Magma includes the Small Groups Library prepared by Besche, Eick and O'Brien. For a description of the algorithms used to generate these groups, details on the data structures used and applications we refer to [BE99a], [BEO01], [BE99b], [O'B90], [BE01], [O'B91], [MNVL04] and the references therein.
The Small Groups Library contains the following groups.
The Magma version of this library uses the same internal data format as the implementation available in GAP. In particular, the numbering of the groups of a given order in both packages is the same.
For a different mechanism for accessing the p-groups in this collection, see the The p-groups of Order Dividing p7 section, specifically the functions SearchPGroups and CountPGroups. These functions also access the groups of order p7 (contributed by O'Brien and Vaughan-Lee).
Many of the functions in this section have an optional parameter Search. It can be used to limit the small group search to soluble (Search := "Soluble") or insoluble (Search := "Insoluble") groups. The default is Search := "All", which allows all groups to be considered.
When a group is extracted from the database, it is returned as a GrpPC if it is soluble, or as a GrpPerm if it is insoluble.
When using the small groups database for an extended search, it is advisable to open the database using the function SmallGroupDatabase, which opens the database and returns a reference to it. This reference can then be passed as first argument to most of the functions described below, and will save that function from opening and closing the database for itself. Doing so will reduce the number of file operations when a lot of use is made of the database. When the database is no longer needed, it can be closed using the delete statement.
Open the small groups database (for extended search) and return a reference to it. This reference may be passed to other functions so that they do fewer file operations.
Close the small groups database D and free the resources associated with its use.
The limiting order up to which all groups (except those of order 1024) are stored in the database of small groups, that is, currently 2000.
Return true if the groups of order o are contained in the database and false otherwise. This function can be used to check whether o is a legitimate argument for other functions described in this section, avoiding runtime errors in user written loops or functions.
Given a positive integer o, return the number of groups of order o in the database. If the groups of order o are not contained in the database, 0 is returned. This function can be used to check whether a pair o, n defines a group contained in the small groups database, that is, whether it is a legitimate argument for other functions described in this section, avoiding runtime errors in user written loops or functions.
Given a positive integer o, such that the groups of order o are contained in the small groups library, and a positive integer n, return the n-th group of order o in the database. If the groups of order o are not contained in the database or if n exceeds the number of groups of order o in the database, an error is reported. The function NumberOfSmallGroups can be used to check whether the arguments are valid.
Search: MonStgElt Default: "All"
Given a positive integer o, such that the groups of order o are contained in the small groups library, return the first group of order o in the database meeting the search criterion set by the parameter Search. If the groups of order o are not contained in the database, an error is reported. The function IsInSmallGroupDatabase can be used to check whether o is a valid argument for this function.
Search: MonStgElt Default: "All"
Given a positive integer o such that the groups of order o are contained in the small groups library and a predicate f (as a function or intrinsic), return the first group of order o in the database meeting the search criterion set by the parameter Search, which satisfies f.
Return true iff SmallGroup(o, n) is soluble. This function does not load the group. If the group specified by the arguments does not exist in the database, an error is reported. The function NumberOfSmallGroups can be used to check whether the arguments are valid.
Return true iff SmallGroup(o, n) is insoluble. This function does not load the group. If the group specified by the arguments does not exist in the database, an error is reported. The function NumberOfSmallGroups can be used to check whether the arguments are valid.
Search: MonStgElt Default: "All"
Given a sequence S of orders or a single order o contained in the database and a predicate f (as a function or intrinsic), return the first group with order in S or equal to o, respectively, which meets the search criterion set by the parameter Search and satisfies f.
Search: MonStgElt Default: "All"
Warning: BoolElt Default: true
Given an order o contained in the database, return a list of all groups of order o, meeting the search criterion set by the parameter Search. Some orders will produce a very large sequence of groups -- in such cases a warning will be printed unless the user specifies Warning := false.
Search: MonStgElt Default: "All"
Warning: BoolElt Default: true
Given a sequence S of orders contained in the database, return a list of all groups with order in S, meeting the search criterion set by the parameter Search. The resulting sequence may be very long -- in such cases a warning will be printed unless the user specifies Warning := false.
Search: MonStgElt Default: "All"
Given an order o contained in the database and a predicate (function or intrinsic) f, return a list containing all groups G of order o, meeting the search criterion set by the parameter Search and satisfying f(G) eq true.
Search: MonStgElt Default: "All"
Given a sequence S of orders contained in the database and a predicate (function or intrinsic) f, return a list containing all groups G with order in S, meeting the search criterion set by the parameter Search and satisfying f(G) eq true.
> list := SmallGroups(27, func<x|not IsAbelian(x)> ); > list; [* GrpPC of order 27 = 3^3 PC-Relations: $.2^$.1 = $.2 * $.3, GrpPC of order 27 = 3^3 PC-Relations: $.1^3 = $.3, $.2^$.1 = $.2 * $.3 *]
> G := SmallGroup([1..100], func<x|DerivedLength(x) gt 2>); > G; GrpPC of order 24 = 2^3 * 3 PC-Relations: G.1^3 = Id(G), G.2^2 = G.4, G.3^2 = G.4, G.4^2 = Id(G), G.2^G.1 = G.3, G.3^G.1 = G.2 * G.3, G.3^G.2 = G.3 * G.4
> list := SmallGroups(240:Search:="Insoluble"); > #list; 8 > list[7]; Permutation group acting on a set of cardinality 7 (1, 2, 3, 4) (1, 5, 2, 4, 3)(6, 7)
> IsInSmallGroupDatabase(2432); true... and determine the number of groups of order 2432.
> NumberOfSmallGroups(2432); 19324
> f := function (G) > Z := Centre (G); > return IsCyclic (Z) and #Z eq 7^2; > end function; > P := SmallGroups(7^6, f); > #P; 30 > NumberOfSmallGroups(7^6); 860
A small group process enables iteration over all groups of specified orders satisfying a given predicate, without having to create and store all such groups together.
A small group process is created via the function SmallGroupProcess (in various forms). The standard process functions IsEmpty, Current, CurrentLabel and Advance can then be applied to the process.
The functions used to create a small group process all have a parameter Search attached to them. It can be used to limit the small group search to soluble (Search := "Soluble") or insoluble (Search := "Insoluble") groups. The default is Search := "All", which allows all groups to be considered.
The Process functions described below do not have a variant with the database as first argument, as each process opens the database for an extended search automatically.
Search: MonStgElt Default: "All"
Given an order o contained in the small groups database, return a small group process which will iterate though all groups of order o meeting the search criterion set by the parameter Search.
Search: MonStgElt Default: "All"
Given a sequence S of orders contained in the small groups database, return a small group process which will iterate though all groups with order in the sequence S meeting the search criterion set by the parameter Search.
Search: MonStgElt Default: "All"
Given an order o contained in the small groups database and a predicate f (as function or intrinsic), return a small group process which will iterate though all groups of order o, which meet the search criterion set by the parameter Search and satisfy the predicate f.
Search: MonStgElt Default: "All"
Given a sequence S of orders contained in the small groups database and a predicate f (as function or intrinsic), return a small group process which will iterate though all groups with order in the sequence S, which meet the search criterion set by the parameter Search and satisfy the predicate f.
Returns true if the process p has passed its last group.
Return the current group of the process p.
Return the label of the current group of the process p. That is, return o and n such that the current group is SmallGroup(o, n).
Move the process p to its next group.
> P := SmallGroupProcess(128); > count := {* *}; > repeat > G := Current(P); > Include(~count, NilpotencyClass(G)); > Advance(~P); > until IsEmpty(P); > count; {* 1^^15, 2^^947, 3^^1137, 4^^197, 5^^29, 6^^3 *}
The following functions perform the inverse operation to the small group functions described earlier. Given a group G such that a group isomorphic to G is in the database and identification of groups of order |G| is supported, the identification functions return a pair < o, n > so that SmallGroup(o, n) is isomorphic to G.
Note that identifying a finitely presented group involves the construction of a permutation representation of this group, which may fail. We refer to IdentifyGroup for details.
Locate the pair of integers < o, n > so that SmallGroup(o, n) is isomorphic to G. If there is no such group in the database or if identification of groups of order |G| is not supported, then an error will result. The function CanIdentifyGroup can be used to test whether groups of a certain order can be identified; this may be useful for avoiding runtime errors in user written loops or functions.
Return true if identification of groups of order o in the database is supported. This function can be used to check whether a group is a legitimate argument for the functions IdentifyGroup described above, avoiding runtime errors in user written loops or functions.
> G := DihedralGroup(10); > G; Permutation group G acting on a set of cardinality 10 Order = 20 = 2^2 * 5 (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) (1, 10)(2, 9)(3, 8)(4, 7)(5, 6) > IdentifyGroup(G); <20, 4> > H := SmallGroup(20, 4); > H; GrpPC : H of order 20 = 2^2 * 5 PC-Relations: H.1^2 = Id(H), H.2^2 = Id(H), H.3^5 = Id(H), H.3^H.1 = H.3^4
The following functions provide access to data used internally by the Small Groups Library for representing groups. They are included just for completeness and are intended to be used by experts only. In particular, we do not give a detailed explanation of the (complicated) data format in this manual.
Returns the data from which the group number n of order o in D is constructed. The format and the meaning of the items in the returned list depends on the group indicated by the pair (o, n).
Given a finite solvable group G in the category GrpPC, return two integers c and o encoding the power conjugate presentation of G.The second return value is the order of G. The first return value is an integer specifying the power conjugate relations in the presentation of G.
Given two integers c and o encoding a power conjugate presentation G, return G as a group in the category GrpPC.The second argument is the order of G. The first return value is an integer specifying the power conjugate relations in the presentation G.
> D := SmallGroupDatabase(); > G := SmallGroup(D,1053,51); > Category(G); GrpPC
> SmallGroupEncoding(G); 100286712487397165939678173 1053
> Data(D,525,2); [* code, 666501 *]We can create the corresponding group by decoding this information.
> G := SmallGroupDecoding(666501, 525); > G; GrpPC : G of order 525 = 3 * 5^2 * 7 PC-Relations: G.1^3 = Id(G), G.2^5 = G.4, G.3^7 = Id(G), G.4^5 = Id(G)This gives the same presentation as accessing the database in the "usual" way.
> SmallGroup(D,525,2); GrpPC of order 525 = 3 * 5^2 * 7 PC-Relations: $.1^3 = Id($), $.2^5 = $.4, $.3^7 = Id($), $.4^5 = Id($)