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7 Technicalities of the AtlasRep Package
 7.1 Global Variables Used by the AtlasRep Package
 7.2 How to Customize the Access to Data files
 7.3 Reading and Writing MeatAxe Format Files
 7.4 Reading and Writing ATLAS Straight Line Programs
 7.5 Data Types Used in the ATLAS of Group Representations
 7.6 Filenames Used in the ATLAS of Group Representations
 7.7 The Tables of Contents of the ATLAS of Group Representations
 7.8 Sanity Checks for the ATLAS of Group Representations

7 Technicalities of the AtlasRep Package

This chapter describes those parts of the GAP interface to the ATLAS of Group Representations that do not belong to the user interface (cf. Chapter 3).

Besides global variables used for administrational purposes (see Section 7.1) and several sanity checks (see Section 7.8), they can be regarded as the interface between the data actually contained in the files and the corresponding GAP objects (see Section 7.2, 7.3, 7.4, and 7.5), and the interface between the remote and the local version of the database (see Section 7.6 and 7.7). The former interface contains functions to read and write files in MeatAxe format, which may be interesting for users familiar with MeatAxe standalones (see for example [Rin]). Other low level functions may be undocumented in the sense that they are not described in this manual. Users interested in them may look at the actual implementation in the gap directory of the package, but it may happen that this will be changed in future versions of the package.

7.1 Global Variables Used by the AtlasRep Package

For debugging purposes, the functions from the GAP interface to the ATLAS of Group Representations print information depending on the info level of the info classes InfoAtlasRep (7.1-1), InfoCMeatAxe (7.1-2), and InfoBBox (7.1-3) (cf. Reference: Info Functions).

The info level of an info class can be changed using SetInfoLevel (Reference: SetInfoLevel). For example, the info level of InfoAtlasRep (7.1-1) can be set to the nonnegative integer n using SetInfoLevel( InfoAtlasRep, n ).

Information about files being read can be obtained by setting the value of the global variable InfoRead1 to Print (Reference: Print).

7.1-1 InfoAtlasRep
‣ InfoAtlasRep( info class )

If the info level of InfoAtlasRep is at least 1 then information about fail results of functions in the AtlasRep package is printed. If the info level is at least 2 then information about calls to external programs is printed. The default level is 0, no information is printed on this level.

7.1-2 InfoCMeatAxe
‣ InfoCMeatAxe( info class )

If the info level of InfoCMeatAxe is at least 1 then information about fail results of C-MeatAxe functions is printed. The default level is zero, no information is printed on this level.

7.1-3 InfoBBox
‣ InfoBBox( info class )

If the info level of InfoBBox is at least 1 then information about fail results of functions dealing with black box programs (see Section 6.2) is printed. The default level is 0, no information is printed on this level.

7.1-4 CMeatAxe.FastRead
‣ CMeatAxe.FastRead( global variable )

If this component is bound and has the value true then ScanMeatAxeFile (7.3-1) reads text files via StringFile (GAPDoc: StringFile). Otherwise each file containing a matrix over a finite field is read line by line via ReadLine (Reference: ReadLine), and the GAP matrix is constructed line by line, in a compressed representation (see Reference: Row Vectors over Finite Fields and Reference: Matrices over Finite Fields), which makes it possible to read large matrices in a reasonable amount of space. The StringFile (GAPDoc: StringFile) approach is faster but needs more intermediate space when text files containing matrices over finite fields are read.

7.1-5 AGR
‣ AGR( global variable )

is a record whose components are functions and data that are used by the higher level interface functions.

7.1-6 AtlasOfGroupRepresentationsInfo
‣ AtlasOfGroupRepresentationsInfo( global variable )

This is a record that is defined in the file gap/types.g of the package, with the following components.

Components corresponding to user parameters (see Section 4.3) are

remote

a boolean that controls what files are available; if the value is true then GAP is allowed to try remotely accessing any ATLAS file from the servers (see below) and thus all files listed in the global table of contents are available, if the value is false then GAP may access only those files that are stored in the database directories of the local GAP installation (see Section 4.3-1),

servers

a list of pairs [ server, path ], where server is a string denoting the http address of a server where files can be fetched that are not stored in the local database, and path is a string describing the path where the data directories on the server reside,

wget

controls whether the GAP package IO [Neu14] or the external program wget is used to fetch data files, see 4.3-3,

compress

a boolean that controls whether MeatAxe format text files are stored in compressed form; if the value is true then these files are compressed with gzip after they have been fetched from a server, see Section 4.3-4,

displayFunction

the function that is used by DisplayAtlasInfo (3.5-1) for printing the formatted data, see Section 4.3-5,

accessFunctions

a list of records, each describing how to access the data files, see Sections 4.3-6 and 7.2, and

markprivate

a string used in DisplayAtlasInfo (3.5-1) to mark private data, see Section  5.2.

System components (which are computed automatically) are

GAPnames

a list of pairs, each containing the GAP name and the ATLAS-file name of a group, see Section 3.2,

groupnames

a list of triples, each containing at the first position the name of the directory on each server that contains data about the group G in question, at the second position the name of the (usually simple) group for which a subdirectory exists that contains the data about G, and at the third position the ATLAS-file name used for G, see Section 7.6,

private

a list of pairs of strings used for administrating private data (see Chapter 5); the value is changed by AtlasOfGroupRepresentationsNotifyPrivateDirectory (5.1-1) and AtlasOfGroupRepresentationsForgetPrivateDirectory (5.1-2),

characterinfo, permrepinfo, ringinfo

additional information about representations, concerning the characters afforded, the point stabilizers of permutation representations, and the ring of definition of matrix representations; this information is used by DisplayAtlasInfo (3.5-1),

TableOfContents

a record with at most the components local, remote, types, and the names of private data directories. The values of the components local and remote can be computed automatically by ReloadAtlasTableOfContents (4.2-1), the value of the component types is set in AGR.DeclareDataType (7.5-1), and the values of the components for local data directories are created by AtlasOfGroupRepresentationsNotifyPrivateDirectory (5.1-1).

7.2 How to Customize the Access to Data files

We discuss the three steps listed in Section 4.3-6.

For creating an overview of the locally available data, the first of these steps must be available independent of actually accessing the file in question. For updating the local copy of the server data, the second of the above steps must be available independent of the third one. Therefore, the package provides the possibility to extend the default behaviour by adding new records to the accessFunctions component of AtlasOfGroupRepresentationsInfo (7.1-6). Its components are as follows.

location( filename, groupname, dirname, type )

Let filename be the default filename (without path) of the required file, or a list of such filenames. Let groupname be the ATLAS name of the group to which the data in these files belong, dirname be the default directory name (one of "datagens", "dataword", or the dirid value of a private directory, see AtlasOfGroupRepresentationsNotifyPrivateDirectory (5.1-1)), and type be the data type (see AGR.DeclareDataType (7.5-1)). This function must return either the absolute path(s) where the mechanism implemented by the current record expects the local version of the given file(s), or fail if this function does not feel responsible for these file(s). In the latter case, the location function in another record will know a path.

The file(s) is/are regarded as not locally available if all installed location functions return either fail or paths of nonexisting files, in the sense of IsExistingFile (Reference: IsExistingFile).

fetch( filepath, filename, groupname, dirname, type )

This function is called when a file is not locally available and if the location function in the current record has returned a path or a list of paths. The arguments dirname and type must be the same as for the location function, and filepath and filename must be strings (not lists of strings).

The return value must be true if the function succeeded with making the file locally available (including postprocessing if applicable), and false otherwise.

contents( filepath, type )

This function is called when the location function in the current record has returned the path(s) filepath, and if either these are paths of existing files or the fetch function in the current record has been called for these paths, and the return value was true. The argument type must be the same as for the location and the fetch functions.

The return value must be the contents of the file(s), in the sense that the GAP matrix, matrix list, permutation, permutation list, or program described by the file(s) is returned. This means that besides reading the file(s) via the appropriate function, interpreting the contents may be necessary.

description

This must be a short string that describes for which kinds of files the functions in the current record are intended, which file formats are supported etc. The value is used by AtlasOfGroupRepresentationsUserParameters (4.3-8).

active

The current accessFunctions record is ignored by AGR.FileContents (7.6-2) if the value is not true.

In AGR.FileContents (7.6-2), the records in the accessFunctions component of AtlasOfGroupRepresentationsInfo (7.1-6) are considered in reversed order.

By default, the accessFunctions list contains three records. Only for one of them, the active component has the value true. One of the other two records can be used to change the access to permutation representations and to matrix representations over finite fields such that MeatAxe binary files are transferred and read instead of MeatAxe text files. The fourth record makes sense only if a local server is accessible, i. e., if the server files can be read directly, without being transferred into the data directories of the package.

7.3 Reading and Writing MeatAxe Format Files

7.3-1 ScanMeatAxeFile
‣ ScanMeatAxeFile( filename[, q][, "string"] )( function )

Returns: the matrix or list of permutations stored in the file or encoded by the string.

Let filename be the name of a GAP readable file (see Reference: Filename) that contains a matrix or a permutation or a list of permutations in MeatAxe text format (see the section about the program zcv in the C-MeatAxe documentation [Rin]), and let q be a prime power. ScanMeatAxeFile returns the corresponding GAP matrix or list of permutations, respectively.

If the file contains a matrix then the way how it is read by ScanMeatAxeFile depends on the value of the global variable CMeatAxe.FastRead (7.1-4).

If the parameter q is given then the result matrix is represented over the field with q elements, the default for q is the field size stored in the file.

If the file contains a list of permutations then it is read with StringFile (GAPDoc: StringFile); the parameter q, if given, is ignored in this case.

If the string "string" is entered as the third argument then the first argument must be a string as obtained by reading a file in MeatAxe text format as a text stream (see InputTextFile (Reference: InputTextFile)). Also in this case, ScanMeatAxeFile returns the corresponding GAP matrix or list of permutations, respectively.

7.3-2 MeatAxeString
‣ MeatAxeString( mat, q )( operation )
‣ MeatAxeString( perms, degree )( operation )
‣ MeatAxeString( perm, q, dims )( operation )

Returns: a string encoding the GAP objects given as input in MeatAxe format.

In the first form, for a matrix mat whose entries lie in the finite field with q elements, MeatAxeString returns a string that encodes mat as a matrix over GF(q), in MeatAxe text format.

In the second form, for a nonempty list perms of permutations that move only points up to the positive integer degree, MeatAxeString returns a string that encodes perms as permutations of degree degree, in C-MeatAxe text format (see [Rin]).

In the third form, for a permutation perm with largest moved point n, say, a prime power q, and a list dims of length two containing two positive integers larger than or equal to n, MeatAxeString returns a string that encodes perm as a matrix over GF(q), of dimensions dims, whose first n rows and columns describe the permutation matrix corresponding to perm, and the remaining rows and columns are zero.

When strings are printed to files using PrintTo (Reference: PrintTo) or AppendTo (Reference: AppendTo) then line breaks are inserted whenever lines exceed the number of characters given by the second entry of the list returned by SizeScreen (Reference: SizeScreen), see Reference: Operations for Output Streams. This behaviour is not desirable for creating data files. So the recommended functions for printing the result of MeatAxeString to a file are FileString (GAPDoc: FileString) and WriteAll (Reference: WriteAll).

gap> mat:= [ [ 1, -1 ], [ 0, 1 ] ] * Z(3)^0;;
gap> str:= MeatAxeString( mat, 3 );
"1 3 2 2\n12\n01\n"
gap> mat = ScanMeatAxeFile( str, "string" );
true
gap> str:= MeatAxeString( mat, 9 );
"1 9 2 2\n12\n01\n"
gap> mat = ScanMeatAxeFile( str, "string" );
true
gap> perms:= [ (1,2,3)(5,6) ];;
gap> str:= MeatAxeString( perms, 6 );
"12 1 6 1\n2\n3\n1\n4\n6\n5\n"
gap> perms = ScanMeatAxeFile( str, "string" );
true
gap> str:= MeatAxeString( perms, 8 );
"12 1 8 1\n2\n3\n1\n4\n6\n5\n7\n8\n"
gap> perms = ScanMeatAxeFile( str, "string" );
true

Note that the output of MeatAxeString in the case of permutation matrices depends on the user preference WriteMeatAxeFilesOfMode2.

gap> perm:= (1,2,4);;
gap> str:= MeatAxeString( perm, 3, [ 5, 6 ] );
"2 3 5 6\n2\n4\n3\n1\n5\n"
gap> mat:= ScanMeatAxeFile( str, "string" );;  Print( mat, "\n" );
[ [ 0*Z(3), Z(3)^0, 0*Z(3), 0*Z(3), 0*Z(3), 0*Z(3) ], 
  [ 0*Z(3), 0*Z(3), 0*Z(3), Z(3)^0, 0*Z(3), 0*Z(3) ], 
  [ 0*Z(3), 0*Z(3), Z(3)^0, 0*Z(3), 0*Z(3), 0*Z(3) ], 
  [ Z(3)^0, 0*Z(3), 0*Z(3), 0*Z(3), 0*Z(3), 0*Z(3) ], 
  [ 0*Z(3), 0*Z(3), 0*Z(3), 0*Z(3), Z(3)^0, 0*Z(3) ] ]
gap> pref:= UserPreference( "AtlasRep", "WriteMeatAxeFilesOfMode2" );;
gap> SetUserPreference( "AtlasRep", "WriteMeatAxeFilesOfMode2", true );
gap> MeatAxeString( mat, 3 ) = str;
true
gap> SetUserPreference( "AtlasRep", "WriteMeatAxeFilesOfMode2", false );
gap> MeatAxeString( mat, 3 );
"1 3 5 6\n010000\n000100\n001000\n100000\n000010\n"
gap> SetUserPreference( "AtlasRep", "WriteMeatAxeFilesOfMode2", pref );

7.3-3 FFList
‣ FFList( F )( function )

Returns: a list of elements in the given finite field.

‣ FFLists( global variable )

FFList is a utility program for the conversion of vectors and matrices from MeatAxe format to GAP format and vice versa. It is used by ScanMeatAxeFile (7.3-1) and MeatAxeString (7.3-2).

For a finite field F, FFList returns a list l giving the correspondence between the MeatAxe numbering and the GAP numbering of the elements in F.

The element of F corresponding to MeatAxe number n is l[ n+1 ], and the MeatAxe number of the field element z is Position( l, z ) - 1.

The global variable FFLists is used to store the information about F once it has been computed.

gap> FFList( GF(4) );
[ 0*Z(2), Z(2)^0, Z(2^2), Z(2^2)^2 ]
gap> IsBound( FFLists[4] );
true

7.3-4 CMtxBinaryFFMatOrPerm
‣ CMtxBinaryFFMatOrPerm( elm, def, outfile[, base] )( function )

Let the pair (elm, def) be either of the form (M, q) where M is a matrix over a finite field F, say, with q ≤ 256 elements, or of the form (π, n) where π is a permutation with largest moved point at most n. Let outfile be a string. CMtxBinaryFFMatOrPerm writes the C-MeatAxe binary format of M, viewed as a matrix over F, or of π, viewed as a permutation on the points up to n, to the file with name outfile.

In the case of a permutation π, the optional argument base prescribes whether the binary file contains the points from 0 to deg- 1 (base= 0, supported by version 2.4 of the C-MeatAxe) or the points from 1 to deg (base= 1, supported by older versions of the C-MeatAxe). The default for base is given by the value of the user preference BaseOfMeatAxePermutation, see Section 4.3-11.

(The binary format is described in the C-MeatAxe manual [Rin].)

gap> tmpdir:= DirectoryTemporary();;
gap> mat:= Filename( tmpdir, "mat" );;
gap> q:= 4;;
gap> mats:= GeneratorsOfGroup( GL(10,q) );;
gap> CMtxBinaryFFMatOrPerm( mats[1], q, Concatenation( mat, "1" ) );
gap> CMtxBinaryFFMatOrPerm( mats[2], q, Concatenation( mat, "2" ) );
gap> prm:= Filename( tmpdir, "prm" );;
gap> n:= 200;;
gap> perms:= GeneratorsOfGroup( SymmetricGroup( n ) );;
gap> CMtxBinaryFFMatOrPerm( perms[1], n, Concatenation( prm, "1" ) );
gap> CMtxBinaryFFMatOrPerm( perms[2], n, Concatenation( prm, "2" ) );
gap> CMtxBinaryFFMatOrPerm( perms[1], n, Concatenation( prm, "1a" ), 0 );
gap> CMtxBinaryFFMatOrPerm( perms[2], n, Concatenation( prm, "2b" ), 1 );

7.3-5 FFMatOrPermCMtxBinary
‣ FFMatOrPermCMtxBinary( fname )( function )

Returns: the matrix or permutation stored in the file.

Let fname be the name of a file that contains the C-MeatAxe binary format of a matrix over a finite field or of a permutation, as is described in [Rin]. FFMatOrPermCMtxBinary returns the corresponding GAP matrix or permutation.

gap> FFMatOrPermCMtxBinary( Concatenation( mat, "1" ) ) = mats[1];
true
gap> FFMatOrPermCMtxBinary( Concatenation( mat, "2" ) ) = mats[2];
true
gap> FFMatOrPermCMtxBinary( Concatenation( prm, "1" ) ) = perms[1];
true
gap> FFMatOrPermCMtxBinary( Concatenation( prm, "2" ) ) = perms[2];
true
gap> FFMatOrPermCMtxBinary( Concatenation( prm, "1a" ) ) = perms[1];
true
gap> FFMatOrPermCMtxBinary( Concatenation( prm, "2b" ) ) = perms[2];
true

7.4 Reading and Writing ATLAS Straight Line Programs

7.4-1 ScanStraightLineProgram
‣ ScanStraightLineProgram( filename[, "string"] )( function )

Returns: a record containing the straight line program.

Let filename be the name of a file that contains a straight line program in the sense that it consists only of lines in the following form.

#anything

lines starting with a hash sign # are ignored,

echo anything

lines starting with echo are ignored for the program component of the result record (see below), they are used to set up the bijection between the labels used in the program and conjugacy class names in the case that the program computes dedicated class representatives,

inp n

means that there are n inputs, referred to via the labels 1, 2, ..., n,

inp k a1 a2 ... ak

means that the next k inputs are referred to via the labels a1, a2, ..., ak,

cjr a b

means that a is replaced by b^(-1) * a * b,

cj a b c

means that c is defined as b^(-1) * a * b,

com a b c

means that c is defined as a^(-1) * b^(-1) * a * b,

iv a b

means that b is defined as a^(-1),

mu a b c

means that c is defined as a * b,

pwr a b c

means that c is defined as b^a,

cp a b

means that b is defined as a copy of a,

oup l

means that there are l outputs, stored in the labels 1, 2, ..., l, and

oup l b1 b2 ... bl

means that the next l outputs are stored in the labels b1, b2, ... bl.

Each of the labels a, b, c can be any nonempty sequence of digits and alphabet characters, except that the first argument of pwr must denote an integer.

If the inp or oup statements are missing then the input or output, respectively, is assumed to be given by the labels 1 and 2. There can be multiple inp lines at the beginning of the program and multiple oup lines at the end of the program. Only the first inp or oup line may omit the names of the elements. For example, an empty file filename or an empty string string represent a straight line program with two inputs that are returned as outputs.

No command except cjr may overwrite its own input. For example, the line mu a b a is not legal. (This is not checked.)

ScanStraightLineProgram returns a record containing as the value of its component program the corresponding GAP straight line program (see IsStraightLineProgram (Reference: IsStraightLineProgram)) if the input string satisfies the syntax rules stated above, and returns fail otherwise. In the latter case, information about the first corrupted line of the program is printed if the info level of InfoCMeatAxe (7.1-2) is at least 1.

If the string "string" is entered as the second argument then the first argument must be a string as obtained by reading a file in MeatAxe text format as a text stream (see InputTextFile (Reference: InputTextFile)). Also in this case, ScanStraightLineProgram returns either a record with the corresponding GAP straight line program or fail.

If the input describes a straight line program that computes certain class representatives of the group in question then the result record also contains the component outputs. Its value is a list of strings, the entry at position i denoting the name of the class in which the i output of the straight line program lies; see Section 3.4 for the definition of the class names that occur.

Such straight line programs must end with a sequence of output specifications of the following form.

echo "Classes 1A 2A 3A 5A 5B"
oup 5 3 1 2 4 5

This example means that the list of outputs of the program contains elements of the classes 1A, 2A, 3A, 5A, and 5B (in this order), and that inside the program, these elements are referred to by the five names 3, 1, 2, 4, and 5.

7.4-2 AtlasStringOfProgram
‣ AtlasStringOfProgram( prog[, outputnames] )( function )
‣ AtlasStringOfProgram( prog[, "mtx"] )( function )

Returns: a string encoding the straight line program/decision in the format used in ATLAS files.

For a straight line program or straight line decision prog (see IsStraightLineProgram (Reference: IsStraightLineProgram) and IsStraightLineDecision (6.1-1)), this function returns a string describing the input format of an equivalent straight line program or straight line decision as used in the ATLAS of Group Representations, that is, the lines are of the form described in ScanStraightLineProgram (7.4-1).

A list of strings that is given as the optional second argument outputnames is interpreted as the class names corresponding to the outputs; this argument has the effect that appropriate echo statements appear in the result string.

If the string "mtx" is given as the second argument then the result has the format used in the C-MeatAxe (see [Rin]) rather than the format described in Section 7.4. (Note that the C-MeatAxe format does not make sense if the argument outputnames is given, and that this format does not support inp and oup statements.)

The argument prog must not be a black box program (see IsBBoxProgram (6.2-1)).

gap> str:= "inp 2\nmu 1 2 3\nmu 3 1 2\niv 2 1\noup 2 1 2";;
gap> prg:= ScanStraightLineProgram( str, "string" );
rec( program := <straight line program> )
gap> prg:= prg.program;;
gap> Display( prg );
# input:
r:= [ g1, g2 ];
# program:
r[3]:= r[1]*r[2];
r[2]:= r[3]*r[1];
r[1]:= r[2]^-1;
# return values:
[ r[1], r[2] ]
gap> StringOfResultOfStraightLineProgram( prg, [ "a", "b" ] );
"[ (aba)^-1, aba ]"
gap> AtlasStringOfProgram( prg );
"inp 2\nmu 1 2 3\nmu 3 1 2\niv 2 1\noup 2\n"
gap> prg:= StraightLineProgram( "(a^2b^3)^-1", [ "a", "b" ] );
<straight line program>
gap> Print( AtlasStringOfProgram( prg ) );
inp 2
pwr 2 1 4
pwr 3 2 5
mu 4 5 3
iv 3 4
oup 1 4
gap> prg:= StraightLineProgram( [ [2,3], [ [3,1,1,4], [1,2,3,1] ] ], 2 );
<straight line program>
gap> Print( AtlasStringOfProgram( prg ) );
inp 2
pwr 3 2 3
pwr 4 1 5
mu 3 5 4
pwr 2 1 6
mu 6 3 5
oup 2 4 5
gap> Print( AtlasStringOfProgram( prg, "mtx" ) );
# inputs are expected in 1 2
zsm pwr3 2 3
zsm pwr4 1 5
zmu 3 5 4
zsm pwr2 1 6
zmu 6 3 5
echo "outputs are in 4 5"
gap> str:= "inp 2\nchor 1 2\nchor 2 3\nmu 1 2 3\nchor 3 5";;
gap> prg:= ScanStraightLineDecision( str );;
gap> AtlasStringOfProgram( prg.program );
"inp 2\nchor 1 2\nchor 2 3\nmu 1 2 3\nchor 3 5\n"

7.5 Data Types Used in the ATLAS of Group Representations

Each representation or program that is administrated by the AtlasRep package belongs to a unique data type. Informally, examples of data types are "permutation representation", "matrix representation over the integers", or "straight line program for computing class representatives".

The idea is that for each data type, there can be

Formally, a data type is defined by a record whose components are used by the interface functions. The details are described in the following.

7.5-1 AGR.DeclareDataType
‣ AGR.DeclareDataType( kind, name, record )( function )

Let kind be one of the strings "rep" or "prg", and record be a record. AGR.DeclareDataType declares a new data type of representations (if kind is "rep") or of programs (if kind is "prg"). For each group used in the AtlasRep package, the record that contains the information about the data will have a component name whose value is a list containing the data about the new type. Examples of name are "perm", "matff", and "classes".

Mandatory components of record are

FilenameFormat

This defines the format of the filenames containing data of the type in question. The value must be a list that can be used as the second argument of AGR.ParseFilenameFormat (7.6-1), such that only filenames of the type in question match. (It is not checked whether this "detection function" matches exactly one type, so declaring a new type needs care.)

AddFileInfo

This defines the information stored in the table of contents for the data of the type. The value must be a function that takes three arguments (the current list of data for the type and the given group, a list returned by AGR.ParseFilenameFormat (7.6-1) for the given type, and a filename). This function adds the necessary parts of the data entry to the list, and returns true if the data belongs to the type, otherwise false is returned; note that the latter case occurs if the filename matches the format description but additional conditions on the parts of the name are not satisfied (for example integer parts may be required to be positive or prime powers).

ReadAndInterpretDefault

This is the function that does the work for the default contents value of the accessFunctions component of AtlasOfGroupRepresentationsInfo (7.1-6), see Section 7.2. This function must take a path and return the GAP object given by this file.

AddDescribingComponents (for rep only)

This function takes two arguments, a record (that will be returned by AtlasGenerators (3.5-2), OneAtlasGeneratingSetInfo (3.5-5), or AllAtlasGeneratingSetInfos (3.5-6)) and the type record record. It sets the components p, dim, id, and ring that are promised for return values of the abovementioned three functions.

DisplayGroup (for rep only)

This defines the format of the lines printed by DisplayAtlasInfo (3.5-1) for a given group. The value must be a function that takes a list as returned by the function given in the component AddFileInfo, and returns the string to be printed for the representation in question.

Optional components of record are

DisplayOverviewInfo

This is used to introduce a new column in the output of DisplayAtlasInfo (3.5-1) when this is called without arguments or with a list of group names as its only argument. The value must be a list of length three, containing at its first position a string used as the header of the column, at its second position one of the strings "r" or "l", denoting right or left aligned column entries, and at its third position a function that takes two arguments (a list of tables of contents of the AtlasRep package and a group name), and returns a list of length two, containing the string to be printed as the column value and true or false, depending on whether private data is involved or not. (The default is fail, indicating that no new column shall be printed.)

DisplayPRG (for prg only)

This is used in DisplayAtlasInfo (3.5-1) for ATLAS programs. The value must be a function that takes four arguments (a list of tables of contents to examine, the name of the given group, a list of integers or true for the required standardization, and a list of all available standardizations), and returns the list of lines (strings) to be printed as the information about the available programs of the current type and for the given group. (The default is to return an empty list.)

AccessGroupCondition (for rep only)

This is used in DisplayAtlasInfo (3.5-1) and OneAtlasGeneratingSetInfo (3.5-5). The value must be a function that takes two arguments (a list as returned by OneAtlasGeneratingSetInfo (3.5-5), and a list of conditions), and returns true or false, depending on whether the first argument satisfies the conditions. (The default value is ReturnFalse (Reference: ReturnFalse).)

The function must support conditions such as [ IsPermGroup, true ] and [ NrMovedPoints, [ 5, 6 ] ], in general a list of functions followed by a prescribed value, a list of prescribed values, another (unary) function, or the string "minimal". For an overview of the interesting functions, see DisplayAtlasInfo (3.5-1).

AccessPRG (for prg only)

This is used in AtlasProgram (3.5-3). The value must be a function that takes three arguments (the record with the information about the given group in the current table of contents, an integer or a list of integers or true for the required standardization, and a list of conditions given by the optional arguments of AtlasProgram (3.5-3)), and returns either fail or a list that together with the group name forms the identifier of a program that matches the conditions. (The default value is ReturnFail (Reference: ReturnFail).)

AtlasProgram (for prg only)

This is used in AtlasProgram (3.5-3) to create the result value from the identifier. (The default value is AtlasProgramDefault, which works whenever the second entry of the identifier is the filename; this is not the case for example if the program is the composition of several programs.)

AtlasProgramInfo (for prg only)

This is used in AtlasProgramInfo (3.5-4) to create the result value from the identifier. (The default value is AtlasProgramDefault.)

TOCEntryString

This is used in StoreAtlasTableOfContents (4.2-2). The value must be a function that takes two arguments (the name name of the type and a list as returned by AGR.ParseFilenameFormat (7.6-1) and returns a string that describes the appropriate function call. (The default value is TOCEntryStringDefault.)

PostprocessFileInfo

This is used in the construction of a table of contents via ReloadAtlasTableOfContents (4.2-1), for testing or rearranging the data of the current table of contents. The value must be a function that takes two arguments, the table of contents record and the record in it that belongs to one fixed group. (The default function does nothing.)

SortTOCEntries

This is used in the construction of a table of contents (see ReloadAtlasTableOfContents (4.2-1)), for sorting the entries after they have been added and after the value of the component PostprocessFileInfo has been called. The value must be a function that takes a list as returned by AGR.ParseFilenameFormat (7.6-1), and returns the sorting key. (There is no default value, which means that no sorting is needed.)

TestFileHeaders (for rep only)

This is used in the function AGR.Test.FileHeaders. The value must be a function that takes the same four arguments as AGR.FileContents (7.6-2), except that the first argument "datagens" can be replaced by "local" and that the third argument is a list as returned by AGR.ParseFilenameFormat (7.6-1). (The default value is ReturnTrue (Reference: ReturnTrue).)

TestFiles (for rep only)

This is used in the function AGR.Test.Files. The format of the value and the default are the same as for the value of the component TestFileHeaders.

TestWords (for prg only)

This is used in the function AGR.Test.Words. The value must be a function that takes five arguments where the first four are the same arguments as for AGR.FileContents (7.6-2), except that the first argument "dataword" can be replaced by "local", and the fifth argument is true or false, indicating verbose mode or not.

7.6 Filenames Used in the ATLAS of Group Representations

The data of each local GAP version of the ATLAS of Group Representations are either private (see Chapter 5) or are stored in the two directories datagens and dataword. In the following, we describe the format of filenames in the latter two directories, as a reference of the "official" part of the ATLAS.

In the directory datagens, the generators for the representations available are stored, the directory dataword contains the programs to compute conjugacy class representatives, generators of maximal subgroups, images of generators under automorphisms of a given group G from standard generators of G, and to check and compute standard generators (see Section 3.3).

The name of each data file in the ATLAS of Group Representations describes the contents of the file. This section lists the definitions of the filenames used.

Each filename consists of two parts, separated by a minus sign -. The first part is always of the form groupnameGi, where the integer i denotes the i-th set of standard generators for the group G, say, with ATLAS-file name groupname (see 3.2). The translations of the name groupname to the name(s) used within GAP is given by the component GAPnames of AtlasOfGroupRepresentationsInfo (7.1-6).

The filenames in the directory dataword have one of the following forms. In each of these cases, the suffix Wn means that n is the version number of the program.

groupnameGi-cycWn

In this case, the file contains a straight line program that returns a list of representatives of generators of maximally cyclic subgroups of G. An example is Co1G1-cycW1.

groupnameGi-cclsWn

In this case, the file contains a straight line program that returns a list of conjugacy class representatives of G. An example is RuG1-cclsW1.

groupnameGicycWn-cclsWm

In this case, the file contains a straight line program that takes the return value of the program in the file groupnameGi-cycWn (see above), and returns a list of conjugacy class representatives of G. An example is M11G1cycW1-cclsW1.

groupnameGi-maxkWn

In this case, the file contains a straight line program that takes generators of G w.r.t. the i-th set of standard generators, and returns a list of generators (in general not standard generators) for a subgroup U in the k-th class of maximal subgroups of G. An example is J1G1-max7W1.

groupnameGimaxkWn-subgroupnameGjWm

In this case, the file contains a straight line program that takes the return value of the program in the file groupnameGi-maxkWn (see above), which are generators for a group U, say; subgroupname is a name for U, and the return value is a list of standard generators for U, w.r.t. the j-th set of standard generators. (Of course this implies that the groups in the k-th class of maximal subgroups of G are isomorphic to the group with name subgroupname.) An example is J1G1max1W1-L211G1W1; the first class of maximal subgroups of the Janko group J_1 consists of groups isomorphic to the linear group L_2(11), for which standard generators are defined.

groupnameGi-aoutnameWn

In this case, the file contains a straight line program that takes generators of G w.r.t. the i-th set of standard generators, and returns the list of their images under the outer automorphism α of G given by the name outname; if this name is empty then α is the unique nontrivial outer automorphism of G; if it is a positive integer k then α is a generator of the unique cyclic order k subgroup of the outer automorphism group of G; if it is of the form 2_1 or 2a, 4_2 or 4b, 3_3 or 3c ... then α generates the cyclic group of automorphisms induced on G by G.2_1, G.4_2, G.3_3 ...; finally, if it is of the form kpd, with k one of the above forms and d an integer then d denotes the number of dashes appended to the automorphism described by k; if d = 1 then d can be omitted. Examples are A5G1-aW1, L34G1-a2_1W1, U43G1-a2_3pW1, and O8p3G1-a2_2p5W1; these file names describe the outer order 2 automorphism of A_5 (induced by the action of S_5) and the order 2 automorphisms of L_3(4), U_4(3), and O_8^+(3) induced by the actions of L_3(4).2_1, U_4(3).2_2^', and O_8^+(3).2_2^{'''''}, respectively.

groupnameGi-GjWn

In this case, the file contains a straight line program that takes generators of G w.r.t. the i-th set of standard generators, and returns standard generators of G w.r.t. the j-th set of standard generators. An example is L35G1-G2W1.

groupnameGi-checkn

In this case, the file contains a straight line decision that takes generators of G, and returns true if these generators are standard generators w.r.t. the i-th standardization, and false otherwise.

groupnameGi-Pn

In this case, the file contains a straight line decision that takes some group elements, and returns true if these elements are standard generators for G, w.r.t. the i-th standardization, and false otherwise.

groupnameGi-findn

In this case, the file contains a black box program that takes a group, and returns (if it is successful) a set of standard generators for G, w.r.t. the i-th standardization.

groupnameGi-XdescrWn

In this case, the file contains a straight line program that takes generators of G w.r.t. the i-th set of standard generators, and whose return value corresponds to descr. This format is used only in private extensions (see Chapter 5), such a script can be accessed with descr as the third argument of AtlasProgram (3.5-3).

The filenames in the directory datagens have one of the following forms. In each of these cases, id is a (possibly empty) string that starts with a lowercase alphabet letter (see IsLowerAlphaChar (Reference: IsLowerAlphaChar)), and m is a nonnegative integer, meaning that the generators are written w.r.t. the m-th basis (the meaning is defined by the ATLAS developers).

groupnameGi-fqrdimidBm.mnr

a file in MeatAxe text file format containing the nr-th generator of a matrix representation over the field with q elements, of dimension dim. An example is S5G1-f2r4aB0.m1.

groupnameGi-pnidBm.mnr

a file in MeatAxe text file format containing the nr-th generator of a permutation representation on n points. An example is M11G1-p11B0.m1.

groupnameGi-ArdimidBm.g

a GAP readable file containing all generators of a matrix representation of dimension dim over an algebraic number field not specified further. An example is A5G1-Ar3aB0.g.

groupnameGi-ZrdimidBm.g

a GAP readable file containing all generators of a matrix representation over the integers, of dimension dim. An example is A5G1-Zr4B0.g.

groupnameGi-HrdimidBm.g

a GAP readable file containing all generators of a matrix representation over a quaternion algebra over an algebraic number field, of dimension dim. An example is 2A6G1-Hr2aB0.g.

groupnameGi-ZnrdimidBm.g

a GAP readable file containing all generators of a matrix representation of dimension dim over the ring of integers mod n. An example is 2A8G1-Z4r4aB0.g.

7.6-1 AGR.ParseFilenameFormat
‣ AGR.ParseFilenameFormat( string, format )( function )

Returns: a list of strings and integers if string matches format, and fail otherwise.

Let string be a filename, and format be a list [ [ c_1, c_2, ..., c_n ], [ f_1, f_2, ..., f_n ] ] such that each entry c_i is a list of strings and of functions that take a character as their argument and return true or false, and such that each entry f_i is a function for parsing a filename, such as the currently undocumented functions ParseForwards and ParseBackwards.

AGR.ParseFilenameFormat returns a list of strings and integers such that the concatenation of their String (Reference: String) values yields string if string matches format, and fail otherwise. Matching is defined as follows. Splitting string at each minus character (-) yields m parts s_1, s_2, ..., s_m. The string string matches format if s_i matches the conditions in c_i, for 1 ≤ i ≤ n, in the sense that applying f_i to s_i and c_i yields a non-fail result.

gap> format:= [ [ [ IsChar, "G", IsDigitChar ],
>                 [ "p", IsDigitChar, AGR.IsLowerAlphaOrDigitChar,
>                   "B", IsDigitChar, ".m", IsDigitChar ] ],
>               [ ParseBackwards, ParseForwards ] ];;
gap> AGR.ParseFilenameFormat( "A6G1-p10B0.m1", format );
[ "A6", "G", 1, "p", 10, "", "B", 0, ".m", 1 ]
gap> AGR.ParseFilenameFormat( "A6G1-p15aB0.m1", format );
[ "A6", "G", 1, "p", 15, "a", "B", 0, ".m", 1 ]
gap> AGR.ParseFilenameFormat( "A6G1-f2r16B0.m1", format );
fail

7.6-2 AGR.FileContents
‣ AGR.FileContents( dirname, groupname, filename, type )( function )

Returns: the GAP object obtained from reading and interpreting the file(s) with name(s) filename.

Let dirname and groupname be strings, filename be a string or a list of strings, and type be a data type (see AGR.DeclareDataType (7.5-1)). dirname must be one of "datagens", "dataword", or the dirid value of a private directory, see AtlasOfGroupRepresentationsNotifyPrivateDirectory (5.1-1). If groupname is the ATLAS-file name of a group G (see Section 3.2), and if filename is either the name of an accessible file in the dirname directory of the ATLAS, or a list of such filenames, with data concerning G and for the data type type, then AGR.FileContents returns the contents of the corresponding file(s), in the sense that the file(s) (or equivalent ones, see Section 4.3-6) is/are read, and the result is interpreted if necessary; otherwise fail is returned.

Note that if filename refers to file(s) already stored in the dirname directory then AGR.FileContents does not check whether the table of contents of the ATLAS of Group Representations actually contains filename.

7.7 The Tables of Contents of the ATLAS of Group Representations

The list of data currently available is stored in several tables of contents, one for the local GAP data, one for the data on remote servers, and one for each private data directory. These tables of contents are created by ReloadAtlasTableOfContents (4.2-1).

It is assumed that the local data directories contain only files that are also available on servers. Private extensions to the database (cf. Section 4.5 and Chapter 5) cannot be handled by putting the data files into the local directories.

Each table of contents is represented by a record whose components are the ATLAS-file names of the groups (see Section 3.2) and lastupdated, a string describing the date of the last update of this table of contents. The value for each group name is a record whose components are the names of those data types (see Section 7.5) for which data are available.

Here are the administrational functions that are used to build the tables of contents. Some of them may be useful also for private extensions of the package (see Chapter 5).

The following functions define group names, available representations, and straight line programs.

AGR.GNAN( gapname, atlasname )

Called with two strings gapname (the GAP name of the group) and atlasname (the ATLAS name of the group), AGR.GNAN stores the information in the list AtlasOfGroupRepresentationsInfo.GAPnames, which defines the name mapping between the ATLAS names and GAP names of the groups.

This function may be used also for private extensions of the database.

An example of a valid call is AGR.GNAN("A5.2","S5").

AGR.GRP( dirname, simpname, groupname)

Called with three strings, AGR.GRP stores in the groupname component of AtlasOfGroupRepresentationsInfo (7.1-6) in which path on the servers the data about the group with ATLAS name groupname can be found.

This function is not intended for private extensions of the database.

An example of a valid call is AGR.GRP("alt","A5","S5").

AGR.TOC( typename, filename, crcfile )

Called with two strings typename and filename, and a list crc of integers, AGR.TOC notifies an entry to the TableOfContents.remote component of AtlasOfGroupRepresentationsInfo (7.1-6), where typename must be the name of the data type to which the entry belongs, filename must be the prefix of the data file(s), and crc must be the list of CrcFile (Reference: CrcFile) values of the file(s).

This function is not intended for private extensions of the database.

An example of a valid call is AGR.TOC("perm","S5G1-p5B0.m",[-3581724,115937465]).

The following functions add data about the groups and their standard generators. The function calls must be executed after the corresponding AGR.GNAN calls.

AGR.GRS( gapname, size )

Called with the string gapname (the GAP name of the group) and the integer size (the order of the group), AGR.GRS stores this information in AtlasOfGroupRepresentationsInfo.GAPnames.

An example of a valid call is AGR.GRS("A5.2",120).

AGR.MXN( gapname, nrMaxes )

Called with the string gapname (the GAP name of the group) and the integer nrMaxes (the number of classes of maximal subgroups of the group), AGR.MXN stores the information in AtlasOfGroupRepresentationsInfo.GAPnames.

An example of a valid call is AGR.MXN("A5.2",4).

AGR.MXO( gapname, sizesMaxes )

Called with the string gapname (the GAP name of the group) and the list sizesMaxes (of subgroup orders of the classes of maximal subgroups of the group, not necessarily dense, in non-increasing order), AGR.MXO stores the information in AtlasOfGroupRepresentationsInfo.GAPnames.

An example of a valid call is AGR.MXO("A5.2",[60,24,20,12]).

AGR.MXS( gapname, structureMaxes )

Called with the string gapname (the GAP name of the group) and the list structureMaxes (of strings describing the structures of the maximal subgroups of the group, not necessarily dense), AGR.MXS stores the information in AtlasOfGroupRepresentationsInfo.GAPnames.

An example of a valid call is AGR.MXS("A5.2",["A5","S4","5:4","S3x2"]).

AGR.KERPRG( gapname, kernelProgram )

Called with the string gapname (the GAP name of the group) and the list kernelProgram (with entries the standardization of the group, the GAP name of a factor group, and the list of lines of a straight line program that computes generators of the kernel of the epimorphism from the group to the factor group), AGR.KERPRG stores the information in AtlasOfGroupRepresentationsInfo.GAPnames.

An example of a valid call is AGR.KERPRG("2.J2",[1,"J2",[[[1,2]]]]).

AGR.STDCOMP

Called with the string gapname (the GAP name of the group) and the list factorCompatibility (with entries the standardization of the group, the GAP name of a factor group, the standardization of this factor group, and true or false, indicating whether mapping the standard generators for gapname to those of factgapname defines an epimorphism), AGR.STDCOMP stores the information in AtlasOfGroupRepresentationsInfo.GAPnames.

An example of a valid call is AGR.STDCOMP("2.A5.2",[1,"A5.2",1,true]).

The following functions add data about representations or straight line programs that are already known. The function calls must be executed after the corresponding AGR.TOC calls.

AGR.RNG( repname, descr )

Called with two strings repname (denoting the name of a file containing the generators of a matrix representation over a ring that is not determined by the filename) and descr (describing this ring R, say), AGR.RNG adds the triple [ repname, descr, R ] to the list stored in the ringinfo component of AtlasOfGroupRepresentationsInfo (7.1-6).

An example of a valid call is AGR.RNG("A5G1-Ar3aB0","Field([Sqrt(5)])").

AGR.TOCEXT( atlasname, std, maxnr, files )

Called with the string atlasname (the ATLAS name of the group), the positive integers std (the standardization) and maxnr (the number of the class of maximal subgroups), and the list files (of filenames of straight line programs for computing generators of the maxnr-th maximal subgroup, using a straight line program for a factor group plus perhaps some straight line program for computing kernel generators), AGR.TOCEXT stores the information in the maxext component of the atlasname component of the "remote" table of contents.

An example of a valid call is AGR.TOCEXT("2A5",1,3,["A5G1-max3W1"]).

AGR.API( repname, info )

Called with the string repname (denoting the name of a permutation representation) and the list info (describing the point stabilizer of this representation), AGR.API binds the component repname of the record AtlasOfGroupRepresentationsInfo.permrepinfo to info.

info has the following entries.

An example of a valid call is AGR.API("A5G1-p5B0",[3,2,"prim","A4",1]).

AGR.CHAR( groupname, repname, char, pos[, charname] )

Called with the strings groupname (the GAP name of the group) and repname (denoting the name of the representation), the integer char (the characteristic of the representation), and pos (the position or list of positions of the irreducible constituent(s)), AGR.CHAR stores the information in AtlasOfGroupRepresentationsInfo.characterinfo. A string describing the character can be entered as charname.

An example of a valid call is AGR.CHAR("M11","M11G1-p11B0",0,[1,2],"1a+10a").

These functions are used to create the initial table of contents for the server data of the AtlasRep package when the file gap/atlasprm.g of the package is read.

7.8 Sanity Checks for the ATLAS of Group Representations

The fact that the ATLAS of Group Representations is designed as an open database (see Section 4.3-1) makes it especially desirable to have consistency checks available which can be run automatically whenever new data are added by the developers of the ATLAS. The tests described in Section 7.8-1 can be used also for data from private extensions of the package (see Chapter 5), Section 7.8-2 lists tests which do not have this property.

All these tests apply only to the local table of contents (see Section 7.7) or to private extensions. So only those data files are checked that are actually available in the local GAP installation. No files are fetched from servers during these tests. The required space and time for running these tests depend on the amount of locally available data.

The file tst/testall.g of the package contains Test (Reference: Test) statements for executing a collection of such sanity checks; one can run them by calling ReadPackage( "AtlasRep", "tst/testall.g" ). If no problem occurs then GAP prints only lines starting with one of the following.

+ Input file:
+ GAP4stones:

Some of the checks compute and verify additional data, such as information about point stabilizers of permutation representations. In these cases, output lines starting with #E are error messages that point to inconsistencies, whereas output lines starting with #I inform about data that have been computed and were not yet stored, or about stored data that were not verified.

The examples in the package manual form a part of the tests, they are collected in the file tst/docxpl.tst of the package.

7.8-1 Sanity Checks for a Table of Contents

The following tests can be used to check the data that belong to a given table of contents. Each of these tests is given by a function with optional argument tocid, the identifying string that had been entered as the second argument of AtlasOfGroupRepresentationsNotifyPrivateDirectory (5.1-1). The contents of the local dataword directory can be checked by entering "local", which is also the default for tocid. The function returns false if an error occurs, otherwise true. Currently the following tests of this kind are available.

AGR.Test.Words( [tocid] )

processes all straight line programs that are stored in the directory with identifier tocid, using the function stored in the TestWords component of the data type in question.

AGR.Test.FileHeaders( [tocid] )

checks whether all MeatAxe text format data files in the directory with identifier tocid have a header line that is consistent with the filename, and whether the contents of all GAP format data files in this directory is consistent with the contents of the file.

AGR.Test.Files( [tocid] )

checks whether the MeatAxe text files that are stored in the directory with identifier tocid can be read with ScanMeatAxeFile (7.3-1) such that the result is not fail. The function does not check whether the first line of a MeatAxe text file is consistent with the filename, since this can be tested with AGR.Test.FileHeaders.

AGR.Test.BinaryFormat( [tocid] )

checks whether all MeatAxe text format data files in the directory with identifier tocid satisfy that applying first CMtxBinaryFFMatOrPerm (7.3-4) and then FFMatOrPermCMtxBinary (7.3-5) yields the same object.

AGR.Test.Primitivity( [tocid] )

checks the stored primitivity information for the permutation representations that are stored in the directory with identifier tocid.

AGR.Test.Characters( [tocid] )

checks the stored character information for the matrix and permutation representations that are stored in the directory with identifier tocid.

7.8-2 Other Sanity Checks

The tests described in this section are not intended for checking data from private extensions of the AtlasRep package. Each of the tests is given by a function without arguments that returns false if a contradiction was found during the test, and true otherwise. Additionally, certain messages are printed when contradictions between stored and computed data are found, when stored data cannot be verified computationally, or when the computations yield improvements of the stored data. Currently the following tests of this kind are available.

AGR.Test.GroupOrders()

checks whether the group orders stored in the GAPnames component of AtlasOfGroupRepresentationsInfo (7.1-6) coincide with the group orders computed from an ATLAS permutation representation of degree up to AGR.Test.MaxTestDegree, from the character table or the table of marks with the given name, or from the structure of the name. Supported is a splitting of the name at the first dot (.), where the two parts of the name are examined with the same criteria in order to derive the group order.

AGR.Test.MaxesOrders()

checks whether the orders of maximal subgroups stored in the component GAPnames of AtlasOfGroupRepresentationsInfo (7.1-6) coincide with the orders computed from the restriction of an ATLAS permutation representation of degree up to AGR.Test.MaxTestDegree, from the character table, or the table of marks with the given name, or from the information about maximal subgroups of a factor group modulo a normal subgroup that is contained in the Frattini subgroup.

AGR.Test.MaxesStructure()

checks whether the names of maximal subgroups stored in the component GAPnames of AtlasOfGroupRepresentationsInfo (7.1-6) coincide with the names computed from the GAP character table with the given name.

AGR.Test.StdCompatibility()

checks whether the information about the compatibility of standard generators of a group and its factor groups that is stored in the GAPnames component of AtlasOfGroupRepresentationsInfo (7.1-6) coincides with computed values.

The following criterion is used for computing the value for a group G. Use the GAP Character Table Library to determine factor groups F of G for which standard generators are defined and moreover a presentation in terms of these standard generators is known. Evaluate the relators of the presentation in the standard generators of G, and let N be the normal closure of these elements in G. Then mapping the standard generators of F to the N-cosets of the standard generators of G is an epimorphism. If |G/N| = |F| holds then G/N and F are isomorphic, and the standard generators of G and F are compatible in the sense that mapping the standard generators of G to their N-cosets yields standard generators of F.

AGR.Test.CompatibleMaxes()

checks whether the information about deriving straight line programs for restricting to subgroups from straight line programs that belong to a factor group coincide with computed values.

The following criterion is used for computing the value for a group G. If F is a factor group of G such that the standard generators of G and F are compatible (see the test function AGR.Test.StdCompatibility) and if there are a presentation for F and a permutation representation of G then it is checked whether the "maxes" type straight line programs for F can be used to compute generators for the maximal subgroups of G; if not then generators of the kernel of the natural epimorphism from G to F, must be added.

AGR.Test.ClassScripts()

checks whether the straight line programs that compute representatives of certain conjugacy classes are consistent with information stored on the GAP character table of the group in question, in the sense that the given class names really occur in the character table and that the element orders and centralizer orders for the classes are correct.

AGR.Test.CycToCcls()

checks whether some straight line program that computes representatives of conjugacy classes of a group can be computed from the ordinary GAP character table of that group and a straight line program that computes representatives of cyclic subgroups. In this case the missing scripts are printed if the level of InfoAtlasRep (7.1-1) is at least 1.

AGR.Test.Standardization()

checks whether all generating sets corresponding to the same set of standard generators have the same element orders; for the case that straight line programs for computing certain class representatives are available, also the orders of these representatives are checked w. r. t. all generating sets.

AGR.Test.StdTomLib()

checks whether the standard generators are compatible with those that occur in the TomLib package.

AGR.Test.KernelGenerators()

checks whether the information stored in the GAPnames component of AtlasOfGroupRepresentationsInfo (7.1-6) about straight line programs for computing generators of the kernels of natural epimorphisms between ATLAS groups coincides with computed values.

The following criterion is used for computing the value for a group G. Use the GAP Character Table Library to determine factor groups F of G for which standard generators are defined such that mapping standard generators of G to those of F defines a homomorphism, and such that a presentation of F in terms of its standard generators is known. Evaluating the relators of the presentation in the standard generators of G yields normal subgroup generators for the kernel.

A message is printed for each group name for which some straight line program for computing kernel generators was not stored but now was computed, or for which the stored info cannot be verified,

AGR.Test.MinimalDegrees()

checks that the (permutation and matrix) representations available in the ATLAS of Group Representations do not have smaller degree than the claimed minimum.

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