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### 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 7.9), 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 7.8). 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, AtlasRep functions 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: InfoLevel). For example, the info level of InfoAtlasRep (7.1-1) can be set to the nonnegative integer $$n$$ using SetInfoLevel( InfoAtlasRep, $$n$$ ).

##### 7.1-1 InfoAtlasRep
 ‣ InfoAtlasRep ( info class )

If the info level of InfoAtlasRep is at least $$1$$ then information about fail results of AtlasRep functions is printed. If the info level is at least $$2$$ then also 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 (see Section 7.3) 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 AGR
 ‣ AGR ( global variable )

is a record whose components are functions and data that are used by the high level interface functions. Some of the components are documented, see for example the index of the package manual.

##### 7.1-5 AtlasOfGroupRepresentationsInfo
 ‣ AtlasOfGroupRepresentationsInfo ( global variable )

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

GAPnames

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

notified

a list used for administrating extensions of the database (see Chapter 5); the value is changed by AtlasOfGroupRepresentationsNotifyData (5.1-1) and AtlasOfGroupRepresentationsForgetData (5.1-2),

characterinfo, permrepinfo, ringinfo

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

TableOfContents

a record with at most the components core, internal, local, merged, types, and the identifiers of database extensions. The value of the component types is set in AGR.DeclareDataType (7.5-1), and the values of the other components are created by AtlasOfGroupRepresentationsNotifyData (5.1-1).

accessFunctions

a list of records, each describing how to access the data files, see Sections 4.2-6 and 7.2, and

By default, locally available data files are stored in prescribed directories, and the files are exactly the text files that have been downloaded from appropriate places in the internet. However, a more flexible approach may be useful.

First, one may want to use different file formats, for example MeatAxe binary files may be provided parallel to MeatAxe text files. Second, one may want to use a different directory structure, for example the same structure as used on some server –this makes sense for example if a local mirror of a server is available, because then one can read the server files directly, without transferring/copying them to another directory.

In order to achieve this (and perhaps more), we admit to customize the meaning of the following three access steps.

Are the required data locally available?

There may be different file formats available, such as text or binary files, and it may happen that the data are available in one file or are distributed to several files.

How can a file be made locally available?

A different remote file may be fetched, or some postprocessing may be required.

How is the data of a file accessed by GAP?

A different function may be needed to evaluate the file contents.

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 (7.1-5). The relevant record components are as follows.

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 as key in the user preference FileAccessFunctions, see Section 4.2-6.

location( $$files, type$$ )

Let $$files$$ be a list of pairs [ dirname, filename ], and $$type$$ be the data type (see AGR.DeclareDataType (7.5-1)) to which the files belong. This function must return either the absolute paths where the mechanism implemented by the current record expects the local version of the given files, or fail if this function does not feel responsible for these files.

The files 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( $$filepath, filename, dirname, type$$ )

This function is called if a file is not locally available and if the location function in the current record has returned a list of paths. The argument $$type$$ 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( $$files, type, filepaths$$ )

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 first three arguments must be the same as for the location function.

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.

In AGR.FileContents (7.6-2), those records in the accessFunctions component of AtlasOfGroupRepresentationsInfo (7.1-5) are considered –in reversed order– whose description component occurs in the user preference FileAccessFunctions, see Section 4.2-6.

#### 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 user preference HowToReadMeatAxeTextFiles, see Section 4.2-8.

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 )
 ‣ MeatAxeString( intmat ) ( operation )

Returns: a string encoding the GAP objects given as input in C-MeatAxe text format, see [Rin].

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 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 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.

In the fourth form, for a matrix intmat of integers, MeatAxeString returns a string that encodes intmat as an integer matrix.

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


The MeatAxe defines the bijection between the elements in the field with $$q = p^d$$ elements and the set $$\{ 0, 1, \ldots, q-1 \}$$ of integers by assigning the field element $$\sum_{{i=0}}^{{d-1}} c_i z^i$$ to the integer $$\sum_{{i=0}}^{{d-1}} c_i p^i$$, where the $$c_i$$ are in the set $$\{ 0, 1, \ldots, p-1 \}$$ and $$z$$ is the primitive root of the field with $$q$$ elements that corresponds to the residue class of the indeterminate, modulo the ideal spanned by the Conway polynomial of degree $$d$$ over the field with $$p$$ elements.

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

Let the pair $$(\textit{elm}, \textit{def})$$ be either of the form $$(M, q)$$ where $$M$$ is a matrix over a finite field $$F$$, say, with $$q \leq 256$$ elements, or of the form $$(\pi, n)$$ where $$\pi$$ 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 $$\pi$$, viewed as a permutation on the points up to $$n$$, to the file with name outfile.

In the case of a permutation $$\pi$$, 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 4.2-11.

(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, or fail.

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, $$\ldots$$, $$n$$,

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, $$\ldots$$, $$l$$, 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 data files, 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 for ScanStraightLineProgram (7.4-1). (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 AtlasRep Package

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

• a column of its own in the output produced by DisplayAtlasInfo (3.5-1) when called without arguments or with only argument a list of group names,

• a line format of its own for the output produced by DisplayAtlasInfo (3.5-1) when called with first argument a group name,

• an input format of its own for AtlasProgram (3.5-4),

• an input format of its own for OneAtlasGeneratingSetInfo (3.5-6), and

• specific tests for the data of this data type; these functions are used by the global tests described in Section 7.9.

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. If kind is "rep" then AGR.DeclareDataType declares a new data type of representations, if kind is "prg" then it declares a new data type of programs. The string name is the name of the type, for example "perm", "matff", or "classes". AtlasRep stores the data for each group internally in a record whose component name holds the list of the data about the type with this name.

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 (7.1-5), 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 (3.5-3), OneAtlasGeneratingSetInfo (3.5-6), or AllAtlasGeneratingSetInfos (3.5-7)) 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, a list containing the GAP name and the ATLAS 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 (3.5-6). The value must be a function that takes two arguments (a list as returned by OneAtlasGeneratingSetInfo (3.5-6), 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 (3.5-4). The value must be a function that takes four arguments (the current table of contents, the group name, 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 (3.5-4)), 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 (3.5-4) 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 (3.5-5) to create the result value from the identifier. (The default value is AtlasProgramDefault.)

TOCEntryString

This is used in StringOfAtlasTableOfContents (5.1-3). The value must be a function that takes two or three arguments (the name name of the type, a list as returned by AGR.ParseFilenameFormat (7.6-1), and optionally a string that indicates the "remote" format) and returns a string that describes the appropriate data format. (The default value is TOCEntryStringDefault.)

PostprocessFileInfo

This is used in the construction of a table of contents 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 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 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 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 fifth argument is true or false, indicating verbose mode or not.

#### 7.6 Filenames Used in the AtlasRep Package

AtlasRep expects that the filename of each data file describes the contents of the file. This section lists the definitions of the supported structures of filenames.

Each filename consists of two parts, separated by a minus sign -. The first part is always of the form $$groupname$$G$$i$$, 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 (7.1-5).

The names of files that contain straight line programs or straight line decisions have one of the following forms. In each of these cases, the suffix W$$n$$ means that $$n$$ is the version number of the program.

$$groupname$$G$$i$$-cycW$$n$$

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.

$$groupname$$G$$i$$-cclsW$$n$$

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.

$$groupname$$G$$i$$cycW$$n$$-cclsW$$m$$

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

$$groupname$$G$$i$$-max$$k$$W$$n$$

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.

$$groupname$$G$$i$$max$$k$$W$$n$$-$$subgroupname$$G$$j$$W$$m$$

In this case, the file contains a straight line program that takes the return value of the program in the file $$groupname$$G$$i$$-max$$k$$W$$n$$ (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.

$$groupname$$G$$i$$-a$$outname$$W$$n$$

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 $$\alpha$$ of $$G$$ given by the name $$outname$$; if this name is empty then $$\alpha$$ is the unique nontrivial outer automorphism of $$G$$; if it is a positive integer $$k$$ then $$\alpha$$ 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 $$\ldots$$ then $$\alpha$$ generates the cyclic group of automorphisms induced on $$G$$ by $$G.2_1$$, $$G.4_2$$, $$G.3_3$$ $$\ldots$$; finally, if it is of the form $$k$$p$$d$$, 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 $$L_3(4).2_1$$, $$U_4(3).2_2^{\prime}$$, and $$O_8^+(3).2_2^{{\prime\prime\prime\prime\prime}}$$, respectively.

$$groupname$$G$$i$$-ker$$factgroupname$$W$$n$$

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 generators of the kernel of an epimorphism that maps $$G$$ to a group with ATLAS-file name $$factgroupname$$. An example is 2A5G1-kerA5W1.

$$groupname$$G$$i$$-G$$j$$W$$n$$

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.

$$groupname$$G$$i$$-check$$n$$

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.

$$groupname$$G$$i$$-P$$n$$

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.

$$groupname$$G$$i$$-find$$n$$

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.

$$groupname$$G$$i$$-X$$descr$$W$$n$$

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 (3.5-4).

The names of files that contain group generators 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).

$$groupname$$G$$i$$-f$$q$$r$$dim$$$$id$$B$$m$$.m$$nr$$

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.

$$groupname$$G$$i$$-p$$n$$$$id$$B$$m$$.m$$nr$$

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.

$$groupname$$G$$i$$-Ar$$dim$$$$id$$B$$m$$.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.

$$groupname$$G$$i$$-Zr$$dim$$$$id$$B$$m$$.g

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

$$groupname$$G$$i$$-Hr$$dim$$$$id$$B$$m$$.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.

$$groupname$$G$$i$$-Z$$n$$r$$dim$$$$id$$B$$m$$.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 $$[ [ c_1, c_2, \ldots, c_n ], [ f_1, f_2, \ldots, f_n ] ]$$ 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 $$s_1, s_2, \ldots, s_m$$. The string string matches format if $$s_i$$ matches the conditions in $$c_i$$, for $$1 \leq i \leq n$$, 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( files, type ) ( function )

Returns: the GAP object obtained from reading and interpreting the file(s) given by files.

Let files be a list of pairs of the form [ dirname, filename ], where dirname and filename are strings, and let type be a data type (see AGR.DeclareDataType (7.5-1)). Each dirname must be one of "datagens", "dataword", or the dirid value of a data extension (see AtlasOfGroupRepresentationsNotifyData (5.1-1)). If the contents of each of the files in question is accessible and their data belong to the data type type then AGR.FileContents returns the contents of the files; otherwise fail is returned.

Note that if some file is already stored in the dirname directory then AGR.FileContents does not check whether the relevant table of contents actually contains filename.

#### 7.7 The record component identifier used by the AtlasRep Package

The functions AtlasGenerators (3.5-3), AtlasProgram (3.5-4), AtlasProgramInfo (3.5-5), OneAtlasGeneratingSetInfo (3.5-6), and AllAtlasGeneratingSetInfos (3.5-7) return records which have a component identifier. The value of this component describes the record in the sense that one can reconstruct the whole record from it, and the identifier value can be used as an input for AtlasGenerators (3.5-3), AtlasProgram (3.5-4), AtlasProgramInfo (3.5-5), AtlasGroup (3.5-8), and AtlasSubgroup (3.5-9).

The identifier component has the following format.

• For records describing representations, it is a list of the form [ gapname, files, std, info ].

• For records describing straight line programs and straight line decisions, it is a list of the form [ gapname, files, std ].

Here gapname is the GAP name of the group in question, files defines the data files, std is the standardization of its generators, and info is some information that depends on the type of the representation, for example the number of moved points in the case of a permutation representation.

The files entry has one of the following formats:

• a string, in the case that exactly one file is needed that does not belong to a private extension; an example of such an identifier value is [ "J1", "J1G1-cycW1", 1 ]

• a list whose entries are strings (which refer to files from the core part of the database) and pairs of the form [ tocid, file ] (which refer to files from the extension given by tocid); examples of identifier values are [ "A5", [ "A5G1-p5B0.m1", "A5G1-p5B0.m2" ], 1, 5 ], [ "2.M12", [ [ "mfer", "2M12G1-cclsW1" ] ], 1 ], [ "2.M12", [ "M12G1-max1W1", [ "internal", "2M12G1-kerM12W1" ] ], 1 ], [ "2.M12", [ [ "mfer", "2M12G1-p24bB0.m1" ], [ "mfer", "2M12G1-p24bB0.m2" ] ], 1, 24 ].

Up to version 1.5 of the AtlasRep package, a different identifier format was used for files from extensions of the database. Namely, the first entry of the list was a pair [ tocid, groupname ], and the second entry was either a string or a list of strings. Note that with that old format, it was not possible to describe a combination of several files from different sources (core part and extension, or different extensions). The function AtlasRepIdentifier (7.7-1) can be used to convert between the two formats.

##### 7.7-1 AtlasRepIdentifier
 ‣ AtlasRepIdentifier( oldid ) ( function )
 ‣ AtlasRepIdentifier( id, "old" ) ( function )

This function converts between the "old format" (the one used up to version 1.5.1 of the package) and the "new format" (the one used since version 2.0) of the identifier component of the records returned by AtlasRep functions. Note that the two formats differ only for identifier components that describe data from non-core parts of the database.

If the only argument is a list oldid that is an identifier in old format then the function returns the corresponding identifier in new format. If there are two arguments, a list id that is an identifier in new format and the string "old", then the function returns the corresponding identifier in old format if this is possible, and fail otherwise.

gap> id:= [ "A5", [ "A5G1-p5B0.m1", "A5G1-p5B0.m2" ], 1, 5 ];;
gap> AtlasRepIdentifier( id ) = id;
true
gap> id:= [ "L2(8)", "L28G1-check1", 1, 1 ];;
gap> AtlasRepIdentifier( id ) = id;
true
gap> oldid:= [ [ "priv", "C4" ], [ "C4G1-p4B0.m1" ], 1, 4 ];;
gap> newid:= AtlasRepIdentifier( oldid );
[ "C4", [ [ "priv", "C4G1-p4B0.m1" ] ], 1, 4 ]
gap> oldid = AtlasRepIdentifier( newid, "old" );
true
gap> oldid:= [ [ "priv", "C4" ], "C4G1-max1W1", 1 ];;
gap> newid:= AtlasRepIdentifier( oldid );
[ "C4", [ [ "priv", "C4G1-max1W1" ] ], 1 ]
gap> oldid = AtlasRepIdentifier( newid, "old" );
true
gap> oldid:= [ [ "priv", "C4" ], "C4G1-Ar1aB0.g", 1, 1 ];;
gap> newid:= AtlasRepIdentifier( oldid );
[ "C4", [ [ "priv", "C4G1-Ar1aB0.g" ] ], 1, 1 ]
gap> oldid = AtlasRepIdentifier( newid, "old" );
true
gap> oldid:= [ [ "priv", "C4" ], "C4G1-XtestW1", 1 ];;
gap> newid:= AtlasRepIdentifier( oldid );
[ "C4", [ [ "priv", "C4G1-XtestW1" ] ], 1 ]
gap> oldid = AtlasRepIdentifier( newid, "old" );
true
gap> oldid:= [ [ "mfer", "2.M12" ],
>  [ "2M12G1-p264aB0.m1", "2M12G1-p264aB0.m2" ], 1, 264 ];;
gap> newid:= AtlasRepIdentifier( oldid );
[ "2.M12",
[ [ "mfer", "2M12G1-p264aB0.m1" ], [ "mfer", "2M12G1-p264aB0.m2" ] ]
, 1, 264 ]
gap> oldid = AtlasRepIdentifier( newid, "old" );
true


#### 7.8 The Tables of Contents of the AtlasRep Package

The list of AtlasRep data is stored in several tables of contents, which are given essentially by JSON documents, one for the core data and one for each data extension in the sense of Chapter 5. The only exception are data extensions by locally available files in a given directory, where the contents of this directory itself describes the data in question. One can create such a JSON document for the contents of a given local data directory with the function StringOfAtlasTableOfContents (5.1-3).

Here are the administrational functions that are called when a data extension gets notified with AtlasOfGroupRepresentationsNotifyData (5.1-1). In each case, $$gapname$$ and $$atlasname$$ denote the GAP and ATLAS name of the group in question (see Section 3.2), and $$dirid$$ denotes the identifier of the data extension.

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

AGR.GNAN( $$gapname, atlasname[, dirid]$$ )

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.

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

AGR.TOC( $$typename, filename, crc[, dirid]$$ )

AGR.TOC notifies an entry to the TableOfContents.( $$dirid$$ ) component of AtlasOfGroupRepresentationsInfo (7.1-5). The string $$typename$$ must be the name of the data type to which the entry belongs, the string $$filename$$ must be the prefix of the data file(s), and $$crc$$ must be a list of integers that are the CRC values of the data files (see CrcFile (Reference: CrcFile); in particular, the number of files that are described by the entry equals the length of $$crc$$.

The optional argument $$dirid$$ is equal to the argument with the same name in the corresponding call of AtlasOfGroupRepresentationsNotifyData (5.1-1). If no $$dirid$$ argument is given then the current value of AGR.DIRID is taken as the default; this value is set automatically before a toc.json file gets evaluated by AtlasOfGroupRepresentationsNotifyData (5.1-1), and is reset afterwards. If AGR.DIRID is not bound and $$dirid$$ is not given then this function has no effect.

An example of a valid call is AGR.TOC("perm","alt/A5/mtx/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( $$gapname, size[, dirid]$$ )

The integer $$size$$ is stored as the order of the group with GAP name $$gapname$$, in AtlasOfGroupRepresentationsInfo.GAPnames.

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

AGR.MXN( $$gapname, nrMaxes[, dirid]$$ )

The integer $$nrMaxes$$ is stored as the number of classes of maximal subgroups of the group with GAP name $$gapname$$, in AtlasOfGroupRepresentationsInfo.GAPnames.

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

AGR.MXO( $$gapname, sizesMaxes[, dirid]$$ )

The list $$sizesMaxes$$ of subgroup orders of the classes of maximal subgroups of the group with GAP name $$gapname$$ (not necessarily dense, in non-increasing order) is stored in AtlasOfGroupRepresentationsInfo.GAPnames.

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

AGR.MXS( $$gapname, structureMaxes[, dirid]$$ )

Called with the string The list $$structureMaxes$$ of strings describing the structures of the maximal subgroups of the group with GAP name $$gapname$$ (not necessarily dense), is stored in AtlasOfGroupRepresentationsInfo.GAPnames.

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

AGR.STDCOMP( $$gapname, factorCompatibility[, dirid]$$ )

The list $$factorCompatibility$$ (with entries the standardization of the group with GAP name $$gapname$$ , 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) is stored 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( $$repname, descr[, dirid]$$ )

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 (7.1-5).

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

AGR.TOCEXT( $$atlasname, std, maxnr, files[, dirid]$$ )

Called with $$atlasname$$, 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 AtlasOfGroupRepresentationsInfo.GAPnames.

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

AGR.API( $$repname, info[, dirid]$$ )

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 a record that describes the contents of $$info$$.

$$info$$ has the following entries.

• At position $$1$$, the transitivity is stored.

• If the transitivity is zero then $$info$$ has length two, and the second entry is the list of orbit lengths.

• If the transitivity is positive then $$info$$ has length four or five, and the second entry is the rank of the action.

• If the transitivity is positive then the third entry is one of the strings "prim", "imprim", denoting primitivity or not.

• If the transitivity is positive then the fourth entry is either the string "???" or a string that describes the structure of the point stabilizer. If the third entry is "imprim" then this description consists of a subgroup part and a maximal subgroup part, separated by " < ".

• If the third entry is "prim" then the fifth entry is either the string "???" or the number of the class of maximal subgroups that are the point stabilizers.

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

AGR.CHAR( $$gapname, repname, char, pos[, charname[, dirid]]$$ )

Called with the strings $$gapname$$ 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 $$charname$$.

If $$dirid$$ is given but no $$charname$$ is known then one can enter fail as the fifth argument.

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

#### 7.9 Sanity Checks for the AtlasRep Package

The file tst/testall.g of the package contains Test (Reference: Test) statements for checking whether the AtlasRep functions behave as documented. One can run these tests by calling ReadPackage( "AtlasRep", "tst/testall.g" ). The examples in the package manual form a part of the tests, they are collected in the file tst/docxpl.tst of the package.

The remainder of this section deals with consistency checks of the data. The tests described in Section 7.9-1 can be used for data from any extension of the database (see Chapter 5), Section 7.9-2 lists tests which apply only to the core part of the database.

All these tests apply only to locally available files (see Section 7.8), no files are downloaded during the tests. Thus the required space and time for running these tests depend on the amount of locally available data.

Some of the tests 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. These tests are experimental in the sense that they involve several heuristics. Depending on the data to which they are applied, it may happen that the tests run out of space or do not finish in acceptable time. Please inform the package maintainer if you run into such problems.

The following tests can be used to check the data that belong to a given part of the database (core data or extension). 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 AtlasOfGroupRepresentationsNotifyData (5.1-1). The contents of the core part can be checked by entering "core", 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. (For some of them, the global option TryToExtendData can be entered in order to try the computation of not yet stored data.)

AGR.Test.GroupOrders()

checks whether the group orders stored in the GAPnames component of AtlasOfGroupRepresentationsInfo (7.1-5) coincide with the group orders computed from an ATLAS permutation representation of degree up to AGR.Test.MaxTestDegree, from the available character table or table of marks with the given name, or from the structure of the name, in the sense that splitting the name at the first dot (.) or colon (:) and applying the same criteria to derive the group order from the two parts may yield enough information.

AGR.Test.Words( [$$tocid$$] )

processes the straight line programs that belong to $$tocid$$, using the function stored in the TestWords component of the data type in question.

The straight line programs for the cases listed in AGR.Test.HardCases.TestWords are omitted.

AGR.Test.ClassScripts( [$$tocid$$] )

checks whether the straight line programs that belong to $$tocid$$ and 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( [$$tocid$$][:TryToExtendData] )

checks whether all straight line programs that belong to $$tocid$$ and that compute class representatives from representatives of cyclic subgroups possess a corresponding straight line program (anywhere in the database) for computing representatives of cyclic subgroups.

AGR.Test.FileHeaders( [$$tocid$$] )

checks whether the MeatAxe text files that belong to $$tocid$$ have a header line that is consistent with the filename, and whether the contents of all GAP format data files that belong to $$tocid$$ is consistent with the filename.

AGR.Test.Files( [$$tocid$$] )

checks whether the MeatAxe text files that belong to $$tocid$$ 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 files that belong to $$tocid$$ satisfy that applying first CMtxBinaryFFMatOrPerm (7.3-4) and then FFMatOrPermCMtxBinary (7.3-5) yields the same object.

AGR.Test.Primitivity( [$$tocid$$][:TryToExtendData] )

checks the stored primitivity information for the permutation representations that belong to $$tocid$$. That is, the number of orbits, in case of a transitive action the transitivity, the rank, the information about the point stabilizers are computed if possible, and compared with the stored information.

AGR.Test.Characters( [$$tocid$$][:TryToExtendData] )

checks the character information (that belongs to $$tocid$$) for the matrix and permutation representations.

AGR.Test.StdCompatibility( [$$tocid$$][:TryToExtendData] )

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 (7.1-5) and belongs to $$tocid$$ 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.KernelGenerators( [$$tocid$$][:TryToExtendData] )

checks whether the straight line programs (that belong to $$tocid$$) for computing generators of kernels of natural epimorphisms between ATLAS groups compute generators of normal subgroups of the right group orders. If it is known that the given standard generators of the given group are compatible with some standard generators of the factor group in question (see the section about AGR.Test.StdCompatibility) then it is also checked whether evaluating the straight line program at these standard generators of the factor group yields only the identity.

Note that the verification of normal subgroups of matrix groups may be very time and space consuming if the package recog [NSA+18] is not available.

The function also tries to find words for computing kernel generators of those epimorphisms for which no straight line programs are stored; the candidates are given by stored factor fusions between the character tables from the GAP Character Table Library.

AGR.Test.MaxesOrders( [$$tocid$$] )

checks whether the orders of maximal subgroups stored in the component GAPnames of AtlasOfGroupRepresentationsInfo (7.1-5) coincide with the orders computed from the restriction of an ATLAS permutation representation of degree up to AGR.Test.MaxTestDegree (using a straight line program that belongs to $$tocid$$), from the character table, or the table of marks with the given name, or from the information about maximal subgroups of the 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 (7.1-5) coincide with the names computed from the GAP character table with the given name.

AGR.Test.MaxesStandardization( [$$tocid$$] )

checks whether the straight line programs (that belong to $$tocid$$) for standardizing the generators of maximal subgroups are correct: If a semi-presentation is available for the maximal subgroup and the standardization in question then it is used, otherwise an explicit isomorphism is tried.

AGR.Test.CompatibleMaxes( [$$tocid$$][:TryToExtendData] )

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.

##### 7.9-2 Other Sanity Checks

The tests described in this section are intended for checking data that do not belong to a particular part of the AtlasRep database. Therefore all locally available data are used in these tests. 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.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.MinimalDegrees()

checks that the (permutation and matrix) representations available in the database do not have smaller degree than the minimum claimed in Section 6.3.

Finally, we reset the user preference and the info level which had been set at the beginning of Chapter 2.

gap> SetUserPreference( "AtlasRep", "DisplayFunction", origpref );
gap> SetInfoLevel( InfoAtlasRep, globallevel );

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