chap7.txt

  
  7 Changes from Earlier Versions
  
  
  7.1 Changes between GAP 4.3 and GAP 4.4
  
  The main changes between GAP 4.3 and GAP 4.4 are:
  
  
  7.1-1 Potentially Incompatible Changes
  
      The  mechanism for the loading of Packages has changed to allow easier
        updates  independent  of  main  GAP  releases. Packages require a file
        PackageInfo.g  now.  The new PackageInfo.g files are available for all
        packages with the new version of GAP (see Example: PackageInfo.g for a
        GAP package).
  
      IsSimpleGroup  (Reference:  IsSimpleGroup)  returns  false now for the
        trivial group.
  
      PrimeBlocks (Reference: PrimeBlocks): The output format has changed.
  
      Division  rings  (see  IsDivisionRing (Reference: IsDivisionRing)) are
        now implemented as IsRingWithOne (Reference: IsRingWithOne).
  
      DirectSumOfAlgebras (Reference: DirectSumOfAlgebras for two algebras):
        p-th power maps are compatible with the input now.
  
      The print order for polynomials has been changed.
  
  These  changes  are,  in  some  respects,  departures  from  our  policy  of
  maintaining  upward  compatibility of documented functions between releases.
  In  the  first  case,  we  felt  that  the  old  behavior  was  sufficiently
  inconsistent,   illogical,  and  impossible  to  document  that  we  had  no
  alternative  but  to  change  it.  In the case of the package interface, the
  change  was necessary to introduce new functionality. The planned and phased
  removal  of  a  few  unnecessary  functions  or  synonyms is needed to avoid
  becoming  buried in legacy interfaces, but we remain committed to our policy
  of maintaining upward compatibility whenever sensibly possible.
  
      Groebner Bases:
  
        Buchberger's  algorithm to compute Groebner Bases has been implemented
        in GAP. (A. Hulpke)
  
      For large scale Groebner Basis computations there also is an interface
        to     the    Singular    system    available    in    the    Singular
        (https://www.gap-system.org/Packages/singular.html)    package.    (M.
        Costantini and W. de Graaf)
  
      New  methods  for factorizing polynomials over algebraic extensions of
        the rationals have been implemented in GAP. (A. Hulpke)
  
      For  more  functionality to compute with algebraic number fields there
        is   an   interface  to  the  Kant  system  available  in  the  Alnuth
        (https://www.gap-system.org/Packages/alnuth.html) package. (B. Assmann
        and B. Eick)
  
      A  new  functionality  to  compute  the  minimal normal subgroups of a
        finite group, as well as its socle, has been installed. (B. Höfling)
  
      A fast method for recognizing whether a permutation group is symmetric
        or alternating is available now (A. Seress)
  
      A  method  for  computing the Galois group of a rational polynomial is
        available again. (A. Hulpke)
  
      The      algorithm      for      BrauerCharacterValue      (Reference:
        BrauerCharacterValue)   has  been  extended  to  the  case  where  the
        splitting field is not supported in GAP. (T. Breuer)
  
      Brauer tables of direct products can now be constructed from the known
        Brauer tables of the direct factors. (T. Breuer)
  
      Basic  support  for  vector  spaces  of  rational functions and of uea
        elements is available now in GAP. (T. Breuer and W. de Graaf)
  
      Various  new  functions  for  computations  with  integer matrices are
        available,  such  as  methods  for  computing  normal forms of integer
        matrices  as well as nullspaces or solutions systems of equations. (W.
        Nickel and F. Gähler)
  
  
  7.1-2 New Packages
  
  The following new Packages have been accepted.
  
      Alnuth:  Algebraic  Number Theory and an interface to the Kant system.
        (https://www.gap-system.org/Packages/alnuth.html) By B. Assmann and B.
        Eick.
  
      LAGUNA:  Computing  with  Lie  Algebras  and  Units of Group Algebras.
        (https://www.gap-system.org/Packages/laguna.html)   By  V.  Bovdi,  A.
        Konovalov, R. Rossmanith, C. Schneider.
  
      NQ:       The       ANU       Nilpotent       Quotient      Algorithm.
        (https://www.gap-system.org/Packages/nq.html) By W. Nickel.
  
      KBMAG:       Knuth-Bendix       for      Monoids      and      Groups.
        (https://www.gap-system.org/Packages/kbmag.html) By D. Holt.
  
      Polycyclic:       Computation       with       polycyclic      groups.
        (https://www.gap-system.org/Packages/polycyclic.html)  By  B. Eick and
        W. Nickel.
  
      QuaGroup:    Computing    with    Quantized    Enveloping    Algebras.
        (https://www.gap-system.org/Packages/quagroup.html) By W. de Graaf.
  
  
  7.1-3 Performance Enhancements
  
      The   computation   of  irreducible  representations  and  irreducible
        characters  using the Baum-Clausen algorithm and the implementation of
        the Dixon-Schneider algorithm have been speeded up.
  
      The      algorithm      for      PossibleClassFusions      (Reference:
        PossibleClassFusions) has been changed: the efficiency is improved and
        a new criterion is used. The algorithm for PossibleFusionsCharTableTom
        (Reference:  PossibleFusionsCharTableTom)  has  been  speeded  up. The
        method  for  PrimeBlocks  (Reference:  PrimeBlocks)  has been improved
        following a suggestion of H. Pahlings.
  
      New  improved  methods  for normalizer and subgroup conjugation in S_n
        have     been    installed    and    new    improved    methods    for
        IsNaturalSymmetricGroup   (Reference:   IsNaturalSymmetricGroup)   and
        IsNaturalAlternatingGroup  (Reference: IsNaturalAlternatingGroup) have
        been  implemented.  These improve the available methods when groups of
        large degrees are given.
  
      The partition split method used in the permutation backtrack is now in
        the  kernel.  Transversal computations in large permutation groups are
        improved.  Homomorphisms  from free groups into permutation groups now
        give substantially shorter words for preimages.
  
      The membership test in SP (Reference: Sp for dimension and field size)
        and  SU  (Reference:  SU) groups has been improved using the invariant
        forms underlying these groups.
  
      An  improvement for the cyclic extension method for the computation of
        subgroup lattices has been implemented.
  
      A  better  method for MinimalPolynomial (Reference: MinimalPolynomial)
        for finite field matrices has been implemented.
  
      The display has changed and the arithmetic of multivariate polynomials
        has been improved.
  
      The  LogMod (Reference: LogMod) function now uses Pollard's rho method
        combined with the Pohlig/Hellmann approach.
  
      Various  functions  for  sets  and  lists have been improved following
        suggestions  of  L.  Teirlinck. These include: Sort (Reference: Sort),
        Sortex  (Reference:  Sortex),  SortParallel (Reference: SortParallel),
        SortingPerm   (Reference:   SortingPerm),  NrArrangements  (Reference:
        NrArrangements).
  
      The      methods      for      StructureConstantsTable     (Reference:
        StructureConstantsTable)      and      GapInputSCTable     (Reference:
        GapInputSCTable)  have  been  improved  in the case of a known (anti-)
        symmetry following a suggestion of M. Costantini.
  
  The  improvements  listed in this Section have been implemented by T. Breuer
  and A. Hulpke.
  
  
  7.1-4 New Programming and User Features
  
      The  2GB limit for workspace size has been removed and version numbers
        for saved workspaces have been introduced. (S. Linton and B. Höfling)
  
      The  limit  on the total number of types created in a session has been
        removed. (S. Linton)
  
      There is a new mechanism for loading packages available. Packages need
        a  file  PackageInfo.g  now.  (T.  Breuer  and F. Lübeck; see Example:
        PackageInfo.g for a GAP package).
  
  Finally,  as  always,  a  number  of bugs have been fixed. This release thus
  incorporates  the  contents of all the bug fixes which were released for GAP
  4.3. It also fixes a number of bugs discovered since the last bug fix.
  
  
  7.2 Earlier Changes
  
  The most important changes between GAP 4.2 and GAP 4.3 were:
  
      The performance of several routines has been substantially improved.
  
      The  functionality  in  the  areas of finitely presented groups, Schur
        covers and the calculation of representations has been extended.
  
      The  data  libraries  of  transitive  groups,  finite  integral matrix
        groups, character tables and tables of marks have been extended.
  
      The  Windows  installation  has been simplified for the case where you
        are installing GAP in its standard location.
  
      Many bugs have been fixed.
  
  The most important changes between GAP 4.1 and GAP 4.2 were:
  
      A  much  extended  and  improved  library  of  small groups as well as
        associated IdGroup (Reference: IdGroup) routines.
  
      The  primitive  groups  library  has been made more independent of the
        rest of GAP, some errors were corrected.
  
      New  (and  often  much  faster)  infrastructure for orbit computation,
        based on a general dictionary abstraction.
  
      New functionality for dealing with representations of algebras, and in
        particular for semisimple Lie algebras.
  
      New  functionality  for binary relations on arbitrary sets, magmas and
        semigroups.
  
      Bidirectional  streams, allowing an external process to be started and
        then controlled interactively by GAP
  
      A  prototype  implementation  of  algorithms  using  general  subgroup
        chains.
  
      Changes in the behavior of vectors over small finite fields.
  
      A  fifth  book  New  features for Developers has been added to the GAP
        manual.
  
      Numerous bug fixes and performance improvements
  
  The changes between the final release of GAP 3 (version 3.4.4) and GAP 4 are
  wide-ranging.  The  general  philosophy of the changes is two-fold. Firstly,
  many  assumptions  in  the  design  of  GAP  3 revealed its authors' primary
  interest  in  group theory, and indeed in finite group theory. Although much
  of  the  GAP 4 library is concerned with groups, the basic design now allows
  extension  to  other  algebraic structures, as witnessed by the inclusion of
  substantial  bodies  of  algorithms  for computation with semigroups and Lie
  algebras.  Secondly,  as  the  scale of the system, and the number of people
  using  and  contributing  to  it  has  grown, some aspects of the underlying
  system  have  proved to be restricting, and these have been improved as part
  of  comprehensive  re-engineering  of  the system. This has included the new
  method  selection  system, which underpins the library, and a new, much more
  flexible, GAP package interface.
  
  Details  of  these  changes  can be found in the document Migrating to GAP 4
  available          at          the          GAP         website,         see
  https://www.gap-system.org/Gap3/migratedoc.pdf.
  
  It is perhaps worth mentioning a few points here.
  
  Firstly,  much  remains  unchanged, from the perspective of the mathematical
  user:
  
      The  syntax  of that part of the GAP language that most users need for
        investigating mathematical problems.
  
      The great majority of function names.
  
      Data libraries and the access to them.
  
  A number of visible aspects have changed:
  
      Some  function names that need finer specifications now that there are
        more structures available in GAP.
  
      The  access  to  information  already  obtained  about  a mathematical
        structure.  In GAP 3 such information about a group could be looked up
        by  directly  inspecting  the group record, whereas in GAP 4 functions
        must be used to access such information.
  
  Behind the scenes, much has changed:
  
      A  new  kernel,  with  improvements  in  memory  management and in the
        language  interpreter,  as  well  as  new  features  such as saving of
        workspaces and the possibility of compilation of GAP code into C.
  
      A  new  structure  to  the  library,  based upon a new type and method
        selection  system,  which  is  able  to  support  a  broader  range of
        algebraic computation and to make the structure of the library simpler
        and more modular.
  
      New and faster algorithms in many mathematical areas.
  
      Data  structures  and algorithms for new mathematical objects, such as
        algebras and semigroups.
  
      A  new  and  more  flexible  structure  for  the  GAP installation and
        documentation,  which  means,  for example, that a GAP package and its
        documentation can be installed and be fully usable without any changes
        to the GAP system.
  
  Very few features of GAP 3 are not yet available in GAP 4.
  
      Not  all  of  the  GAP 3 packages have yet been converted for use with
        GAP 4.
  
      The  library  of crystallographic groups which was present in GAP 3 is
        now       part       of       a       GAP 4      package      CrystCat
        (https://www.gap-system.org/Packages/crystcat.html)  by  V. Felsch and
        F. Gähler.