This chapter contains

the introduction of **GAP3** character tables (see Some Notes on Character
Theory in GAP, Character Table Records, Brauer Table Records,
IsCharTable, PrintCharTable, TestCharTable, Operations Records
for Character Tables, Functions for Character Tables, Operators
for Character Tables) and some conventions for their usage (see
Conventions for Character Tables),

the description how to construct or get character tables (see Getting Character Tables, CharTable; for the contents of the table library, see Chapter Character Table Libraries), matrix representations (see MatRepresentationsPGroup).

the description of some functions which give information about the conjugacy classes of character tables, that is, to compute classlengths (see InitClassesCharTable), inverse classes (see InverseClassesCharTable) and classnames (see ClassNamesCharTable), structure constants (see ClassMultCoeffCharTable, MatClassMultCoeffsCharTable, ClassStructureCharTable), the set of real classes (see RealClassesCharTable), orbits of the Galois group on the classes (see ClassOrbitCharTable) and roots of classes (see ClassRootsCharTable),

the description how character tables or parts of them can be displayed (see DisplayCharTable) and sorted (see SortCharactersCharTable, SortClassesCharTable, SortCharTable).

the description of functions which compute the automorphism group of a matrix (see MatAutomorphisms) or character table (see TableAutomorphisms), or which compute permutations relating permutation equivalent matrices (see TransformingPermutations) or character tables (see TransformingPermutationsCharTables),

the description of functions which get fusions from and store fusions on tables (see GetFusionMap, StoreFusion, FusionConjugacyClasses),

the description of the interface between **GAP3** and the MOC3 system (see
MAKElb11, ScanMOC, MOCChars, GAPChars, MOCTable, PrintToMOC
), and of a function which converts **GAP3** tables to **CAS** tables (see
PrintToCAS).

This chapter does **not** contain information about

functions to construct characters (see Chapter Characters), or functions to construct and use maps (see Chapter Maps and Parametrized Maps).

For some elaborate examples how character tables are handled in **GAP3**,
see About Character Tables.

- Some Notes on Character Theory in GAP
- Character Table Records
- Brauer Table Records
- IsCharTable
- PrintCharTable
- TestCharTable
- Operations Records for Character Tables
- Functions for Character Tables
- Operators for Character Tables
- Conventions for Character Tables
- Getting Character Tables
- CharTable
- Advanced Methods for Dixon Schneider Calculations
- An Example of Advanced Dixon Schneider Calculations
- CharTableFactorGroup
- CharTableNormalSubgroup
- CharTableDirectProduct
- CharTableWreathSymmetric
- CharTableRegular
- CharTableIsoclinic
- CharTableSplitClasses
- CharTableCollapsedClasses
- CharDegAgGroup
- CharTableSSGroup
- MatRepresentationsPGroup
- CharTablePGroup
- InitClassesCharTable
- InverseClassesCharTable
- ClassNamesCharTable
- ClassMultCoeffCharTable
- MatClassMultCoeffsCharTable
- ClassStructureCharTable
- RealClassesCharTable
- ClassOrbitCharTable
- ClassRootsCharTable
- NrPolyhedralSubgroups
- DisplayCharTable
- SortCharactersCharTable
- SortClassesCharTable
- SortCharTable
- MatAutomorphisms
- TableAutomorphisms
- TransformingPermutations
- TransformingPermutationsCharTables
- GetFusionMap
- StoreFusion
- FusionConjugacyClasses
- MAKElb11
- ScanMOC
- MOCChars
- GAPChars
- MOCTable
- PrintToMOC
- PrintToCAS

It seems to be necessary to state some basic facts --and maybe warnings--
at the beginning of the character theory package. This holds for people
who are familiar with character theory because there is no global
reference on computational character theory, although there are many
papers on this topic, like NPP84 or LP91. It holds,
however, also for people who are familiar with **GAP3** because the general
concept of categories and domains (see About Domains and Categories and
chapter Domains) plays no important role here --we will justify this
later in this section.

Intuitively, characters of the finite group *G* can be thought of as
certain mappings defined on *G*, with values in the complex number field;
the set of all characters of *G* forms a semiring with addition and
multiplication both defined pointwise, which is embedded in the ring of
generalized (or virtual) characters in the natural way. A ** Z**--basis
of this ring, and also a vector space base of the vector space of class
functions, is given by the irreducible characters.

At this stage one could ask where there is a problem, since all these
algebraic structures are supported by **GAP3**, as is described in chapters
Domains, Rings, Vector Spaces, Mappings, and others.

Now, we first should say that characters are **not** implemented as
mappings, that there are **no** **GAP3** domains denoting character rings,
and that a character table is **not** a domain.

For computations with characters of a finite group *G* with *n* conjugacy
classes, say, we fix an order of the classes, and then identify each
class with its position according to this order. Each character of *G*
will be represented as list of length *n* where at the *i*--th position
the character value for elements of the *i*--th class is stored. Note
that we do not need to know the conjugacy classes of *G* physically, even
our ``knowledge'' of the group may be implicit in the sense that e.g.
we know how many classes of involutions *G* has, and which length these
classes have, but we never have seen an element of *G*, or a presentation
or representation of *G*. This allows to work with the character tables
of very large groups, e.g., of the so--called monster, where **GAP3** has
no chance to work with the group.

As a consequence, also other information involving characters is given implicitly. For example, we can talk about the kernel of a character not as a group but as a list of classes (more exactly: a list of their positions according to the order of classes) forming this kernel; we can deduce the group order, the contained cyclic subgroups and so on, but we do not get the group itself.

Characters are one kind of class functions, and we also represent general
class functions as lists. Two important kinds of these functions which
are not characters are power maps and fusion maps. The *k*--th power map
maps each class to the class of *k*--th powers of its elements, the
corresponding list contains at each position the position of the image.
A subgroup fusion map between the classes of a subgroup *H* of *G* and
the classes of *G* maps each class *c* of *H* to that class of *G* that
contains *c*; if we know only the character tables of the two groups,
this means with respect to a fixed embedding of *H* in *G*.

So the data mainly consist of lists, and typical calculations with
character tables are more or less loops over these lists. For example,
the known scalar product of two characters *χ*, *ψ* of *G* given by

[χ,ψ] = 1/|G| ∑_{g∈ G} χ(g) ψ(g^{-1}) |

` Sum( [1..n], i -> t.classes[i]*chi[i]*GaloisCyc(psi[i],-1) );`

where `t.classes`

is the list of classlengths, and `chi`

, `psi`

are the
lists corresponding to *χ*, *ψ*, respectively. Characters,
classlengths, element orders, power maps, fusion maps and other
information about a group is stored in a common character table record
just to avoid confusion, not to indicate an algebraic structure (which
would mean a domain in the sense of **GAP3**).

A character table is not determined by something similar to generators
for groups or rings in **GAP3** where other components (the knowledge about
the domain) is stored for the sake of efficiency. In many situations one
works with incomplete tables or preliminary tables which are, strictly
speaking, no character tables but shall be handled like character tables.
Moreover, the correctness or even the consistency of a character table is
hard to prove. Thus it is not sufficient to view a character table as a
black box, and to get information about it using a few property test
functions. In fact there are very few functions that return character
tables or that are property tests. Most **GAP3** functions dealing with
character tables return class functions, or lists of them, or information
about class functions. For that, **GAP3** directly accesses the components
of the table record, and the user will have to look at the record
components, too, in order to put the pieces of the puzzle together, and
to decide how to go on.

So it is not easy to say what a character table **is**; it **describes** some
properties of the underlying group, and it describes them in a rather
abstract way. Also **GAP3** does not know whether or not a list **is** a
character, it will e.g. regard a list with all entries equal to 1 as the
trivial character if it is passed to a function that expects characters.

It is one of the advantages of character theory that after one has translated a problem concerning groups into a problem concerning their character tables the calculations are mostly simple. For example, one can often prove that a group is a Galois group over the rationals using calculations of structure constants that can be computed from the character table, and informations on (the character tables of) maximal subgroups.

In this kind of problems the translation back to the group is just an
interpretation by the user, it does not take place in **GAP3**. At the
moment, the only interface between handling groups and handling character
tables is the fixed order of conjugacy classes.

Note that algebraic structures are not of much interest in character theory. The main reason for this is that we have no homomorphisms since we need not to know anything about the group multiplication.

For **GAP3**, a character table is any record that has the components
`centralizers`

and `identifier`

(see IsCharTable).

There are three different but very similar types of character tables in
**GAP3**, namely ordinary tables, Brauer tables and generic tables.
Generic tables are described in Chapter Generic Character Tables.
Brauer tables are defined and stored relative to ordinary tables, so they
will be described in Brauer Table Records, and we start with ordinary
tables.

You may store arbitrary information on an ordinary character table, but
these are the only fields used by **GAP3** functions:

`centralizers`

:

the list of centralizer orders which should be positive integers

`identifier`

:

a string that identifies the table, sometimes also called he table name; it is used for fusions (see below), programs for generic tables (see chapter Generic Character Tables) and for access to library tables (see CharTable, Contents of the Table Libraries)

`order`

:

the group order, a positive integer; in most cases, it is equal to`centralizers[1]`

`classes`

:

the lengths of conjugacy classes, a list of positive integers

`orders`

:

the list of representative orders

`powermap`

:

a list where at position`p`, if bound, the`p`-th powermap is stored; the`p`-th powermap is a -possibly parametrized- map (see More about Maps and Parametrized Maps)

`fusions`

:

a list of records which describe the fusions into other character tables, that is subgroup fusions and factor fusions; any record has fields`name`

(the`identifier`

component of the destination table) and`map`

(a list of images for the classes, it may be parametrized (see More about Maps and Parametrized Maps)); if there are different fusions with same destination table, the field`specification`

is used to distinguish them; optional fields are`type`

(a string that is`"normal"`

for normal subgroup fusions and`"factor"`

for factor fusions) and`text`

(a string with information about the fusion)

`fusionsource`

:

a list of table names of those tables which contain a fusion into the actual table

`irreducibles`

:

a list of irreducible characters (see below)

`irredinfo`

:

a list of records with information about`irreducibles`

, usual entries are`indicator`

,`pblock`

and`charparam`

(see Indicator, PrimeBlocks, Generic Character Tables); if the field`irreducibles`

is sorted using SortCharactersCharTable, the`irredinfo`

field is sorted, too. So any information about`irreducibles`

should be stored here.

`projectives`

:

(only for**ATLAS**tables, see ATLAS Tables) a list of records, each with fields`name`

(of the table of a covering group) and`chars`

(a list of --in general not all-- faithful irreducibles of the covering group)

`permutation`

:

the actual permutation of the classes (see Conventions for Character Tables, SortClassesCharTable)

`classparam`

:

a list of parameter values specifying the classes of tables constructed via specialisation of a generic character table (see chapter Generic Character Tables)

`classtext`

:

a list of additional information about the conjugacy classes (e.g. representatives of the class for matrix groups or permutation groups)

`text`

:

a string containing information about the table; these are e.g. its source (see Chapter Character Table Libraries), the tests it has passed (`1.o.r.`

for the test of orthogonality,`pow[`

for the construction of the`p`]`p`-th powermap,`DEC`

for the decomposition of ordinary characters in Brauer characters), and choices made without loss of generality where possible

`automorphisms`

:

the permutation group of column permutations preserving the set`irreducibles`

(see MatAutomorphisms, TableAutomorphisms)

`classnames`

:

a list of names for the classes, a string each (see ClassNamesCharTable)

`classnames`:

for each entry`clname`in`classnames`

, a field`tbl`.`clname`that has the position of`clname`in`classnames`

as value (see ClassNamesCharTable)

`operations`

:

a record with fields`Print`

(see DisplayCharTable) and`ScalarProduct`

(see ScalarProduct); the default value of the`operations`

field is`CharTableOps`

(see Operations Records for Character Tables)

`CAS`

:

a list of records, each with fields`permchars`

,`permclasses`

(both permutations),`name`

and eventually`text`

and`classtext`

; application of the two permutations to`irreducibles`

and classes yields the original**CAS**library table with name`name`

and text`text`

(see CAS Tables)

`libinfo`

:

a record with components`othernames`

and perhaps`CASnames`

which are all admissible names of the table (see CharTable); using these records, the list`LIBLIST.ORDINARY`

can be constructed from the library using`MakeLIBLIST`

(see Organization of the Table Libraries)

`group`

:

the group the table belongs to; if the table was computed using`CharTable`

(see CharTable) then this component holds the group, with conjugacy classes sorted compatible with the columns of the table

**Note** that tables in library files may have different format
(see chapter Character Table Libraries).

This is a typical example of a character table, first the ``naked'' record, then the displayed version:

gap> t:= CharTable( "2.A5" );; PrintCharTable( t ); rec( text := "origin: ATLAS of finite groups, tests: 1.o.r., pow[2,3,5\ ]", centralizers := [ 120, 120, 4, 6, 6, 10, 10, 10, 10 ], powermap := [ , [ 1, 1, 2, 4, 4, 8, 8, 6, 6 ], [ 1, 2, 3, 1, 2, 8, 9, 6, 7 ],, [ 1, 2, 3, 4, 5, 1, 2, 1, 2 ] ], fusions := [ rec( name := "A5", map := [ 1, 1, 2, 3, 3, 4, 4, 5, 5 ] ), rec( name := "2.A5.2", map := [ 1, 2, 3, 4, 5, 6, 7, 6, 7 ] ), rec( name := "2.J2", map := [ 1, 2, 5, 8, 9, 16, 17, 18, 19 ], text := [ 'f', 'u', 's', 'i', 'o', 'n', ' ', 'o', 'f', ' ', 'm', 'a', 'x', 'i', 'm', 'a', 'l', ' ', '2', '.', 'A', '5', ' ', 'd', 'e', 't', 'e', 'r', 'm', 'i', 'n', 'e', 'd', ' ', 'b', 'y', ' ', 't', 'h', 'e', ' ', '3', 'B', ' ', 'e', 'l', 'e', 'm', 'e', 'n', 't', 's' ] ) ], irreducibles := [ [ 1, 1, 1, 1, 1, 1, 1, 1, 1 ], [ 3, 3, -1, 0, 0, -E(5)-E(5)^4, -E(5)-E(5)^4, -E(5)^2-E(5)^3, -E(5)^2-E(5)^3 ], [ 3, 3, -1, 0, 0, -E(5)^2-E(5)^3, -E(5)^2-E(5)^3, -E(5)-E(5)^4, -E(5)-E(5)^4 ], [ 4, 4, 0, 1, 1, -1, -1, -1, -1 ], [ 5, 5, 1, -1, -1, 0, 0, 0, 0 ], [ 2, -2, 0, -1, 1, E(5)+E(5)^4, -E(5)-E(5)^4, E(5)^2+E(5)^3, -E(5)^2-E(5)^3 ], [ 2, -2, 0, -1, 1, E(5)^2+E(5)^3, -E(5)^2-E(5)^3, E(5)+E(5)^4, -E(5)-E(5)^4 ], [ 4, -4, 0, 1, -1, -1, 1, -1, 1 ], [ 6, -6, 0, 0, 0, 1, -1, 1, -1 ] ], automorphisms := Group( (6,8) (7,9) ), construction := function ( tbl ) ConstructProj( tbl ); end, irredinfo := [ rec( pblock := [ , 1, 1,, 1 ] ), rec( pblock := [ , 1, 2,, 1 ] ), rec( pblock := [ , 1, 3,, 1 ] ), rec( pblock := [ , 2, 1,, 1 ] ), rec( pblock := [ , 1, 1,, 2 ] ), rec( pblock := [ , 1, 4,, 3 ] ), rec( pblock := [ , 1, 4,, 3 ] ), rec( pblock := [ , 2, 4,, 3 ] ), rec( pblock := [ , 1, 5,, 3 ] ) ], identifier := "2.A5", operations := CharTableOps, fusionsource := [ "P2/G1/L1/V1/ext2", "P2/G1/L1/V1/ext3", "P2/G2/L1/V1/ext2", "P2/G2/L1/V1/ext3", "P2/G2/L1/V2/ext2" ], name := "2.A5", size := 120, order := 120, classes := [ 1, 1, 30, 20, 20, 12, 12, 12, 12 ], orders := [ 1, 2, 4, 3, 6, 5, 10, 5, 10 ] )

gap> DisplayCharTable( t ); 2.A5 2 3 3 2 1 1 1 1 1 1 3 1 1 . 1 1 . . . . 5 1 1 . . . 1 1 1 1 1a 2a 4a 3a 6a 5a 10a 5b 10b 2P 1a 1a 2a 3a 3a 5b 5b 5a 5a 3P 1a 2a 4a 1a 2a 5b 10b 5a 10a 5P 1a 2a 4a 3a 6a 1a 2a 1a 2a X.1 1 1 1 1 1 1 1 1 1 X.2 3 3 -1 . . A A *A *A X.3 3 3 -1 . . *A *A A A X.4 4 4 . 1 1 -1 -1 -1 -1 X.5 5 5 1 -1 -1 . . . . X.6 2 -2 . -1 1 -A A -*A *A X.7 2 -2 . -1 1 -*A *A -A A X.8 4 -4 . 1 -1 -1 1 -1 1 X.9 6 -6 . . . 1 -1 1 -1 A = -E(5)-E(5)^4 = (1-ER(5))/2 = -b5

Brauer table records are similar to the records which represent ordinary
character tables. They contain many of the well--known record
components, like `identifier`

, `centralizers`

, `irreducibles`

etc.; but
there are two kinds of differences:

First, the operations record is `BrauerTableOps`

instead of
`CharTableOps`

(see Operations Records for Character Tables). Second,
there are two extra components, namely

`ordinary`

, which contains the ordinary character table corresponding to
the Brauer table, and

`blocks`

, which reflects the **block** information; it is a list of records
with components

`defect`

:-

the defect of the block,

`ordchars`

:-

a list of integers indexing the ordinary irreducibles in the block,

`modchars`

:-

a list of integers indexing the Brauer characters in the block,

`basicset`

:-

a list of integers indexing the ordinary irreducibles of a basic set;**note**that the indices refer to the positions in the whole`irreducibles`

list of the ordinary table, not to the positions in the block,

`decinv`

:-

the inverse of the restriction of the decomposition matrix of the block to the basic set given by the`basicset`

component, and possibly

`brauertree`

:-

if exists, a list that represents the decomposition matrix which in this case is viewed as incidence matrix of a tree (the so--called Brauer tree); the entries of the list correspond to the edges of the tree, they refer to positions in the block, not in the whole`irreducibles`

list of the tables. Brauer trees are mainly used to store the information in a more compact way than by decomposition matrices, planar embeddings etc. are not (or not yet) included.

**Note** that Brauer tables in the library have different format
(see Organization of the Table Libraries).

We give an example:

gap> PrintCharTable( CharTable( "M11" ) mod 11 ); rec( identifier := "M11mod11", text := "origin: modular ATLAS of finit\ e groups, tests: DEC, TENS", prime := 11, size := 7920, centralizers := [ 7920, 48, 18, 8, 5, 6, 8, 8 ], orders := [ 1, 2, 3, 4, 5, 6, 8, 8 ], classes := [ 1, 165, 440, 990, 1584, 1320, 990, 990 ], powermap := [ , [ 1, 1, 3, 2, 5, 3, 4, 4 ], [ 1, 2, 1, 4, 5, 2, 7, 8 ],, [ 1, 2, 3, 4, 1, 6, 8, 7 ],,,,,, [ 1, 2, 3, 4, 5, 6, 7, 8 ] ], fusions := [ rec( name := "M11", map := [ 1, 2, 3, 4, 5, 6, 7, 8 ], type := "choice" ) ], irreducibles := [ [ 1, 1, 1, 1, 1, 1, 1, 1 ], [ 9, 1, 0, 1, -1, -2, -1, -1 ], [ 10, -2, 1, 0, 0, 1, E(8)+E(8)^3, -E(8)-E(8)^3 ], [ 10, -2, 1, 0, 0, 1, -E(8)-E(8)^3, E(8)+E(8)^3 ], [ 11, 3, 2, -1, 1, 0, -1, -1 ], [ 16, 0, -2, 0, 1, 0, 0, 0 ], [ 44, 4, -1, 0, -1, 1, 0, 0 ], [ 55, -1, 1, -1, 0, -1, 1, 1 ] ], irredinfo := [ rec( ), rec( ), rec( ), rec( ), rec( ), rec( ), rec( ), rec( ) ], blocks := [ rec( defect := 1, ordchars := [ 1, 2, 3, 4, 6, 7, 9 ], modchars := [ 1, 2, 3, 4, 6 ], decinv := [ [ 1, 0, 0, 0, 0 ], [ -1, 1, 0, 0, 0 ], [ 0, 0, 1, 0, 0 ], [ 0, 0, 0, 1, 0 ], [ 0, 0, 0, 0, 1 ] ], basicset := [ 1, 2, 3, 4, 6 ], brauertree := [ [ 1, 2 ], [ 2, 7 ], [ 3, 7 ], [ 4, 7 ], [ 5 .. 7 ] ] ), rec( defect := 0, ordchars := [ 5 ], modchars := [ 5 ], decinv := [ [ 1 ] ], basicset := [ 5 ] ), rec( defect := 0, ordchars := [ 8 ], modchars := [ 7 ], decinv := [ [ 1 ] ], basicset := [ 8 ] ), rec( defect := 0, ordchars := [ 10 ], modchars := [ 8 ], decinv := [ [ 1 ] ], basicset := [ 10 ] ) ], ordinary := CharTable( "M11" ), operations := BrauerTableOps, orde\ r := 7920, name := "M11mod11", automorphisms := Group( (7,8) ) )

`IsCharTable( `

`obj` )

returns `true`

if `obj` is a record with fields `centralizers`

(a list)
and `identifier`

(a string), otherwise it returns `false`

.

gap> IsCharTable( rec( centralizers:= [ 2,2 ], identifier:= "C2" ) ); true

There is one exception: If the record does not contain an `identifier`

component, but a `name`

component instead, then the function returns
`true`

. Note, however, that this exception will disappear in forthcoming
**GAP3** versions.

`PrintCharTable( `

`tbl` )

prints the information stored in the character table `tbl` in a format
that is **GAP3** readable. The call can be used as argument of `PrintTo`

in order to save the table to a file.

gap> t:= CharTable( "Cyclic", 3 ); CharTable( "C3" ) gap> PrintCharTable( t ); rec( identifier := "C3", name := "C3", size := 3, order := 3, centralizers := [ 3, 3, 3 ], orders := [ 1, 3, 3 ], powermap := [ ,, [ 1, 1, 1 ] ], irreducibles := [ [ 1, 1, 1 ], [ 1, E(3), E(3)^2 ], [ 1, E(3)^2, E(3) ] ], classparam := [ [ 1, 0 ], [ 1, 1 ], [ 1, 2 ] ], irredinfo := [ rec( charparam := [ 1, 0 ] ), rec( charparam := [ 1, 1 ] ), rec( charparam := [ 1, 2 ] ) ], text := "computed using generic character table for cyclic groups"\ , classes := [ 1, 1, 1 ], operations := CharTableOps, fusions := [ ], fusionsource := [ ], projections := [ ], projectionsource := [ ] )

`TestCharTable( `

`tbl` )

- checks the character table
`tbl`:

if

,`tbl`.centralizers

,`tbl`.classes

and the entries of`tbl`.orders

have same length,`tbl`.powermap

if the product of

with`tbl`.centralizers[`i`]

is equal to`tbl`.classes[`i`]

,`tbl`.order

if

divides`tbl`.orders[`i`]

,`tbl`.centralizers[`i`]

if the entries of

and the corresponding record fields are consistent,`tbl`.classnames

if the first orthogonality relation for

is satisfied,`tbl`.irreducibles

if the centralizers agree with the sums of squared absolute values of

and`tbl`.irreducibles

if powermaps and representative orders are consistent.

If no inconsistency occurs, `true`

is returned, otherwise each error is
signalled, and `false`

is returned at the end.

gap> t:= CharTable("A5");; TestCharTable(t); true gap> t.irreducibles[2]:= t.irreducibles[3] - t.irreducibles[1];; gap> TestCharTable(t); #E TestCharTable(A5): Scpr( ., X[2], X[1] ) = -1 #E TestCharTable(A5): Scpr( ., X[2], X[2] ) = 2 #E TestCharTable(A5): Scpr( ., X[3], X[2] ) = 1 #E TestCharTable(A5): centralizer orders inconsistent with irreducibles false

Although a character table is not a domain (see Some Notes on Character
Theory in GAP), it needs an operations record.
That for **ordinary character tables** is `CharTableOps`

, that for
**Brauer tables** is `BrauerTableOps`

. The functions in these records
are listed in section Functions for Character Tables.

In the following two cases it may be useful to overlay these functions.

Character tables are printed using the `Print`

component, one can for
example replace the default `Print`

by DisplayCharTable
`DisplayCharTable`

.

Whenever a library function calls the scalar product this is the
`ScalarProduct`

field of the operations record, so one can replace the
default function (see ScalarProduct) by a more efficient one for special
cases.

The following polymorphic functions are overlaid in the `operations`

record of character tables.
They are listed in alphabetical order.

`ElementaryAbelianSeries( `

`tbl` )

`FusionConjugacyClasses( `

`tbl1`, `tbl2` )

`NoMessageScalarProduct( `

`tbl`, `chi1`, `chi2` )

`ScalarProduct( `

`tbl`, `chi1`, `chi2` )

The following operators are defined for character tables.

:`tbl1`*`tbl2`-

direct product of two character tables (see CharTableDirectProduct),

:`tbl`/`list`-

table of the factor group modulo the classes in the list`list`(see CharTableFactorGroup),

:`tbl`mod`p`-

`p`--modular table corresponding to`tbl`(see CharTable).

The following few conventions should be noted:
beg-description~~
~~

•[The identity element] is expected to be in the first class.

•[Characters] are lists of cyclotomics (see Chapter Cyclotomics) or unknowns (see chapter Unknowns); they do not physically ``belong'' to a table, so when necessary, functions ``regard'' them as characters of a table which is given as another parameter.

•[Conversely], most functions that take a character table as a parameter and work with characters expect these characters as a parameter, too.

Some functions, however, expect the characters to be stored in the
`irreducibles`

field of the table (e.g. TestCharTable
`TestCharTable`

)
or allow application either to a list of characters given by a
parameter or to the `irreducibles`

field (e.g. Indicator
`Indicator`

) if this parameter is missing.

•[The trivial character] need not be the first one in a list of characters.

•[Sort convention:]
Whenever SortClassesCharTable `SortClassesCharTable`

or
SortCharTable `SortCharTable`

is used to sort the classes of a
character table, the fusions into that table are **not** adjusted;
only the `permutation`

field of the sorted table will be
actualized.

If one handles fusions only using GetFusionMap `GetFusionMap`

and
StoreFusion `StoreFusion`

, the maps are adjusted automatically
with respect to the value of the field `permutation`

of the
destination table. So one should not change this field by hand.
Fusion maps that are entered explicitly (e.g. because they are not
stored on a table) are expected to be sorted, they will not be
adjusted.
end-description~~
~~

There are in general four different ways to get a character table which
**GAP3** already ``knows'': You can either

read a file that contains the table record,

construct the table using generic formulae,

derive it from known tables or

use a presentation or representation of the group.

The first two methods are used by CharTable `CharTable`

.
For the conception of generic character tables,
see chapter Generic Character Tables.
**Note** that library files often contain something that is much different
from the tables returned by `CharTable`

, see chapter Character Table
Libraries. Especially see Selecting Library Tables.

As for the third method, some generic ways to derive a character table

- are implemented::

One can obtain it as table of a factor group where the table of the group is given (see CharTableFactorGroup),

for given tables the table of the direct product can be constructed (see CharTableDirectProduct),

the restriction of a table to the*p*-regular classes can be formed (see CharTableRegular),

for special cases, an isoclinic table of a given table can be constructed (see CharTableIsoclinic),

the splitting and fusion of classes may be viewed as a generic process (see CharTableSplitClasses, CharTableCollapsedClasses).

At the moment, for the last method there are algorithms dealing with arbitrary groups (see CharTable), and with finite polycyclic groups with special properties (see CharTablePGroup).

**Note** that whenever fusions between tables occur in these functions,
they are stored on the concerned tables, and the `fusionsource`

fields
are updated (see Character Table Records).

`CharTable( `

`G` )

`CharTable( `

`tblname` )

`CharTable( `

`series`, `parameter1`, `parameter2` ... )

`CharTable( `

`G` )

returns the character table of the group `G`. If

is bound,
the table is baptized the same. Otherwise it is given the identifier
component `G`.name`""`

(empty string). This is necessary since every character table needs an
identifier in **GAP3** (see IsCharTable).

`CharTable`

first computes the linear characters, using the commutator
factor group. If irreducible characters are missing afterwards, they are
computed using the algorithm of Dixon and Schneider (see Dix67 and
Sch90).

gap> M11 := Group((1,2,3,4,5,6,7,8,9,10,11), (3,7,11,8)(4,10,5,6));; gap> M11.name := "M11";; gap> PrintCharTable( CharTable( M11 ) ); rec( size := 7920, centralizers := [ 7920, 11, 11, 8, 48, 8, 8, 18, 5, 6 ], orders := [ 1, 11, 11, 4, 2, 8, 8, 3, 5, 6 ], classes := [ 1, 720, 720, 990, 165, 990, 990, 440, 1584, 1320 ], irreducibles := [ [ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 ], [ 10, -1, -1, 2, 2, 0, 0, 1, 0, -1 ], [ 10, -1, -1, 0, -2, E(8)+E(8)^3, -E(8)-E(8)^3, 1, 0, 1 ], [ 10, -1, -1, 0, -2, -E(8)-E(8)^3, E(8)+E(8)^3, 1, 0, 1 ], [ 11, 0, 0, -1, 3, -1, -1, 2, 1, 0 ], [ 16, E(11)^2+E(11)^6+E(11)^7+E(11)^8+E(11)^10, E(11)+E(11)^3+E(11)^4+E(11)^5+E(11)^9, 0, 0, 0, 0, -2, 1, 0 ], [ 16, E(11)+E(11)^3+E(11)^4+E(11)^5+E(11)^9, E(11)^2+E(11)^6+E(11)^7+E(11)^8+E(11)^10, 0, 0, 0, 0, -2, 1, 0 ] , [ 44, 0, 0, 0, 4, 0, 0, -1, -1, 1 ], [ 45, 1, 1, 1, -3, -1, -1, 0, 0, 0 ], [ 55, 0, 0, -1, -1, 1, 1, 1, 0, -1 ] ], operations := CharTableOps, identifier := "M11", order := 7920, name := "M11", powermap := [ , [ 1, 3, 2, 5, 1, 4, 4, 8, 9, 8 ], [ 1, 2, 3, 4, 5, 6, 7, 1, 9, 5 ] ,, [ 1, 2, 3, 4, 5, 7, 6, 8, 1, 10 ],, [ 1, 3, 2, 4, 5, 7, 6, 8, 9, 10 ],,,, [ 1, 1, 1, 4, 5, 6, 7, 8, 9, 10 ] ], galomorphisms := Group( ( 6, 7), ( 2, 3) ), text := "origin: Dixon's Algorithm", group := M11 )

The columns of the table will be sorted in the same order, as the classes
of the group, thus allowing a bijection between group and table. If the
conjugacy classes are bound in

the order is not
changed. Otherwise the routine itself computes the classes. One can
sort them in the canonical way, using `G`.conjugacyClasses`SortClassesCharTable`

(see
SortClassesCharTable). If an entry

exists the routine
uses information contained in this table. This also provides a facility
for entering known characters, but then the user assumes responsibility
for the correctness of the characters (There is little use in providing
the trivial character to the routine).
`G`.charTable

**Note**: The algorithm binds the record component `galomorphisms`

of the
character table. This is a permutation group generated by the
**Galois**-morphisms only. If there is no `automorphisms`

component in the
table then this group is used by routines like `SubgroupFusion`

.

The computation of character tables needs to identify the classes of
group elements very often, so it can be helpful to store a class list of
all group elements. Since this is obviously limited by the group size, it
is controlled by the global variable `LARGEGROUPORDER`

, which is set by
standard to 10000. If the group is smaller, the class map is stored.
Otherwise each occuring element is identified individually.

**Limitations{\:}** At the moment there is a limitation to the group size
given by the following condition: the routine computes in a prime
field of size *p*. *p* is a prime number, such that the exponent of the
group divides *(p-1)* and such that *2 √|G| < p*. At the
moment, **GAP3** provides only prime fields up to size 65535.

The routine also sets up a component

. Using this component,
routines that identify classes, for example `G`.dixon`FusionConjugacyClasses`

,
will work much faster. When interrupting the algorithm, however, a
neccessary cleanup has not taken place. Thus you should call ```
Unbind(
```

to avoid possible further confusion. This is also a good
idea because `G`.dixon )

may become very large. When the computation by
`G`.dixon`CharTable`

is complete, this record is shrunk to an acceptable size,
something that could not be done when interrupting.

`CharTable( `

`tblname` )

If the only parameter is a string `tblname` and this is an admissible
name of a library table, `CharTable`

returns this library table,
otherwise `false`

. A call of `CharTable`

may cause to read some library
files and to construct the table from the data in the files, see chapter
Character Table Libraries for the details.

Admissible names for the **ordinary character table** `tbl` of the group
`grp` are

• the **ATLAS** name if `tbl` is an **ATLAS** table (see ATLAS Tables),
e.g., `M22`

for the table of the Mathieu group *M _{22}*,

`L2(13)`

for `12_1.U4(3).2_1`

for • the names that were admissible for tables of `grp` in **CAS** if the
**CAS** table library contained a table of `grp`, e.g., `sl42`

for
the table of the alternating group *A _{8}* (but note that the table
may be different from that in

• some ``relative'' names:

For `grp` the `n`--th maximal subgroup (in decreasing group order)
of a sporadic simple group with admissible name `name`, `name`M`n`
is admissible for `tbl`, e.g., `J3M2`

for the second maximal
subgroup of the Janko group *J _{3}* which has the name

`J3`

.
For `grp` a nontrivial Sylow normalizer of a sporadic simple group
with admissible name `name`, where nontrivial means that the group
is not contained in *p*:*(p-1)*, `name`N`p` is an admissible name
of `tbl`, e.g., *J4N11* for the Sylow 11 normalizer of the Janko
group *J _{4}*.

In a few cases, the table of the Sylow *p* subgroup of `grp` is
accessible by `name`Syl`p` where `name` is an admissible name of
the table of `grp`, e.g., `A11Syl2`

for the Sylow 2 subgroup of the
alternating group *A _{11}*.

In a few cases, the table of an element centralizer of `grp` is
accessible by `name`C`cl` where `name` is an admissible name of the
table of `grp`, e.g., `M11C2`

for an involution centralizer in the
Mathieu group *M _{11}*.

Admissible names for a **Brauer table** `tbl` (modulo the prime *p*) are
all names

where `name`mod`p``name` is admissible for the corresponding
ordinary table, e.g., `M12mod11`

for the 11 modular table of *M _{12}*,
and

`L2(25).2_1mod3`

for the 3 modular table of `mod`

operator, as in the following example.

gap> CharTable( "A5" ) mod 2; CharTable( "A5mod2" )

**Generic tables** are accessible only by the name given by their
`identifier`

component (see below).

Case is not significant for table names, e.g., `suzm3`

and `SuzM3`

are
both admissible names for the third maximal subgroup of the sporadic
Suzuki group.

The admissible names reflect the structure of the libraries, see Contents of the Table Libraries and Organization of the Table Libraries.

gap> CharTable( "A5.2" );; # returns the character table of the # symmetric group on five letters # (inATLASformat) gap> CharTable( "Symmetric" );; # returns the generic table of the # symmetric group gap> CharTable( "J5" ); #E CharTableLibrary: no library table with name 'J5' false

If `CharTable`

is called with more than one parameter, the first must be
a string specifying a series of groups which is implemented via a generic
character table (see chapter Generic Character Tables), e.g.
`"Symmetric"`

for the symmetric groups; the following parameters
specialise the required member of the series:

gap> CharTable( "Symmetric", 5 );; # the table of the symmetric # groupS(got by specializing # the generic table)_{5}

These are the valid calls of `CharTable`

with parameter `series`:

`CharTable( "Alternating",`

:`n`)

returns the table of the alternating group on`n`letters,

`CharTable( "Cyclic",`

:`n`)

returns the table of the cyclic group of order`n`,

`CharTable( "Dihedral",`

:`2n`)

returns the table of the dihedral group of order`2n`,

`CharTable( "GL", 2,`

:`q`)

returns the table of the general linear group \rm GL*(2,q)*for a prime power`q`,

`CharTable( "GU", 3,`

:`q`)

returns the table of the general unitary group \rm GU*(3,q)*for a prime power`q`,

`CharTable( "P:Q", [`

:`p`,`q`] )

returns the table of the extension of the cyclic group of prime order`p`by a cyclic group of order`q`where`q`divides*p-1*,

`CharTable( "PSL", 2,`

:`q`)

returns the table of the projective special linear group \rm PSL*(2,q)*for a prime power`q`,

`CharTable( "SL", 2,`

:`q`)

returns the table of the special linear group \rm SL*(2,q)*for a prime power`q`,

`CharTable( "SU", 3,`

:`q`)

returns the table of the special unitary group \rm SU*(3,q)*for a prime power`q`,

`CharTable( "Quaternionic",`

:`4n`)

returns the table of the quaternionic (dicyclic) group of order`4n`,

`CharTable( "Suzuki",`

:`q`)

returns the table of the Suzuki group*Sz(q) =*for^{2}B_{2}(q)`q`an odd power of 2,

`CharTable( "Symmetric",`

:`n`)

returns the table of the symmetric group on`n`letters.

`CharTable( "WeylB",`

:`n`)

returns the table of the Weyl group of type*B*._{n}

`CharTable( "WeylD",`

:`n`)

returns the table of the Weyl group of type*D*._{n}

The computation of character tables of very large groups may take quite
some time. On the other hand, for the expert only a few irreducible
characters may be needed, since the other ones can be computed using
character theoretic methods like tensoring, induction, and restriction.
Thus **GAP3** provides also step-by-step routines for doing the
calculations, that will allow to compute some characters, and stop before
all are calculated. Note that there is no 'safety net', i.e., the
routines, being somehow internal, do no error checking, and assume the
information given are correct.

When the global variable `InfoCharTable1`

if set to `Print`

, information
about the progress of splitting is printed. The default value of
`InfoCharTable1`

is `Ignore`

.

does the setup for the computation of characters: It computes
conjugacy classes, power maps and linear characters (in the case of
AgGroups it also contains a call of `CharTablePGroup`

). `DixonInit`

returns a special record `D` (see below), which stores all informations
needed for the further computations. The power maps are computed for all
primes smaller than the exponent of `G`, thus allowing to induce the
characters of all cyclic subgroups by `InducedCyclic`

(see
InducedCyclic). For internal purposes, the algorithm uses a permuted
arrangement of the classes and probably a different ---but isomorphic---
group. It is possible to obtain different informations about the
progress of the splitting process as well as the partially computed
character table from the record `D`.

is the reverse function: It takes a Dixon record `D` and returns the
old group `G`. It also does the cleanup of `D`. The returned group
contains the component `charTable`

, containing the character table as far
as known. The classes are arranged in the same way, as the classes of
`G`.

will do the main splitting task: It chooses a class and splits the character spaces using the corresponding class matrix. Characters are computed as far as possible.

tries to split two-dimensional character spaces by combinatoric means. It
is called automatically by `DixonSplit`

. A separate call can be useful,
when new characters have been found, that reduce the size of the
character spaces.

`IncludeIrreducibles( `

`D`, `list` )

If you have found irreducible characters by other means ---like tensoring
etc.--- you must not include them in the character table yourself, but
let them include, using this routine. Otherwise **GAP3** would lose control
of the characters yet known. The characters given in `list` must be
according to the arrangement of classes in `D`. **GAP3** will automatically
take the closure of `list` under the galoisgroup and tensor products with
one-dimensional characters.

This routine decomposes the characters, given in `list` according to the
character spaces found up to this point. By applying this routine to
tensor products etc., it may result in characters with smaller norm, even
irreducible ones. Since the recalculation of characters is only possible,
if the degree is small enough, the splitting process is applied only to
characters of sufficiently small degree.

Some notes on the record `D` returned by `DixonInit`

:

This record stores several items of mainly internal interest. There are
some entries, however, that may be useful to know about when using the
advanced methods described above. The computation need not to take place
in the original group, but in an isomorphic image `W`. This may be the
same group as the group given, but --- depending on the group --- also a
new one. Additionally the initialisation process will create a new list
of the conjugacy classes with possibly different arrangement. For access
to these informations, the following record components of the ``Dixon
Record'' `D` might be of interest:

`group`

:

the group`W`,

`oldG`

:

the group`G`, of which the character table is to be computed,

`conjugacyClasses`

:

classes of`W`; this list contains the**same**classes as

, only the arrangement is different,`W`.conjugacyClasses

`charTable`

:

contains the partially computed character table. The classes are arranged according to

,`D`.conjugacyClasses

`classPermutation`

:

permutation to apply to the classes to obtain the old arrangement.

First, we set

` gap> InfoCharTable1 := Print;;`

for printout of some internal results. We now define our group, which is
isomorphic to * PSL_{4}(3)* (we use a permutation representation of

gap> g := PrimitiveGroup(40,5); PSL(4,3) gap> Size(g); 6065280 gap> d := DixonInit(g);; #I 29 classes gap> c := d.charTable;;

After the initialisation, one structure matrix is evaluated, yielding smaller spaces and several irreducible characters.

gap> DixonSplit(d); #I Matrix 2, Representative of Order 3, Centralizer: 5832 #I Dimensions: [ 1, 12, 2, 2, 4, 2, 1, 1, 1, 1, 1 ] #I Two-dim space split #I Two-dim space split #I Two-dim space split

In this case spaces of the listed dimensions are a result of the splitting process. The three two dimensional spaces are split successfully by combinatoric means.

We obtain several characters by tensor products and notify them to the program. The tensor products of the nonlinear characters are reduced with the irreducible characters. The result is split according to the spaces found, which yields characters of smaller norms, but no new irreducibles.

gap> asp:= AntiSymmetricParts( c, c.irreducibles, 2 );; gap> ro:= ReducedOrdinary( c, c.irreducibles, asp );; gap> Length( ro.irreducibles ); 3 gap> IncludeIrreducibles( d, ro.irreducibles ); gap> nlc:= Filtered( c.irreducibles, i -> i[1] > 1 );; gap> t:= Tensored( nlc, nlc );; gap> ro:= ReducedOrdinary( c, c.irreducibles, t );; ro.irreducibles; [ ] gap> List( ro.remainders, i -> ScalarProduct( c, i, i) ); [ 2, 2, 4, 4, 4, 4, 13, 13, 18, 18, 19, 21, 21, 36, 36, 29, 34, 34, 42, 34, 48, 54, 62, 68, 68, 78, 84, 84, 88, 90, 159, 169, 169, 172, 172, 266, 271, 271, 268, 274, 274, 280, 328, 373, 373, 456, 532, 576, 679, 683, 683, 754, 768, 768, 890, 912, 962, 1453, 1453, 1601, 1601, 1728, 1739, 1739, 1802, 2058, 2379, 2414, 2543, 2744, 2744, 2920, 3078, 3078, 4275, 4275, 4494, 4760, 5112, 5115, 5115, 5414, 6080, 6318, 7100, 7369, 7369, 7798, 8644, 10392, 12373, 12922, 14122, 14122, 18948, 21886, 24641, 24641, 25056, 38942, 44950, 78778 ] gap> t := SplitCharacters( d, ro.remainders );; gap> List( t, i -> ScalarProduct( c, i, i ) ); [ 2, 2, 4, 2, 2, 4, 4, 3, 6, 5, 5, 9, 9, 4, 12, 13, 18, 18, 18, 26, 32, 32, 16, 42, 36, 84, 84, 88, 90, 159, 169, 169, 172, 172, 266, 271, 271, 268, 274, 274, 280, 328, 373, 373, 456, 532, 576, 679, 683, 683, 754, 768, 768, 890, 912, 962, 1453, 1453, 1601, 1601, 1728, 1739, 1739, 1802, 2058, 2379, 2414, 2543, 2744, 2744, 2920, 3078, 3078, 4275, 4275, 4494, 4760, 5112, 5115, 5115, 5414, 6080, 6318, 7100, 7369, 7369, 7798, 8644, 10392, 12373, 12922, 14122, 14122, 18948, 21886, 24641, 24641, 25056, 38942, 44950, 78778 ]

Finally we calculate the characters induced from all cyclic subgroups and obtain the missing irreducibles by applying the LLL-algorithm to them.

gap> ic:= InducedCyclic( c, "all" );; gap> ro:= ReducedOrdinary( c, c.irreducibles, ic );; gap> Length( ro.irreducibles ); 0 gap> l:= LLL( c, ro.remainders );; gap> Length( l.irreducibles ); 13 gap> IncludeIrreducibles( d, l.irreducibles ); gap> Length( c.irreducibles ); 29 gap> Length( c.classes ); 29

As the last step, we return to our original group.

gap> g:= DixontinI( d ); #I Total:1 matrices, [ 2 ] PSL(4,3) gap> c:= g.charTable;; gap> List( c.irreducibles, i -> i[1] ); [ 1, 26, 26, 39, 52, 65, 65, 90, 234, 234, 260, 260, 260, 351, 390, 416, 416, 416, 416, 468, 585, 585, 640, 640, 640, 640, 729, 780, 1040 ] gap> Sum( last, i -> i^2 ); 6065280

`CharTableFactorGroup( `

`tbl`, `classes\_of\_normal\_subgroup` )

returns the table of the factor group of `tbl` with respect to a
particular normal subgroup: If the list of irreducibles stored in

is complete, this normal subgroup is the normal
closure of `tbl`.irreducibles`classes\_of\_normal\_subgroup`;
otherwise it is the intersection of kernels of those irreducibles stored
on `tbl` which contain `classes\_of\_normal\_subgroups` in their kernel
--that may cause strange results.

gap> s4:= CharTable( "Symmetric", 4 );; gap> PrintCharTable( CharTableFactorGroup( s4, [ 3 ] ) ); rec( size := 6, identifier := "S4/[ 3 ]", order := 6, name := "S4/[ 3 ]", centralizers := [ 6, 2, 3 ], powermap := [ , [ 1, 1, 3 ], [ 1, 2, 1 ] ], fusions := [ ], fusionsource := [ "S4" ], irreducibles := [ [ 1, -1, 1 ], [ 2, 0, -1 ], [ 1, 1, 1 ] ], orders := [ 1, 2, 3 ], classes := [ 1, 3, 2 ], operations := CharTableOps ) gap> s4.fusions; [ rec( map := [ 1, 2, 1, 3, 2 ], type := "factor", name := "S4/[ 3 ]" ) ]

`CharTableNormalSubgroup( `

`tbl`, `normal\_subgroup` )

returns the restriction of the character table `tbl` to the classes in
the list `normal\_subgroup`.
This table is an approximation of the character table of this normal
subgroup. It has components `order`

, `identifier`

, `centralizers`

,
`orders`

, `classes`

, `powermap`

, `irreducibles`

(contains the set of
those restrictions of irreducibles of `tbl` which are irreducible), and
`fusions`

(contains the fusion in `tbl`).

In most cases, some classes of the normal subgroup must be split, see CharTableSplitClasses.

gap> s5:= CharTable( "A5.2" );; gap> s3:= CharTable( "Symmetric", 3 );; gap> SortCharactersCharTable( s3 );; gap> s5xs3:= CharTableDirectProduct( s5, s3 );; gap> nsg:= [ 1, 3, 4, 6, 7, 9, 10, 12, 14, 17, 20 ];; gap> sub:= CharTableNormalSubgroup( s5xs3, nsg );; #I CharTableNormalSubgroup: classes in [ 8 ] necessarily split gap> PrintCharTable( sub ); rec( identifier := "Rest(A5.2xS3,[ 1, 3, 4, 6, 7, 9, 10, 12, 14, 17, 2\ 0 ])", size := 360, name := "Rest(A5.2xS3,[ 1, 3, 4, 6, 7, 9, 10, 12, 14, 17, 20 ])",\ order := 360, centralizers := [ 360, 180, 24, 12, 18, 9, 15, 15/2, 12, 4, 6 ], orders := [ 1, 3, 2, 6, 3, 3, 5, 15, 2, 4, 6 ], powermap := [ , [ 1, 2, 1, 2, 5, 6, 7, 8, 1, 3, 5 ], [ 1, 1, 3, 3, 1, 1, 7, 7, 9, 10, 9 ],, [ 1, 2, 3, 4, 5, 6, 1, 2, 9, 10, 11 ] ], classes := [ 1, 2, 15, 30, 20, 40, 24, 48, 30, 90, 60 ], operations := CharTableOps, irreducibles := [ [ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 ], [ 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1 ], [ 2, -1, 2, -1, 2, -1, 2, -1, 0, 0, 0 ], [ 6, 6, -2, -2, 0, 0, 1, 1, 0, 0, 0 ], [ 4, 4, 0, 0, 1, 1, -1, -1, 2, 0, -1 ], [ 4, 4, 0, 0, 1, 1, -1, -1, -2, 0, 1 ], [ 8, -4, 0, 0, 2, -1, -2, 1, 0, 0, 0 ], [ 5, 5, 1, 1, -1, -1, 0, 0, 1, -1, 1 ], [ 5, 5, 1, 1, -1, -1, 0, 0, -1, 1, -1 ], [ 10, -5, 2, -1, -2, 1, 0, 0, 0, 0, 0 ] ], fusions := [ rec( name := [ 'A', '5', '.', '2', 'x', 'S', '3' ], map := [ 1, 3, 4, 6, 7, 9, 10, 12, 14, 17, 20 ] ) ] )

`CharTableDirectProduct( `

`tbl1`, `tbl2` )

returns the character table of the direct product of the groups given by
the character tables `tbl1` and `tbl2`.

The matrix of irreducibles is the Kronecker product (see
KroneckerProduct) of

with `tbl1`.irreducibles

.
`tbl2`.irreducibles

gap> c2:= CharTable( "Cyclic", 2 );; s2:= CharTable( "Symmetric", 2 );; gap> SortCharactersCharTable( s2 );; gap> v4:= CharTableDirectProduct( c2, s2 );; gap> PrintCharTable( v4 ); rec( size := 4, identifier := "C2xS2", centralizers := [ 4, 4, 4, 4 ], order := 4, name := "C2xS2", classparam := [ [ [ 1, 0 ], [ 1, [ 1, 1 ] ] ], [ [ 1, 0 ], [ 1, [ 2 ] ] ], [ [ 1, 1 ], [ 1, [ 1, 1 ] ] ], [ [ 1, 1 ], [ 1, [ 2 ] ] ] ], orders := [ 1, 2, 2, 2 ], powermap := [ , [ 1, 1, 1, 1 ] ], irreducibles := [ [ 1, 1, 1, 1 ], [ 1, -1, 1, -1 ], [ 1, 1, -1, -1 ], [ 1, -1, -1, 1 ] ], irredinfo := [ rec( charparam := [ [ 1, 0 ], [ 1, [ 2 ] ] ] ), rec( charparam := [ [ 1, 0 ], [ 1, [ 1, 1 ] ] ] ), rec( charparam := [ [ 1, 1 ], [ 1, [ 2 ] ] ] ), rec( charparam := [ [ 1, 1 ], [ 1, [ 1, 1 ] ] ] ) ], charparam := [ ], fusionsource := [ [ 'C', '2' ], "S2" ], fusions := [ rec( name := [ 'C', '2' ], map := [ 1, 1, 2, 2 ], type := "factor" ), rec( name := "S2", map := [ 1, 2, 1, 2 ], type := "factor" ) ], classes := [ 1, 1, 1, 1 ], operations := CharTableOps ) gap> c2.fusions; [ rec( map := [ 1, 3 ], type := "normal", name := "C2xS2" ) ]

**Note**: The result will contain those *p*-th powermaps for primes *p*
where both `tbl1` and `tbl2` contain the *p*-th powermap.
Additionally, if one of the tables contains it, and *p* does not divide
the order of the other table, and the *p*-th powermap is uniquely
determined (see Powermap), it will be computed; then the table of the
direct product will contain the *p*-th powermap, too.

`CharTableWreathSymmetric( `

`tbl`, `n` )

returns the character table of the wreath product of an arbitrary group
*G* with the full symmetric group *S _{n}*, where

gap> c3:= CharTable("Cyclic", 3);; gap> wr:= CharTableWreathSymmetric(c3, 2);; gap> PrintCharTable( wr ); rec( size := 18, identifier := "C3wrS2", centralizers := [ 18, 9, 9, 18, 9, 18, 6, 6, 6 ], classes := [ 1, 2, 2, 1, 2, 1, 3, 3, 3 ], orders := [ 1, 3, 3, 3, 3, 3, 2, 6, 6 ], irredinfo := [ rec( charparam := [ [ 1, 1 ], [ ], [ ] ] ), rec( charparam := [ [ 1 ], [ 1 ], [ ] ] ), rec( charparam := [ [ 1 ], [ ], [ 1 ] ] ), rec( charparam := [ [ ], [ 1, 1 ], [ ] ] ), rec( charparam := [ [ ], [ 1 ], [ 1 ] ] ), rec( charparam := [ [ ], [ ], [ 1, 1 ] ] ), rec( charparam := [ [ 2 ], [ ], [ ] ] ), rec( charparam := [ [ ], [ 2 ], [ ] ] ), rec( charparam := [ [ ], [ ], [ 2 ] ] ) ], name := "C3wrS2", order := 18, classparam := [ [ [ 1, 1 ], [ ], [ ] ], [ [ 1 ], [ 1 ], [ ] ], [ [ 1 ], [ ], [ 1 ] ], [ [ ], [ 1, 1 ], [ ] ], [ [ ], [ 1 ], [ 1 ] ], [ [ ], [ ], [ 1, 1 ] ], [ [ 2 ], [ ], [ ] ], [ [ ], [ 2 ], [ ] ], [ [ ], [ ], [ 2 ] ] ], powermap := [ , [ 1, 3, 2, 6, 5, 4, 1, 4, 6 ], [ 1, 1, 1, 1, 1, 1, 7, 7, 7 ] ], irreducibles := [ [ 1, 1, 1, 1, 1, 1, -1, -1, -1 ], [ 2, -E(3)^2, -E(3), 2*E(3), -1, 2*E(3)^2, 0, 0, 0 ], [ 2, -E(3), -E(3)^2, 2*E(3)^2, -1, 2*E(3), 0, 0, 0 ], [ 1, E(3), E(3)^2, E(3)^2, 1, E(3), -1, -E(3), -E(3)^2 ], [ 2, -1, -1, 2, -1, 2, 0, 0, 0 ], [ 1, E(3)^2, E(3), E(3), 1, E(3)^2, -1, -E(3)^2, -E(3) ], [ 1, 1, 1, 1, 1, 1, 1, 1, 1 ], [ 1, E(3), E(3)^2, E(3)^2, 1, E(3), 1, E(3), E(3)^2 ], [ 1, E(3)^2, E(3), E(3), 1, E(3)^2, 1, E(3)^2, E(3) ] ], operations := CharTableOps )

gap> DisplayCharTable( wr ); C3wrS2 2 1 . . 1 . 1 1 1 1 3 2 2 2 2 2 2 1 1 1 1a 3a 3b 3c 3d 3e 2a 6a 6b 2P 1a 3b 3a 3e 3d 3c 1a 3c 3e 3P 1a 1a 1a 1a 1a 1a 2a 2a 2a X.1 1 1 1 1 1 1 -1 -1 -1 X.2 2 A /A B -1 /B . . . X.3 2 /A A /B -1 B . . . X.4 1 -/A -A -A 1 -/A -1 /A A X.5 2 -1 -1 2 -1 2 . . . X.6 1 -A -/A -/A 1 -A -1 A /A X.7 1 1 1 1 1 1 1 1 1 X.8 1 -/A -A -A 1 -/A 1 -/A -A X.9 1 -A -/A -/A 1 -A 1 -A -/A A = -E(3)^2 = (1+ER(-3))/2 = 1+b3 B = 2*E(3) = -1+ER(-3) = 2b3

The record component `classparam`

contains the sequences of partitions
that parametrize the classes as well as the characters of the wreath
product. Note that this parametrization prevents the principal character
from being the first one in the list `irreducibles`

.

`CharTableRegular( `

`tbl`, `prime` )

returns the character table consisting of the `prime`-regular classes of
the character table `tbl`.

gap> a5:= CharTable( "Alternating", 5 );; gap> PrintCharTable( CharTableRegular( a5, 2 ) ); rec( identifier := "Regular(A5,2)", prime := 2, size := 60, orders := [ 1, 3, 5, 5 ], centralizers := [ 60, 3, 5, 5 ], powermap := [ , [ 1, 2, 4, 3 ], [ 1, 1, 4, 3 ],, [ 1, 2, 1, 1 ] ], fusions := [ rec( map := [ 1, 3, 4, 5 ], type := "choice", name := "A5" ) ], ordinary := CharTable( "A5" ), operations := CharTableOps, order :\ = 60, name := "Regular(A5,2)", classes := [ 1, 20, 12, 12 ] ) gap> a5.fusionsource; [ "Regular(A5,2)" ]

`CharTableIsoclinic( `

`tbl` )

`CharTableIsoclinic( `

`tbl`, `classes\_of\_normal\_subgroup` )

If `tbl` is a character table of a group with structure *2.G.2* with a
unique central subgroup of order 2 and a unique subgroup of index 2,
`CharTableIsoclinic( `

returns the table of the isoclinic group
(see CCN85, Chapter 6, Section 7);
if the subgroup of index 2 is not unique, it must be specified by
enumeration of its classes in `tbl` )`classes\_of\_normal\_subgroup`.

gap> d8:= CharTable( "Dihedral", 8 );; gap> PrintCharTable( CharTableIsoclinic( d8, [ 1, 2, 3 ] ) ); rec( identifier := "Isoclinic(D8)", size := 8, centralizers := [ 8, 4, 8, 4, 4 ], classes := [ 1, 2, 1, 2, 2 ], orders := [ 1, 4, 2, 4, 4 ], fusions := [ ], fusionsource := [ ], powermap := [ , [ 1, 3, 1, 3, 3 ] ], irreducibles := [ [ 1, 1, 1, 1, 1 ], [ 1, 1, 1, -1, -1 ], [ 1, -1, 1, 1, -1 ], [ 1, -1, 1, -1, 1 ], [ 2, 0, -2, 0, 0 ] ], operations := CharTableOps, order := 8, name := "Isoclinic(D8)" )

`CharTableSplitClasses( `

`tbl`, `fusionmap` )

`CharTableSplitClasses( `

`tbl`, `fusionmap`, `exponent` )

returns a character table where the classes of the character table `tbl`
are split according to the fusion map `fusionmap`.

The two forms correspond to the two different situations to split classes:

`CharTableSplitClasses( `

`tbl`, `fusionmap` )

If one constructs a normal subgroup (see CharTableNormalSubgroup),
the order remains unchanged, powermaps, classlengths and centralizer
orders are changed with respect to the fusion, representative orders and
irreducibles are simply split.
The ``factor fusion'' `fusionmap` to `tbl` is stored on the result.

# see example in CharTableNormalSubgroup gap> split:= CharTableSplitClasses(sub,[1,2,3,4,5,6,7,8,8,9,10,11]);; gap> PrintCharTable( split ); rec( identifier := "Split(Rest(A5.2xS3,[ 1, 3, 4, 6, 7, 9, 10, 12, 14,\ 17, 20 ]),[ 1, 2, 3, 4, 5, 6, 7, 8, 8, 9, 10, 11 ])", size := 360, order := 360, name := "Split(Rest(A5.2xS3,[ 1, 3, 4, 6, 7, 9, 10, 12, 14, 17, 2\ 0 ]),[ 1, 2, 3, 4, 5, 6, 7, 8, 8, 9, 10, 11 ])", centralizers := [ 360, 180, 24, 12, 18, 9, 15, 15, 15, 12, 4, 6 ], classes := [ 1, 2, 15, 30, 20, 40, 24, 24, 24, 30, 90, 60 ], orders := [ 1, 3, 2, 6, 3, 3, 5, 15, 15, 2, 4, 6 ], powermap := [ , [ 1, 2, 1, 2, 5, 6, 7, [ 8, 9 ], [ 8, 9 ], 1, 3, 5 ], [ 1, 1, 3, 3, 1, 1, 7, 7, 7, 10, 11, 10 ],, [ 1, 2, 3, 4, 5, 6, 1, 2, 2, 10, 11, 12 ] ], irreducibles := [ [ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 ], [ 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1 ], [ 2, -1, 2, -1, 2, -1, 2, -1, -1, 0, 0, 0 ], [ 6, 6, -2, -2, 0, 0, 1, 1, 1, 0, 0, 0 ], [ 4, 4, 0, 0, 1, 1, -1, -1, -1, 2, 0, -1 ], [ 4, 4, 0, 0, 1, 1, -1, -1, -1, -2, 0, 1 ], [ 8, -4, 0, 0, 2, -1, -2, 1, 1, 0, 0, 0 ], [ 5, 5, 1, 1, -1, -1, 0, 0, 0, 1, -1, 1 ], [ 5, 5, 1, 1, -1, -1, 0, 0, 0, -1, 1, -1 ], [ 10, -5, 2, -1, -2, 1, 0, 0, 0, 0, 0, 0 ] ], fusions := [ rec( name := "Rest(A5.2xS3,[ 1, 3, 4, 6, 7, 9, 10, 12, 14, 17, 20 ])", map := [ 1, 2, 3, 4, 5, 6, 7, 8, 8, 9, 10, 11 ] ) ], operations := CharTableOps ) gap> # the table of(3× A(incomplete)_{5})\!:\! 2

`CharTableSplitClasses( `

`tbl`, `fusionmap`, `exponent` )

To construct a downward extension is somewhat more complicated, since the
new order, representative orders, centralizer orders and classlengths are
not known at the moment when the classes are split.
So the order remains unchanged, centralizer orders will just be split,
classlengths are divided by the number of image classes, and the
representative orders become parametrized with respect to the exponent
`exponent` of the normal subgroup.
Power maps and irreducibles are computed from `tbl` and `fusionmap`,
and the factor fusion `fusionmap` to `tbl` is stored on the result.

gap> a5:= CharTable( "Alternating", 5 );; gap> CharTableSplitClasses( a5, [ 1, 1, 2, 3, 3, 4, 4, 5, 5 ], 2 );; gap> PrintCharTable( last ); rec( identifier := "Split(A5,[ 1, 1, 2, 3, 3, 4, 4, 5, 5 ])", size := 60, order := 60, name := "Split(A5,[ 1, 1, 2, 3, 3, 4, 4, 5, 5 ])", centralizers :=\ [ 60, 60, 4, 3, 3, 5, 5, 5, 5 ], classes := [ 1/2, 1/2, 15, 10, 10, 6, 6, 6, 6 ], orders := [ 1, 2, [ 2, 4 ], [ 3, 6 ], [ 3, 6 ], [ 5, 10 ], [ 5, 10 ], [ 5, 10 ], [ 5, 10 ] ], powermap := [ , [ 1, 1, [ 1, 2 ], [ 4, 5 ], [ 4, 5 ], [ 8, 9 ], [ 8, 9 ], [ 6, 7 ], [ 6, 7 ] ], [ 1, 2, 3, [ 1, 2 ], [ 1, 2 ], [ 8, 9 ], [ 8, 9 ], [ 6, 7 ], [ 6, 7 ] ],, [ 1, 2, 3, [ 4, 5 ], [ 4, 5 ], [ 1, 2 ], [ 1, 2 ], [ 1, 2 ], [ 1, 2 ] ] ], irreducibles := [ [ 1, 1, 1, 1, 1, 1, 1, 1, 1 ], [ 4, 4, 0, 1, 1, -1, -1, -1, -1 ], [ 5, 5, 1, -1, -1, 0, 0, 0, 0 ], [ 3, 3, -1, 0, 0, -E(5)-E(5)^4, -E(5)-E(5)^4, -E(5)^2-E(5)^3, -E(5)^2-E(5)^3 ], [ 3, 3, -1, 0, 0, -E(5)^2-E(5)^3, -E(5)^2-E(5)^3, -E(5)-E(5)^4, -E(5)-E(5)^4 ] ], fusions := [ rec( name := "A5", map := [ 1, 1, 2, 3, 3, 4, 4, 5, 5 ] ) ], operations := CharTableOps )

**Note** that powermaps (and in the second case also the representative
orders) may become parametrized maps
(see Chapter Maps and Parametrized Maps).

The inverse process of splitting is the fusion of classes, see CharTableCollapsedClasses.

`CharTableCollapsedClasses( `

`tbl`, `fusionmap` )

returns a character table where all classes of the character table `tbl`
with equal images under the map `fusionmap` are collapsed;
the fields `orders`

, `classes`

, and the characters in `irreducibles`

are
the images under `fusionmap`, the powermaps are obtained on conjugation
(see TransferDiagram) with `fusionmap`, `order`

remains unchanged,
and `centralizers`

arise from `classes`

and `order`

.

The fusion to the returned table is stored on `tbl`.

gap> c3:= CharTable( "Cyclic", 3 );; gap> t:= CharTableSplitClasses( c3, [ 1, 2, 2, 3, 3 ] );; gap> PrintCharTable( t ); rec( identifier := "Split(C3,[ 1, 2, 2, 3, 3 ])", size := 3, order := 3, name := "Split(C3,[ 1, 2, 2, 3, 3 ])", centralizers := [ 3, 6, 6, 6, 6 ], classes := [ 1, 1/2, 1/2, 1/2, 1/2 ], orders := [ 1, 3, 3, 3, 3 ], powermap := [ ,, [ 1, 1, 1, 1, 1 ] ], irreducibles := [ [ 1, 1, 1, 1, 1 ], [ 1, E(3), E(3), E(3)^2, E(3)^2 ], [ 1, E(3)^2, E(3)^2, E(3), E(3) ] ], fusions := [ rec( name := [ 'C', '3' ], map := [ 1, 2, 2, 3, 3 ] ) ], operations := CharTableOps ) gap> c:= CharTableCollapsedClasses( t, [ 1, 2, 2, 3, 3 ] );; gap> PrintCharTable( c ); rec( identifier := "Collapsed(Split(C3,[ 1, 2, 2, 3, 3 ]),[ 1, 2, 2, 3\ , 3 ])", size := 3, order := 3, name := "Collapsed(Split(C3,[ 1, 2, 2, 3, 3 ]),[ 1, 2, 2, 3, 3 ])",\ centralizers := [ 3, 3, 3 ], orders := [ 1, 3, 3 ], powermap := [ ,, [ 1, 1, 1 ] ], fusionsource := [ "Split(C3,[ 1, 2, 2, 3, 3 ])" ], irreducibles := [ [ 1, 1, 1 ], [ 1, E(3), E(3)^2 ], [ 1, E(3)^2, E(3) ] ], classes := [ 1, 1, 1 ], operations := CharTableOps )

The inverse process of fusion is the splitting of classes, see CharTableSplitClasses.

`CharDegAgGroup( `

`G` [, `q` ] )

`CharDegAgGroup`

computes the degrees of irreducible characters
of the finite polycyclic group `G` over the algebraic closed field of
characteristic `q`. The default value for `q` is zero.
The degrees are returned as a list of pairs, the first entry denoting a
degree, and the second denoting its multiplicity.

gap> g:= SolvableGroup( 24, 15 ); S4 gap> CharDegAgGroup( g ); [ [ 1, 2 ], [ 2, 1 ], [ 3, 2 ] ] # two linear characters, one of # degree 2, two of degree 3 gap> CharDegAgGroup( g, 3 ); [ [ 1, 2 ], [ 3, 2 ] ]

The algorithm bases on Con90b. It works for all solvable groups.

`CharTableSSGroup( `

`G` )

`CharTableSSGroup`

returns the character table of the supersolvable
ag-group `G` and stores it in

. If `G`.charTable`G` is not
supersolvable not all irreducible characters migth be calculated and a
warning will be printed out. The algorithm bases on Con90a and
Con90b.

All the characters calculated are monomial, so they are the induced of a
linear character of some subgroup of `G`. For every character the
subgroup it is induced from and the kernel the linear character has are
written down in

and
`t`.irredinfo[i].inducedFrom.subgroup

.
`t`.irredinfo[i].inducedFrom.kernel

gap> t:= CharTableSSGroup( SolvableGroup( 8 , 5 ) );; gap> PrintCharTable( t ); rec( size := 8, classes := [ 1, 1, 2, 2, 2 ], powermap := [ , [ 1, 1, 2, 2, 2 ] ], operations := CharTableOps, group := Q8, irreducibles := [ [ 1, 1, 1, 1, 1 ], [ 1, 1, 1, -1, -1 ], [ 1, 1, -1, 1, -1 ], [ 1, 1, -1, -1, 1 ], [ 2, -2, 0, 0, 0 ] ], orders := [ 1, 2, 4, 4, 4 ], irredinfo := [ rec( inducedFrom := rec( subgroup := Q8, kernel := Q8 ) ), rec( inducedFrom := rec( subgroup := Q8, kernel := Subgroup( Q8, [ b, c ] ) ) ), rec( inducedFrom := rec( subgroup := Q8, kernel := Subgroup( Q8, [ a, c ] ) ) ), rec( inducedFrom := rec( subgroup := Q8, kernel := Subgroup( Q8, [ a*b, c ] ) ) ), rec( inducedFrom := rec( subgroup := Subgroup( Q8, [ b, c ] ), kernel := Subgroup( Q8, [ ] ) ) ) ], order := 8, centralizers := [ 8, 8, 4, 4, 4 ], identifier := "Q8", name := "Q8" )

`MatRepresentationsPGroup( `

`G` )

`MatRepresentationsPGroup( `

`G` [, `int` ] )

`MatRepresentationsPGroup( `

returns a list of homomorphisms from
the finite polycyclic group `G` )`G` to irreducible complex matrix groups.
These matrix groups form a system of representatives of the complex
irreducible representations of `G`.

`MatRepresentationsPGroup( `

returns only the `G`, `int` )`int`-th
representation.

Let `G` be a finite polycyclic group with an abelian normal subgroup `N`
such that the factorgroup *<G> / N* is supersolvable.

`MatRepresentationsPGroup`

uses the algorithm described in Bau91.
Note that for such groups all such representations are equivalent to
monomial ones, and in fact `MatRepresentationsPGroup`

only returns
monomial representations.
If `G` has not the property stated above, a system of representatives of
irreducible representations and characters only for the factor group
*<G> / M* can be computed using this algorithm, where

`MatRepresentationsPGroup`

returns
the irreducible representations of

gap> g:= SolvableGroup( 6, 2 ); S3 gap> MatRepresentationsPGroup( g ); [ GroupHomomorphismByImages( S3, Group( [ [ 1 ] ] ), [ a, b ], [ [ [ 1 ] ], [ [ 1 ] ] ] ), GroupHomomorphismByImages( S3, Group( [ [ -1 ] ] ), [ a, b ], [ [ [ -1 ] ], [ [ 1 ] ] ] ), GroupHomomorphismByImages( S3, Group( [ [ 0, 1 ], [ 1, 0 ] ], [ [ E(3), 0 ], [ 0, E(3)^2 ] ] ), [ a, b ], [ [ [ 0, 1 ], [ 1, 0 ] ], [ [ E(3), 0 ], [ 0, E(3)^2 ] ] ] ) ]

`CharTablePGroup`

can be used to compute the character table of a group
with the above properties (see CharTablePGroup).

`CharTablePGroup( `

`G` )

`CharTablePGroup`

returns the character table of the finite polycyclic
group `G`, and stores it in

. Do not change the order of
`G`.charTable

after having called `G`.conjugacyClasses`CharTablePGroup`

.

Let `G` be a finite polycyclic group with an abelian normal subgroup `N`
such that the factorgroup *<G> / N* is supersolvable.

`CharTablePGroup`

uses the algorithm described in Bau91.
If `G` has not the property stated above, a system of representatives of
irreducible representations and characters only for the factor group *<G>
/ M* can be computed using this algorithm, where

`CharTablePGroup`

returns an incomplete table
containing exactly those irreducibles with kernel containing

gap> t:= CharTablePGroup( SolvableGroup( 8, 4 ) );; gap> PrintCharTable( t ); rec( size := 8, centralizers := [ 8, 8, 4, 4, 4 ], classes := [ 1, 1, 2, 2, 2 ], orders := [ 1, 2, 2, 2, 4 ], irreducibles := [ [ 1, 1, 1, 1, 1 ], [ 1, 1, -1, 1, -1 ], [ 1, 1, 1, -1, -1 ], [ 1, 1, -1, -1, 1 ], [ 2, -2, 0, 0, 0 ] ], operations := CharTableOps, order := 8, powermap := [ , [ 1, 1, 1, 1, 2 ] ], identifier := "D8", name := "D8", group := D8 )

`MatRepresentationsPGroup`

can be used to compute representatives of
the complex irreducible representations (see MatRepresentationsPGroup).

`InitClassesCharTable( `

`tbl` )

returns the list of conjugacy class lengths of the character table `tbl`,
and assigns it to the field

; the classlengths are
computed from the centralizer orders of `tbl`.classes`tbl`.

`InitClassesCharTable`

is called automatically for tables that are read
from the library (see CharTable) or constructed as generic character
tables (see Generic Character Tables).

gap> t:= rec( centralizers:= [ 2, 2 ], identifier:= "C2" );; gap> InitClassesCharTable( t ); t; [ 1, 1 ] rec( centralizers := [ 2, 2 ], identifier := "C2", classes := [ 1, 1 ] )

`InverseClassesCharTable( `

`tbl` )

returns the list mapping each class of the character table `tbl` to its
inverse class. This list can be regarded as (-1)-st powermap; it is
computed using

.
`tbl`.irreducibles

gap> InverseClassesCharTable( CharTable( "L3(2)" ) ); [ 1, 2, 3, 4, 6, 5 ]

`ClassNamesCharTable( `

`tbl` )

`ClassNamesCharTable`

computes names for the classes of the character
table `tbl` as strings consisting of the order of an element of the class
and and least one distinguishing letter.

The list of these names at the same time is returned by this
function and stored in the table `tbl` as record component `classnames`

.

Moreover for each class a component with its name is constructed,
containing the position of this name in the list `classnames`

as its
value.

gap> c3:= CharTable( "Cyclic", 3 );; gap> ClassNamesCharTable( c3 ); [ "1a", "3a", "3b" ] gap> PrintCharTable( c3 ); rec( identifier := "C3", name := "C3", size := 3, order := 3, centralizers := [ 3, 3, 3 ], orders := [ 1, 3, 3 ], powermap := [ ,, [ 1, 1, 1 ] ], irreducibles := [ [ 1, 1, 1 ], [ 1, E(3), E(3)^2 ], [ 1, E(3)^2, E(3) ] ], classparam := [ [ 1, 0 ], [ 1, 1 ], [ 1, 2 ] ], irredinfo := [ rec( charparam := [ 1, 0 ] ), rec( charparam := [ 1, 1 ] ), rec( charparam := [ 1, 2 ] ) ], text := "computed using generic character table for cyclic groups"\ , classes := [ 1, 1, 1 ], operations := CharTableOps, fusions := [ ], fusionsource := [ ], projections := [ ], projectionsource := [ ], classnames := [ "1a", "3a", "3b" ], 1a := 1, 3a := 2, 3b := 3 )

If the record component `classnames`

of `tbl` is unbound,
`ClassNamesCharTable`

is automatically called by `DisplayCharTable`

(see
DisplayCharTable).

Note that once the class names are computed the resulting record fields
are stored on `tbl`. They are not deleted by another call of
`ClassNamesCharTable`

.

`ClassMultCoeffCharTable( `

`tbl`, `c1`, `c2`, `c3` )

returns the class multiplication coefficient of the classes `c1`, `c2`
and `c3` of the group *G* with character table `tbl`.

gap> t:= CharTable( "L3(2)" );; gap> ClassMultCoeffCharTable( t, 2, 2, 4 ); 4

The class multiplication coefficient *c _{1,2,3}* of the classes

Also in the center of the group algebra these numbers are found as
coefficients of the decomposition of the product of two class sums *K _{i}*
and

K_{i} K_{j} = ∑_{k} c_{ijk} K_{k}. |

Given the character table of a finite group *G*, whose classes are *C _{1},
..., C_{r}* with representatives

c\footnotesize Irr_{ijk} = (|C_{i}||C_{j}|)/(|G|)
∑_{χ ∈ }(G)
(χ(g_{i}) χ(g_{j}) χ(g_{k}))/(χ(1)) |

On the other hand the knowledge of the class multiplication coefficients enables the computation of the character table (see CharTable).

`MatClassMultCoeffsCharTable( `

`tbl`, `class` )

returns the matrix *<C _{i}> = [ a_{ijk}]_{j,k}* of structure constants
(see ClassMultCoeffCharTable).

gap> L3_2:= CharTable( "L3(2)" );; gap> MatClassMultCoeffsCharTable( t, 2 ); [ [ 0, 1, 0, 0, 0, 0 ], [ 21, 4, 3, 4, 0, 0 ], [ 0, 8, 6, 8, 7, 7 ], [ 0, 8, 6, 1, 7, 7 ], [ 0, 0, 3, 4, 0, 7 ], [ 0, 0, 3, 4, 7, 0 ] ]

`ClassStructureCharTable( `

`tbl`, `classes` )

returns the so--called class structure of the classes in the list
`classes`, for the character table `tbl` of the group *G*.
The length of `classes` must be at least 2.

gap> t:= CharTable( "M12" );; gap> ClassStructureCharTable( t, [2,6,9,13] ); 916185600 gap> ClassStructureCharTable( t, [2,9,13] ); # equals the group order 95040

Let *C _{1}, ..., C_{n}* denote the conjugacy classes of

`ClassMultCoeffCharTable`

.
*n(C _{1}, C_{2}, ..., C_{n})* is computed using the formula

n(C\footnotesize Irr_{1}, C_{2}, ..., C_{n}) = (|C_{1}||C_{2}|...|C_{n}|)/(|G|)
∑_{χ ∈ }(G)
(χ(g_{1})χ(g_{2})...χ(g_{n}))/(χ(1)^{n-2}) . |

`RealClassesCharTable( `

`tbl` )

returns a list of the real classes of the group *G* with character table
`tbl`.

gap> RealClassesCharTable(L3_2); [ 1, 2, 3, 4 ]

An element *x ∈ G* is called **real**, if it is conjugate with its
inverse. And as *x ^{-1} = x^{o(x)-1}*, this fact is tested by looking
at the powermap of

Real elements take only real character values.

`ClassOrbitCharTable( `

`tbl`, `class` )

returns a list of classes containing elements of
the cyclic subgroup generated by an element *x* of class `class`.

gap> ClassOrbitCharTable(L3_2, 5); [ 5, 6 ]

Being all powers of *x* this data is recovered from the powermap
of `tbl`.

`ClassRootsCharTable( `

`tbl` )

returns a list of the classes of all nontrivial *p*--th roots of the
classes of `tbl` where for each class, *p* runs over the prime divisors
of the representative order.

gap> ClassRootsCharTable(L3_2); [ [ 2, 3, 5, 6 ], [ 4 ], [ ], [ ], [ ], [ ] ]

This information is found by looking at the powermap of `tbl`, too.

`NrPolyhedralSubgroups( `

`tbl`, `c1`, `c2`, `c3` )

returns the number and isomorphism type of polyhedral subgroups of the
group with character table `tbl` which are generated by an element *g* of
class `c1` and an element *h* of class `c2` with the property that the
product *gh* lies in class `c3`.

gap> NrPolyhedralSubgroups(L3_2, 2, 2, 4); rec( number := 21, type := "D8" )

According to NPP84, p.~233 the number of polyhedral subgroups of
isomorphism type *V _{4}*,

Note that the classes `c1`, `c2` and `c3` in the parameter list must be
ordered according to the order of the elements in these classes.

`DisplayCharTable( `

`tbl` )

`DisplayCharTable( `

`tbl`, `arec` )

`DisplayCharTable`

prepares the data contained in the character table
`tbl` for a pretty columnwise output.

In the first form `DisplayCharTable`

prints all irreducible characters
of the table `tbl`, together with the orders of the centralizers in
factorized form and the available powermaps.

Thus it can be used to echo character tables in interactive use, being
the value of the record field `Print`

of a record field `operations`

of `tbl` (see Character Table Records,
Operations Records for Character Tables).

Each displayed character is given a name `X.`

.
`n`

The number of columns printed at one time depends on the actual
linelength, which is restored by the function `SizeScreen`

(see
SizeScreen).

The first lines of the output describe the order of the centralizer of an element of the class factorized into its prime divisor.

The next line gives the name of the class. If the record field
`classnames`

of the table `tbl` is not bound, `DisplayCharTable`

calls the function `ClassNamesCharTable`

to determine the class names
and to store them on the table `tbl` (see ClassNamesCharTable).

Preceded by a name `P`

the next lines show the `n``n`th powermaps
of `tbl` in terms of the former shown class names.

Every ambiguous or unknown (see Unknown) value of the table is
displayed as a question mark `?`

.

Irrational character values are not printed explicitly because the lengths of their printed representation might disturb the view. Instead of that every irrational value is indicated by a name, which is a string of a least one capital letter.

Once a name for an irrational number is found, it is used all over the
printed table. Moreover the complex conjugate and the star of an
irrationality are represented by that very name preceded by a `/`

resp. a `*`

.

The printed character table is then followed by a legend, a list
identifying the occurred symbols with their actual irrational value.
Occasionally this identity is supplemented by a quadratic representation
of the irrationality together with the corresponding **ATLAS**--notation.

gap> a5:= CharTable("A5");; gap> DisplayCharTable(a5); A5 2 2 2 . . . 3 1 . 1 . . 5 1 . . 1 1 1a 2a 3a 5a 5b 2P 1a 1a 3a 5b 5a 3P 1a 2a 1a 5b 5a 5P 1a 2a 3a 1a 1a X.1 1 1 1 1 1 X.2 3 -1 . A *A X.3 3 -1 . *A A X.4 4 . 1 -1 -1 X.5 5 1 -1 . . A = -E(5)-E(5)^4 = (1-ER(5))/2 = -b5

In the second form `DisplayCharTable`

takes an argument record `arec` as
an additional argument. This record can be used to change the default
style for displaying a character as shown above. Its relevant fields
are

`chars`

:-

an integer or a list of integers to select a sublist of the irreducible characters of`tbl`, or a list of characters of`tbl`(in this case the letter`"X"`

is replaced by`"Y"`

),

`classes`

:-

an integer or a list of integers to select a sublist of the classes of`tbl`,

`centralizers`

:-

suppresses the printing of the orders of the centralizers if`false`

,

`powermap`

:-

an integer or a list of integers to select a subset of the available powermaps, or`false`

to suppress the powermaps,

`letter`

:-

a single capital letter (e. g.`"P"`

for permutation characters) to replace`"X"`

,

`indicator`

:-

`true`

enables the printing of the second Schur indicator, a list of integers enables the printing of the corresponding indicators.

gap> arec:= rec( chars:= 4, classes:= [a5.3a..a5.5a], > centralizers:= false, indicator:= true, powermap:= [2] );; gap> Indicator( a5, 2 );; gap> DisplayCharTable( a5, arec ); A5 3a 5a 2P 3a 5b 2 X.4 + 1 -1

`SortCharactersCharTable( `

`tbl` )

`SortCharactersCharTable( `

`tbl`, `permutation` )

`SortCharactersCharTable( `

`tbl`, `chars` )

`SortCharactersCharTable( `

`tbl`, `chars`, `permutation` )

`SortCharactersCharTable( `

`tbl`, `chars`, "norm" )

`SortCharactersCharTable( `

`tbl`, `chars`, "degree" )

If no list `chars` of characters of the character table `tbl` is
entered, `SortCharactersCharTable`

sorts

; then
additionally the list `tbl`.irreducibles

is permuted by the same
permutation. Otherwise `tbl`.irredinfo`SortCharactersCharTable`

sorts the list `chars`.

There are four possibilities to sort characters:
Besides the application of an explicitly given permutation (see
Permuted), they can be sorted according to ascending norms (parameter
`"norm"`

), to ascending degree (parameter `"degree"`

) or both (no
third parameter), i.e., characters with same norm are sorted according to
ascending degree, and characters with smaller norm precede those with
bigger norm.

If the trivial character is contained in the sorted list, it will be sorted to the first position. Rational characters always will precede other ones with same norm resp. same degree afterwards.

`SortCharactersCharTable`

returns the permutation that was applied to
`chars`.

gap> t:= CharTable( "Symmetric", 5 );; gap> PrintCharTable( t ); rec( identifier := "S5", name := "S5", size := 120, order := 120, centralizers := [ 120, 12, 8, 6, 6, 4, 5 ], orders := [ 1, 2, 2, 3, 6, 4, 5 ], powermap := [ , [ 1, 1, 1, 4, 4, 3, 7 ], [ 1, 2, 3, 1, 2, 6, 7 ],, [ 1, 2, 3, 4, 5, 6, 1 ] ], irreducibles := [ [ 1, -1, 1, 1, -1, -1, 1 ], [ 4, -2, 0, 1, 1, 0, -1 ], [ 5, -1, 1, -1, -1, 1, 0 ], [ 6, 0, -2, 0, 0, 0, 1 ], [ 5, 1, 1, -1, 1, -1, 0 ], [ 4, 2, 0, 1, -1, 0, -1 ], [ 1, 1, 1, 1, 1, 1, 1 ] ], classparam := [ [ 1, [ 1, 1, 1, 1, 1 ] ], [ 1, [ 2, 1, 1, 1 ] ], [ 1, [ 2, 2, 1 ] ], [ 1, [ 3, 1, 1 ] ], [ 1, [ 3, 2 ] ], [ 1, [ 4, 1 ] ], [ 1, [ 5 ] ] ], irredinfo := [ rec( charparam := [ 1, [ 1, 1, 1, 1, 1 ] ] ), rec( charparam := [ 1, [ 2, 1, 1, 1 ] ] ), rec( charparam := [ 1, [ 2, 2, 1 ] ] ), rec( charparam := [ 1, [ 3, 1, 1 ] ] ), rec( charparam := [ 1, [ 3, 2 ] ] ), rec( charparam := [ 1, [ 4, 1 ] ] ), rec( charparam := [ 1, [ 5 ] ] ) ], text := "computed using generic character table for symmetric grou\ ps", classes := [ 1, 10, 15, 20, 20, 30, 24 ], operations := CharTableOps, fusions := [ ], fusionsource := [ ], projections := [ ], projectionsource := [ ] ) gap> SortCharactersCharTable( t, t.irreducibles, "norm" ); (1,2,3,4,5,6,7) # sort the trivial character to the first position gap> SortCharactersCharTable( t ); (4,5,7) gap> t.irreducibles; [ [ 1, 1, 1, 1, 1, 1, 1 ], [ 1, -1, 1, 1, -1, -1, 1 ], [ 4, -2, 0, 1, 1, 0, -1 ], [ 4, 2, 0, 1, -1, 0, -1 ], [ 5, -1, 1, -1, -1, 1, 0 ], [ 5, 1, 1, -1, 1, -1, 0 ], [ 6, 0, -2, 0, 0, 0, 1 ] ]

`SortClassesCharTable( `

`tbl` )

`SortClassesCharTable( `

`tbl`, "centralizers" )

`SortClassesCharTable( `

`tbl`, "representatives" )

`SortClassesCharTable( `

`tbl`, `permutation` )

`SortClassesCharTable( `

`chars`, `permutation` )

The last form simply permutes the classes of all elements of `chars`
with `permutation`. All other forms take a character table `tbl` as
parameter, and `SortClassesCharTable`

permutes the classes of `tbl`:

`SortClassesCharTable(`

:`tbl`, "centralizers" )

sorts the classes according to descending centralizer orders,

`SortClassesCharTable(`

:`tbl`, "representatives" )

sorts the classes according to ascending representative orders,

`SortClassesCharTable(`

:`tbl`)

sorts the classes according to ascending representative orders, and classes with equal representative orders according to descending centralizer orders,

`SortClassesCharTable(`

:`tbl`,`permutation`)

sorts the classes by application of`permutation`

After having calculated the permutation, `SortClassesCharTable`

will
adjust the following fields of `tbl`:

by application of the permutation: `orders`

, `centralizers`

, `classes`

,
`print`

, all entries of `irreducibles`

, `classtext`

, `classparam`

,
`classnames`

, all fusion maps, all entries of the `chars`

lists in the
records of `projectives`

by conjugation with the permutation: all powermaps,
`automorphisms`

,

by multiplication with the permutation: `permutation`

,

and the fields corresponding to

(see ClassNamesCharTable).
`tbl`.classnames

The applied permutation is returned by `SortClassesCharTable`

.

**Note** that many programs expect the class `1A`

to be the first one
(see Conventions for Character Tables).

gap> t:= CharTable( "Symmetric", 5 );; gap> PrintCharTable( t ); rec( identifier := "S5", name := "S5", size := 120, order := 120, centralizers := [ 120, 12, 8, 6, 6, 4, 5 ], orders := [ 1, 2, 2, 3, 6, 4, 5 ], powermap := [ , [ 1, 1, 1, 4, 4, 3, 7 ], [ 1, 2, 3, 1, 2, 6, 7 ],, [ 1, 2, 3, 4, 5, 6, 1 ] ], irreducibles := [ [ 1, -1, 1, 1, -1, -1, 1 ], [ 4, -2, 0, 1, 1, 0, -1 ], [ 5, -1, 1, -1, -1, 1, 0 ], [ 6, 0, -2, 0, 0, 0, 1 ], [ 5, 1, 1, -1, 1, -1, 0 ], [ 4, 2, 0, 1, -1, 0, -1 ], [ 1, 1, 1, 1, 1, 1, 1 ] ], classparam := [ [ 1, [ 1, 1, 1, 1, 1 ] ], [ 1, [ 2, 1, 1, 1 ] ], [ 1, [ 2, 2, 1 ] ], [ 1, [ 3, 1, 1 ] ], [ 1, [ 3, 2 ] ], [ 1, [ 4, 1 ] ], [ 1, [ 5 ] ] ], irredinfo := [ rec( charparam := [ 1, [ 1, 1, 1, 1, 1 ] ] ), rec( charparam := [ 1, [ 2, 1, 1, 1 ] ] ), rec( charparam := [ 1, [ 2, 2, 1 ] ] ), rec( charparam := [ 1, [ 3, 1, 1 ] ] ), rec( charparam := [ 1, [ 3, 2 ] ] ), rec( charparam := [ 1, [ 4, 1 ] ] ), rec( charparam := [ 1, [ 5 ] ] ) ], text := "computed using generic character table for symmetric grou\ ps", classes := [ 1, 10, 15, 20, 20, 30, 24 ], operations := CharTableOps, fusions := [ ], fusionsource := [ ], projections := [ ], projectionsource := [ ] ) gap> SortClassesCharTable( t, "centralizers" ); (6,7) gap> SortClassesCharTable( t, "representatives" ); (5,7) gap> t.centralizers; t.orders; [ 120, 12, 8, 6, 4, 5, 6 ] [ 1, 2, 2, 3, 4, 5, 6 ]

`SortCharTable( `

`tbl`, `kernel` )

`SortCharTable( `

`tbl`, `normalseries` )

`SortCharTable( `

`tbl`, `facttbl`, `kernel` )

sorts classes and `irreducibles`

of the character table `tbl`, and
returns a record with components `columns`

and `rows`

, which are the
permutations applied to classes and characters.

The first form sorts the classes at positions contained in the list
`kernel` to the beginning, and sorts all characters in

such that the first characters are those that
contain `tbl`.irreducibles`kernel` in their kernel.

The second form does the same successively for all kernels *k _{i}* in
the list

`normalseries`

= [ k
The third form computes the table `F` of the factor group of `tbl`
modulo the normal subgroup formed by the classes whose positions are
contained in the list `kernel`;
`F` must be permutation equivalent to the table `facttbl` (in the
sense of TransformingPermutationsCharTables), else `false`

is
returned. The classes of `tbl` are sorted such that the preimages
of a class of `F` are consecutive, and that the succession of
preimages is that of `facttbl`.

is sorted as
by `tbl`.irreducibles`SortCharTable( `

.
(`tbl`, `kernel` )**Note** that the transformation is only unique up to table automorphisms
of `F`, and this need not be unique up to table automorphisms of `tbl`.)

All rearrangements of classes and characters are stable, i.e., the relative positions of classes and characters that are not distinguished by any relevant property is not changed.

`SortCharTable`

uses SortClassesCharTable `SortClassesCharTable`

and
SortCharactersCharTable `SortCharactersCharTable`

.

gap> t:= CharTable("Symmetric",4);; gap> Set( List( t.irreducibles, KernelChar ) ); [ [ 1 ], [ 1, 2, 3, 4, 5 ], [ 1, 3 ], [ 1, 3, 4 ] ] gap> SortCharTable( t, Permuted( last, (2,4,3) ) ); rec( columns := (2,4,3), rows := (1,2,4,5) ) gap> DisplayCharTable( t ); S4 2 3 3 . 2 2 3 1 . 1 . . 1a 2a 3a 2b 4a 2P 1a 1a 3a 1a 2a 3P 1a 2a 1a 2b 4a X.1 1 1 1 1 1 X.2 1 1 1 -1 -1 X.3 2 2 -1 . . X.4 3 -1 . -1 1 X.5 3 -1 . 1 -1

`MatAutomorphisms( `

`mat`, `maps`, `subgroup` )

returns the permutation group record representing the matrix
automorphisms of the matrix `mat` that respect all lists in the list
`maps`, i.e. representing the group of those permutations of columns of
`mat` which acts on the set of rows of `mat` and additionally fixes all
lists in `maps`.

`subgroup` is a list of permutation generators of a subgroup of this
group. E.g. generators of the Galois automorphisms of a matrix of
ordinary characters may be entered here.

gap> t:= CharTable( "Dihedral", 8 );; gap> PrintCharTable( t ); rec( identifier := "D8", name := "D8", size := 8, order := 8, centralizers := [ 8, 4, 8, 4, 4 ], orders := [ 1, 4, 2, 2, 2 ], powermap := [ , [ 1, 3, 1, 1, 1 ] ], irreducibles := [ [ 1, 1, 1, 1, 1 ], [ 1, 1, 1, -1, -1 ], [ 1, -1, 1, 1, -1 ], [ 1, -1, 1, -1, 1 ], [ 2, 0, -2, 0, 0 ] ], classparam := [ [ 1, 0 ], [ 1, 1 ], [ 1, 2 ], [ 2, 0 ], [ 2, 1 ] ], irredinfo := [ rec( charparam := [ 1, 0 ] ), rec( charparam := [ 1, 1 ] ), rec( charparam := [ 1, 2 ] ), rec( charparam := [ 1, 3 ] ), rec( charparam := [ 2, 1 ] ) ], text := "computed using generic character table for dihedral group\ s", classes := [ 1, 2, 1, 2, 2 ], operations := CharTableOps, fusions := [ ], fusionsource := [ ], projections := [ ], projectionsource := [ ] ) gap> MatAutomorphisms( t.irreducibles, [], Group( () ) ); Group( (4,5), (2,4) ) gap> MatAutomorphisms( t.irreducibles, [ t.orders ], Group( () ) ); Group( (4,5) )

`TableAutomorphisms( `

`tbl`, `chars` )

`TableAutomorphisms( `

`tbl`, `chars`, "closed" )

returns a permutation group record for the group of those matrix
automorphisms of `chars` (see MatAutomorphisms) which are
admissible by (i.e. which fix) the fields `orders`

and all uniquely
determined (i.e. not parametrized) maps in `powermap`

of
the character table `tbl`; the action on `orders`

is the natural
permutation, that on the powermaps is conjugation.

If `chars` is closed under galois conjugacy --this is always satisfied
for ordinary character tables-- the parameter "closed" may be entered.
In that case the subgroup of Galois automorphisms is computed by
GaloisMat `GaloisMat`

.

gap> t:= CharTable( "Dihedral", 8 );; # as in MatAutomorphisms gap> TableAutomorphisms( t, t.irreducibles ); Group( (4,5) )

`TransformingPermutations( `

`mat1`, `mat2` )

tries to construct a permutation *π* that transforms the set of rows of
the matrix `mat1` to the set of rows of the matrix `mat2` by permutation
of columns.
If such a permutation exists, a record with fields `columns`

, `rows`

and `group`

is returned, otherwise `false`

:
If * TransformingPermutations( *
then

`Permuted( List(`

,
`mat1`,x->Permuted(x,`r`.columns)),`r`.rows ) = `mat2`

and

is the group of matrix automorphisms of `r`.group`mat2`;
this group stabilizes the transformation, i.e. for *g* in that group and
*π* the value of the `columns`

field, also *π g* would be a valid
permutation of columns.

gap> mat1:= CharTable( "Alternating", 5 ).irreducibles; [ [ 1, 1, 1, 1, 1 ], [ 4, 0, 1, -1, -1 ], [ 5, 1, -1, 0, 0 ], [ 3, -1, 0, -E(5)-E(5)^4, -E(5)^2-E(5)^3 ], [ 3, -1, 0, -E(5)^2-E(5)^3, -E(5)-E(5)^4 ] ] gap> mat2:= CharTable( "A5" ).irreducibles; [ [ 1, 1, 1, 1, 1 ], [ 3, -1, 0, -E(5)-E(5)^4, -E(5)^2-E(5)^3 ], [ 3, -1, 0, -E(5)^2-E(5)^3, -E(5)-E(5)^4 ], [ 4, 0, 1, -1, -1 ], [ 5, 1, -1, 0, 0 ] ] gap> TransformingPermutations( mat1, mat2 ); rec( columns := (), rows := (2,4)(3,5), group := Group( (4,5) ) )

`TransformingPermutationsCharTables( `

`tbl1`, `tbl2` )

tries to construct a permutation *π* that transforms the set of rows of

to the set of rows of `tbl1`.irreducibles

by
permutation of columns (see TransformingPermutations) and that also
transforms the powermaps and the `tbl2`.irreducibles`orders`

field. If such a permutation
exists, it returns a record with components `columns`

(a valid
permutation of columns), `rows`

(the permutation of

corresponding to that permutation), and `tbl`.irreducibles`group`

(the permutation group
record of table automorphisms of `tbl2`, see TableAutomorphisms). If
no such permutation exists, it returns `false`

.

gap> t1:= CharTable("Dihedral",8);;t2:= CharTable("Quaternionic",8);; gap> TransformingPermutations( t1.irreducibles, t2.irreducibles ); rec( columns := (), rows := (), group := Group( (4,5), (2,4) ) ) gap> TransformingPermutationsCharTables( t1, t2 ); false gap> t1:= CharTable( "Dihedral", 6 );; t2:= CharTable("Symmetric",3);; gap> TransformingPermutationsCharTables( t1, t2 ); rec( columns := (2,3), rows := (1,3,2), group := Group( () ) )

`GetFusionMap( `

`source`, `destination` )

`GetFusionMap( `

`source`, `destination`, `specification` )

For character tables `source` and `destination`,
`GetFusionMap( `

returns the `source`, `destination` )`map`

field of the
fusion stored on the character table `source` that has the `identifier`

component

;
`destination`.name

`GetFusionMap( `

gets that
fusion that additionally has the `source`, `destination`, `specification` )`specification`

field `specification`.

Both versions adjust the ordering of classes of `destination` using

(see SortClassesCharTable, Conventions for
Character Tables).
That is the reason why `destination`.permutation`destination` cannot be simply the identifier of
the destination table.

If both `source` and `destination` are Brauer tables, `GetFusionMap`

returns the fusion corresponding to that between the ordinary tables;
for that, this fusion must be stored on

.
`source`.ordinary

If no appropriate fusion is found, `false`

is returned.

gap> s:= CharTable( "L2(11)" );; gap> t:= CharTable( "J1" );; gap> SortClassesCharTable( t, ( 3, 4, 5, 6 ) );; gap> t.permutation; (3,4,5,6) gap> GetFusionMap( s, t ); [ 1, 2, 4, 6, 5, 3, 10, 10 ] gap> s.fusions[5]; rec( name := "J1", map := [ 1, 2, 3, 5, 4, 6, 10, 10 ], text := [ 'f', 'u', 's', 'i', 'o', 'n', ' ', 'i', 's', ' ', 'u', 'n', 'i', 'q', 'u', 'e', ' ', 'u', 'p', ' ', 't', 'o', ' ', 't', 'a', 'b', 'l', 'e', ' ', 'a', 'u', 't', 'o', 'm', 'o', 'r', 'p', 'h', 'i', 's', 'm', 's', ',', '\n', 't', 'h', 'e', ' ', 'r', 'e', 'p', 'r', 'e', 's', 'e', 'n', 't', 'a', 't', 'i', 'v', 'e', ' ', 'i', 's', ' ', 'e', 'q', 'u', 'a', 'l', ' ', 't', 'o', ' ', 't', 'h', 'e', ' ', 'f', 'u', 's', 'i', 'o', 'n', ' ', 'm', 'a', 'p', ' ', 'o', 'n', ' ', 't', 'h', 'e', ' ', 'C', 'A', 'S', ' ', 't', 'a', 'b', 'l', 'e' ] )

`StoreFusion( `

`source`, `destination`, `fusion` )

`StoreFusion( `

`source`, `destination`, `fusionmap` )

For character tables `source` and `destination`, `fusion` must be a
record containing at least the field `map`

which is regarded as a fusion
from `source` to `destination`.
`fusion` is stored on `source` if no ambiguity arises, i.e. if there is
not yet a fusion into `destination` stored on `source` or if any fusion
into destination stored on `source` has a `specification`

field different
from that of `fusion`.
The `map`

field of `fusion` is adjusted by

.
(Thus the map will remain correct even if the classes of a concerned
table are sorted, see SortClassesCharTable and Conventions for
Character Tables; the
correct fusion can be got using GetFusionMap, so be careful!).
Additionally, `destination`.permutation

is added to
`source`.identifier

.
`destination`.fusionsource

The second form works like the first, with

.
`fusion` = rec( map:= `fusionmap` )

gap> s:= CharTable( "A6.2_1" );; t:= CharTable( "A7.2" );; gap> fus:= RepresentativesFusions( s, SubgroupFusions( s, t ), t ); [ [ 1, 2, 3, 4, 5, 6, 9, 10, 11, 12, 13 ] ] gap> s.fusions; t.fusionsource; [ ] [ "2.A7.2", "3.A7.2", "6.A7.2", "A7" ] gap> StoreFusion( s, t, fus[1] ); gap> s.fusions; t.fusionsource; [ rec( name := "A7.2", map := [ 1, 2, 3, 4, 5, 6, 9, 10, 11, 12, 13 ] ) ] [ "2.A7.2", "3.A7.2", "6.A7.2", "A6.2_1", "A7" ]

`FusionConjugacyClasses( `

`subgroup`, `group` )

`FusionConjugacyClasses( `

`group` , `factorgroup` )

`FusionConjugacyClasses`

returns a list denoting the fusion of
conjugacy classes from
the first group to the second one. If both groups have components
`charTable`

this list is written to the character tables, too.

gap> g := SolvableGroup( 24, 14 ); Sl(2,3) gap> FusionConjugacyClasses( g, g / Subgroup( g, [ g.4 ] ) ); [ 1, 1, 2, 3, 3, 4, 4 ] gap> FusionConjugacyClasses( Subgroup( g, [ g.2, g.3, g.4 ] ), g ); [ 1, 2, 3, 3, 3 ]

`MAKElb11( `

`listofns` )

prints field information for fields with conductor *Q _{n}* where

`MAKElb11( [ 3 .. 189 ] )`

will print something very similar to
Richard Parker's file `lb11`

.

gap> MAKElb11( [ 3, 4 ] ); 3 2 0 1 0 4 2 0 1 0

`ScanMOC( `

`list` )

returns a record containing the information encoded in the list `list`,
the components of the result are the labels in `list`. If `list` is in
MOC2 format (10000--format) the names of components are 30000--numbers,
if it is in MOC3 format the names of components have yABC--format.

gap> ScanMOC( "y100y105ay110t28t22z" ); rec( y105 := [ 0 ], y110 := [ 28, 22 ] )

`MOCChars( `

`tbl`, `gapchars` )

returns translations of **GAP3** format characters `gapchars` to MOC
format. `tbl` must be a **GAP3** format table or a MOC format table.

`GAPChars( `

`tbl`, `mocchars` )

returns translations of MOC format characters `mocchars` to **GAP3**
format. `tbl` must be a **GAP3** format table or a MOC format table.

`mocchars` may also be a list of integers, e.g., a component containing
characters in a record produced by ScanMOC.

`MOCTable( `

`gaptbl` )

`MOCTable( `

`gaptbl`, `basicset` )

return the MOC format table record of the **GAP3** table `gaptbl`, and
stores it in the component `MOCtbl`

of `gaptbl`.

The first form can be used for ordinary (*G.0*) tables only, for modular
(*G.p*) tables one has to specify a basic set `basicset` of ordinary
irreducibles which must be the list of positions of these characters in
the `irreducibles`

component of the corresponding ordinary table (which
is stored in `gaptbl`.ordinary).

The result contains the information of `gaptbl` in a format similar to
the MOC 3 format, the table itself can e.g. easily be printed out or be
used to print out characters using PrintToMOC.

The components of the result are

`identifier`

:- the string
`MOCTable(`

where`name`)`name`is the`identifier`

component of`gaptbl`,

`isMOCformat`

:- has value
`true`

,

`GAPtbl`

:- the record
`gaptbl`,

`operations`

:- equal to
`MOCTableOps`

, containing just an appropriate`Print`

function,

`prime`

:- the characteristic of the field (label 30105 in MOC),

`centralizers`

:- centralizer orders for cyclic subgroups (label 30130)

`orders`

:- element orders for cyclic subgroups (label 30140)

`fields`

:- at position
`i`

the number field generated by the character values of the`i`

--th cyclic subgroup; the`base`

component of each field is a Parker base, (the length of`fields`

is equal to the value of label 30110 in MOC).

`cycsubgps`

:-
`cycsubgps[i] = j`

means that class`i`

of the**GAP3**table belongs to the`j`

--th cyclic subgroup of the**GAP3**table,

`repcycsub`

:-
`repcycsub[j] = i`

means that class`i`

of the**GAP3**table is the representative of the`j`

--th cyclic subgroup of the**GAP3**table.**Note**that the representatives of**GAP3**table and MOC table need not agree!

`galconjinfo`

:- a list
*[ r*which means that the_{1},c_{1},r_{2},c_{2},...,r_{n},c_{n}]*i*--th class of the GAP table is the*c*--th conjugate of the representative of the_{i}*r*--th cyclic subgroup on the MOC table. (This is used to translate back to GAP format, stored under label 30160)_{i}

`30170`

:- (power maps) for each cyclic subgroup (except
the trivial one) and each prime divisor of
the representative order store four values, the number
of the subgroup, the power, the number of the cyclic
subgroup containing the image, and the power to which
the representative must be raised to give the image
class. (This is used only to construct the
`30230`

power map/embedding information.) In`result.30170`

only a list of lists (one for each cyclic subgroup) of all these values is stored, it will not be used by**GAP3**.

`tensinfo`

:- tensor product information, used to compute the
coefficients of the Parker base for tensor products
of characters (label 30210 in MOC).
For a field with vector space base
*(v*the tensor product information of a cyclic subgroup in MOC (as computed by_{1},v_{2},...,v_{n})`fct`

) is either 1 (for rational classes) or a sequence which means that the coefficient of*n x*_{1,1}y_{1,1}z_{1,1}x_{1,2}y_{1,2}z_{1,2}... x_{1,m1}y_{1,m1}z_{1,m1}0 x_{2,1}... z_{2,m2}0 ... x_{n,mn}y_{n,mn}z_{n,mn}0*v*in the product_{k} is equal to*( ∑*_{i=1}^{n}a_{i}v_{i}) ( ∑_{j=1}^{n}b_{j}v_{j}) On a MOC table in*∑*_{i=1}^{mk}x_{k,i}a_{yk,i}b_{zk,i}.**GAP3**the`tensinfo`

component is a list of lists, each containing exactly the sequence

`invmap`

:- inverse map to compute complex conjugate characters, label 30220 in MOC.

`powerinfo`

:- field embeddings for
*p*--th symmetrizations,*p*prime in`[ 2 .. 19 ]`

; note that the necessary power maps must be stored on`gaptbl`to compute this component. (label 30230 in MOC)

`30900`

:- basic set of restricted ordinary irreducibles in the case of nonzero characteristic, all ordinary irreducibles else.

`PrintToMOC( `

`moctbl` )

`PrintToMOC( `

`moctbl`, `chars` )

The first form prints the MOC3 format of the character table `moctbl`
which must be an character table in MOC format (as produced by
MOCTable). The second form prints a table in MOC3 format that
contains the MOC format characters `chars` (as produced by MOCChars)
under label `y900`

.

gap> t:= CharTable( "A5mod3" );; gap> moct:= MOCTable( t, [ 1, 2, 3, 4 ] );; gap> PrintTo( "a5mod3", PrintToMOC( moct ), "\n" );

produces a file `a5mod3`

whose first characters are

` y100y105dy110edy130t60efy140bcfy150bbfcabbey160bbcbdbdcy170ccbbefbb`

`PrintToCAS( `

`filename`, `tbl` )

`PrintToCAS( `

`tbl`, `filename` )

produces a file with name `filename` which contains a **CAS** library table
of the **GAP3** character table `tbl`; this file can be read into **CAS**
using the `get`

-command (see NPP84).

The line length in the file is at most the current value `SizeScreen()[1]`

(see SizeScreen).

Only the components `identifier`

, `text`

, `order`

, `centralizers`

,
`orders`

, `print`

, `powermap`

, `classtext`

(for partitions only),
`fusions`

, `irredinfo`

, `characters`

, `irreducibles`

of `tbl` are
considered.

If

is bound, this list is taken as `tbl`.characters`characters`

entry
of the **CAS** table, otherwise

(if exists) will form
the list `tbl`.irreducibles`characters`

of the **CAS** table.

` gap> PrintToCAS( "c2", CharTable( "Cyclic", 2 ) );`

produces a file with name `c2`

containing the following data:

'C2' 00/00/00. 00.00.00. (2,2,0,2,-1,0) text: (#computed using generic character table for cyclic groups#), order=2, centralizers:(2,2), reps:(1,2), powermap:2(1,1), characters: (1,1) (1,-1); /// converted from GAP

gap3-jm

24 Apr 2021