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#############################################################################
##
## attributes/acting.gi
## Copyright (C) 2013-2022 James D. Mitchell
##
## Licensing information can be found in the README file of this package.
##
#############################################################################
##
# This file contains methods for finding various attributes of acting
# semigroups, sometimes there is no better method than that given in
# attr.gi.
# same method for ideals
InstallMethod(IsMultiplicativeZero,
"for an acting semigroup and element",
[IsActingSemigroup, IsMultiplicativeElement],
{S, x} -> MultiplicativeZero(S) <> fail and x = MultiplicativeZero(S));
# same method for ideals
InstallMethod(IsGreensDGreaterThanFunc, "for an acting semigroup",
[IsActingSemigroup],
function(S)
local D, data;
D := PartialOrderOfDClasses(S);
data := SemigroupData(S);
return
function(x, y)
local u, v;
if x = y then
return false;
fi;
x := ConvertToInternalElement(S, x);
y := ConvertToInternalElement(S, y);
u := OrbSCCLookup(data)[Position(data, x)] - 1;
v := OrbSCCLookup(data)[Position(data, y)] - 1;
return u <> v and IsReachable(D, u, v);
end;
end);
# same method for ideals
InstallMethod(StructureDescriptionSchutzenbergerGroups,
"for an acting semigroup", [IsActingSemigroup],
function(S)
local o, scc, out, m;
o := LambdaOrb(S);
Enumerate(o, infinity);
scc := OrbSCC(o);
out := [];
for m in [2 .. Length(scc)] do
AddSet(out, StructureDescription(LambdaOrbSchutzGp(o, m)));
od;
return out;
end);
# different method for ideals
InstallMethod(InversesOfSemigroupElementNC,
"for an acting semigroup and multiplicative element",
[IsActingSemigroup and HasGeneratorsOfSemigroup, IsMultiplicativeElement],
function(S, x)
local regular, lambda, rank, rhorank, tester, j, o, rhos, opts, gens, grades,
rho_x, lambdarank, creator, inv, out, k, y, i, name, rho;
regular := IsRegularSemigroup(S);
if not (regular or IsRegularSemigroupElementNC(S, x)) then
return [];
fi;
x := ConvertToInternalElement(S, x);
lambda := LambdaFunc(S)(x);
rank := LambdaRank(S)(LambdaFunc(S)(x));
rhorank := RhoRank(S);
tester := IdempotentTester(S);
j := 0;
# can't use GradedRhoOrb here since there may be inverses not D-related to f
if HasRhoOrb(S) and IsClosedOrbit(RhoOrb(S)) then
o := RhoOrb(S);
rhos := EmptyPlist(Length(o));
for i in [2 .. Length(o)] do
if rhorank(o[i]) = rank and tester(lambda, o[i]) then
j := j + 1;
rhos[j] := o[i];
fi;
od;
else
opts := rec(treehashsize := SEMIGROUPS.OptionsRec(S).hashlen,
gradingfunc := {o, x} -> rhorank(x),
onlygrades := {x, y} -> x >= rank,
onlygradesdata := fail);
for name in RecNames(LambdaOrbOpts(S)) do
opts.(name) := LambdaOrbOpts(S).(name);
od;
gens := List(GeneratorsOfSemigroup(S),
x -> ConvertToInternalElement(S, x));
o := Enumerate(Orb(gens, RhoOrbSeed(S), RhoAct(S), opts));
grades := Grades(o);
rhos := EmptyPlist(Length(o));
for i in [2 .. Length(o)] do
if grades[i] = rank and tester(lambda, o[i]) then
j := j + 1;
rhos[j] := o[i];
fi;
od;
fi;
ShrinkAllocationPlist(rhos);
rho_x := RhoFunc(S)(x);
lambdarank := LambdaRank(S);
creator := IdempotentCreator(S);
inv := LambdaInverse(S);
out := [];
k := 0;
# Notes: it seems that LambdaOrb(S) is always closed at this point
o := LambdaOrb(S);
Enumerate(o); # just in case
for i in [2 .. Length(o)] do
if lambdarank(o[i]) = rank and tester(o[i], rho_x) then
for rho in rhos do
y := creator(lambda, rho) * inv(o[i], x);
if regular or y in S then
k := k + 1;
out[k] := ConvertToExternalElement(S, y);
fi;
od;
fi;
od;
return out;
end);
# same method for ideals
InstallMethod(MultiplicativeNeutralElement, "for an acting semigroup",
[IsActingSemigroup],
function(S)
local gens, rank, lambda, max, rep, r, e, lo, ro, lact, ract, ie;
gens := Generators(S);
rank := LambdaRank(S);
lambda := LambdaFunc(S);
max := 0;
rep := gens[1];
for e in gens do
r := rank(lambda(e));
if r > max then
max := r;
rep := e;
fi;
od;
if max = ActionDegree(S)
and (IsMultiplicativeElementWithOneCollection(S)
or IsFFECollCollColl(S)) then
return One(S);
fi;
r := GreensRClassOfElementNC(S, rep);
if NrIdempotents(r) <> 1 or NrHClasses(r) <> 1 or
NrHClasses(GreensLClassOfElementNC(S, rep)) <> 1 then
Info(InfoSemigroups, 2, "the D-class of the first maximum rank generator ",
"is not a group");
return fail;
fi;
e := Idempotents(r)[1];
if HasGeneratorsOfSemigroup(S) then
if ForAll(GeneratorsOfSemigroup(S), x -> x * e = x and e * x = x) then
return e;
fi;
return fail;
fi;
lo := LambdaOrb(S);
ro := RhoOrb(S);
lact := LambdaAct(S);
ract := RhoAct(S);
ie := ConvertToInternalElement(S, e);
# S is an ideal without GeneratorsOfSemigroup
if ForAll(gens, x -> x * e = x and e * x = x)
and ForAll([2 .. Length(Enumerate(lo))], i -> lact(lo[i], ie) = lo[i])
and ForAll([2 .. Length(Enumerate(ro))], i -> ract(ro[i], ie) = ro[i])
then
return e;
fi;
return fail;
end);
InstallMethod(RepresentativeOfMinimalIdealNC,
"for an acting semigroup with generators",
[IsActingSemigroup and HasGeneratorsOfSemigroup],
function(S)
local rank, o, pos, min, len, m, result, i;
rank := LambdaRank(S);
o := LambdaOrb(S);
pos := LookForInOrb(o, {o, x} -> rank(x) = MinActionRank(S), 2);
if pos = false then
min := rank(o[2]);
pos := 2;
len := Length(o);
for i in [3 .. len] do
m := rank(o[i]);
if m < min then
pos := i;
min := m;
fi;
od;
fi;
result := EvaluateWord(o, TraceSchreierTreeForward(o, pos));
return ConvertToExternalElement(S, result);
end);
InstallMethod(RightIdentity,
"for an acting semigroup with generators + mult. elt.",
[IsActingSemigroup and HasGeneratorsOfSemigroup, IsMultiplicativeElement],
function(S, x)
local o, l, m, scc, f, p;
if not x in S then
ErrorNoReturn("the 2nd argument (a mult. elt.) does not belong to ",
"the 1st argument (a semigroup)");
elif IsMonoid(S) then
return One(S);
elif IsMonoidAsSemigroup(S) then
return MultiplicativeNeutralElement(S);
elif IsIdempotent(x) then
return x;
fi;
x := ConvertToInternalElement(S, x);
o := Enumerate(LambdaOrb(S));
l := Position(o, LambdaFunc(S)(x));
m := OrbSCCLookup(o)[l];
scc := OrbSCC(o)[m];
if l <> scc[1] then
f := LambdaOrbMult(o, m, l);
return ConvertToExternalElement(S, f[2] * f[1]);
else
p := Factorization(o, m, LambdaIdentity(S)(true));
if p = fail then
return fail;
else
return ConvertToExternalElement(S, EvaluateWord(o!.gens, p));
fi;
fi;
end);
InstallMethod(LeftIdentity,
"for an acting semigroup with generators + mult. elt.",
[IsActingSemigroup and HasGeneratorsOfSemigroup, IsMultiplicativeElement],
function(S, x)
local l, D, p, result;
if not x in S then
ErrorNoReturn("the 2nd argument (a mult. elt.) does not belong to ",
"the 1st argument (a semigroup)");
elif IsMonoid(S) then
return One(S);
elif IsMonoidAsSemigroup(S) then
return MultiplicativeNeutralElement(S);
elif IsIdempotent(x) then
return x;
fi;
x := ConvertToInternalElement(S, x);
l := Position(Enumerate(RhoOrb(S)), RhoFunc(S)(x));
D := Digraph(OrbitGraph(RhoOrb(S)));
p := DigraphPath(D, l, l);
if p = fail then
return fail;
fi;
result := EvaluateWord(RhoOrb(S)!.gens, Reversed(p[2]));
result := ConvertToExternalElement(S, result);
return result ^ SmallestIdempotentPower(result);
end);
[ Dauer der Verarbeitung: 0.27 Sekunden
(vorverarbeitet)
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