<Chapter Label="Changes from Earlier Versions">
<Heading>Changes from Earlier Versions</Heading>

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<Section Label="ChangesGAP43toGAP44">
<Heading>Changes between &GAP; 4.3 and &GAP; 4.4</Heading>

The main changes between &GAP; 4.3 and &GAP; 4.4 are:

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<Subsection Label="Potentially Incompatible Changes">
<Heading>Potentially Incompatible Changes</Heading>

<List>
<Item>
  The mechanism for the loading of Packages has changed to allow easier
  updates independent of main &GAP; releases. Packages require a
  file <F>PackageInfo.g</F> now. The new <F>PackageInfo.g</F> files are 
  available for all packages with the new version of GAP
  (see <Ref BookName="Example" Label="PackageInfo.g"/>).
</Item>
<Item>
  <Ref Oper="IsSimpleGroup" BookName="ref"/> returns false now for the trivial group.
</Item>
<Item>
  <Ref Oper="PrimeBlocks" BookName="ref"/>: The output format has changed.
</Item>
<Item>
  Division rings (see <Ref Filt="IsDivisionRing" BookName="ref"/>) 
  are now implemented as <Ref Filt="IsRingWithOne" BookName="ref"/>.
</Item>
<Item>
  <Ref Oper="DirectSumOfAlgebras" Label="for two algebras" BookName="ref"/>: 
  <M>p</M>-th power maps are compatible with the input now.
</Item>
<Item>
  The print order for polynomials has been changed.
</Item>
</List>
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 <Q>legacy</Q> interfaces, but we remain committed to
our policy of maintaining upward compatibility whenever sensibly possible.
<P/>

<List>
<Item>
  Groebner Bases:
<P/>
    Buchberger's algorithm to compute Groebner Bases has been implemented
    in GAP. (A. Hulpke)
</Item>
<Item>
    For large scale Groebner Basis computations there also is an interface
    to the Singular system available in the
    <URL>
    <Link>http://www.gap-system.org/Packages/singular.html</Link>
    <LinkText><Package>Singular</Package></LinkText>
    </URL>
    package. (M. Costantini and W. de Graaf)
</Item>
<Item>
    New methods for factorizing polynomials over algebraic extensions of
    the rationals have been implemented in GAP. (A. Hulpke)
</Item>
<Item>
    For more functionality to compute with algebraic number fields there
    is an interface to the Kant system available in the 
    <URL>
    <Link>http://www.gap-system.org/Packages/alnuth.html</Link>
    <LinkText><Package>Alnuth</Package></LinkText>
    </URL>
    package. (B. Assmann and B. Eick)
</Item>
<Item>
    A new functionality to compute the minimal normal subgroups
    of a finite group, as well as its socle, has been installed. 
    (B. Höfling)
</Item>
<Item>
    A fast method for recognizing whether a permutation group is symmetric
    or alternating is available now (A. Seress)
</Item>
<Item>
    A method for computing the Galois group of a rational polynomial is
    available again.  (A. Hulpke)
</Item>
<Item>
    The algorithm for <Ref Attr="BrauerCharacterValue" BookName="ref"/> 
    has been extended to the case where the splitting field is not 
    supported in &GAP;. (T. Breuer)
</Item>
<Item>
    Brauer tables of direct products can now be constructed from the
    known Brauer tables of the direct factors. (T. Breuer)
</Item>
<Item>
    Basic support for vector spaces of rational functions and of uea
    elements is available now in &GAP;. (T. Breuer and W. de Graaf)
</Item>
<Item>
    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)
</Item>
</List>

</Subsection>


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<Subsection Label="New Packages">
<Heading>New Packages</Heading>

The following new Packages have been accepted.
<P/>
<List>
<Item>
    <URL>
    <Link>http://www.gap-system.org/Packages/alnuth.html</Link>
    <LinkText>
    <Package>Alnuth</Package>: Algebraic Number Theory and an interface to the Kant system.
    </LinkText>
    </URL>
    By B. Assmann and B. Eick.
</Item>
<Item>
    <URL>
    <Link>http://www.gap-system.org/Packages/laguna.html</Link>
    <LinkText>
    <Package>LAGUNA</Package>: Computing with Lie Algebras and Units of Group Algebras.
    </LinkText>
    </URL>
    By V. Bovdi, A. Konovalov, R. Rossmanith, C. Schneider.
</Item>
<Item>
    <URL>
    <Link>http://www.gap-system.org/Packages/nq.html</Link>
    <LinkText>
    <Package>NQ</Package>: The ANU Nilpotent Quotient Algorithm.
    </LinkText>
    </URL>
    By W. Nickel.
</Item>
<Item>
    <URL>
    <Link>http://www.gap-system.org/Packages/kbmag.html</Link>
    <LinkText>
    <Package>KBMAG</Package>: Knuth-Bendix for Monoids and Groups.
    </LinkText>
    </URL>
    By D. Holt.
</Item>
<Item>
    <URL>
    <Link>http://www.gap-system.org/Packages/polycyclic.html</Link>
    <LinkText>
    <Package>Polycyclic</Package>: Computation with polycyclic groups.
    </LinkText>
    </URL>
    By B. Eick and W. Nickel.
</Item>
<Item>
    <URL>
    <Link>http://www.gap-system.org/Packages/quagroup.html</Link>
    <LinkText>
    <Package>QuaGroup</Package>: Computing with Quantized Enveloping Algebras.
    </LinkText>
    </URL>
    By W. de Graaf.
</Item>
</List>

</Subsection>


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<Subsection Label="Performance Enhancements">
<Heading>Performance Enhancements</Heading>

<List>
<Item>
    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.
</Item>
<Item>
    The algorithm for <Ref Oper="PossibleClassFusions" BookName="ref"/> 
    has been changed: the efficiency is improved and a new criterion is used. 
    The algorithm for <Ref Oper="PossibleFusionsCharTableTom" BookName="ref"/> 
    has been speeded up. The method for <Ref Oper="PrimeBlocks" BookName="ref"/> 
    has been improved following a suggestion of H. Pahlings.
</Item>
<Item>
    New improved methods for normalizer and subgroup conjugation in <M>S_n</M> 
    have been installed and new improved methods for 
    <Ref Filt="IsNaturalSymmetricGroup" BookName="ref"/> and 
    <Ref Filt="IsNaturalAlternatingGroup" BookName="ref"/> have been 
    implemented. These improve the available methods when groups of large 
    degrees are given.
</Item>
<Item>
    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.
</Item>
<Item>
    The membership test in 
    <Ref Func="SP" Label="for dimension and field size" BookName="ref"/> 
    and <Ref Func="SU" BookName="ref"/> groups has been improved using 
    the invariant forms underlying these groups.
</Item>
<Item>
    An improvement for the cyclic extension method for the computation of
    subgroup lattices has been implemented.
</Item>
<Item>
    A better method for <Ref Oper="MinimalPolynomial" BookName="ref"/> for 
    finite field matrices has been implemented.
</Item>
<Item>
    The display has changed and the arithmetic of multivariate polynomials
    has been improved.
</Item>
<Item>
    The <Ref Func="LogMod" BookName="ref"/> function now uses Pollard's rho method 
    combined with the Pohlig/Hellmann approach.
</Item>
<Item>
    Various functions for sets and lists have been improved following
    suggestions of L. Teirlinck. These include: <Ref Oper="Sort" BookName="ref"/>, 
    <Ref Oper="Sortex" BookName="ref"/>, <Ref Oper="SortParallel" BookName="ref"/>,
    <Ref Attr="SortingPerm" BookName="ref"/>, <Ref Func="NrArrangements" BookName="ref"/>.
</Item>
<Item>
    The methods for <Ref Attr="StructureConstantsTable" BookName="ref"/> and 
    <Ref Func="GapInputSCTable" BookName="ref"/> have been improved in the case of a
    known (anti-) symmetry following a suggestion of M. Costantini.
</Item>
</List>
<P/>
The improvements listed in this Section have been implemented by T. Breuer
and A. Hulpke.

</Subsection>


<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
<Subsection Label="New Programming and User Features">
<Heading>New Programming and User Features</Heading>

<List>
<Item>
The 2GB limit for workspace size has been removed and version numbers for
saved workspaces have been introduced. (S. Linton and B. Höfling)
</Item>
<Item>
  The limit on the total number of types created in a session
           has been removed. (S. Linton)
</Item>
<Item>
  There is a new mechanism for loading packages available.
              Packages need a file <F>PackageInfo.g</F> now. (T. Breuer and
              F. Lübeck; see <Ref BookName="Example" Label="PackageInfo.g"/>).
</Item>
</List>
<P/>
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.

</Subsection>

</Section>


<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
<Section Label="Earlier Changes">
<Heading>Earlier Changes</Heading>

The most important changes between &GAP; 4.2 and &GAP; 4.3 were:
<P/>
<List>
<Item>
The performance of several routines has been substantially improved.
</Item>
<Item>
The functionality in the areas of finitely presented groups, Schur covers
and the calculation of representations has been extended.
</Item>
<Item>
The data libraries of transitive groups, finite integral matrix groups,
character tables and tables of marks have been extended.
</Item>
<Item>
The Windows installation has been simplified for the case where you
are installing &GAP; in its standard location.
</Item>
<Item>
Many bugs have been fixed.
<P/>
</Item>
</List>
<P/>

The most important changes between &GAP; 4.1 and &GAP; 4.2 were:
<P/>
<List>
<Item>
A much extended and improved library of small groups as well as
associated <Ref Attr="IdGroup" BookName="ref"/> routines.
</Item>
<Item>
The primitive groups library has been made more independent of the
rest of &GAP;, some errors were corrected.
</Item>
<Item>
New (and often much faster) infrastructure for orbit computation, based on a
general <Q>dictionary</Q> abstraction.
</Item>
<Item>
New functionality for dealing with representations of algebras, and
in particular for semisimple Lie algebras. 
</Item>
<Item>
New functionality for binary relations on arbitrary sets, magmas and
semigroups.
</Item>
<Item>
Bidirectional streams, allowing an external process to be started and then
controlled <Q>interactively</Q> by &GAP; 
</Item>
<Item>
A prototype implementation of algorithms using general subgroup chains.
</Item>
<Item>
Changes in the behavior of vectors over small finite fields.
</Item>
<Item>
A fifth book <Q>New features for Developers</Q> has been added to the &GAP; manual.
</Item>
<Item>
Numerous bug fixes and performance improvements 
</Item>
</List>

<P/>
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.
<P/>
Details of these changes can be found in the document
<Q>Migrating to GAP 4</Q> available at the &GAP; website, 
see <URL>http://www.gap-system.org/Gap3/migratedoc.pdf</URL>.
<P/>
It is perhaps worth mentioning a few points here. 
<P/>
Firstly, much remains unchanged, from the perspective of the mathematical 
user:
<P/>
<List>
<Item>
    The syntax of that part  of the &GAP; language  that most users need
    for investigating mathematical problems.
<P/>
  
</Item>
<Item>
    The great majority of function names.
<P/>
  
</Item>
<Item>
    Data libraries and the access to them.
</Item>
</List>
<P/>
A number of visible aspects have changed:
<P/>
<List>
<Item>
    Some function names that need finer specifications now that there are
    more structures available in &GAP;.
</Item>
<Item>
    The    access to information   already  obtained about a mathematical
    structure. In &GAP;&nbsp;3 such information about a group could be looked
    up  by  directly inspecting  the  group record,  whereas in  &GAP;&nbsp;4
    functions must be used to access such information.
</Item>
</List>
<P/>
Behind the scenes, much has changed: 
<P/>
<List>
<Item>
  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.
</Item>
<Item>
  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.
</Item>
<Item>
    New and faster algorithms in many mathematical areas.
</Item>
<Item>
    Data structures and algorithms for new mathematical objects, such as
    algebras and semigroups.
</Item>
<Item>
    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.
</Item>
</List>
<P/>
Very few features of &GAP;&nbsp;3 are not yet available in  &GAP;&nbsp;4.
<P/>
<List>
<Item>
     Not all of the &GAP;&nbsp;3 packages have yet been converted
     for use with  &GAP;&nbsp;4.
</Item>
<Item>
   The library of crystallographic groups which was present in
   &GAP;&nbsp;3 is now part of a &GAP;&nbsp;4 package 
   <URL>
   <Link>http://www.gap-system.org/Packages/crystcat.html</Link>
   <LinkText>
   <Package>CrystCat</Package>
   </LinkText>
   </URL>
   by V. Felsch and F. Gähler.
</Item>
</List>

</Section>

</Chapter>


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