gap-libs 4r6p5-3 / usr / share / gap / lib / fitfree.gd

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#W  fitfree.gd                  GAP library                  Alexander Hulpke
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#Y  Copyright (C) 2012 The GAP Group
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##  This file contains functions using the trivial-fitting paradigm.
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#F  CanComputeFittingFree( <grp> ) . . . . .  TF approach is possible
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##  <#GAPDoc Label="CanComputeFittingFree">
##  <ManSection>
##  <Func Name="CanComputeFittingFree" Arg='grp'/>
##
##  <Description>
##  This filter indicates whether algorithms using the TF-paradigm (Trivial
##  Fitting) can be used for a group, that is whether a method for
##  <Ref Func="FittingFreeLiftSetup"/> is available for <A>grp</A>.
##  Note that this filter may change its value from <K>false</K> to
##  <K>true</K>. 
##  </Description>
##  </ManSection>
##  <#/GAPDoc>
##
DeclareFilter( "CanComputeFittingFree" );

# to satisfy method installation requirements
InstallTrueMethod(IsFinite,CanComputeFittingFree);
InstallTrueMethod(IsGroup,CanComputeFittingFree);

InstallTrueMethod(CanComputeFittingFree, IsPermGroup);



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#A  FittingFreeLiftSetup( <G> )
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##  <#GAPDoc Label="FittingFreeLiftSetup">
##  <ManSection>
##  <Attr Name="FittingFreeLiftSetup" Arg='G'/>
##
##  <Description>
##  for a finite group <A>G</A>, this returns a record with the following
##  components:
##  <C>radical</C> The solvable radical <M>Rad(G)</M>.
##  <C>pcgs</C> A pcgs for <M>Rad(G)</M> that refines a
##  <M>G</M>-normal series
##  with elementary abelian factors.
##  <C>depths</C>
##  A list of indices in the pcgs, indicating the <M>G</M>-normal subgroups in
##  the series for the pcgs, including an entry for the trivial subgroup.
##  <C>pcisom</C>  An effective isomorphism from <M>Rad(G)</M> to a pc group
##  <C>factorhom</C> A epimorphism from <M>G</M> onto <M>G/Rad(G)</M>,
##  the image group being
##  represented in a way that decomposition into generators will work
##  efficiently. In particular, it is possible to use
##  <Ref Func="PreImagesRepresentative"/> to take the pre-image of elements
##  in the image. For a subgroup <M>U\le G</M>, it is possible to apply
##  <Ref Func="RestrictedMapping"> to the homomorphism to obtain a
##  corresponding homomorphism for <M>U</M>.
##
##  The redundancy amongst the components is deliberate, as the redundant
##  objects can be created at minimal extra cost and not doing so risks the
##  creation of duplicate objects by user code later on.
##  The record may hold other components that are germane to the recognition
##  setup. These components may not be modified by user code.
DeclareAttribute("FittingFreeLiftSetup",IsGroup);

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#F  FittingFreeSubgroupSetup( <G>, <U> )
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##  <#GAPDoc Label="FittingFreeSubgroupSetup">
##  <ManSection>
##  <Attr Name="FittingFreeSubgroupSetup" Arg='G,U'/>
##
##  <Description>
##  for a subgroup <A>U</A> of a finite group <A>G</A>, for which
##  <Ref Func="FittingFreeLiftSetup"> has been computed, this function
##  computes a compatible setup for <A>U</A>. (This information is cached in
##  <A>U</A>
##  for further calculation later.)
##  It returns a record with the following
##  components:
##  <C>parentffs</C> The record returned by
##  <Ref Func="FittingFreeLiftSetup"> for <G>.
##  <C>rest</C> A restriction of 
##  the <C>factorhom</C> for <A>G</A> to <A>U</A>, defined on generators of
##  <A>U</A>.
##  <C>ker</C> The kernel of this map.
##  <C>pcgs</C> A pcgs for this kernel.
##  <C>serdepths</C>
##  For each depth step in the pcgs for the radical of <G>, as stored in
##  <C>parentffs</C>, this indicates the index in <C>pcgs</C> for <A>U</A>,
##  at which this depth is achieved.
##
##  The record may hold other components that are germane to the recognition
##  setup. These components may not be modified by user code.
DeclareGlobalFunction("FittingFreeSubgroupSetup");

# This attribute is used for groups treated by constructive recognition and
# a composition tree. It is declared in the library such that the function
# FittingFreeSubgroupSetup can maintain it.
DeclareAttribute("RecogDecompinfoHomomorphism",IsMapping);

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#F  SubgroupByFittingFreeData( <G>, <gens>, <imgs>, <ipcgs> )
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##  <#GAPDoc Label="SubgroupByFittingFreeData">
##  <ManSection>
##  <Attr Name="SubgroupByFittingFreeData" Arg='G,U'/>
##
##  <Description>
##  For a finite group <A>G</A>, for which
##  <Ref Func="FittingFreeLiftSetup"> <A>ffs</A> has been computed,
##  this function returns a subgroup <A>U</A> build from data compatible with
##  <A>ffs</A>: <A>U</A> is the subgroup generated by <A>gens</A> and
##  <A>ipcgs</A>.
##  <A>ipcgs</A> is an induced Pcgs for <M>U\cap Rad(G)</M>, with respect to
##  the Pcgs stored in <A>ffs</A>. <A>imgs</A> are images of <A>gens</A>
##  under <A>ffs<C>.factorhom</C></A>.
DeclareGlobalFunction("SubgroupByFittingFreeData");

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#A  DirectFactorsFittingFreeSocle( <G> )
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##  <#GAPDoc Label="DirectFactorsFittingFreeSocle">
##  <ManSection>
##  <Attr Name="DirectFactorsFittingFreeSocle" Arg='G'/>
##
##  <Description>
##  for a finite fitting-free group <A>G</A>, this function retuns a list of
##  the direct factors of the socle of <A>G</A>. If <A>G</A> is not
##  fitting-free then <K>fail</K> is returned.
DeclareAttribute("DirectFactorsFittingFreeSocle",IsGroup);

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#F  HallViaRadical( <G>, <pi> )
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DeclareGlobalFunction("HallViaRadical");