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performance enhancements in subgroup lattice #3384

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Mar 28, 2019
Merged

performance enhancements in subgroup lattice #3384

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04e91d2
ENHANCE: Memory use in subgroup lattice, subspaces of layer
hulpke Mar 23, 2019
0ac827a
ENHANCE: Option for perm group closure to get order of closure
hulpke Mar 27, 2019
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25 changes: 21 additions & 4 deletions lib/grppclat.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -259,7 +259,7 @@ end);
##
InstallGlobalFunction(ActionSubspacesElementaryAbelianGroup,function(arg)
local P,g,op,act,a,pcgs,ma,mat,d,f,i,j,new,newmat,id,p,dodim,compldim,compl,
dims,Pgens,Pcgens,Pu,Pc,perms,one,par,ker,kersz;
dims,Pgens,Pcgens,Pu,Pc,perms,one,par,ker,kersz,pcelm,pccache,asz;

P:=arg[1];
if IsModuloPcgs(arg[2]) then
Expand Down Expand Up @@ -432,15 +432,32 @@ local P,g,op,act,a,pcgs,ma,mat,d,f,i,j,new,newmat,id,p,dodim,compldim,compl,
ma:=new;

# convert to grps
pccache:=[]; # avoid recerating different copies of same element
pcelm:=function(vec)
local e,p;
e:=Immutable([vec]);
p:=PositionSorted(pccache,e);
if IsBound(pccache[p]) and pccache[p][1]=vec then
return pccache[p][2];
else
e:=Immutable([vec,PcElementByExponentsNC(pcgs,vec)]);
AddSet(pccache,e);
return e[2];
fi;
end;

new:=[];
for i in ma do
#a:=SubgroupNC(Parent(g),List(i,j->Product([1..d],k->pcgs[k]^j[k])));
asz:=kersz*p^Length(i);
if kersz=1 then
a:=SubgroupNC(par,List(i,j->PcElementByExponentsNC(pcgs,j)));
a:=SubgroupNC(par,List(i,j->pcelm(j)));
else
a:=ClosureGroup(ker,List(i,j->PcElementByExponentsNC(pcgs,j)));
#a:=ClosureGroup(ker,List(i,j->pcelm(j)):knownClosureSize:=asz);
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Why did you replace the ClosureGroup with the SubgroupNC? Is it faster? And given the replacement, why have you kept the ClosureGroup line as a comment?

a:=SubgroupNC(par,Concatenation(GeneratorsOfGroup(ker),
List(i,j->pcelm(j))));
fi;
SetSize(a,kersz*p^Length(i));
SetSize(a,asz);
Add(new,a);
od;

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2 changes: 2 additions & 0 deletions lib/grpperm.gi
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Expand Up @@ -736,6 +736,8 @@ BindGlobal("DoClosurePrmGp",function( G, gens, options )
fi;
od;
else
o:=ValueOption("knownClosureSize");
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What do you intend for the knownClosureSize value option: if you're not using it in the code in the rest of the PR, and it's not documented, is there any point in it being there?

if IsInt(o) then options.limit:=o;fi;
chain := ClosureRandomPermGroup( chain, gens, options );
fi;

Expand Down