Updates to FreeAssAlgIdeal

src/Rings/FreeAssAlgIdeal.jl

@@ -17,18 +17,24 @@ Two-sided ideal of a free associative algebra with elements of type `T`.
 mutable struct FreeAssAlgIdeal{T} <: Ideal{T}
   gens::IdealGens{T}
   gb::IdealGens{T}
-
-  function FreeAssAlgIdeal(R::FreeAssAlgebra, g::Vector{T}) where T <: FreeAssAlgElem
+  deg_bound::Int
+  function FreeAssAlgIdeal(g::IdealGens{T}, check_groebner_basis::Bool=false) where T <: FreeAssAlgElem
     r = new{T}()
-    r.gens = IdealGens(R, g)
+    r.gens = g
+    @req !check_groebner_basis || base_ring(base_ring(g)) isa Field "Groebner basis check requires a field base ring"
+    if check_groebner_basis && base_ring(base_ring(g)) isa Field && is_groebner_basis(g)
+      r.gb = g
+      r.deg_bound = -1
+    end
     return r
   end
 end
 
-function AbstractAlgebra.expressify(a::FreeAssAlgIdeal; context = nothing)
-  return Expr(:call, :ideal, [expressify(g, context = context) for g in collect(a.gens)]...)
+Base.show(io::IO, a::FreeAssAlgIdeal) = print(io, "Ideal of ", base_ring(a), " with ", number_of_generators(a), " generators")
+
+function Base.:(==)(I2::FreeAssAlgIdeal, I1::FreeAssAlgIdeal)
+  return is_subset(I1,I2) && is_subset(I2,I1)
 end
-@enable_all_show_via_expressify FreeAssAlgIdeal
 
 @doc raw"""
     ideal(R::FreeAssAlgebra, g::Vector{<:FreeAssAlgElem})
@@ -37,16 +43,20 @@ Return the two-sided ideal of $R$ generated by $g$.
 """
 function ideal(R::FreeAssAlgebra, g::Vector{<:FreeAssAlgElem})
   @assert all(x -> parent(x) == R, g) "parent mismatch"
-  return FreeAssAlgIdeal(R, g)
+  return FreeAssAlgIdeal(IdealGens(R, g))
 end
 
 function ideal(g::Vector{<:FreeAssAlgElem})
   @assert length(g) > 0 "cannot infer base ring"
   algebra = parent(g[1]) 
   return ideal(algebra, g)
+end
 
+function ideal(g::IdealGens{T}, check_groebner_basis::Bool=false) where T <: FreeAssAlgElem
+  return FreeAssAlgIdeal(g, check_groebner_basis)
 end
 
+
 function base_ring(I::FreeAssAlgIdeal{T}) where T
   return I.gens.Ox::parent_type(T)
 end
@@ -79,6 +89,9 @@ function Base.:*(a::FreeAssAlgIdeal{T}, b::FreeAssAlgIdeal{T}) where T
   return ideal(R, [i*j for i in gens(a) for j in gens(b)])
 end
 
+AbstractAlgebra.normal_form(f::FreeAssAlgElem, I::FreeAssAlgIdeal) = normal_form(f, gens(I))
+AbstractAlgebra.normal_form(f::FreeAssAlgElem, I::IdealGens{<:FreeAssAlgElem}) = normal_form(f, collect(I))
+
 @doc raw"""
     ideal_membership(a::FreeAssAlgElem, I::FreeAssAlgIdeal, deg_bound::Int)
 
@@ -98,24 +111,26 @@ true
 ```
 """
 function ideal_membership(a::FreeAssAlgElem, I::FreeAssAlgIdeal, deg_bound::Int=-1)
-  return ideal_membership(a, IdealGens(gens(I)), deg_bound)
+  isdefined(I, :gb) && (I.deg_bound == -1 || I.deg_bound >= deg_bound) && return iszero(normal_form(a, I.gb))
+  groebner_basis(I, deg_bound)
+  return ideal_membership(a, I, deg_bound)
 end
 function ideal_membership(a::FreeAssAlgElem, I::IdealGens{<:FreeAssAlgElem}, deg_bound::Int=-1)
   return ideal_membership(a, collect(I), deg_bound)
 end
 function ideal_membership(a::FreeAssAlgElem, I::Vector{<:FreeAssAlgElem}, deg_bound::Int=-1)
   R = parent(a)
   @assert all(x -> parent(x) == R, I) "parent mismatch"
-  gb = groebner_basis(I, deg_bound; protocol=false)
-  deg_bound = max(maximum(total_degree.(gb)),total_degree(a))
-  lpring, _ = _to_lpring(R, deg_bound)
+  gb = groebner_basis(I, deg_bound)
+  return iszero(normal_form(a, gb))
+end
 
-  lp_I = Singular.Ideal(lpring, lpring.(gb))
-  return iszero(reduce(lpring(a), lp_I))
+function Base.in(a::FreeAssAlgElem, I::FreeAssAlgIdeal)
+  return ideal_membership(a, I)
 end
 
-function Base.in(a::FreeAssAlgElem, I::FreeAssAlgIdeal, deg_bound::Int)
-  return ideal_membership(a, I, deg_bound)
+function is_subset(I1::FreeAssAlgIdeal, I2::FreeAssAlgIdeal)
+  return all(x -> in(x, I2), gens(I1))
 end
 
 function (R::Singular.LPRing)(a::FreeAssAlgElem)
@@ -134,7 +149,7 @@ function (A::FreeAssAlgebra)(a::Singular.slpalg)
   return finish(B)
 end
 
-_to_lpring(a::FreeAssAlgebra, deg_bound::Int) = Singular.FreeAlgebra(base_ring(a), String.(symbols(a)), deg_bound)
+_to_lpring(a::FreeAssAlgebra, deg_bound::Int; ordering::Symbol=:deglex) = Singular.FreeAlgebra(base_ring(a), String.(symbols(a)), deg_bound; ordering=ordering)
 
 @doc raw"""
     groebner_basis(I::FreeAssAlgIdeal, deg_bound::Int=-1; protocol::Bool=false)
@@ -161,25 +176,41 @@ Ideal generating system with elements
   4 -> y^2*x + y*z*y
 ```
 """
-function groebner_basis(I::FreeAssAlgIdeal, deg_bound::Int=-1; protocol::Bool=false)
-  isdefined(I, :gb) && return I.gb
-  I.gb = groebner_basis(IdealGens(gens(I)), deg_bound, protocol=protocol)
+function groebner_basis(I::FreeAssAlgIdeal,
+  deg_bound::Int=-1;
+  protocol::Bool=false,
+  interreduce::Bool=false)
+  isdefined(I, :gb) && (I.deg_bound == -1 || I.deg_bound >= deg_bound) && return I.gb
+  I.gb = groebner_basis(IdealGens(gens(I)), deg_bound; ordering=:deglex, protocol=protocol, interreduce=interreduce)
+  I.deg_bound = deg_bound
   return I.gb
 end
-function groebner_basis(g::IdealGens{<:FreeAssAlgElem}, deg_bound::Int=-1; protocol::Bool=false)
-  gb = groebner_basis(collect(g), deg_bound, protocol=protocol)
+function groebner_basis(g::IdealGens{<:FreeAssAlgElem},
+  deg_bound::Int=-1;
+  ordering::Symbol=:deglex,
+  protocol::Bool=false,
+  interreduce::Bool=false)
+  gb = groebner_basis(collect(g), deg_bound; ordering=ordering, protocol=protocol, interreduce=interreduce)
   return IdealGens(gb)
 end
-function groebner_basis(g::Vector{<:FreeAssAlgElem}, deg_bound::Int=-1; protocol::Bool=false)
+function groebner_basis(g::Vector{<:FreeAssAlgElem},
+  deg_bound::Int=-1;
+  ordering::Symbol=:deglex,
+  protocol::Bool=false,
+  interreduce::Bool=false)
+
   R = parent(g[1])
   @assert all(x -> parent(x) == R, g) "parent mismatch"
   @assert deg_bound >= 0 || !protocol "computing with a protocol requires a degree bound"
+  @assert ordering == :deglex || deg_bound > 0 "only :deglex ordering is supported for no degree bound"
 
   if deg_bound == -1
-      return AbstractAlgebra.groebner_basis(g)
+      gb = AbstractAlgebra.groebner_basis(g)
+      interreduce && return interreduce!(gb)
+      return gb
   end
 
-  lpring, _ = _to_lpring(R, deg_bound)
+  lpring, _ = _to_lpring(R, deg_bound; ordering=ordering)
   lp_I_gens = lpring.(g)
 
   I = Singular.Ideal(lpring, lp_I_gens)
@@ -188,5 +219,27 @@ function groebner_basis(g::Vector{<:FreeAssAlgElem}, deg_bound::Int=-1; protocol
   Singular.with_prot(protocol) do; 
     gb = gens(Singular.std(I))
   end
-  return R.(gb)
+  gb = R.(gb)
+  interreduce && return interreduce!(gb)
+  return gb
+end
+
+is_groebner_basis(g::IdealGens{<:FreeAssAlgElem}) = is_groebner_basis(collect(g))
+
+function is_groebner_basis(gb::Vector{<:FreeAssAlgElem})
+  obsructions =  AbstractAlgebra.Generic.get_obstructions(gb)
+  while !isempty(obsructions)
+    f = AbstractAlgebra.Generic.s_polynomial(popfirst!(obsructions)[1])
+    iszero(normal_form(f, gb)) || return false  
+  end
+  return true
+end
+
+
+function interreduce!(I::FreeAssAlgIdeal)
+  I.gb = interreduce!(I.gb)
+  return I
+end
+function interreduce!(gb::IdealGens{<:FreeAssAlgElem})
+  return IdealGens(interreduce!(collect(gb)))
 end

src/exports.jl

@@ -703,6 +703,7 @@ export inradical
 export integral_basis
 export integrate
 export interior_lattice_points
+export interreduce!
 export intersect
 export intersection_form
 export intersection_multiplicity

src/imports.jl

@@ -75,6 +75,7 @@ import AbstractAlgebra:
   gen,
   Generic,
   Generic.finish,
+  Generic.interreduce!,
   Generic.MPolyBuildCtx,
   Generic.MPolyCoeffs,
   Generic.MPolyExponentVectors,

test/Rings/FreeAssAlgIdeal.jl

@@ -17,23 +17,26 @@ end
 @testset "FreeAssAlgIdeal.membership" begin
   R, (x, y, z) = free_associative_algebra(QQ, ["x", "y", "z"])
   I = ideal(R, [x*y - y*x, x*z - z*x])
-  @test !in(x, I, 5)
-  @test !in(x, I, 10)
-  @test in(x*y*z - y*z*x, I, 9) # 9 should be enough
+  @test !ideal_membership(x, I, 5)
+  @test !ideal_membership(x, I, 10)
+  @test ideal_membership(x*y*z - y*z*x, I, 9) # 9 should be enough
 
   f1 = x*y + y*z
   I2 = ideal([f1])
   @test !ideal_membership(x*y, I2, 3)
   @test ideal_membership(f1, I2, 4) 
+  @test ideal_membership(f1, I2.gens, 4)
   @test ideal_membership(f1, I2) 
-  @test !isdefined(I2, :gb)
-  gb = groebner_basis(I2, 3; protocol=true)
+  @test ideal_membership(f1, I2.gens)
+  gb = groebner_basis(I2, 3; protocol=false)
   @test isdefined(I2, :gb)
+  @test length(gens(I * I2)) == 2
 end
 
 @testset "FreeAssAlgIdeal.utils" begin
   R, (x, y, z) = free_associative_algebra(QQ, ["x", "y", "z"])
-  I = Oscar.ideal(R, [x*y - y*x, x*z - z*x])
+  I = ideal(R, [x*y - y*x, x*z - z*x])
+  @test base_ring(I) == R
   @test isa(ngens(I),Int)
   @test isequal(ngens(I),2)
   @test isa(gen(I,ngens(I)),FreeAssAlgElem{QQFieldElem})
@@ -56,9 +59,58 @@ end
     f2 = x^2 + y^2
     I = ideal([f1, f2])
 
-    gb = groebner_basis(I, 3; protocol=true)
+    gb = groebner_basis(I, 3; protocol=false)
+    @test !is_groebner_basis(gb)
     @test maximum(total_degree.(gb))==3
     @test isdefined(I, :gb)
     gb2 = groebner_basis([f1, f2], 5; protocol=false)
     @test maximum(total_degree.(gb2))==5
+    @test !is_groebner_basis(gb2)
+end
+
+@testset "FreeAssAlgIdeal.groebner_basis.quantum_automorphism_group" begin
+  M = uniform_matroid(3,4)
+  qAut1 = gens(quantum_automorphism_group(M))
+  gb1 = groebner_basis(qAut1; interreduce=true)
+  gb2 = groebner_basis(qAut1, 4,ordering=:deglex,interreduce=true)
+  @test sort(leading_monomial.(gb2)) == sort(leading_monomial.(gb1))
+  @test is_groebner_basis(gb1)
+  @test is_groebner_basis(gb2)
+  I1 = ideal(gb1); I2 = ideal(gb2)
+  @test I1 == I2
+
+  qAut2 = quantum_symmetric_group(4)
+  gena = gens(qAut2)
+
+  gb3 = groebner_basis(gena; interreduce=false)
+  I1 = ideal(copy(gb3))
+  groebner_basis(I1)
+  @test length(gb3) == 146
+  interreduce!(gb3)
+  @test length(I1.gb) == 146
+  interreduce!(I1)
+  @test length(I1.gb) == 78
+  @test length(gb3) == 78
+
+
+  gb4 = groebner_basis(gena, 4,ordering=:deglex,interreduce=true)
+  @test is_groebner_basis(gb3)
+  @test is_groebner_basis(gb4)
+  @test sort(leading_monomial.(gb3)) == sort(leading_monomial.(gb4))
+
+  I1 = ideal(gb3); I2 = ideal(gb4)
+  @test gb4[end] in I1
+  @test normal_form(gb4[end],I1) == 0
+  @test I1 == I2
+
+  x = base_ring(I1)[1]; y = base_ring(I1)[7]
+  @test !(x*y - y*x in I1)
+
+  gb5 = groebner_basis(gens(quantum_symmetric_group(3)); interreduce=true)
+  A = parent(gb5[1])
+  I3 = ideal(Oscar.IdealGens(A, gb5),true)
+  @test is_groebner_basis(I3.gens)
+
+  x = base_ring(ideal(gb5))[1]; y = base_ring(ideal(gb5))[7]
+  @test x*y - y*x in ideal(gb5)
 end