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Views: 418346############################################################################# ## #W README The SmallGroups Library Hans Ulrich Besche ## Bettina Eick ## Eamonn O'Brien ## ## This file contains information about the SmallGroups Library ## ############################################################################# # # Copyright # ############################################################################# The SmallGroups Library is copyright by Hans Ulrich Besche, Bettina Eick and Eamonn O'Brien in 2007. You are free to distribute the SmallGroups Library, provided that you make no modifications nor remove this copyright notice. ############################################################################# # # Authors # ############################################################################# The SmallGroups Library has been developed by Hans Ulrich Besche Fachbereich Mathematik und Informatik Technische Universität Braunschweig Pockelsstrasse 14 38106 Braunschweig Germany e-mail: [email protected] http://www-public.tu-bs.de/~hubesche/ Bettina Eick Fachbereich Mathematik und Informatik Technische Universität Braunschweig Pockelsstr. 14 38106 Braunschweig Germany e-mail: [email protected] http://www-public.tu-bs.de/~beick/ Eamonn A. O'Brien Department of Mathematics University of Auckland Private Bag 92019 Auckland New Zealand e-mail: [email protected] http://www.scitec.auckland.ac.nz/~obrien/ ############################################################################# # # Introduction # ############################################################################# The SmallGroups Library is a catalogue of groups of `small' order. Currently, (May 2008) it contains the groups * of order at most 2000 except 1024. * of squarefree order. * of cubefree order at most 50 000. * of order p^n for n <= 6 and all primes p. * of order p^7 for the primes p = 2,3,5,7,11. * whose order factorises in at most 3 primes. * of order q^n * p for q^n dividing 2^8, 3^6, 5^5, 7^4 and p a prime different to q The SmallGroups Library provides access to the groups of these orders and a method to identify the catalogue number of a given group for many of these orders. Here we describe the organisation of this catalogue. We include information on the determination of the groups, the encoding of the stored groups and the algorithms used for the identification routine. ############################################################################# # # Available functions # ############################################################################# SmallGroup( order, number ) returns the specified group. AllSmallGroups( order, selection-args ) returns all or certain groups of the given order. The optional argument list of selection-args can be used to specify certain properties to the function and only the groups with these properties are returned then. For some properties and some group orders the desired groups are pre- computed and stored. Otherwise the desired groups are filtered out of the catalogue. See the GAP 4 manual for some examples. Synonym: AllGroups OneSmallGroup( order, selection-args ) returns one group of the given order with the specified properties or fail. Synonym: OneGroup SmallGroupsInformation( order ) prints information on the groups of the given order. This includes a description of the determination and sorting of the groups of the given order. NumberSmallGroups( order ) returns the number of groups of the given order. Synonym: NrSmallGroups IdGroup( G ) returns the catalogue number of the group G. Clearly, the groups of order |G| must be available in the library for this purpose. Moreover, the groups of orders 512 and 1536 are excluded. IdsOfAllSmallGroups( order, selection-args ) similar to AllSmallGroups, but returns the catalogue numbers of the desired groups only. This can be useful if the list of explicit groups would need too much storage space to load them. Synonym: IdsOfAllGroups UnloadSmallGroupsData() clears the workspace of loaded data. If some groups of the catalogue are requested from GAP afterwards, then the data will be loaded again automatically. ############################################################################# # # Layers # ############################################################################# The SmallGroups Library is organised in 11 layers. Each layer contains the groups of certain orders: Layer 1: the orders with at most 3 prime factors; that is, the orders of type p, p^2, pq, p^3, pq^2 and pqr. Layer 2: all remaining orders <= 1000 except 512 and 768. Layer 3: all remaining orders of type 2^n * p with n <= 8 and p an arbitrary odd prime. Layer 4: the orders 7^4 and 5^5 and all remaining orders of type q^n * p with q^n dividing 3^6, 5^5 or 7^4 and p a prime different to q. Layer 5: all remaining orders <= 2000 except 512, 1024, 1152, 1536 and 1920. Layer 6: the orders 1152 and 1920. Layer 7: the order 512. Layer 8: the order 1536. Layer 9: the remaining groups of order p^4, p^5 and p^6. Layer 10: the remaining groups of squarefree order and of cubefree order at most 50000. Layer 11: the orders p^7 with p = 3,5,7,11. This setup has been chosen for two reasons. First, the organisation in layers permits to add new layers (and thus new group orders) without changes to the existing catalogue. Secondly, it is possible to install a part of the layers only. This might be interesting for computer-systems with little hard disk space available. For each layer i there are two internal functions: `SMALL_AVAILABLE_FUNCS[i]( order )' and `ID_AVAILABLE_FUNCS[i]( order )'. Both functions return fail, if the given order is not contained in this layer. Otherwise the functions return an information record on the layer and the order. This record contains the information needed to handle the groups of the specified order internally. If the layer i is not installed, then the entries SMALL_AVAILABLE_FUNCS[i] and ID_AVAILABLE_FUNCS[i] are unbound. Moreover, there are two internal header functions: `SMALL_AVAILABLE( order )' and `ID_AVAILABLE( order )'. These two functions are used to loop over the layer functions and find the first layer containing the given order. If this layer is found, then an information record on the order is returned. If there is no layer installed containing the groups of this order, then the functions return fail. ############################################################################# # # Files and Directories # ############################################################################# For each layer x there are either one or two directories in small: `smallx' or `smallx' and `idx' The directory `smallx' contains the groups of layer x and the directory `idx' contains the corresponding identification routine if available. An exception to this rule is the first layer; here all the code for the groups is contained in the files smlgp1.g and idgrp1.g in the main directory of small. For the layers 7 and 8 there is no identitfication routine available at the moment and thus there are no directories id7 and id8. The other files in the small main directory are: * README - this file * readsml.g - for loading the small groups catalogue into GAP * small.gi/gd - these are the files where the main functions for the small groups catalogue are defined. * gap3cat.g - identification of a small group in the Gap 3 `SolvableGroup' catalogue * smlinfo.gi - the code for the function `SmallGroupsInformation' ############################################################################# # # Layer 1 # ############################################################################# The groups whose order factorises in at most 3 primes have been classified by H"older, see [11]. An algorithm to find the isomorphism type of such groups was first implemented in Gap 3 by Frank Celler and Hans-Georg Esser. H"olders classification distinguishes the groups of the following order types. Let p, q and r be different primes with p < q < r. p - 1 cyclic group p^2 - 1 cyclic and 1 elementary abelian group p^3 - 3 abelian groups and 2 extraspecial groups pq - 1 cyclic group 1 group of type q:p if q = 1 mod p p^2q - 2 abelian groups 1 group of type q:p x p if q = 1 mod p 1 group of type A4 if p = 2 and q = 3 1 group of type (pxq).p if q = 1 mod p 1 group of type q:C(p^2) if q = 1 mod p^2 pq^2 - 2 abelian groups 1 group of type q:p x q if q = 1 mod p 1 group of type C(q^2):p if q = 1 mod p 1 group of type (qxq):p if p > 2 and q+1 = 0 mod p groups of type q:p + q:p (1 group for p = 2 and (p+1)/2 groups otherwise) pqr - 1 cyclic group 1 group of type q:p x r if q = 1 mod p 1 group of type r:p x q if r = 1 mod p 1 group of type r:q x p if r = 1 mod q 1 group of type r:(pxq) if r = 1 mod (p*q) p-1 groups of type q:p + r:p The groups in this layer are stored `generically'; that is, using functions instead of explicit presentations. The identification routine follows the classification as well. ############################################################################# # # Layer 2 # ############################################################################# DETERMINATION: The nilpotent groups of this layer have been constructed using p-group generation, see [14] and [16]. The 2- and 3-groups of this layer have also been avaliable in the Two- and ThreeGroup library of Gap 3, see [12] and [15] also. The non-nilpotent groups in this layer have been determined using the Frattini extension method, the cyclic split extension method and cyclic extension for the non-soluble groups, see [1], [2] and [3]. STORING: The solvable groups in this layer are stored by a single long integer describing a pc presentation of the group (see `PcGroupCode' or [1]). For p-groups the encoded pc presentations are standard presentations and they are equal to the presentations known in the 2- and 3-groups libraries of GAP 3. The non-solvable groups are stored by generating permutations. SELECTION-ARGS: For the selection functions the values of the following attributes are precomputed and stored: for p-groups: IsAbelian, PClassPGroup, RankPGroup, FrattinifactorSize and FrattinifactorId for non-p-groups: IsAbelian, IsNilpotentGroup, IsSupersolvableGroup, IsSolvableGroup, LGLength, FrattinifactorSize and FrattinifactorId IDENTIFICATION: The identification routine uses invariants of groups to identify a given group. The invariants are organised as tree and stored in `ID_GROUP_TREE', which contains a leaf for every group. In some cases this invariants tree is not sufficient to distinguish all groups. In this case the tree is used to reduce to a small number of possible groups and then a special random isomorphism test finds the correct group among the possible ones. ############################################################################# # # Layer 3 # ############################################################################# DETERMINATION: These groups have been determined using the generic variation of the cyclic split extension method and the Frattini extension method, see [3]. STORING: * Nilpotent groups: For each order in this layer we first list the nilpotent groups P x Q where P is the cyclic group of order p and Q is a group of order 2^n. These groups are sorted by the catalogue number of Q and the group Q is stored in layer 2. * Groups with normal Sylow p-subgroup: Then we consider the remaining groups with normal Sylow p-subgroup. These are split extensions of type P : Q. The isomorphism type of these groups depends on the isomorphism type of Q and the action homomorphism Q -> Aut(P). Let K be the kernel of this homomorphism with [Q : K] = 2^i for some i. We encode the homomorphisms for fixed Q and fixed i as follows. Consider a generator g of P and let g1, ..., gr be a generating set of Q (we choose the first r pc generators of Q for r the rank of Q). Consider a homomorphism a : Q -> Aut(P) and let ai be the image of gi. Clearly, ai is of the form ai : g -> g^li with 0 <= li <= 2^i-1. Thus we describe the homomorphism a by the sequence l1, ..., lr. We encode this sequence as (2^i-1)-adic number of length r; that is, we encode this sequence as l1 * q^(r-1) + l2 * q^(r-2) + ... + lr * q^0 where q = 2^i. Hence each homomorphism a is encoded as integer and for fixed Q and i we write all these integers into a list. A special case occurs if there are two homomorphisms a and b such that ai = bi^j for some integer j; that is, the images of a are powers of the images of b. In this case a is stored directly after b and we only store the integer -j instead of encoding for the sequence l1, ..., lr for a. Now we consider the case that for certain Q and i we have a list L consisting of non-negative integers only; that is, the special power-case did not occur for this group Q and index i. In some cases we encode such a list L further. Recall that the integers in L correspond to different homomorphisms. Thus the integers are all different and we may sort them in increasing order. Then we can store this sorted list as binary number; that is, the list c1, ..., cs is encoded as 2^(c1-1) + ... + 2^(cs-1). This is only useful, if the list L does not contain large numbers. Thus for Q and i we have either a list or an integer stored to encode the corresponding homorphisms. For each index i we write all lists or integers into a list such that at position Id(Q) the corresponding list or integer to Q and i is found. For i = 1 this list has no holes, since there exists at least one group P : Q with K of index 2 for each group Q. Often the entry at position j in this list is equal to the entry at position j-1. In this case we delete the entry at position j and thus create a hole in the list. For i > 1 there might be holes in the list if there is no group P : Q with K of index 2^i. Hence the previous idea cannot be applied for i > 1. However, in all the lists we have equal entries in various places. If this is the case, then we substitute an entry in a list by a negative integer -j meaning that the entry at this position is equal to the entry at position j. Finally, if the list for some index i has only few entries left, then we substitute the list by a record containing two lists: first the non-empty positions and secondly their entries. * Groups with normal Sylow 2-subgroup: Next we consider the remaining groups of type Q : P. These exist for a few primes q only. These groups are described by operation homomorphisms of the type P -> Aut(Q). Here we store the catalogue number of Q and a long integer for each such homomorphism a : P -> Aut(Q). Consider a generator g of P. Clearly, we just need to store the image of g for each homomorphism a. The image g^a is an automorphism of Q and thus we store the images under g^a of a fixed generating set of Q. For this purpose we consider a canonical numbering of the elements of Q and store the generator images by storing their number in the element list. The sequence of these numbers are encoded as (|Q|+1)-adic number; that is, the sequence e1, ..., er is stored as e1 * q^(r-1) + e2 * q^(r-2) + ... + er where q = |Q| + 1. * Groups without normal Sylow subgroup: Now there are the groups of order 2^n * p without any normal Sylow subgroup left. These exist for very few primes p only. They have been computed as in layer 2 using the Frattini extension method. They are stored as described in layer 2 using one long integer for each group. IDENTIFICATION: The identification of nilpotent groups P x Q relies on the identification of Q only and this is done as in layer 2. Similarly, the groups without normal Sylow subgroup are identified as described in layer 2. For the groups Q : P with normal Sylow q-subgroup we first determine the prime p and the isomorphism type of Q. If this is not sufficient, then we use the methods as described in layer 2. (Recall that there are only finitely many primes p possible here.) For the groups P : Q with normal Sylow p-subgroup we first determine the prime p and the isomorphism type of Q as well. Moreover, we compute the centralizer K of P in Q and consider its index [Q : K] = 2^i. In a large number of cases the catalogue numbers Id(Q) and Id(K) are sufficient to determine the group P:Q uniquely. Moreover, this feature is independent of p. We can recognise these cases using the tree of invariants: if we can determine P:Q uniquely with Id(Q) and Id(K) only, then there is no node corresponding to this case in the tree. If there is a node in the tree, then Id(Q) and Id(K) are not sufficient to determine the group uniquely. In this case we apply methods similar to layer 2; that is, we use invariants. Since there are infinitely many primes p which might turn up here, we need an additional idea to use the invariant tree for this purpose. In the invariant tree we have invariants stored for groups of type R : Q of order 2^n * r for primes r in 3, 5, 17 and 97. Now we first choose the smallest prime r such that r is congruent 1 mod [Q : K]. The cases that [Q : K] = 2^i for i = 6, 7 or 8 cannot occur here, because in this cases Id(Q) and Id(K) are allways sufficient to determine the group. Then we use that the groups P : Q behave essentially similar to the groups R : Q for the chosen r. Thus we can construct a group R : Q corresponding to P : Q and identify R : Q instead of P : Q. ############################################################################# # # Layer 4 # ############################################################################# DETERMINATION: The groups of order 2401 = 7^4 and 3125 = 5^5 have been computed using p-group generation as described in layer 2 and they are stored and handled similarly. The other groups in this layer have been determined as outlined in layer 3 and, again, they are organised similarly. STORING: There is a difference to layer 3 in the compression of the group data; that is, the groups in this layer are not compressed as efficiently as the groups in layer 3. We consider the groups of type P : Q for P the cyclic group of order p and Q a group of order q^n. These groups are determined by Q and an operation homomorphism Q -> Aut(P). As in layer 3 we first compute one integer for each operation homomorphism and then proceed to compress the lists of integers for each Q and each i where q^i is the index of the centralizer of P in Q. Different to layer 3 we do not compress the lists of non-negative integers to a single integer and we not reduce the list for i = 1 further, since in both cases the obtained compression is very small. IDENTIFICATION: The group identification is essentially similar to the procedure described in layer 3. However, for the groups with normal Sylow p-subgroup we use a special random isomorphism test additionally to identify groups. It is a `special' version of the general algorithm: in the general algorithm we use certain sets to choose generating sets from. In this special version we restrict these sets suitably. (We use non-trivial elements of P and certain elements of Q.) This is necessary, since the groups which appear here can be to large to compute explicitly the elements sorted in conjugacy classes. ############################################################################# # # Layer 5 # ############################################################################# This layer is similar to layer 2. ############################################################################# # # Layer 6 # ############################################################################# DETERMINATION: The nilpotent groups in this layer are determined as direct products of p-groups. Most of the groups of orders 1152 and 1920 have a normal Sylow 3-subgroup or Hall (3,5)-subgroup, resp. They are constructed using the coprime split extension method, see [5]. The remaining groups of these or- ders (without normal 2-complement) have been determined using the Frattini extension method and the cyclic split extension method, see [1] also. STORING: Only the non-nilpotent groups with normal Sylow 3-subgroup or Hall (3,5)-subgroup are stored in a special way. The remaining groups are organised similar to layer 2. For the groups of type P : Q where P is the normal Sylow 3-subgroup or the Hall (3,5)-subgroup and Q is a group of order 2^7 we split a pc presentation in two parts. The first part are the relators of Q. These are stored within the groups of order 2^7 and thus can be considered as known. The second part of the relators determine P and the operation of Q on P. These second parts are stored as long integers. If we consider these second parts for all the groups, then we find that they are highly redundant. There are only 921 (1722) different long integers for the groups of order 1152 and 1920, resp. Thus we store these two sets of long integers only. Then for each group Q of order 2^7 we store for each extension P : Q the position of the corresponding long integer. Hence we obtain a list of integers for Q. Again we note that the lists of integers obtained for all the groups Q of order 2^7 are highly redundant. There are only 1298 (722) different lists for the groups of order 1152 (1920). Thus we can compress the lists using the same idea again. IDENTIFICATION: The identification of groups of these orders is similar to layer 2. ############################################################################# # # Layer 7 # ############################################################################# DETERMINATION: The groups of order 512 have first been enumerated, see [8] and [9]. Later they have been determined explicitly using p-group generation, see [14] and [5]. There are 10494213 groups of this order. STORING: We introduce a special method to store such groups. Consider a pc presen- tation of a given group of order 512. If we concatenate the exponent vectors of the right hand sides of such a presentation, then we obtain a bit vector of length 120. This can be used as encoding of a group of order 512. We compress the list of such encodings further using the following method. First we split the list of all groups of order 512 in sublists containing 1000 groups each. Let L be such a sublist. We suppose that L consists of 1000 bitlists of length 120 and we describe a method to encode this list of bitlists in a single vector V using an alphabet of 83 symbols. (81 symbols for the encoding and 2 special symbols as signs.) First we find those indices i in the range 1 to 120 such that for all lists in L the entries at position i are fixed. Thus we note for each of the 120 entries whether the entries are all 0, all 1 or variable in L. There are 3^120 combinations possible which we store in a vector of length 30 using 81 symbols. This vector of length 30 is the initial segment of V. Now we can reduce to consider the variable positions only and thus work with bitlists of shorter length. We split the shorter bitlists in blocks such that the bitlists in each block have at most 6 variable entries. For this purpose we start at the beginning of L and add bitlists to the current block until the next bitlist would lead to more than 6 variable entries for this block. Each block can contain 1 up to 64 bitlists. Now we determine a `headcode' and a `tailcode' to describe the block. The head and tail codes are then concatenated to V. The head contains an encoding of the variable bits for this block as above. The tail then describes the vectors in the variable bits. Since they are at most 64 possible combinations arising here, we need only one letter in the 81-alpha- bet to describe a single vector of variable bits. Finally, we note that some of the tailcodes arise for many blocks. These tailcodes are stored in a special list. If such a tailcode is occuring in V, then only the reference to the special list is stored instead of the full tailcode. This special list contains 1890 different tailcodes, 2 letters in the alphabet are sufficient to refer a tailcode. To distinguish references and actual tailcodes we use a special sign. Each new head begins with a special symbol in V. There are two special symbols available for this purpose. One is used, if the corresponding tailcode is referenced, and the other, if it is an ordinary tailcode. This compression allows to store the groups of order 512 in 4.4 mb. ############################################################################# # # Layer 8 # ############################################################################# DETERMINATION: The 408641062 groups of order 1536 have been determined using the cyclic split extension method and the improved version of the Frattini extension method, see [1] and [3]. Note that the number of groups of this order is too large to be an ordinary GAP integer. Thus it is not possible to loop over these groups with a for-loop in GAP. STORING: We store these groups in a special way as well and we obtain a compression to 6.1 mb. The groups are stored using references to the groups of order 512 of layer 7. The nilpotent groups C3 x Q for Q a group of order 512 are based on the groups of order 512. The major part of the groups are the 398032384 non-nilpotent groups with normal Sylow 3-subgroup. The compression of these groups follows the one outlined in layer 3. As described there for each group Q of order 512 we compute an integer which determines all groups of type C3 : Q. There are only 15249 different integers of this type. In a first compression we create a list of references to the different integers. Now we note that a group often has the same reference as the previous one. Thus we split the groups of order 512 in sets of 100 000 groups and create a record for each set. The record contains two lists which are used to recall the blocks in a set having the same reference. Thus the first list contains the length of the blocks and the second list contains the corresponding references. Again, in both lists certain patters occur often. In the first list the length `1' appears often. Thus the `1' is not stored explicitly, but a blank in this lists has to be considered as `1'. In the second list often an entry is the same as the one 2 places bevor. Thus these entries are deleted as well and blanks can be reconstructed by this rule. Additionally we store the number of resulting groups for each integer to speed up the method to find the group with a given catalogue number. The 18028 groups with normal Sylow 2-subgroup are stored similarly to layer 3. As described for layer 3 we determine a long integer for each homomorphism Q -> Aut(P) for Q of order 512 and P the cyclic group of order 3. The occuring integers are highly redundant - there are 6774 different ones. Thus we use a list of references again. The 96437 groups without normal Sylow subgroup are determined using the Frattini extension method. As described in layer 2 they can be stored by encoding the relators of a pc presentation as long integer. However, the relators corresponding to the Frattini factors of the groups are known. Thus it is sufficient to store the relators of the Frattini factors once for all groups with this factor and encode the remaining relators only. Note that there are only 16 different Frattini factors and only 12 of them have order less than 1536. The groups are stored in lists corresponding to the 12 Frattini factors. ############################################################################# # # Layer 9 # ############################################################################# This layer contains the generic construction of groups of order p^4, p^5 and p^6 with order > 3125 (those with order up to 3125 are contained in the lower layers of the small groups library). DETERMINATION: The groups of order p^4 were first determined by H\"older (1893)[11]. The groups of order p^5 were first determined by Bagnera (1898). The groups of order p^6 were first (correctly) determined by Newman, O'Brien and Vaughan-Lee (2003)[13]. STORING: The groups of order p^4 (p >= 11) are given by pc presentations which are produced at run-time by a function SMALL_GROUPS_FUNCS[ 19 ] provided by Newman. The groups of order p^5 (p >= 7) are given by pc presentations which are produced at run-time by a function SMALL_GROUPS_FUNCS[ 20 ] provided by Girnat (2004) [10]. The groups of order p^6 (p >= 5) are given by pc presentations which are produced at run-time by a function SMALL_GROUPS_FUNCS[ 21 ] provided by Newman, O'Brien and Vaughan-Lee (2003) [13]. The groups of order p^6 are given as a list of partially repetitive structures. These are compressed into the file 'sml1.z'. At run-time, this compressed structure will be expanded, but restricted to those parts of the structure relevant for the given p when needed. It is cached into SMALL_GROUP_LIB[1]. As parts of this structure contain long ( O(p^2) ) lists of groups which are classified by additional parameters and these lists are not dense, it might be neccessary to set up the complete list of indices to find the presentation of a single group. IDENTIFICATION: A group of order p^4 can be identified and its catalogue number found by the function ID_SMALL_GROUPS_FUNCS[ 19 ] based on a function provided by Newman and modified by Besche. There is no identification available for the groups of order p^5 and p^6 at current. ############################################################################# # # Layer 10 # ############################################################################# GROUPS OF SQUAREFREE ORDER: DETERMINATION: These groups have first been determined by H\"older (1895). The implemented construction is based on the determination given in [7]. The key invariants are the socle and socle factor. STORING: The groups of squarefree order which are not contained in lower layers are given by pc presentations which are produced at run-time by a function SMALL_GROUPS_FUNCS[ 24 ] written specially for this library. IDENTIFICATION: A group of this kind can be identified and its catalogue number found by the function ID_SMALL_GROUPS_FUNCS[ 24 ]. GROUPS OF CUBEFREE but not SQUAREFREE ORDER: DETERMINATION: First determined in [7]. Every group with cubefree order is either solvable or has a direct decomposition into a solvable group and PSL(2,p) for a suitable prime. STORING: The groups of cubefree order < 50000 which are not contained in lower layers and are not squarefree are given by pc presentations which are produced at run-time by a function SMALL_GROUPS_FUNCS[ 25 ] written specially for this library. IDENTIFICATION: A group of this kind can be identified and its catalogue number found by the function ID_SMALL_GROUPS_FUNCS[ 24 ]. ############################################################################# # # Layer 11 # ############################################################################# DETERMINATION: The groups of order p^7 have been determined by O'Brien and Vaughan-Lee, see [17]. This layer contains these groups for some small primes: p = 3,5,7,11. STORING: The groups are encoded by PcGroupCode and then the various codes are stored in compressed form. See the groups of order 512 for details. Pc presentations for the groups are produced at run-time for these groups. IDENTIFICATION: There is no identification function available for the groups in this layer. ############################################################################# # # Concluding remarks # ############################################################################# The compression of group data for layer 2 has been developed long ago. A first version has been used in the p-group generation algorithm and thus to encode the 2- and 3-groups library of Gap 3. This compression is des- cribed in [1]. The remaining compression methods for layers 3 - 8 have been introduced by Hans Ulrich Besche specially for this library. They are designed to store the groups in as few space as possible. For different layers there are different methods, since certain approaches had been successful for certain groups but not for others. Moreover, already published layers have not been changed again and thus useful concepts sometimes have not been applied to earlier layers. ############################################################################# # # References # ############################################################################# [1] Hans Ulrich Besche and Bettina Eick. The construction of finite groups. J. Symbolic Comput. 27, 387 - 404 (1999). [2] Hans Ulrich Besche and Bettina Eick. The groups of order at most 1000 except 512 and 768. J. Symbolic Comput. 27, 405 - 413 (1999). [3] Hans Ulrich Besche and Bettina Eick. The groups of order q^n * p. Comm. Alg. 29, 1759 - 1772 (2001) [4] Hans Ulrich Besche and Bettina Eick. The GrpConst share package of GAP 4. [5] Hans Ulrich Besche, Bettina Eick and E. A. O'Brien. A millenium project: constructing small groups. Internat. J. Algebra Comput. 12, 623 - 644 (2002) [6] Hans Ulrich Besche, Bettina Eick and E. A. O'Brien. The groups of order at most 2000. Electronic Research Announcements of the AMS 7, 1 - 4 (2001) [7] Heiko Dietrich and Bettina Eick. Groups of cube-free order. J. Algebra. (To Appear) [8] Bettina Eick and E. A. O'Brien. The groups of order 512. Proceedings of the `Abschlusstagung des DFG Schwerpunktes Algorithmische Algebra und Zahlentheorie', Springer (1998) [9] Bettina Eick and E. A. O'Brien. Enumerating p-groups. Austal. Math. Soc. Ser. A, 67, 191 - 205 (1999). [10] B. Girnat. Klassifikation der Gruppen bis zur Ordnung p^5. Staatsexamensarbeit, TU Braunschweig. [11] Otto H"older. Die Gruppen der Ordnungen p^3, pq^2, pqr, p^4. Math. Ann. 43, 301 - 412 (1893). [12] Rodney James, M. F. Newman and E. A. O'Brien. The groups of order 128. J. Algebra 129 (1), 136 - 158 (1990) [13] M. F. Newman, E. A. O'Brien and M. R. Vaughan-Lee. Groups and nilpotent Lie rings whose order is the sixth power of a prime. J. Algebra 278, 383 - 401 (2003) [14] E. A. O'Brien. The p-group generation algorithm. J. Symbolic Comput. 9, 677 - 698 (1990) [15] E. A. O'Brien. The groups of order 256. J. Algebra 143 (1), 219 - 235 (1991) [16] E. A. O'Brien. The ANUPQ share package of Gap 3. [17] E. A. O'Brien and M. R. Vaughan-Lee. The groups of order p^7 for odd prime p. J. Algebra 292, 243 - 258 (2005) ############################################################################# # # Bugs and problems # ############################################################################# Please report bugs/problems/feedback to the authors or to gap-support [email protected] [email protected] [email protected] [email protected]