REBASE: Simplify presentation before finding subgroup quotients

Run Tietze in LargerAbelianQuotient with different heuristics
gap-system · Apr 28, 2019 · 7dbac5b · 7dbac5b
1 parent b62ac95
commit 7dbac5b
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Showing 2 changed files with 15 additions and 6 deletions.
diff --git a/lib/ghomfp.gi b/lib/ghomfp.gi
@@ -799,6 +799,7 @@ local aug,w,p,pres,f,fam,opt;
   pres := PresentationAugmentedCosetTable( aug, "y",0# printlevel
                     ,true) ;# intialize tracking before the `1or2' routine!
   opt:=TzOptions(pres);
+
   if ValueOption("expandLimit")<>fail then
     opt.expandLimit:=ValueOption("expandLimit");
   else
@@ -815,12 +816,16 @@ local aug,w,p,pres,f,fam,opt;
     opt.lengthLimit:=Int(3/2*pres!.tietze[TZ_TOTAL]); # not too big.
   fi;
   if ValueOption("generatorsLimit")<>fail then
-    opt.lengthLimit:=ValueOption("generatorsLimit");
+    opt.generatorsLimit:=ValueOption("generatorsLimit");
   fi;
 
   TzOptions(pres).printLevel:=InfoLevel(InfoFpGroup); 
-  TzEliminateRareOcurrences(pres,50);
-  TzGoGo(pres); # cleanup
+  if ValueOption("quick")=true then
+    TzGo(pres);
+  else
+    TzEliminateRareOcurrences(pres,50);
+    TzGoGo(pres); # cleanup
+  fi;
 
   # new free group
   f:=FpGroupPresentation(pres,str);
@@ -1143,7 +1148,11 @@ InstallMethod(MaximalAbelianQuotient,
         true, [IsSubgroupFpGroup], 0,
 function(U)
 local phi,m;
-  phi:=IsomorphismFpGroup(U);
+  # do cheaper Tietze (and thus do not store)
+  phi:=AttributeValueNotSet(IsomorphismFpGroup,U:
+    eliminationsLimit:=50,
+    generatorsLimit:=Length(GeneratorsOfGroup(Parent(U)))*LogInt(IndexInWholeGroup(U),2),
+    quick); 
   m:=MaximalAbelianQuotient(Image(phi));
   SetAbelianInvariants(U,AbelianInvariants(Image(phi)));
   return phi*MaximalAbelianQuotient(Image(phi));

diff --git a/lib/twocohom.gi b/lib/twocohom.gi
@@ -1408,8 +1408,8 @@ local r,z,ogens,n,gens,str,dim,i,j,f,rels,new,quot,g,p,lay,m,e,fp,old,sim;
   SetSize(fp,Size(r.group)*Size(r.module.field)^r.module.dimension);
 
   if Length(arg)>2 and arg[3]=true then
-    #sim:=IsomorphismSimplifiedFpGroup(fp);
-    sim:=IdentityMapping(fp);
+    sim:=IsomorphismSimplifiedFpGroup(fp);
+    #sim:=IdentityMapping(fp);
 
     g:=r.group;
     quot:=InverseGeneralMapping(sim)*GroupHomomorphismByImages(fp,g,GeneratorsOfGroup(fp),