feat: add copy keyword to basis of fractional ideals (#1579)

- Closes #1578
thofma · Aug 17, 2024 · ffa4484 · ffa4484
1 parent 1a438c4
commit ffa4484
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Showing 3 changed files with 11 additions and 2 deletions.
diff --git a/src/HeckeTypes.jl b/src/HeckeTypes.jl
@@ -1101,6 +1101,7 @@ mutable struct AbsNumFieldOrderFractionalIdeal{S, T} <: NumFieldOrderFractionalI
   norm::QQFieldElem
   basis_matrix::FakeFmpqMat
   basis_mat_inv::FakeFmpqMat
+  basis::Vector{T}
 
   function AbsNumFieldOrderFractionalIdeal{S, T}(O::AbsNumFieldOrder{S, T}) where {S, T}
     z = new{S, T}()

diff --git a/src/NumFieldOrd/NfOrd/FracIdeal.jl b/src/NumFieldOrd/NfOrd/FracIdeal.jl
@@ -248,7 +248,11 @@ end
 
 Returns the $\mathbf Z$-basis of $I$.
 """
-function basis(a::AbsNumFieldOrderFractionalIdeal{S, T}) where {S, T}
+function basis(a::AbsNumFieldOrderFractionalIdeal{S, T}; copy::Bool = true) where {S, T}
+  if isdefined(a, :basis)
+    copy && return Base.copy(a.basis)
+    return a.basis
+  end
   B = basis_matrix(FakeFmpqMat, a; copy = false)
   d = degree(order(a))
   O = order(a)
@@ -263,7 +267,7 @@ function basis(a::AbsNumFieldOrderFractionalIdeal{S, T}) where {S, T}
     z = divexact(z, B.den)
     res[i] = z
   end
-
+  a.basis = res
   return res
 end
 

diff --git a/test/NfOrd/FracIdl.jl b/test/NfOrd/FracIdl.jl
@@ -49,6 +49,10 @@ K3, (a3,) = number_field([x^3 - 2], "a2")
     @test b == [ K1(8), a1, 2*a1^2 ]
     b = @inferred basis(M)
     @test b == [ K1(8), a1, 2*a1^2 ]
+
+    b = basis(J)
+    @test b !== basis(J)
+    @test basis(J, copy = false) === basis(J, copy = false)
   end
 
   @testset "Norm" begin