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Slightly extend MinimalGeneratingSet for groups #1755

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Oct 2, 2017
Merged

Slightly extend MinimalGeneratingSet for groups #1755

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2767d14
grp.gi: fix typo in MinimalGeneratingSet Error
wilfwilson Sep 29, 2017
43f45d7
grp.gi: add special case to MinimalGeneratingSet
wilfwilson Sep 29, 2017
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9 changes: 7 additions & 2 deletions lib/grp.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -103,6 +103,10 @@ InstallMethod(MinimalGeneratingSet,"solvable group via pc",true,
function(G)
local i;
if not IsSolvableGroup(G) then
if IsGroup(G) and HasGeneratorsOfGroup(G)
and Length(GeneratorsOfGroup(G)) = 2 then
return GeneratorsOfGroup(G);
fi;
TryNextMethod();
fi;
i:=IsomorphismPcGroup(G);
Expand All @@ -122,9 +126,10 @@ function(G)
TryNextMethod();
else
Error(
"`MinimalGeneratingSet' currently assumes that the group must be solvable.\n",
"`MinimalGeneratingSet' currently assumes that the group is solvable, or\n",
"already possesses a generating set of size 2.\n",
"In general, try `SmallGeneratingSet' instead, which returns a generating\n",
"set that is small but not of guarateed smallest cardinality");
"set that is small but not of guaranteed smallest cardinality");
fi;
end);

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5 changes: 5 additions & 0 deletions tst/testinstall/grpperm.tst
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Expand Up @@ -72,4 +72,9 @@ gap> Length(MaximalSubgroupClassReps(g));
gap> g:=PSL(8,2);;
gap> Length(MaximalSubgroupClassReps(g));
10
gap> G := SymmetricGroup(6);;
gap> IsSolvable(G);
false
gap> Length(MinimalGeneratingSet(G));
2
gap> STOP_TEST( "grpperm.tst", 1);