
<Item>
  The group names that are entered in <Ref Func="DisplayAtlasInfo"/>,
  <Ref Func="OneAtlasGeneratingSetInfo"/>, etc., are now case insensitive,
  and if the package <Package>CTblLib</Package> is available then the
  admissible group names for the &GAP; character table of the group in
  question can be used in these functions.
</Item>
<Item>
  In order to reduce the number of global variables, several functions
  have been turned into components of the new global variable
  <Ref Var="AGR"/>.
  A few of these functions had been documented in the previous version,
  the old values are still available if the package files
  <F>gap/obsolete.gd</F> and <F>gap/obsolete.gi</F> have been read.
  These files are read automatically if &GAP;'s user preference
  <C>"ReadObsolete"</C> is <K>true</K> when the package gets loaded,
  see <Ref Subsect="The gap.ini file" BookName="ref"/>.
</Item>
<Item>
  A few nicer characters are used by <Ref Func="DisplayAtlasInfo"/>
  if <C>GAPInfo.TermEncoding</C> has the value <C>"UTF-8"</C> and if
  <Ref Func="Print" BookName="ref"/> is not the display function to be used,
  see Section&nbsp;<Ref Subsect="subsect:DisplayFunction"/>.
</Item>
<Item>
  A bug in the function <C>ReloadAtlasTableOfContents</C> was fixed.
  Thanks to Jack Schmidt for reporting this bug.
</Item>
</List>

</Subsection>


<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
<Subsection Label="sect:What's New in Version 1.4?">
<Heading>What's New in Version 1.4? (June 2008)</Heading>

<List>
<Item>
  In addition to the group orders that were added in version 1.3
  (see Section <Ref Sect="sect:What's New in Version 1.3?"/>),
  also many orders of maximal subgroups are now available.
  These values occur in the records returned by <Ref Func="AtlasProgram"/>
  (for the case of <C>"maxes"</C> type programs)
  and of the three argument version of <Ref Func="AtlasGenerators"/>;
  now a <C>size</C> component may be bound.
  In these cases, the groups returned by
  <Ref Func="AtlasSubgroup" Label="for a group name (and various arguments) and a number"/>
  have the <Ref Attr="Size" BookName="ref"/> attribute set.
</Item>
<Item>
  The information about the number of maximal subgroups, if available,
  is now used in <Ref Func="DisplayAtlasInfo"/>.
</Item>
<Item>
  In many cases, straight line programs for computing generators of maximal
  subgroups of a group <M>G</M>, say, can in fact be used to compute also
  generators of maximal subgroups of downward extensions of <M>G</M>;
  if not then it may suffice to extend the given straight line programs by
  additional generators.
  <P/>
  Currently this yields more than <M>200</M> new possibilities to compute
  maximal subgroups, this means a growth by about <M>25</M> percent.
  For example, all maximal subgroups of <M>12.M_{22}</M> and <M>2.Fi_{22}</M>
  can now be accessed via <Ref Func="AtlasGenerators"/>.
  <P/>
  (Of course this extension means only that one can access the straight
  line programs in question automatically via the &GAP; interface.
  In principle one could have used them already before, by explicitly
  applying a straight line program for a factor group to generators of a
  group, and perhaps adding some element in the kernel of the natural
  epimorphism.)
  <P/>
  For this feature,
  information about the compatibility of standard generators of groups and
  their factor groups was added.
</Item>
<Item>
  The bibliographies contained in the &ATLAS; of Finite Groups
  <Cite Key="CCN85"/> and in the &ATLAS; of Brauer Characters
  <Cite Key="JLPW95"/> are now available
  as HTML files, as BibXMLext files, and within &GAP;,
  see <Ref Func="BrowseBibliographySporadicSimple"/>.
</Item>
<Item>
  <!-- changed handling of minimal degrees! -->
  If the &GAP; package <Package>Browse</Package>
  (see <Cite Key="Browse"/>) is loaded then the new functions
  <Ref Func="BrowseMinimalDegrees"/> and
  <Ref Func="BrowseBibliographySporadicSimple"/> are available;
  these functions can be called also by choosing the
  corresponding menu entries of the <Package>Browse</Package> application
  <Ref Func="BrowseGapData" BookName="Browse"/>.
</Item>
<Item>
  The function <Ref Func="AtlasGroup" Label="for various arguments"/>
  now admits also the return value of
  <Ref Func="OneAtlasGeneratingSetInfo"/> as its argument.
</Item>
</List>

</Subsection>


<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
<Subsection Label="sect:What's New in Version 1.3.1?">
<Heading>What's New in Version 1.3.1? (October 2007)</Heading>

This version was mainly released in order to fix a few problems.
Now one does not get warnings about unbound variables
when the package is loaded
and the &GAP; package <Package>IO</Package> <Cite Key="IO"/>
is not available,
and pathological situations in <Ref Func="FFMatOrPermCMtxBinary"/>
(concerning extremely short corrupted data files and different
byte orderings in binary files) are handled more carefully.

<P/>

Besides this, the two functions
<Ref Func="AtlasGroup" Label="for various arguments"/> and
<Ref Func="AtlasSubgroup" Label="for a group name (and various arguments) and a number"/> were introduced,
and the extended function <Ref Func="QuaternionAlgebra" BookName="ref"/>
of &GAP;&nbsp;4.4.10 can now be used for describing base rings in
<Ref Func="OneAtlasGeneratingSetInfo"/> and
<Ref Func="AllAtlasGeneratingSetInfos"/>.
(This is the reason why this version of the package requires at least
version 4.4.10 of &GAP;.)

</Subsection>


<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
<Subsection Label="sect:What's New in Version 1.3?">
<Heading>What's New in Version 1.3? (June 2007)</Heading>

<List>
<Item>
  The database was extended, see
  Section&nbsp;<Ref Subsect="subsect:CompressDownloadedMeatAxeFiles"/>
  for the number and size of files.
</Item>
<Item>
  New data types and corresponding &GAP; objects have been introduced,
  for representing semi-presentations, presentations,
  and programs for finding standard generators.
  For details, see
  <Ref Func="AtlasProgram"/>,
  Chapter&nbsp;<Ref Chap="chap:utilities"/>, and
  Section&nbsp;<Ref Sect="sect:Filenames Used in the AGR"/>.
</Item>
<Item>
  The records returned by the functions <Ref Func="AtlasGenerators"/>,
  <Ref Func="OneAtlasGeneratingSetInfo"/>, and
  <Ref Func="AllAtlasGeneratingSetInfos"/>
  now contain the name and (if known) the order of the group in question,
  and also components describing the degree in the case of permutation
  representations
  or the dimension and the base ring of the natural module in the case of
  matrix representations.
</Item>
<Item>
  For many of the groups, information about the minimal degree of faithful
  permutation representations and the minimal dimensions of faithful matrix
  representations in various characteristics is available for
  <Ref Func="DisplayAtlasInfo"/>,
  <Ref Func="OneAtlasGeneratingSetInfo"/>, and
  <Ref Func="AllAtlasGeneratingSetInfos"/>,
  see also Section <Ref Sect="sect:Representations of Minimal Degree"/>.
  For these functions,
  also properties such as <Ref Func="IsPrimeInt" BookName="ref"/> can be used
  to describe the intended restriction of the output.
</Item>
<Item>
  One can now use <Ref Func="Pager" BookName="ref"/> functionality
  in <Ref Func="DisplayAtlasInfo"/>,
  see Section&nbsp;<Ref Subsect="subsect:DisplayFunction"/>.

  <P/>

  An interactive alternative to <Ref Func="DisplayAtlasInfo"/> is provided by
  the function <Ref Func="BrowseAtlasInfo" BookName="Browse"/> from the
  new (recommended) &GAP; package <Package>Browse</Package>
  (see <Cite Key="Browse"/>).
</Item>
<Item>
  The functions <Ref Func="OneAtlasGeneratingSetInfo"/> and
  <Ref Func="AllAtlasGeneratingSetInfos"/> now admit also
  a list of group names as the first argument.
</Item>
<Item>
  The functions for actually accessing the data are more flexible now, see
  Section&nbsp;<Ref Subsect="sect:How to Customize the Access to Data files"/>.
</Item>
<Item>
  For transferring remote data,
  the &GAP; package <Package>IO</Package> (see <Cite Key="IO"/>)
  can now be used (and is recommended) as an alternative to <F>wget</F>.
  <Index Key="wget"><F>wget</F></Index>
</Item>
<Item>
  The address of the data server has changed.
  <Index Key="ftp"><F>ftp</F></Index>
  The access to the server is no longer possible via <F>ftp</F>,
  thus the mechanism used up to version 1.2, which was based on <F>ftp</F>,
  had to be rewritten.

  <P/>

  The main consequence of this change is that information about updates
  of the table of contents is now provided at the package's homepage.
  This means that on the one hand,
  now package users cannot <E>compute</E> the table of contents directly
  from the server data,
  but on the other hand the update information can be <E>downloaded</E>
  without the necessity to install <F>perl</F>.
  <Index Key="perl"><F>perl</F></Index>

  <P/>

  Another consequence is that the system program <F>ls</F> is no longer
  needed,
  see Section&nbsp;<Ref Subsect="sect:What's New in Version 1.1?"/>.
</Item>
<Item>
  The package manual has been restructured, extended and improved.
  It is now based on the package &GAPDoc; (see <Cite Key="GAPDoc"/>).
</Item>
</List>

</Subsection>


<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
<Subsection Label="sect:What's New in Version 1.2?">
<Heading>What's New in Version 1.2? (November 2003)</Heading>

Not much.

<P/>

The release of Version&nbsp;1.2 became necessary first of all
in order to provide a package version that is compatible with &GAP;&nbsp;4.4,
since some cross-references into the &GAP; Reference Manual were broken
due to changes of section names.
Additionally, several web addresses concerning the package itself
were changed and thus had to be adjusted.

<P/>

This opportunity was used
<List>
<Item>
    to upgrade the administrational part for
    loading the package to the mechanism that is recommended
    for &GAP;&nbsp;4.4,
</Item>
<Item>
    to extend the test suite,
    which now covers more consistency checks using
    the &GAP; Character Table Library (see <Cite Key="CTblLib"/>),
</Item>
<Item>
    to make the function <Ref Func="ScanMeatAxeFile"/> more robust,
    due to the fact that the &GAP; function
    <Ref Func="PermList" BookName="ref"/> now
    returns <K>fail</K> instead of raising an error,
</Item>
<Item>
    to change the way how representations with prescribed properties are
    accessed (the new function <Ref Func="OneAtlasGeneratingSetInfo"/> is now
    preferred to the former <C>OneAtlasGeneratingSet</C>,
    and <Ref Func="AllAtlasGeneratingSetInfos"/>
    has been added in order to provide programmatic access in parallel to the
    human readable descriptions printed by <Ref Func="DisplayAtlasInfo"/>),
</Item>
<Item>
    and last but not least to include the current table of contents of the
    underlying database.
</Item>
</List>

<P/>

For &AtlasRep; users, the new feature of &GAP;&nbsp;4.4 is particularly
interesting that due to better kernel support, reading large matrices
over finite fields is now faster than it was in &GAP;&nbsp;4.3.

</Subsection>


<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
<Subsection Label="sect:What's New in Version 1.1?">
<Heading>What's New in Version 1.1? (October 2002)</Heading>

The biggest change w.&nbsp;r.&nbsp;t.&nbsp;Version&nbsp;1.1 is the addition
of private extensions
(see Chapter&nbsp;<Ref Chap="chap:Private Extensions"/>).
It includes a new <Q>free format</Q> for straight line programs
(see Section&nbsp;<Ref Sect="sect:Effect of Private Extensions"/>).
Unfortunately, this feature requires the system program <F>ls</F>,
so it may be not available for example under MS Windows operating systems.
[But see Section&nbsp;<Ref Subsect="sect:What's New in Version 1.3?"/>.]

<P/>

In order to admit the addition of other types of data,
the implementation of several functions has been changed.
Data types are described in
Section&nbsp;<Ref Sect="sect:Data Types Used in the AGR"/>.
An example of a new data type are quaternionic representations
(see Section&nbsp;<Ref Sect="sect:Filenames Used in the AGR"/>).
The user interface itself
(see Chapter&nbsp;<Ref Chap="chap:The User Interface of the AtlasRep Package"/>)
remained the same.

<P/>

<Index Key="wget"><F>wget</F></Index>
As an alternative to <C>perl</C>, one can use <C>wget</C> now
for transferring data files
(see&nbsp;<Ref Sect="sect:atlasrep user preferences"/>).

<P/>

Data files can be read much more efficiently in &GAP;&nbsp;4.3 than in
&GAP;&nbsp;4.2.
In Version&nbsp;1.1 of the &AtlasRep; package,
this feature is used for reading
matrices and permutations in &MeatAxe; text format with
<Ref Func="ScanMeatAxeFile"/>.
As a consequence, (at least) &GAP;&nbsp;4.3 is required for
&AtlasRep; Version&nbsp;1.1.

<P/>

<Index Key="gzip"><F>gzip</F></Index>
The new <C>compress</C> component of the global variable
<Ref Var="AtlasOfGroupRepresentationsInfo"/>
allows one to store data files automatically in <F>gzip</F>ped form.

<P/>

For matrix representations in characteristic zero, invariant forms and
generators for the centralizer algebra are now accessible in &GAP; if they
are contained in the source files
&ndash;this information had been ignored in Version&nbsp;1.0.
<!-- (see&nbsp;<Ref
Func="AtlasOfGroupRepresentationsTestTableOfContentsRemoteUpdates"/>
for necessary updates). -->

<P/>

Additional information is now available via the internet
(see&nbsp;<Ref Sect="sect:Web Contents for the AtlasRep Package"/>).

<P/>

The facilities for updating the table of contents have been extended.

<P/>

The manual is now distributed also in PDF and HTML format; on the other hand,
the PostScript format manual is no longer contained in the archives.

<P/>

Apart from these changes,
a few minor bugs in the handling of &MeatAxe; files have been fixed,
typos in the documentation have been corrected,
and the syntax checks for &ATLAS; straight line programs
(see&nbsp;<Ref Sect="sect:Reading and Writing Atlas Straight Line Programs"/>)
have been improved.

</Subsection>
</Section>


<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
<Section Label="sect:Acknowledgements">
<Heading>Acknowledgements</Heading>

<List>
<Item>
    Frank Lübeck and Max Neunhöffer kindly provided
    the perl script<Index Key="perl"><F>perl</F></Index> that had been used
    for fetching remote data until version&nbsp;1.2.
    Thanks also to Greg Gamble and Alexander Hulpke for technical hints
    concerning <Q>standard</Q> perl.
</Item>
<Item>
    Ulrich Kaiser helped with preparing the package for MS Windows.
</Item>
<Item>
    Klaus Lux had the idea to support data extensions,
    see Chapter&nbsp;<Ref Chap="chap:Private Extensions"/>,
    he did a lot of beta testing, and helped to fix several bugs.
</Item>
<Item>
    Frank Lübeck contributed the functions
    <Ref Func="CMtxBinaryFFMatOrPerm"/> and
    <Ref Func="FFMatOrPermCMtxBinary"/>.
</Item>
<Item>
    Frank Lübeck and Max Neunhöffer wrote
    the &GAPDoc; package <Cite Key="GAPDoc"/>,
    which is used for processing the documentation of the
    &AtlasRep; package
    and for processing the bibliographies included in this package
    (see <Ref Func="BrowseBibliographySporadicSimple"/>),
</Item>
<Item>
    Max Neunhöffer wrote the &GAP; package <Package>IO</Package>
    <Cite Key="IO"/>, which is recommended for transferring data.
</Item>
<Item>
    Max Neunhöffer has also suggested the generalization of the data access
    described in
    Section&nbsp;<Ref Sect="sect:How to Customize the Access to Data files"/>,
    the admissibility of the function
    <Ref Func="Character" Label="for a character table and a list" BookName="ref"/>
    as a filter in <Ref Func="DisplayAtlasInfo"/>,
    <Ref Func="OneAtlasGeneratingSetInfo"/>, and
    <Ref Func="AllAtlasGeneratingSetInfos"/>,
    and the variant of <Ref Attr="AtlasRepInfoRecord" Label="for a string"/>
    that takes a group name as its input.
</Item>
<Item>
    Gunter Malle suggested to make the information about representations
    of minimal degree accessible,
    see Section&nbsp;<Ref Sect="sect:Representations of Minimal Degree"/>.
</Item>
<Item>
    Andries Brouwer suggested to add a tutorial
    (see Chapter <Ref Chap="chap:tutorial"/>),
    Klaus Lux suggested several improvements of this chapter.
</Item>
<Item>
    The development of this &GAP; package has been supported
    by the <URL><Link>https://www.computeralgebra.de/sfb/</Link>
    <LinkText>SFB-TRR 195
    <Q>Symbolic Tools in Mathematics and their Applications</Q></LinkText></URL>
    (from 2017 until 2022).
</Item>
</List>

</Section>


<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->

</Chapter>