Change psylow_subgroup to sylow_subgroup (#1355)

thofma · Jan 26, 2024 · ea33652 · ea33652
1 parent bf8c367
commit ea33652
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Showing 10 changed files with 36 additions and 16 deletions.
diff --git a/docs/src/abelian/structural.md b/docs/src/abelian/structural.md
@@ -19,7 +19,7 @@ sub(s::Vector{GrpAbFinGenElem})
 sub(G::GrpAbFinGen, M::ZZMatrix)
 sub(G::GrpAbFinGen, n::ZZRingElem)
 sub(G::GrpAbFinGen, n::Integer)
-psylow_subgroup(G::GrpAbFinGen, p::Union{ZZRingElem, Integer})
+sylow_subgroup(G::GrpAbFinGen, p::Union{ZZRingElem, Integer})
 Hecke.has_quotient(G::GrpAbFinGen, invariant::Vector{Int})
 Hecke.has_complement(f::GrpAbFinGenMap)
 is_pure(U::GrpAbFinGen, G::GrpAbFinGen)

diff --git a/ext/GAPExt/maximal_abelian_subextension.jl b/ext/GAPExt/maximal_abelian_subextension.jl
@@ -101,7 +101,7 @@ function check_abelian_extension(C::Hecke.ClassField, res_act::Vector{GrpAbFinGe
   new_prime = false
   for (P, v) in fac
     # I check that the action of the P-Sylow has no fixed points.
-    PS, mPS = psylow_subgroup(G, P, false)
+    PS, mPS = sylow_subgroup(G, P, false)
     s, ms = snf(PS)
     act_sub = induce_action_on_subgroup(ms*mPS, res_act)
     if !is_fixed_point_free(act_sub)

diff --git a/src/Deprecations.jl b/src/Deprecations.jl
@@ -143,3 +143,7 @@ simplest_inside(x::arb) = simplest_rational_inside(x)
 # Deprecated during 0.18.*
 
 @deprecate abelian_fields abelian_extensions
+
+# Deprecated during 0.24.*
+
+@deprecate psylow_subgroup sylow_subgroup
diff --git a/src/Grp/GenGrp.jl b/src/Grp/GenGrp.jl
@@ -749,7 +749,7 @@ elements(G::GrpGen) = collect(G)
 
 elements(HtoG::GrpGenToGrpGenMor) = unique(HtoG.img)
 
-function psylow_subgroup(G::GrpGen, p::IntegerUnion)
+function sylow_subgroup(G::GrpGen, p::IntegerUnion)
   if !is_prime(p)
     error("$p not prime")
   end

diff --git a/src/GrpAb/GrpAbFinGen.jl b/src/GrpAb/GrpAbFinGen.jl
@@ -1525,12 +1525,28 @@ function _psylow_subgroup_gens(G::GrpAbFinGen, p::IntegerUnion)
 end
 
 @doc raw"""
-    psylow_subgroup(G::GrpAbFinGen, p::IntegerUnion) -> GrpAbFinGen, GrpAbFinGenMap
+    sylow_subgroup(G::GrpAbFinGen, p::IntegerUnion) -> GrpAbFinGen, GrpAbFinGenMap
 
-Return the $p$-Sylow subgroup of `G`.
+Return the Sylow $p-$subgroup of the finitely generated abelian group `G`, for a
+prime `p`. This is the subgroup of `p`-power order in `G` whose index in `G` is
+coprime to `p`.
+
+# Examples
+```jldoctest
+julia> A = abelian_group(ZZRingElem[2, 6, 30])
+GrpAb: Z/2 x Z/6 x Z/30
+
+julia> H, j = sylow_subgroup(A, 2);
+
+julia> H
+GrpAb: (Z/2)^3
+
+julia> divexact(order(A), order(H))
+45
+```
 """
-function psylow_subgroup(G::GrpAbFinGen, p::IntegerUnion,
-                         to_lattice::Bool = true)
+function sylow_subgroup(G::GrpAbFinGen, p::IntegerUnion,
+                        to_lattice::Bool = true)
   @req is_prime(p) "Number ($p) must be prime"
   S, mS = snf(G)
   z = _psylow_subgroup_gens(S, p)

diff --git a/src/GrpAb/SubgroupEnum.jl b/src/GrpAb/SubgroupEnum.jl
@@ -613,7 +613,7 @@ function _psubgroups(G::GrpAbFinGen, p::IntegerUnion; subtype = [-1],
                                                               order = -1,
                                                               index = -1,
                                                               fun = sub)
-  P, mP = psylow_subgroup(G, p, false)
+  P, mP = sylow_subgroup(G, p, false)
 
   if quotype != [-1]
     return ( fun(G, map(mP, z))

diff --git a/src/GrpAb/stable_sub.jl b/src/GrpAb/stable_sub.jl
@@ -888,7 +888,7 @@ function _stable_subgroup_snf(R::GrpAbFinGen, act::Vector{GrpAbFinGenMap}; quoty
   list = Base.Generator[]
   for p in keys(lf.fac)
     x1 = valuation(c, p)
-    G, mG = psylow_subgroup(R, p, false)
+    G, mG = sylow_subgroup(R, p, false)
     S, mS = snf(G)
     comp = mS*mG
 

diff --git a/src/exports.jl b/src/exports.jl
@@ -764,7 +764,6 @@ export pseudo_matrix
 export psi_lower
 export psi_upper
 export psubgroups
-export psylow_subgroup
 export push!
 export push_through_isogeny
 export qAdicConj
@@ -899,6 +898,7 @@ export supersingular_polynomial
 export support
 export swan_module
 export swap_rows!
+export sylow_subgroup
 export symbol
 export t2
 export tamagawa_number

diff --git a/test/Grp/GenGrp.jl b/test/Grp/GenGrp.jl
@@ -50,9 +50,9 @@
 
     @testset "psylow" begin
         G,AtoG,GtoA = Hecke.generic_group([1, -1, im, -im], *)
-        @test order(psylow_subgroup(G,2)[1]) == 4
-        @test order(psylow_subgroup(G,3)[1]) == 1
-        @test_throws ErrorException psylow_subgroup(G,10)
+        @test order(sylow_subgroup(G,2)[1]) == 4
+        @test order(sylow_subgroup(G,3)[1]) == 1
+        @test_throws ErrorException sylow_subgroup(G,10)
     end
 
     @testset "GrpGenToGrpAb" begin

diff --git a/test/GrpAb/GrpAbFinGen.jl b/test/GrpAb/GrpAbFinGen.jl
@@ -307,11 +307,11 @@
 
   @testset "p-Sylow subgroup" begin
     G = abelian_group([1, 3, 9, 5, 15, 20, 7])
-    P, mP = psylow_subgroup(G, 3)
+    P, mP = sylow_subgroup(G, 3)
     @test order(P) == 3^valuation(order(G), 3)
-    P, mP = psylow_subgroup(G, 5)
+    P, mP = sylow_subgroup(G, 5)
     @test order(P) == 5^valuation(order(G), 5)
-    P, mP = psylow_subgroup(G, 11)
+    P, mP = sylow_subgroup(G, 11)
     @test order(P) == 11^valuation(order(G), 11)
   end