Add Matrix/Vector conversion for named tensors

Project.toml

@@ -1,6 +1,6 @@
 name = "ITensorBase"
 uuid = "4795dd04-0d67-49bb-8f44-b89c448a1dc7"
-version = "0.13.3"
+version = "0.13.4"
 authors = ["ITensor developers <support@itensor.org> and contributors"]
 
 [workspace]

src/abstractnamedtensor.jl

@@ -271,17 +271,6 @@ end
 
 # Conversion
 
-# Copied from `Base` (defined in abstractarray.jl).
-@noinline function _checkaxs(axd, axs)
-    axd == axs || throw(DimensionMismatch("axes must agree, got $axd and $axs"))
-    return nothing
-end
-function copyto_axcheck!(dest, src)
-    _checkaxs(axes(dest), axes(src))
-    copyto!(dest, src)
-    return dest
-end
-
 # These are defined since the Base versions assume the eltype and ndims are known
 # at compile time, which isn't true for ITensors.
 # Workaround: `Array(::TensorKit.AbstractTensorMap)` is not defined yet (it should be), so a
@@ -295,12 +284,8 @@ function Base.Array(a::AbstractNamedTensor)
 end
 Base.Array{T}(a::AbstractNamedTensor) where {T} = Array{T}(unnamed(a))
 Base.Array{T, N}(a::AbstractNamedTensor) where {T, N} = Array{T, N}(unnamed(a))
-Base.AbstractArray{T}(a::AbstractNamedTensor) where {T} = AbstractArray{T, ndims(a)}(a)
-function Base.AbstractArray{T, N}(a::AbstractNamedTensor) where {T, N}
-    dest = similar(a, T)
-    copyto_axcheck!(unnamed(dest), unnamed(a))
-    return dest
-end
+# Catches the bare `Matrix`/`Vector` (`Array{T, N} where T`, ndims fixed), defaulting the eltype.
+Base.Array{<:Any, N}(a::AbstractNamedTensor) where {N} = Array{eltype(a), N}(a)
 
 # Read the parent's axes through TensorAlgebra's interface (not `Base.axes`) so a non-array
 # backend like a TensorMap, whose axes are its native spaces, is supported.

test/test_nameddims_basics.jl

@@ -89,6 +89,15 @@ end
         @test eltype(a′) ≡ elt
         @test a′ isa Matrix{elt}
         @test a′ == a
+        # `Matrix`/`Vector` densify when the rank matches the leg count.
+        m = Matrix(na)
+        @test m isa Matrix{elt}
+        @test m == a
+        @test_throws Exception Vector(na)                 # two legs, not a vector
+        v = nameddims(randn(elt, 4), ("i",))
+        @test Vector(v) isa Vector{elt}
+        @test Vector(v) == unnamed(v)
+        @test_throws Exception Matrix(v)                  # one leg, not a matrix
 
         if elt <: Real
             a = randn(elt, 3, 4)