GAP (ANUPQ) - Chapter 6: ANUPQ Options

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6 ANUPQ Options
6.1 Overview
6.1-1 AllANUPQoptions
6.1-2 ANUPQoptions
6.2 Detailed descriptions of ANUPQ Options

### 6 ANUPQ Options

#### 6.1 Overview

In this chapter we describe in detail all the options used by functions of the ANUPQ package. Note that by "options" we mean GAP options that are passed to functions after the arguments and separated from the arguments by a colon as described in Chapter Reference: Function Calls in the Reference Manual. The user is strongly advised to read Section Hints and Warnings regarding the use of Options.

##### 6.1-1 AllANUPQoptions

`‣ AllANUPQoptions`( ) | ( function )

lists all the GAP options defined for functions of the ANUPQ package:

    gap> AllANUPQoptions();
    [ "AllDescendants", "BasicAlgorithm", "Bounds", "CapableDescendants",
      "ClassBound", "CustomiseOutput", "Exponent", "Filename", "GroupName",
      "Identities", "Metabelian", "NumberOfSolubleAutomorphisms", "OrderBound",
      "OutputLevel", "PcgsAutomorphisms", "PqWorkspace", "Prime",
      "PrintAutomorphisms", "PrintPermutations", "QueueFactor",
      "RankInitialSegmentSubgroups", "RedoPcp", "RelativeOrders", "Relators",
      "SetupFile", "SpaceEfficient", "StandardPresentationFile", "StepSize",
      "SubList", "TreeDepth", "pQuotient" ]

The following global variable gives a partial breakdown of where the above options are used.

##### 6.1-2 ANUPQoptions

`‣ ANUPQoptions` | ( global variable )

is a record of lists of names of admissible ANUPQ options, such that each field is either the name of a "key" ANUPQ function or `other` (for a miscellaneous list of functions) and the corresponding value is the list of option names that are admissible for the function (or miscellaneous list of functions).

Also, from within a GAP session, you may use GAP's help browser (see Chapter Reference: The Help System in the GAP Reference Manual); to find out about any particular ANUPQ option, simply type: "`?option option`", where option is one of the options listed above without any quotes, e.g.

    gap> ?option Prime

will display the sections in this manual that describe the `Prime` option. In fact the first 4 are for the functions that have `Prime` as an option and the last actually describes the option. So follow up by choosing

    gap> ?5

This is also the pattern for other options (the last section of the list always describes the option; the other sections are the functions with which the option may be used).

In the section following we describe in detail all ANUPQ options. To continue onto the next section on-line using GAP's help browser, type:

    gap> ?>

#### 6.2 Detailed descriptions of ANUPQ Options

`Prime := p`

  Specifies that the p-quotient for the prime p should be computed.

`ClassBound := n`

  Specifies that the p-quotient to be computed has lower exponent-p class at most n. If this option is omitted a default of 63 (which is the maximum possible for the `pq` program) is taken, except for `PqDescendants` (see `PqDescendants` (4.4-1)) and in a special case of `PqPCover` (see `PqPCover` (4.1-3)). Let F be the argument (or start group of the process in the interactive case) for the function; then for `PqDescendants` the default is `PClassPGroup(F) + 1`, and for the special case of `PqPCover` the default is `PClassPGroup(F)`.

`pQuotient := Q`

  This option is only available for the standard presentation functions. It specifies that a p-quotient of the group argument of the function or group of the process is the pc p-group Q, where Q is of class less than the provided (or default) value of `ClassBound`. If `pQuotient` is provided, then the option `Prime` if also provided, is ignored; the prime p is discovered by computing `PrimePGroup(Q)`.

`Exponent := n`

  Specifies that the p-quotient to be computed has exponent n. For an interactive process, `Exponent` defaults to a previously supplied value for the process. Otherwise (and non-interactively), the default is 0, which means that no exponent law is enforced.

`Relators := rels`

  Specifies that the relators sent to the `pq` program should be rels instead of the relators of the argument group F (or start group in the interactive case) of the calling function; rels should be a list of strings in the string representations of the generators of F, and F must be an fp group (even if the calling function accepts a pc group). This option provides a way of giving relators to the `pq` program, without having them pre-expanded by GAP, which can sometimes effect a performance loss of the order of 100 (see Section The Relators Option).

  Notes

  1. The `pq` program does not use `/` to indicate multiplication by an inverse and uses square brackets to represent (left normed) commutators. Also, even though the `pq` program accepts relations, all elements of rels must be in relator form, i.e. a relation of form `w1 = w2` must be written as `w1*(w2)^-1` and then put in a pair of double-quotes to make it a string. See the example below.

  2. To ensure there are no syntax errors in rels, each relator is parsed for validity via `PqParseWord` (see `PqParseWord` (3.4-3)). If they are ok, a message to say so is `Info`-ed at `InfoANUPQ` level 2.

`Metabelian`

  Specifies that the largest metabelian p-quotient subject to any other conditions specified by other options be constructed. By default this restriction is not enforced.

`GroupName := name`

  Specifies that the `pq` program should refer to the group by the name name (a string). If `GroupName` is not set and the group has been assigned a name via `SetName` (see Reference: Name) it is set as the name the `pq` program should use. Otherwise, the "generic" name `"[grp]"` is set as a default.

`Identities := funcs`

  Specifies that the pc presentation should satisfy the laws defined by each function in the list funcs. This option may be called by `Pq`, `PqEpimorphism`, or `PqPCover` (see `Pq` (4.1-1)). Each function in the list funcs must return a word in its arguments (there may be any number of arguments). Let identity be one such function in funcs. Then as each lower exponent p-class quotient is formed, instances identity(w1, dots, wn) are added as relators to the pc presentation, where w1, dots, wn are words in the pc generators of the quotient. At each class the class and number of pc generators is `Info`-ed at `InfoANUPQ` level 1, the number of instances is `Info`-ed at `InfoANUPQ` level 2, and the instances that are evaluated are `Info`-ed at `InfoANUPQ` level 3. As usual timing information is `Info`-ed at `InfoANUPQ` level 2; and details of the processing of each instance from the `pq` program (which is often quite voluminous) is `Info`-ed at `InfoANUPQ` level 3. Try the examples `"B2-4-Id"` and `"11gp-3-Engel-Id"` which demonstrate the usage of the `Identities` option; these are run using `PqExample` (see `PqExample` (3.4-4)). Take note of Note 1. below in relation to the example `"B2-4-Id"`; the companion example `"B2-4"` generates the same group using the `Exponent` option. These examples are discussed at length in Section The Identities Option and PqEvaluateIdentities Function.

  Notes

  1. Setting the `InfoANUPQ` level to 3 or more when setting the `Identities` option may slow down the computation considerably, by overloading GAP with io operations.

  2. The `Identities` option is implemented at the GAP level. An identity that is just an exponent law should be specified using the `Exponent` option (see `option Exponent`), which is implemented at the C level and is highly optimised and so is much more efficient.

  3. The number of instances of each identity tends to grow combinatorially with the class. So care should be exercised in using the `Identities` option, by including other restrictions, e.g. by using the `ClassBound` option (see `option ClassBound`).

`OutputLevel := n`

  Specifies the level of "verbosity" of the information output by the ANU `pq` program when computing a pc presentation; n must be an integer in the range 0 to 3. `OutputLevel := 0` displays at most one line of output and is the default; `OutputLevel := 1` displays (usually) slightly more output and `OutputLevel`s of 2 and 3 are two levels of verbose output. To see these messages from the `pq` program, the `InfoANUPQ` level must be set to at least 1 (see `InfoANUPQ` (3.3-1)). See Section Hints and Warnings regarding the use of Options for an example of how `OutputLevel` can be used as a troubleshooting tool.

`RedoPcp`

  Specifies that the current pc presentation (for an interactive process) stored by the `pq` program be scrapped and clears the current values stored for the options `Prime`, `ClassBound`, `Exponent` and `Metabelian` and also clears the `pQuotient`, `pQepi` and `pCover` fields of the data record of the process.

`SetupFile := filename`

  Non-interactively, this option directs that `pq` should not be called and that an input file with name filename (a string), containing the commands necessary for the ANU `pq` standalone, be constructed. The commands written to filename are also `Info`-ed behind a "`ToPQ>` " prompt at `InfoANUPQ` level 4 (see `InfoANUPQ` (3.3-1)). Except in the case following, the calling function returns `true`. If the calling function is the non-interactive version of one of `Pq`, `PqPCover` or `PqEpimorphism` and the group provided as argument is trivial given with an empty set of generators, then no setup file is written and `fail` is returned (the `pq` program cannot do anything useful with such a group). Interactively, `SetupFile` is ignored.

  Note: Since commands emitted to the `pq` program may depend on knowing what the "current state" is, to form a setup file some "close enough guesses" may sometimes be necessary; when this occurs a warning is `Info`-ed at `InfoANUPQ` or `InfoWarning` level 1. To determine whether the "close enough guesses" give an accurate setup file, it is necessary to run the command without the `SetupFile` option, after either setting the `InfoANUPQ` level to at least 4 (the setup file script can then be compared with the "`ToPQ>` " commands that are `Info`-ed) or setting a `pq` command log file by using `ToPQLog` (see `ToPQLog` (3.4-7)).

`PqWorkspace := workspace`

  Non-interactively, this option sets the memory used by the `pq` program. It sets the maximum number of integer-sized elements to allocate in its main storage array. By default, the `pq` program sets this figure to 10000000. Interactively, `PqWorkspace` is ignored; the memory used in this case may be set by giving `PqStart` a second argument (see `PqStart` (5.1-1)).

`PcgsAutomorphisms`
`PcgsAutomorphisms := false`

  Let G be the group associated with the calling function (or associated interactive process). Passing the option `PcgsAutomorphisms` without a value (or equivalently setting it to `true`), specifies that a polycyclic generating sequence for the automorphism group (which must be soluble) of G, be computed and passed to the `pq` program. This increases the efficiency of the computation; it also prevents the `pq` from calling GAP for orbit-stabilizer calculations. By default, `PcgsAutomorphisms` is set to the value returned by `IsSolvable( AutomorphismGroup( G ) )`, and uses the package AutPGrp to compute `AutomorphismGroup( G )` if it is installed. This flag is set to `true` or `false` in the background according to the above criterion by the function `PqDescendants` (see `PqDescendants` (4.4-1) and `PqDescendants` (5.3-6)).

  Note: If `PcgsAutomorphisms` is used when the automorphism group of G is insoluble, an error message occurs.

`OrderBound := n`

  Specifies that only descendants of size at most p^n, where n is a non-negative integer, be generated. Note that you cannot set both `OrderBound` and `StepSize`.

`StepSize := n`
`StepSize := list`

  For a positive integer n, `StepSize` specifies that only those immediate descendants which are a factor p^n bigger than their parent group be generated.

  For a list list of positive integers such that the sum of the length of list and the exponent-p class of G is equal to the class bound defined by the option `ClassBound`, `StepSize` specifies that the integers of list are the step sizes for each additional class.

`RankInitialSegmentSubgroups := n`

  Sets the rank of the initial segment subgroup chosen to be n. By default, this has value 0.

`SpaceEfficient`

  Specifies that the `pq` program performs certain calculations of p-group generation more slowly but with greater space efficiency. This flag is frequently necessary for groups of large Frattini quotient rank. The space saving occurs because only one permutation is stored at any one time. This option is only available if the `PcgsAutomorphisms` flag is set to `true` (see `option PcgsAutomorphisms`). For an interactive process, `SpaceEfficient` defaults to a previously supplied value for the process. Otherwise (and non-interactively), `SpaceEfficient` is by default `false`.

`CapableDescendants`

  By default, all (i.e. capable and terminal) descendants are computed. If this flag is set, only capable descendants are computed. Setting this option is equivalent to setting `AllDescendants := false` (see `option AllDescendants`), except if both `CapableDescendants` and `AllDescendants` are passed, `AllDescendants` is essentially ignored.

`AllDescendants := false`

  By default, all descendants are constructed. If this flag is set to `false`, only capable descendants are computed. Passing `AllDescendants` without a value (which is equivalent to setting it to `true`) is superfluous. This option is provided only for backward compatibility with the GAP 3 version of the ANUPQ package, where by default `AllDescendants` was set to `false` (rather than `true`). It is preferable to use `CapableDescendants` (see `option CapableDescendants`).

`TreeDepth := class`

  Specifies that the descendants tree developed by `PqDescendantsTreeCoclassOne` (see `PqDescendantsTreeCoclassOne` (A.4-1)) should be extended to class class, where class is a positive integer.

`SubList := sub`

  Suppose that L is the list of descendants generated, then for a list sub of integers this option causes `PqDescendants` to return `Sublist( L, sub )`. If an integer n is supplied, `PqDescendants` returns `L[n]`.

`NumberOfSolubleAutomorphisms := n`

  Specifies that the number of soluble automorphisms of the automorphism group supplied by `PqPGSupplyAutomorphisms` (see `PqPGSupplyAutomorphisms` (5.9-1)) in a p-group generation calculation is n. By default, n is taken to be 0; n must be a non-negative integer. If n ≥ 0 then a value for the option `RelativeOrders` (see 6.2) must also be supplied.

`RelativeOrders := list`

  Specifies the relative orders of each soluble automorphism of the automorphism group supplied by `PqPGSupplyAutomorphisms` (see `PqPGSupplyAutomorphisms` (5.9-1)) in a p-group generation calculation. The list list must consist of n positive integers, where n is the value of the option `NumberOfSolubleAutomorphisms` (see 6.2). By default list is empty.

`BasicAlgorithm`

  Specifies that an algorithm that the `pq` program calls its "default" algorithm be used for p-group generation. By default this algorithm is not used. If this option is supplied the settings of options `RankInitialSegmentSubgroups`, `AllDescendants`, `Exponent` and `Metabelian` are ignored.

`CustomiseOutput := rec`

  Specifies that fine tuning of the output is desired. The record rec should have any subset (or all) of the the following fields:

  `perm := list`

    where list is a list of booleans which determine whether the permutation group output for the automorphism group should contain: the degree, the extended automorphisms, the automorphism matrices, and the permutations, respectively.

  `orbit := list`

    where list is a list of booleans which determine whether the orbit output of the action of the automorphism group should contain: a summary, and a complete listing of orbits, respectively. (It's possible to have both a summary and a complete listing.)

  `group := list`

    where list is a list of booleans which determine whether the group output should contain: the standard matrix of each allowable subgroup, the presentation of reduced p-covering groups, the presentation of immediate descendants, the nuclear rank of descendants, and the p-multiplicator rank of descendants, respectively.

  `autgroup := list`

    where list is a list of booleans which determine whether the automorphism group output should contain: the commutator matrix, the automorphism group description of descendants, and the automorphism group order of descendants, respectively.

  `trace := val`

    where val is a boolean which if `true` specifies algorithm trace data is desired. By default, one does not get algorithm trace data.

  Not providing a field (or mis-spelling it!), specifies that the default output is desired. As a convenience, `1` is also accepted as `true`, and any value that is neither `1` nor `true` is taken as `false`. Also for each list above, an unbound list entry is taken as `false`. Thus, for example

      CustomiseOutput := rec(group := [,,1], autgroup := [,1])

  specifies for the group output that only the presentation of immediate descendants is desired, for the automorphism group output only the automorphism group description of descendants should be printed, that there should be no algorithm trace data, and that the default output should be provided for the permutation group and orbit output.

`StandardPresentationFile := filename`

  Specifies that the file to which the standard presentation is written has name filename. If the first character of the string filename is not `/`, filename is assumed to be the path of a writable file relative to the directory in which GAP was started. If this option is omitted it is written to the file with the name generated by the command `Filename( ANUPQData.tmpdir, "SPres" );`, i.e. the file with name `"SPres"` in the temporary directory in which the `pq` program executes.

`QueueFactor := n`

  Specifies a queue factor of n, where n must be a positive integer. This option may be used with `PqNextClass` (see `PqNextClass` (5.6-4)).

  The queue factor is used when the `pq` program uses automorphisms to close a set of elements of the p-multiplicator under their action.

  The algorithm used is a spinning algorithm: it starts with a set of vectors in echelonized form (elements of the p-multiplicator) and closes the span of these vectors under the action of the automorphisms. For this each automorphism is applied to each vector and it is checked if the result is contained in the span computed so far. If not, the span becomes bigger and the vector is put into a queue and the automorphisms are applied to this vector at a later stage. The process terminates when the automorphisms have been applied to all vectors and no new vectors have been produced.

  For each new vector it is decided, if its processing should be delayed. If the vector contains too many non-zero entries, it is put into a second queue. The elements in this queue are processed only when there are no elements in the first queue left.

  The queue factor is a percentage figure. A vector is put into the second queue if the percentage of its non-zero entries exceeds the queue factor.

`Bounds := list`

  Specifies a lower and upper bound on the indices of a list, where list is a pair of positive non-decreasing integers. See `PqDisplayStructure` (5.7-23) and `PqDisplayAutomorphisms` (5.7-24) where this option may be used.

`PrintAutomorphisms := list`

  Specifies that automorphism matrices be printed.

`PrintPermutations := list`

  Specifies that permutations of the subgroups be printed.

`Filename := string`

  Specifies that an output or input file to be written to or read from by the `pq` program should have the name string.

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