Merge branch 'stable-4.8'

doc/changes/changes48.xml

@@ -2,7 +2,7 @@
 <Heading>Changes between &GAP; 4.7 and &GAP; 4.8</Heading>
 
 This chapter contains an overview of the most important changes
-introduced in &GAP; 4.8.1 release (the 2nd beta release of &GAP; 4.8).
+introduced in &GAP; 4.8.2 release (the 1st public release of &GAP; 4.8).
 Later it will also contain information about subsequent update 
 releases for &GAP; 4.8.
 
@@ -16,8 +16,8 @@ and you may use appropriate milestones from
 that were introduced in corresponding &GAP; releases. An overview of the
 most significant ones is provided below.
 
-<Section Label="gap480"> 
-<Heading>&GAP; 4.8.1 (December 2015)</Heading>
+<Section Label="gap482">
+<Heading>&GAP; 4.8.2 (February 2016)</Heading>
 
 <Subsection Label="Changes in the core GAP48 system"> 
 <Heading>Changes in the core &GAP; system introduced in &GAP; 4.8</Heading>
@@ -146,6 +146,10 @@ belong to the <Package>Semigroups</Package> and <Package>Smallsemi</Package> pac
 <Ref Func="Test" BookName="ref"/> with the option to compare the output up to
 whitespaces.
 </Item>
+<Item>The function `ErrorMayQuit`, which differs from
+<Ref Func="Error" BookName="ref"/> by not allowing execution to continue,
+has been renamed to <Ref Func="ErrorNoReturn" BookName="ref"/>.
+</Item>
 </List>
 
 Fixed bugs:
@@ -182,10 +186,18 @@ Including a <C>break</C> or <C>continue</C> statement in a function body
 but not in a loop now gives a syntax error instead of failing at run time.
 </Item>
 <Item>
+<Ref Oper="GroupGeneralMappingByImages" BookName="ref"/> now verifies that
+that image of a mapping is contained in its range.
+</Item>
+<Item>
 Fixed a bug in caching the degree of transformation that could lead to a
 non-identity transformation accidentally changing its value to the identity
 transformation.
 </Item>
+<Item>
+Fixed the problem with using Windows default browser as a help viewer using
+<C>SetHelpViewer("browser");</C>.
+</Item>
 </List>
 
 </Subsection>
@@ -209,20 +221,52 @@ together with three associated packages
 (all three - by Sebastian Gutsche and Sebastian Posur).
 </Item>
 <Item>
+<Package>Digraphs</Package> package by Jan De Beule, Julius Jonušas,
+James Mitchell, Michael Torpey and Wilf Wilson, which provides
+functionality to work with graphs, digraphs, and multidigraphs.
+</Item>
+<Item>
 <Package>FinInG</Package> package by John Bamberg, Anton Betten,
 Philippe Cara, Jan De Beule, Michel Lavrauw and Max Neunhöffer
 for computation in Finite Incidence Geometry.
 </Item>
 <Item>
+<Package>HeLP</Package> package by Andreas Bächle and Leo Margolis,
+which computes constraints on partial augmentations of torsion units
+in integral group rings using a method developed by Luthar, Passi and
+Hertweck. The package can be employed to verify the Zassenhaus
+Conjecture and the Prime Graph Question for finite groups, once
+their characters are known. It uses an interface to the software
+package <Package>4ti2</Package> to solve integral linear inequalities.
+</Item>
+<Item>
 <Package>matgrp</Package> package by Alexander Hulpke, which provides
 an interface to the solvable radical functionality for matrix groups,
 building on constructive recognition.
 </Item>
 <Item>
+<Package>NormalizInterface</Package> package by Sebastian Gutsche,
+Max Horn and Christof Söger, which provides a GAP interface to
+<Package>Normaliz</Package>, enabling direct access to the complete
+functionality of <Package>Normaliz</Package>, such as computations
+in affine monoids, vector configurations, lattice polytopes, and
+rational cones.
+</Item>
+<Item>
 <Package>profiling</Package> package by Christopher Jefferson for
 transforming profiles produced by <Ref Func="ProfileLineByLine" BookName="ref"/>
 and <Ref Func="CoverageLineByLine" BookName="ref"/> into a human-readable form.
 </Item>
+<Item>
+<Package>Utils</Package> package by Sebastian Gutsche, Stefan Kohl and
+Christopher Wensley, which provides a collection of utility functions
+gleaned from many packages.
+</Item>
+<Item>
+<Package>XModAlg</Package> package by Zekeriya Arvasi and Alper Odabas,
+which provides a collection of functions for computing with crossed
+modules and Cat1-algebras and morphisms of these structures.
+</Item>
 </List>
 
 </Subsection>

doc/ref/grppc.xml

@@ -458,7 +458,7 @@ the groups of a given order.
 Finally we note that for the computation of split extensions it is not
 necessary that <A>M</A> must correspond to an elementary abelian group. Here
 it is possible to construct split extensions of arbitrary pc groups,
-see <Ref Func="SplitExtension"/>.
+see <Ref Oper="SplitExtension"/>.
 
 <#Include Label="TwoCoboundaries">
 <#Include Label="TwoCocycles">
@@ -471,6 +471,8 @@ see <Ref Func="SplitExtension"/>.
 
 <Description>
 returns the split extension of <A>G</A> by the <A>G</A>-module <A>M</A>.
+See also <Ref Oper="SplitExtension" Label="with specified homomorphism"/>
+for its 3-argument version.
 </Description>
 </ManSection>
 
@@ -514,7 +516,7 @@ up to equivalence, but not up to isomorphism.
 <#Include Label="ExtensionRepresentatives">
 
 <ManSection>
-<Oper Name="SplitExtension" Arg='G, aut, N'/>
+<Oper Name="SplitExtension" Arg='G, aut, N' Label="with specified homomorphism"/>
 
 <Description>
 returns the split extensions of the pc group <A>G</A> by the pc group

lib/galois.gd

@@ -29,7 +29,7 @@ DeclareInfoClass("InfoGalois");
 ##
 ## <#GAPDoc Label="GaloisType">
 ## <ManSection>
-## <Attr Name="GaloisType" Arg='f[,cand]'/>
+## <Attr Name="GaloisType" Arg='f'/>
 ##
 ## <Description>
 ## Let <A>f</A> be an irreducible polynomial with rational coefficients. This

lib/galois.gi

@@ -687,6 +687,10 @@ end);
 ##
 #F GaloisType(<pol>,[<cands>]) . . . . . . . . . . . . . compute Galois type
 ##
+## The optional 2nd argument may be used to restrict the range of transitive
+## permutation groups that will be considered as possible Galois groups.
+## The use of the 2nd argument is experimental and is not documented.
+##
 BindGlobal("DoGaloisType",function(arg)
 local f,n,sh,p,ind,cand,noca,alt,d,df,co,dco,res,resf,pat,pps,i,j,k,
  orbs,GetResolvent,norb,act,repro,minpol,ext,ncand,pos,step,lens,gudeg,

lib/ghomperm.gi

@@ -700,10 +700,16 @@ InstallOtherMethod( StabChainMutable, "perm mapping by images", true,
 
  # build short words by an orbit algorithm on genimg
  BuildOrb:=function(genimg)
- local orb,dict,orbf,T,elm,img,i,n;
- dict:=NewDictionary(genimg[1][1],false);
- AddDictionary(dict,One(genimg[1][1]));
- orb:=[Immutable([One(genimg[1][1]),One(genimg[2][1])])];
+ local a,orb,dict,orbf,T,elm,img,i,n;
+ if Length(genimg[1])>0 then
+ a:=genimg[1][1];
+ else
+ a:=One(Source(hom));
+ fi;
+ dict:=NewDictionary(a,false);
+ a:=One(Source(hom));
+ AddDictionary(dict,a);
+ orb:=[Immutable([a,One(Range(hom))])];
  orbf:=[0];
  i:=1;
  n:=Length(genimg[1]);

lib/grp.gd

@@ -4254,7 +4254,14 @@ DeclareGlobalFunction( "PowerMapOfGroupWithInvariants" );
 ##
 ## <Description>
 ## tests whether <A>G</A> <M>/</M> <A>N</A> is abelian
-## (without explicitly constructing the factor group).
+## (without explicitly constructing the factor group and without testing
+## whether <A>N</A> is in fact a normal subgroup).
+## <Example><![CDATA[
+## gap> HasAbelianFactorGroup(g,n);
+## false
+## gap> HasAbelianFactorGroup(DerivedSubgroup(g),n);
+## true
+## ]]></Example>
 ## </Description>
 ## </ManSection>
 ## <#/GAPDoc>
@@ -4271,7 +4278,8 @@ DeclareGlobalFunction("HasAbelianFactorGroup");
 ##
 ## <Description>
 ## tests whether <A>G</A> <M>/</M> <A>N</A> is solvable
-## (without explicitly constructing the factor group).
+## (without explicitly constructing the factor group and without testing
+## whether <A>N</A> is in fact a normal subgroup).
 ## </Description>
 ## </ManSection>
 ## <#/GAPDoc>
@@ -4289,13 +4297,8 @@ DeclareGlobalFunction("HasSolvableFactorGroup");
 ##
 ## <Description>
 ## tests whether <A>G</A> <M>/</M> <A>N</A> is elementary abelian
-## (without explicitly constructing the factor group).
-## <Example><![CDATA[
-## gap> HasAbelianFactorGroup(g,n);
-## false
-## gap> HasAbelianFactorGroup(DerivedSubgroup(g),n);
-## true
-## ]]></Example>
+## (without explicitly constructing the factor group and without testing
+## whether <A>N</A> is in fact a normal subgroup).
 ## </Description>
 ## </ManSection>
 ## <#/GAPDoc>

lib/grp.gi

@@ -4530,16 +4530,18 @@ InstallMethod( KnowsHowToDecompose,
 ##
 InstallGlobalFunction(HasAbelianFactorGroup,function(G,N)
 local gen;
+ Assert(2,IsNormal(G,N) and IsSubgroup(G,N));
  gen:=Filtered(GeneratorsOfGroup(G),i->not i in N);
  return ForAll([1..Length(gen)],
  i->ForAll([1..i-1],j->Comm(gen[i],gen[j]) in N));
 end);
 
 #############################################################################
 ##
-#M HasSolvableFactorGroup(<G>,<N>) test whether G/N is abelian
+#M HasSolvableFactorGroup(<G>,<N>) test whether G/N is solvable
 ##
 InstallGlobalFunction(HasSolvableFactorGroup,function(G,N)
+ Assert(2,IsNormal(G,N) and IsSubgroup(G,N));
  return ForAny(DerivedSeriesOfGroup(G),x->IsSubset(N,x));
 end);
 

lib/helpview.gi

@@ -69,20 +69,19 @@ if ARCH_IS_WINDOWS() then
  HELP_VIEWER_INFO.browser := rec(
  type := "url",
  show := function( filename )
- local pos;
+ local pos, winfilename;
  if not filename{[1..9]}="/cygdrive" then
- Error( "corrupted name of the help file ", filename );
+ Error( "the name of the help file ", filename , " must start with /cygdrive" );
+ else
+ winfilename:=MakeExternalFilename( SplitString( filename, "#" )[1] );
  fi;
- Print( "Opening help page in default windows browser ... \c" );
- Process( DirectoryCurrent(),
- Filename( DirectoriesLibrary( "bin" ), "cygstart.exe" ),
- InputTextNone(),
- OutputTextNone(),
- [ SplitString( filename, "#" )[1] ] );
+ Print( "Opening help page ", winfilename, " in default windows browser ... \c" );
+ Exec( Concatenation("start ", winfilename ) );
  Print( "done! \n" ); 
  end
  );
 
+
 elif ARCH_IS_MAC_OS_X() then
  # html version using Mac OS X default browser
  HELP_VIEWER_INFO.("mac default browser") := rec (

lib/mapping.gi

@@ -516,57 +516,63 @@ InstallGlobalFunction( CompositionMapping, function ( arg )
 end );
 
 
-#############################################################################
-##
-#M IsInjective( <map> ) . . . . . for gen. mapp. with known inv. gen. mapp.
-#M IsSingleValued( <map> ) . . . . for gen. mapp. with known inv. gen. mapp.
-#M IsSurjective( <map> ) . . . . . for gen. mapp. with known inv. gen. mapp.
-#M IsTotal( <map> ) . . . . . . . for gen. mapp. with known inv. gen. mapp.
-##
-InstallImmediateMethod( IsInjective,
- IsGeneralMapping and HasInverseGeneralMapping, 0,
- function( map )
- map:= InverseGeneralMapping( map );
- if HasIsSingleValued( map ) then
- return IsSingleValued( map );
- else
- TryNextMethod();
- fi;
- end );
-
-InstallImmediateMethod( IsSingleValued,
- IsGeneralMapping and HasInverseGeneralMapping, 0,
- function( map )
- map:= InverseGeneralMapping( map );
- if HasIsInjective( map ) then
- return IsInjective( map );
- else
- TryNextMethod();
- fi;
- end );
-
-InstallImmediateMethod( IsSurjective,
- IsGeneralMapping and HasInverseGeneralMapping, 0,
- function( map )
- map:= InverseGeneralMapping( map );
- if HasIsTotal( map ) then
- return IsTotal( map );
- else
- TryNextMethod();
- fi;
- end );
-
-InstallImmediateMethod( IsTotal,
- IsGeneralMapping and HasInverseGeneralMapping, 0,
- function( map )
- map:= InverseGeneralMapping( map );
- if HasIsSurjective( map ) then
- return IsSurjective( map );
- else
- TryNextMethod();
- fi;
- end );
-
+# Temporarily disabled -- See #569
+# Currently some group homomrophisms construct inverse maps that are really
+# restricted inverses (i.e. defined only on the image). Together with these
+# immediate methods this can cause wrong indications of IsSurjective etc.
+# for these maps. While this needs to be fixed in the future properly, the
+# immediate methods are temporarily disabled to avoid this error having
+# further effects.
+# #############################################################################
+# ##
+# #M IsInjective( <map> ) . . . . . for gen. mapp. with known inv. gen. mapp.
+# #M IsSingleValued( <map> ) . . . . for gen. mapp. with known inv. gen. mapp.
+# #M IsSurjective( <map> ) . . . . . for gen. mapp. with known inv. gen. mapp.
+# #M IsTotal( <map> ) . . . . . . . for gen. mapp. with known inv. gen. mapp.
+# ##
+# InstallImmediateMethod( IsInjective,
+# IsGeneralMapping and HasInverseGeneralMapping, 0,
+# function( map )
+# map:= InverseGeneralMapping( map );
+# if HasIsSingleValued( map ) then
+# return IsSingleValued( map );
+# else
+# TryNextMethod();
+# fi;
+# end );
+# 
+# InstallImmediateMethod( IsSingleValued,
+# IsGeneralMapping and HasInverseGeneralMapping, 0,
+# function( map )
+# map:= InverseGeneralMapping( map );
+# if HasIsInjective( map ) then
+# return IsInjective( map );
+# else
+# TryNextMethod();
+# fi;
+# end );
+# 
+# InstallImmediateMethod( IsSurjective,
+# IsGeneralMapping and HasInverseGeneralMapping, 0,
+# function( map )
+# map:= InverseGeneralMapping( map );
+# if HasIsTotal( map ) then
+# return IsTotal( map );
+# else
+# TryNextMethod();
+# fi;
+# end );
+# 
+# InstallImmediateMethod( IsTotal,
+# IsGeneralMapping and HasInverseGeneralMapping, 0,
+# function( map )
+# map:= InverseGeneralMapping( map );
+# if HasIsSurjective( map ) then
+# return IsSurjective( map );
+# else
+# TryNextMethod();
+# fi;
+# end );
 
 #############################################################################
 ##

lib/set.gi

@@ -72,7 +72,9 @@ InstallMethod( AddSet,
  Error( "<set> must be a mutable proper set" );
  fi;
  pos:= PositionSorted( set, obj );
- if set[ pos ] <> obj then
+ if pos>Length(set) then
+ set[ pos ]:= obj;
+ elif set[ pos ] <> obj then
  len:= Length( set );
  set{ [ pos+1 .. len+1 ] }:= set{ [ pos .. len ] };
  set[ pos ]:= obj;