chap3.txt

  
  3 Changes between GAP 4.6 and GAP 4.7
  
  This  chapter  contains  an overview of most important changes introduced in
  GAP  4.7.2  release  (the first public release of GAP 4.7). It also contains
  information about subsequent update releases for GAP 4.7.
  
  
  3.1 GAP 4.7.2 (December 2013)
  
  
  3.1-1 Changes in the core GAP system introduced in GAP 4.7
  
  Improved and extended functionality:
  
      The methods for computing conjugacy classes of permutation groups have
        been  rewritten  from  scratch  to  enable potential use for groups in
        different  representations.  As  a  byproduct  the  resulting  code is
        (sometimes  notably)  faster.  It  also  now  is possible to calculate
        canonical conjugacy class representatives in permutation groups, which
        can be beneficial when calculating character tables.
  
      The  methods  for  determining  (conjugacy  classes  of)  subgroups in
        non-solvable  groups  have  been  substantially  improved in speed and
        scope for groups with multiple nonabelian composition factors.
  
      There  is  a  new  method  for  calculating the maximal subgroups of a
        permutation  group  (with  chief  factors  of  width  less or equal 5)
        without calculating the whole subgroup lattice.
  
      If  available,  information from the table of marks library is used to
        speed up subgroup calculations in almost simple factor groups.
  
      The  broader  availability of maximal subgroups is used to improve the
        calculation of double cosets.
  
      To  illustrate  the  improvements  listed  above,  one  could try, for
        example
  
          Example  
          g:=WreathProduct(MathieuGroup(11),Group((1,2)));
          Length(ConjugacyClassesSubgroups(g));
        
  
        and
  
          Example  
          g:=SemidirectProduct(GL(3,5),GF(5)^3);
          g:=Image(IsomorphismPermGroup(g));
          MaximalSubgroupClassReps(g);
        
  
      Computing  the  exponent  of a finite group G could be extremely slow.
        This  was  due to a slow default method being used, which computed all
        conjugacy classes of elements in order to compute the exponent. We now
        instead  compute Sylow subgroups P_1, ..., P_k of G and use the easily
        verified  equality exp(G) = exp(P_1) x ... x exp(P_k). This is usually
        at least as fast and in many cases orders of magnitude faster.
  
          Example  
          gap> G:=SmallGroup(2^7*9,33);;
          gap> H:=DirectProduct(G, ElementaryAbelianGroup(2^10));;
          gap> Exponent(H); # should take at most a few milliseconds
          72
          gap> K := PerfectGroup(2688,3);;
          gap> Exponent(K); # should take at most a few seconds
          168
        
  
      The  functionality  in  GAP  for  transformations  and  transformation
        semigroups  has  been rewritten and extended. Partial permutations and
        inverse  semigroups have been newly implemented. The documentation for
        transformations  and  transformation  semigroups  has  been  improved.
        Transformations  and  partial  permutations are implemented in the GAP
        kernel.  Methods  for  calculating  attributes  of transformations and
        partial permutations, and taking products, and so are also implemented
        in   the   kernel.  The  new  implementations  are  largely  backwards
        compatible; some exceptions are given below.
  
        The  degree  of  a  transformation f is usually defined as the largest
        positive  integer  where  f  is  defined. In previous versions of GAP,
        transformations were only defined on positive integers less than their
        degree,  it  was  only  possible  to multiply transformations of equal
        degree,  and  a  transformation did not act on any point exceeding its
        degree.  Starting  with  GAP  4.7,  transformations  behave  more like
        permutations,  in  that they fix unspecified points and it is possible
        to multiply arbitrary transformations.
  
            in  the  display  of a transformation, the trailing fixed points
              are  no  longer  printed.  More  precisely,  in the display of a
              transformation  f  if n is the largest value such that n^f<>n or
              i^f=n  for  some  i<>n,  then  the  values  exceeding  n are not
              printed.
  
            the  display for semigroups of transformations now includes more
              information,  for  example  <transformation  semigroup on 10 pts
              with  10  generators>  and <inverse partial perm semigroup on 10
              pts with 10 generators>.
  
            transformations  which define a permutation can be inverted, and
              groups of transformations can be created.
  
        Further    information    regarding    transformations   and   partial
        permutations,  can  be found in the relevant chapters of the reference
        manual.
  
        The  code  for Rees matrix semigroups has been completely rewritten to
        fix  the numerous bugs in the previous versions. The display of a Rees
        matrix semigroup has also been improved to include the numbers of rows
        and   columns,   and   the   underlying   semigroup.   Again  the  new
        implementations should be backwards compatible with the exception that
        the display is different.
  
        The  code for magmas with a zero adjoined has been improved so that it
        is  possible  to access more information about the original magma. The
        display  has also been changed to indicate that the created magma is a
        magma  with zero adjoined (incorporating the display of the underlying
        magma).  Elements  of a magma with zero are also printed so that it is
        clear that they belong to a magma with zero.
  
        If   a   semigroup   is   created   by   generators  in  the  category
        IsMultiplicativeElementWithOneCollection and CanEasilyCompareElements,
        then  it  is  now  checked  if the One of the generators is given as a
        generator. In this case, the semigroup is created as a monoid.
  
      Added    a    new    operation    GrowthFunctionOfGroup    (Reference:
        GrowthFunctionOfGroup)  that  gives  sizes  of distance spheres in the
        Cayley graph of a group.
  
      A new group constructor FreeAbelianGroup (Reference: FreeAbelianGroup)
        for  free  abelian  groups  has  been  added.  By  default, it creates
        suitable  fp  groups.  Though  free abelian groups groups do not offer
        much  functionality right now, in the future other implementations may
        be provided, e.g. by the Polycyclic package.
  
      The  message about halving the pool size at startup is only shown when
        -D   command  line  option  is  used  (see  'Reference:  Command  Line
        Options'). [Suggested by Volker Braun]
  
      An  info  class called InfoObsolete (Reference: InfoObsolete) with the
        default  level  0 is introduced. Setting it to 1 will trigger warnings
        at     runtime    if    an    obsolete    variable    declared    with
        DeclareObsoleteSynonym  is  used.  This is recommended for testing GAP
        distribution and packages.
  
      The  GAP  help  system  now  recognises some common different spelling
        patterns (for example, -ise/-ize, -isation/-ization, solvable/soluble)
        and  searches for all possible spelling options even when the synonyms
        are not declared.
  
      Added  new  function  Cite  (Reference:  Cite) which produces citation
        samples for GAP and packages.
  
      It  is now possible to compile GAP with user-supplied CFLAGS which now
        will  not be overwritten by GAP default settings. [Suggested by Jeroen
        Demeyer]
  
  Fixed bugs:
  
      Union  (Reference:  Union) had O(n^3) behaviour when given many ranges
        (e.g.  it  could  take  10  seconds  to find a union of 1000 1-element
        sets).  The new implementation reduces that to O(n log n) (and 4ms for
        the  10  second example), at the cost of not merging ranges as well as
        before in some rare cases.
  
      IsLatticeOrderBinaryRelation  only  checked  the  existence  of  upper
        bounds but not the uniqueness of the least upper bound (and dually for
        lower  bounds),  so  in  some  cases it could return the wrong answer.
        [Reported by Attila Egri-Nagy]
  
      LowIndexSubgroupsFpGroup     (Reference:     LowIndexSubgroupsFpGroup)
        triggered  a  break loop if the list of generators of the 2nd argument
        contained  the  identity  element  of  the  group.  [Reported by Ignat
        Soroko]
  
      Fixed        regression        in       heuristics       used       by
        NaturalHomomorphismByNormalSubgroup                        (Reference:
        NaturalHomomorphismByNormalSubgroup)  that could produce a permutation
        representation  of  an  unreasonably  large degree. [Reported by Izumi
        Miyamoto]
  
      Fixed  inconsistent  behaviour  of QuotientMod( Integers, r, s, m ) in
        the  case  where  s  and m are not coprime. This fix also corrects the
        division  behaviour  of  ZmodnZ  objects,  see QuotientMod (Reference:
        QuotientMod)   and  ZmodnZ  (Reference:  ZmodnZ).  [Reported  by  Mark
        Dickinson]
  
      Fixed  an  oversight in the loading process causing OnQuit (Reference:
        OnQuit) not resetting the options stack after exiting the break loop.
  
      Empty  strings were treated slightly differently than other strings in
        the  GAP  kernel,  for  historical  reasons.  This resulted in various
        inconsistencies.  For  example,  IsStringRep("")  returned true, but a
        method  installed  for  arguments  of  type  IsStringRep  would NOT be
        invoked when called with an empty string.
  
        We  remove  this  special case in the GAP kernel (which dates back the
        very  early  days  of  GAP 4 in 1996). This uncovered one issue in the
        kernel  function  POSITION_SUBSTRING  (when  calling  it with an empty
        string as second argument), which was also fixed.
  
      The parser for floating point numbers contained a bug that could cause
        GAP  to crash or to get into a state where the only action left to the
        user  was to exit GAP via Ctrl-D. For example, entering four dots with
        spaces between them on the GAP prompt and then pressing the return key
        caused GAP to exit.
  
        The reason was (ironically) an error check in the innards of the float
        parser code which invoked the GAP Error() function at a point where it
        should not have.
  
      Removing  the last character in a string was supposed to overwrite the
        old  removed character in memory with a zero byte, but failed to do so
        due  to  an  off-by-one  error.  For  most GAP operations, this has no
        visible  effect,  except  for  those  which  directly  operate  on the
        underlying  memory representation of strings. For example, when trying
        to  use  such  a string to reference a record entry, a (strange) error
        could be triggered.
  
      ViewString   (Reference:  ViewString)  and  DisplayString  (Reference:
        DisplayString) are now handling strings, characters and immediate FFEs
        in a consistent manner.
  
      Multiple  fixes  to the build process for less common Debian platforms
        (arm, ia64, mips, sparc, GNU/Hurd). [Suggested by Bill Allombert]
  
      Fixes  for  several  regressions in the gac script. [Suggested by Bill
        Allombert]
  
  Changed functionality:
  
      It   is   not   possible   now   to   call  WreathProduct  (Reference:
        WreathProduct)  with  2nd  argument  H  not being a permutation group,
        without   using   the   3rd   argument   specifying   the  permutation
        representation.  This is an incompatible change but it will produce an
        error instead of a wrong result. The former behaviour of WreathProduct
        (Reference:    WreathProduct)   may   now   be   achieved   by   using
        StandardWreathProduct (Reference: StandardWreathProduct) which returns
        the  wreath product for the (right regular) permutation action of H on
        its elements.
  
      The  function  ViewLength  to specify the maximal number of lines that
        are  printed  in  ViewObj  (Reference: ViewObj) became obsolete, since
        there  was  already  a user preference ViewLength to specify this. The
        value of this preference is also accessible in GAPInfo.ViewLength.
  
  
  3.1-2 New and updated packages since GAP 4.6.5
  
  At   the  time  of  the  release  of  GAP  4.6.5  there  were  107  packages
  redistributed  with  GAP.  The  first public release of GAP 4.7 contains 114
  packages.
  
  One  of  essential changes is that the Citrus package by J.Mitchell has been
  renamed  to  Semigroups.  The  package  has  been completely overhauled, the
  performance  has been improved, and the code has been generalized so that in
  the  future  the  same  code  can  be  used  to  compute with other types of
  semigroups.
  
  Furthermore,  new  packages that have been added to the redistribution since
  the release of GAP 4.6.5 are:
  
      4ti2interface  package by Sebastian Gutsche, providing an interface to
        4ti2,  a  software  package for algebraic, geometric and combinatorial
        problems on linear spaces (http://www.4ti2.de).
  
      CoReLG  by  Heiko  Dietrich,  Paolo  Faccin  and  Willem  de Graaf for
        calculations in real semisimple Lie algebras.
  
      IntPic  package  by Manuel Delgado, aimed at providing a simple way of
        getting  a  pictorial  view  of sets of integers. The main goal of the
        package  is  producing  Tikz  code  for  arrays  of integers. The code
        produced  is  to  be  included  in  a  LaTeX  file,  which can then be
        processed.  Some  of  the  integers  are emphasized by using different
        colors for the cells containing them.
  
      LieRing  by  Serena  Cicalo  and  Willem  de  Graaf  for  constructing
        finitely-presented    Lie    rings    and   calculating   the   Lazard
        correspondence.  The package also provides a database of small n-Engel
        Lie rings.
  
      LiePRing  package by Michael Vaughan-Lee and Bettina Eick, introducing
        a new datastructure for nilpotent Lie rings of prime-power order. This
        allows  to  define  such  Lie rings for specific primes as well as for
        symbolic  primes  and  other  symbolic  parameters.  The  package also
        includes  a  database  of nilpotent Lie rings of order at most p^7 for
        all primes p > 3.
  
      ModIsom  by Bettina Eick, which contains various methods for computing
        with  nilpotent  associative  algebras.  In  particular, it contains a
        method to determine the automorphism group and to test isomorphisms of
        such  algebras  over  finite  fields  and of modular group algebras of
        finite  p-groups.  Further, it contains a nilpotent quotient algorithm
        for  finitely presented associative algebras and a method to determine
        Kurosh algebras.
  
      SLA  by Willem de Graaf for computations with simple Lie algebras. The
        main  topics  of  the  package  are nilpotent orbits, theta-groups and
        semisimple subalgebras.
  
  Furthermore,  some  packages  have  been  upgraded  substantially  since the
  GAP 4.6.5 release:
  
      ANUPQ  package  by  Greg  Gamble, Werner Nickel and Eamonn O'Brien has
        been updated after Max Horn joined it as a maintainer. As a result, it
        is now much easier to install and use it with the current GAP release.
  
      Wedderga  package  by  Osnel  Broche  Cristo,  Allen Herman, Alexander
        Konovalov, Aurora Olivieri, Gabriela Olteanu, Ángel del Río and Inneke
        Van  Gelder  has  been  extended  to include functions for calculating
        local  and  global Schur indices of ordinary irreducible characters of
        finite  groups,  cyclotomic  algebras  over abelian number fields, and
        rational quaternion algebras (contribution by Allen Herman).
  
  
  3.2 GAP 4.7.3 (February 2014)
  
  Fixed bugs which could lead to incorrect results:
  
      Incorrect  result returned by AutomorphismGroup(PSp(4,2^n)). [Reported
        by Anvita]
  
      The  Order  (Reference:  Order)  method  for group homomorphisms newly
        introduced  in  GAP 4.7  had  a bug that caused it to sometimes return
        incorrect results. [Reported by Benjamin Sambale]
  
  Fixed bugs that could lead to break loops:
  
      Several bugs were fixed and missing methods were introduced in the new
        code for transformations, partial permutations and semigroups that was
        first  included  in  GAP 4.7.  Some minor corrections were made in the
        documentation for transformations.
  
      Break  loop  in  IsomorphismFpMonoid when prefixes in generators names
        were  longer  than  one letter. [Reported by Dmytro Savchuk and Yevgen
        Muntyan]
  
      Break      loop      while      displaying      the      result     of
        MagmaWithInversesByMultiplicationTable                     (Reference:
        MagmaWithInversesByMultiplicationTable). [Reported by Grahame Erskine]
  
  Improved functionality:
  
      Better   detection   of  UTF-8  terminal  encoding  on  some  systems.
        [Suggested by Andries Brouwer]
  
  
  3.3 GAP 4.7.4 (February 2014)
  
  This  release  was prepared immediately after GAP 4.7.3 to revert the fix of
  the  error  handling  for  the  single  quote  at  the end of an input line,
  contained  in  GAP  4.7.3. It happened that (only on Windows) the fix caused
  error messages in one of the packages.
  
  
  3.4 GAP 4.7.5 (May 2014)
  
  Fixed bugs which could lead to incorrect results:
  
      InstallValue (Reference: InstallValue) cannot handle immediate values,
        characters  or booleans for technical reasons. A check for such values
        was  introduced  to  trigger  an  error  message and prevent incorrect
        results caused by this. [Reported by Sebastian Gutsche]
  
      KnowsDictionary   (Reference:  KnowsDictionary)  and  LookupDictionary
        (Reference:  LookupDictionary) methods for IsListLookupDictionary were
        using  PositionFirstComponent (Reference: PositionFirstComponent); the
        latter  is  only  valid on sorted lists, but in IsListLookupDictionary
        the  underlying  list  is  NOT  sorted  in  general,  leading to bogus
        results.
  
  Other fixed bugs:
  
      A      bug      in      DirectProductElementsFamily     which     used
        CanEasilyCompareElements (Reference: CanEasilyCompareElements) instead
        of CanEasilySortElements (Reference: CanEasilySortElements).
  
      Fixed  wrong  Infolevel  message  that  caused  a  break loop for some
        automorphism group computations.
  
      Fixed  an  error  that  sometimes  caused a break loop in HallSubgroup
        (Reference: HallSubgroup). [Reported by Benjamin Sambale]
  
      Fixed  a  rare  error  in computation of conjugacy classes of a finite
        group   by   homomorphic  images,  providing  fallback  to  a  default
        algorithm.
  
      Fixed  an error in the calculation of Frattini subgroup in the case of
        the trivial radical.
  
      Several  minor  bugs  were  fixed  in  the  documentation, kernel, and
        library code for transformations.
  
      Fixed  errors  in NumberPerfectGroups (Reference: NumberPerfectGroups)
        and NumberPerfectLibraryGroups (Reference: NumberPerfectLibraryGroups)
        not being aware that there are no perfect groups of odd order.
  
      Restored  the  ability  to  build  GAP on OS X 10.4 and 10.5 which was
        accidentally  broken  in  the  previous GAP release by using the build
        option not supported by these versions.
  
      Fixed  some  problems  for  ia64 and sparc architectures. [Reported by
        Bill Allombert and Volker Braun]
  
  New package added for the redistribution with GAP:
  
      permut   package   by   A.Ballester-Bolinches,   E.Cosme-Llópez,   and
        R.Esteban-Romero to deal with permutability in finite groups.
  
  
  3.5 GAP 4.7.6 (November 2014)
  
  Fixed bugs which could lead to incorrect results:
  
      A  bug  that may cause ShortestVectors (Reference: ShortestVectors) to
        return an incomplete list. [Reported by Florian Beye]
  
      A  bug  that may lead to incorrect results and infinite loops when GAP
        is compiled without GMP support using gcc 4.9.
  
      A    bug    that    may    cause    OrthogonalEmbeddings   (Reference:
        OrthogonalEmbeddings)  to  return  an  incomplete result. [Reported by
        Benjamin Sambale]
  
  Fixed bugs that could lead to break loops:
  
      ClosureGroup  (Reference:  ClosureGroup)  should  be  used  instead of
        ClosureSubgroup  (Reference:  ClosureSubgroup)  in  case  there  is no
        parent group, otherwise some calculations such as e.g. NormalSubgroups
        (Reference: NormalSubgroups) may fail. [Reported by Dmitrii Pasechnik]
  
      Fixed  a line in the code that used a hard-coded identity permutation,
        not a generic identity element of a group. [Reported by Toshio Sumi]
  
      Fixed a problem in the new code for calculating maximal subgroups that
        caused  a  break  loop  for  some  groups  from  the transitive groups
        library. [Reported by Petr Savicky]
  
      Fixed  a  problem  in ClosureSubgroup (Reference: ClosureSubgroup) not
        accepting some groups without Parent (Reference: Parent). [Reported by
        Inneke van Gelder]
  
  Other fixed bugs:
  
      Eliminated  a  number  of  compiler  warnings detected with some newer
        versions of C compilers.
  
      Some minor bugs in the transformation and partial permutation code and
        documentation were resolved.
  
  
  3.6 GAP 4.7.7 (February 2015)
  
  New features:
  
      Introduced  some  arithmetic  operations  for  infinity  and  negative
        infinity, see Reference: infinity.
  
      Introduced    new    property    IsGeneratorsOfSemigroup   (Reference:
        IsGeneratorsOfSemigroup)  which reflects wheter the list or collection
        generates a semigroup.
  
  Fixed bugs which could lead to incorrect results:
  
      Fixed  a  bug  in  Union (Reference: Union) (actually, in the internal
        library  function  JoinRanges)  caused  by  downward  running  ranges.
        [Reported by Matt Fayers]
  
      Fixed  a  bug  where recursive records might be printed with the wrong
        component  name, coming from component names being ordered differently
        in two different pieces of code. [Reported by Thomas Breuer]
  
      The  usage  of abs in src/gmpints.c was replaced by AbsInt. The former
        is  defined  to  operate on 32-bit integers even if GAP is compiled in
        64-bit  mode.  That lead to truncating GAP integers and caused a crash
        in  RemInt  (Reference: RemInt), reported by Willem De Graaf and Heiko
        Dietrich.  Using  AbsInt  fixes  the  crash,  and  ensures the correct
        behaviour on 32-bit and 64-bit builds.
  
  Fixed bugs that could lead to break loops:
  
      A  problem  with  ProbabilityShapes (Reference: ProbabilityShapes) not
        setting  frequencies  list  for  small  degrees.  [Reported  by Daniel
        Błażewicz and independently by Mathieu Gagne]
  
      An  error when generating a free monoid of rank infinity. [Reported by
        Nick Loughlin]
  
      Several  bugs  with  the  code for Rees matrix semigroups not handling
        trivial cases properly.
  
      A     bug    in    IsomorphismTypeInfoFiniteSimpleGroup    (Reference:
        IsomorphismTypeInfoFiniteSimpleGroup)  affecting  one particular group
        due  to  a  misformatting  in  a  routine  that translates between the
        Chevalley  type  and the name used in the table (in this case, "T" was
        used instead of ["T"]). [Reported by Petr Savicky]
  
  Other fixed bugs:
  
      The  Basis  (Reference:  Basis) method for full homomorphism spaces of
        linear  mappings  did not set basis vectors which could be obtained by
        GeneratorsOfLeftModule (Reference: GeneratorsOfLeftModule).
  
      A problem with GaloisType (Reference: GaloisType) entering an infinite
        loop  in  the  routine  for  approximating a root. [Reported by Daniel
        Błażewicz]
  
      Fixed the crash when GAP is called when the environment variables HOME
        or PATH are unset. [Reported by Bill Allombert]
  
  Furthermore,  new  packages that have been added to the redistribution since
  the release of GAP 4.7.6 are:
  
      json package by Christopher Jefferson, providing a mapping between the
        JSON markup language and GAP
  
      SglPPow package by Bettina Eick and Michael Vaughan-Lee, providing the
        database of p-groups of order p^7 for p > 11, and of order 3^8.
  
  
  3.7 GAP 4.7.8 (June 2015)
  
  Fixed bugs which could lead to incorrect results:
  
      Added  two  groups of degree 1575 which were missing in the library of
        first primitive groups. [Reported by Gordon Royle]
  
      Fixed  the  error  in  the  code for algebra module elements in packed
        representation  caused  by the use of Objectify (Reference: Objectify)
        with  the  type of the given object instead of ObjByExtRep (Reference:
        ObjByExtRep)  as  recommended  in  'Reference: Further Improvements in
        Implementing   Residue  Class  Rings'.  The  problem  was  that  after
        calculating  u+v  where one of the summands was known to be zero, this
        knowledge  was  wrongly  passed  to the sum via the type. [Reported by
        Istvan Szollosi]
  
      Fixed  a  bug  in PowerMod (Reference: PowerMod) causing wrong results
        for  univariate  Laurent polynomials when the two polynomial arguments
        are stored with the same non-zero shift. [Reported by Max Horn]
  
  Furthermore,  new  packages that have been added to the redistribution since
  the release of GAP 4.7.7 are:
  
      PatternClass  by  Michael  Albert,  Ruth  Hoffmann  and  Steve Linton,
        allowing  to  explore  the  permutation pattern classes build by token
        passing  networks. Amongst other things, it can compute the basis of a
        permutation pattern class, create automata from token passing networks
        and  check if the deterministic automaton is a possible representative
        of a token passing network.
  
      QPA  by Edward Green and Øyvind Solberg, providing data structures and
        algorithms  for computations with finite dimensional quotients of path
        algebras,  and  with finitely generated modules over such algebras. It
        implements  data  structures  for quivers, quotients of path algebras,
        and  modules, homomorphisms and complexes of modules over quotients of
        path algebras.