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FIX: Sparse Action homomorphisms cannot use OrbitishFO
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but need to use their own creator function (as point seed is list of points and
thus need to apply `TestIdentityAction` differently.)

This fixes #3279
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hulpke committed Feb 12, 2019
1 parent baed10d commit ef066c0
Showing 1 changed file with 79 additions and 4 deletions.
83 changes: 79 additions & 4 deletions lib/oprt.gd
Original file line number Diff line number Diff line change
Expand Up @@ -1075,10 +1075,85 @@ DeclareGlobalFunction("MultiActionsHomomorphism");
## </ManSection>
## <#/GAPDoc>
##
OrbitishFO( "SparseActionHomomorphism", OrbitishReq,
IsIdenticalObj, false,false );
OrbitishFO( "SortedSparseActionHomomorphism", OrbitishReq,
IsIdenticalObj, false,false );

BindGlobal( "SparseActHomFO", function( name, reqs, famrel )
local str, orbish, func;

# Create the operation.
str:= SHALLOW_COPY_OBJ( name );

APPEND_LIST_INTR( str, "Op" );
orbish := NewOperation( str, reqs );
BIND_GLOBAL( str, orbish );

# Create the wrapper function.
func := function( arg )
local G, D, pnt, gens, acts, act, xset, p, attrG, result,le;

# Get the arguments.
if 2 <= Length( arg ) then
le:=Length(arg);
G := arg[ 1 ];
if IsFunction( arg[ le ] ) then
act := arg[ le ];
le:=le-1;
else
act := OnPoints;
fi;
if Length( arg ) > 2
and famrel( FamilyObj( arg[ 2 ] ), FamilyObj( arg[ 3 ] ) )
then
D := arg[ 2 ];
if IsDomain( D ) then
if IsFinite( D ) then D:= AsSSortedList( D ); else D:= Enumerator( D ); fi;
fi;
p := 3;
else
p := 2;
fi;
pnt := Immutable(arg[ p ]);
if Length( arg ) > p + 1 then
gens := arg[ p + 1 ];
acts := arg[ p + 2 ];
fi;
else
Error( "usage: ", name, "(<xset>,<pnt>)\n",
"or ", name, "(<G>[,<Omega>],<pnt>[,<gens>,<acts>][,<act>])" );
fi;

G := PreOrbishProcessing(G);

if not IsBound( gens ) then
if (not IsPermGroup(G)) and CanEasilyComputePcgs( G ) then
gens := Pcgs( G );
else
gens := GeneratorsOfGroup( G );
fi;
acts := gens;
fi;

for p in pnt do
TestIdentityAction(acts,p,act);
od;

if IsBound( D ) then
result := orbish( G, D, pnt, gens, acts, act );
else

# The following line is also executed when `Blocks(<G>, <Omega>, <act>)'
# is called to compute blocks with no seed, but then <pnt> is really
# <Omega>, i.e., the operation domain!
result := orbish( G, pnt, gens, acts, act );

fi;

return result;
end;
BIND_GLOBAL( name, func );
end );

SparseActHomFO( "SparseActionHomomorphism", OrbitishReq, IsIdenticalObj );
SparseActHomFO( "SortedSparseActionHomomorphism", OrbitishReq, IsIdenticalObj );

#############################################################################
##
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