Delta tensors (#6)

Project.toml

@@ -1,17 +1,19 @@
 name = "DiagonalArrays"
 uuid = "74fd4be6-21e2-4f6f-823a-4360d37c7a77"
 authors = ["ITensor developers <support@itensor.org> and contributors"]
-version = "0.2.2"
+version = "0.2.3"
 
 [deps]
 ArrayLayouts = "4c555306-a7a7-4459-81d9-ec55ddd5c99a"
 DerivableInterfaces = "6c5e35bf-e59e-4898-b73c-732dcc4ba65f"
+FillArrays = "1a297f60-69ca-5386-bcde-b61e274b549b"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 SparseArraysBase = "0d5efcca-f356-4864-8770-e1ed8d78f208"
 
 [compat]
 ArrayLayouts = "1.10.4"
 DerivableInterfaces = "0.3.7"
+FillArrays = "1.13.0"
 LinearAlgebra = "1.10.0"
 SparseArraysBase = "0.2.1"
 julia = "1.10"

src/DiagonalArrays.jl

@@ -12,5 +12,6 @@ include("diagonalarray/diagonalarray.jl")
 include("diagonalarray/diagonalmatrix.jl")
 include("diagonalarray/diagonalvector.jl")
 include("diagonalarray/arraylayouts.jl")
+include("diagonalarray/delta.jl")
 
 end

src/diagonalarray/delta.jl

@@ -0,0 +1,26 @@
+using FillArrays: Ones
+
+function delta(elt::Type, size::Tuple{Vararg{Int}})
+  return DiagonalArray(Ones{elt}(minimum(size)), size)
+end
+function δ(elt::Type, size::Tuple{Vararg{Int}})
+  return delta(elt, size)
+end
+function delta(elt::Type, size::Int...)
+  return delta(elt, size)
+end
+function δ(elt::Type, size::Int...)
+  return delta(elt, size...)
+end
+function delta(size::Tuple{Vararg{Int}})
+  return delta(Float64, size)
+end
+function δ(size::Tuple{Vararg{Int}})
+  return delta(size)
+end
+function delta(size::Int...)
+  return delta(size)
+end
+function δ(size::Int...)
+  return delta(size...)
+end

test/Project.toml

@@ -1,6 +1,7 @@
 [deps]
 Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
 DiagonalArrays = "74fd4be6-21e2-4f6f-823a-4360d37c7a77"
+FillArrays = "1a297f60-69ca-5386-bcde-b61e274b549b"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 SafeTestsets = "1bc83da4-3b8d-516f-aca4-4fe02f6d838f"
 SparseArraysBase = "0d5efcca-f356-4864-8770-e1ed8d78f208"

test/test_basics.jl

@@ -1,5 +1,7 @@
 using Test: @test, @testset, @test_broken, @inferred
-using DiagonalArrays: DiagonalArrays, DiagonalArray, DiagonalMatrix, diaglength, diagonal
+using DiagonalArrays:
+  DiagonalArrays, DiagonalArray, DiagonalMatrix, δ, delta, diaglength, diagonal, diagview
+using FillArrays: Fill, Ones
 using SparseArraysBase: SparseArrayDOK, storedlength
 using LinearAlgebra: Diagonal
 
@@ -52,5 +54,38 @@ using LinearAlgebra: Diagonal
       @test @inferred(diagonal(rand(2))) isa AbstractMatrix
       @test diagonal(zeros(Int, 2)) isa Diagonal
     end
+    @testset "delta" begin
+      for (a, elt′) in (
+        (delta(2, 3), Float64),
+        (δ(2, 3), Float64),
+        (delta((2, 3)), Float64),
+        (δ((2, 3)), Float64),
+        (delta(Bool, 2, 3), Bool),
+        (δ(Bool, 2, 3), Bool),
+        (delta(Bool, (2, 3)), Bool),
+        (δ(Bool, (2, 3)), Bool),
+      )
+        @test eltype(a) === elt′
+        @test diaglength(a) == 2
+        @test a isa DiagonalArray{elt′}
+        @test size(a) == (2, 3)
+        @test diaglength(a) == 2
+        @test storedlength(a) == 2
+        @test a == DiagonalArray(ones(2), (2, 3))
+        @test diagview(a) == ones(2)
+        @test diagview(a) isa Ones{elt′}
+
+        a′ = 2a
+        @test diagview(a′) == 2ones(2)
+        # TODO: Fix this. Mapping doesn't preserve
+        # the diagonal structure properly.
+        # https://github.com/ITensor/DiagonalArrays.jl/issues/7
+        @test_broken diagview(a′) isa Fill
+
+        b = randn(elt, (3, 4))
+        a_dest = a * b
+        @test a_dest ≈ Array(a) * Array(b)
+      end
+    end
   end
 end