Better definition of isapprox

Project.toml

@@ -1,7 +1,7 @@
 name = "KroneckerArrays"
 uuid = "05d0b138-81bc-4ff7-84be-08becefb1ccc"
 authors = ["ITensor developers <[email protected]> and contributors"]
-version = "0.2.8"
+version = "0.2.9"
 
 [deps]
 Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"

src/kroneckerarray.jl

@@ -357,11 +357,49 @@ function Base.:(==)(a::AbstractKroneckerArray, b::AbstractKroneckerArray)
     return arg1(a) == arg1(b) && arg2(a) == arg2(b)
 end
 
-# TODO: this definition doesn't fully retain the original meaning:
-# ‖a - b‖ < atol could be true even if the following check isn't
-function Base.isapprox(a::AbstractKroneckerArray, b::AbstractKroneckerArray; kwargs...)
-    return isapprox(arg1(a), arg1(b); kwargs...) && isapprox(arg2(a), arg2(b); kwargs...)
+# norm(a - b) = norm(a1 ⊗ a2 - b1 ⊗ b2)
+#             = norm((a1 - b1) ⊗ a2 + b1 ⊗ (a2 - b2) + (a1 - b1) ⊗ (a2 - b2))
+function dist_kronecker(a::AbstractKroneckerArray, b::AbstractKroneckerArray)
+    a1, a2 = arg1(a), arg2(a)
+    b1, b2 = arg1(b), arg2(b)
+    diff1 = a1 - b1
+    diff2 = a2 - b2
+    # x = (a1 - b1) ⊗ a2
+    # y = b1 ⊗ (a2 - b2)
+    # z = (a1 - b1) ⊗ (a2 - b2)
+    xx = norm(diff1)^2 * norm(a2)^2
+    yy = norm(b1)^2 * norm(diff2)^2
+    zz = norm(diff1)^2 * norm(diff2)^2
+    xy = real(dot(diff1, b1) * dot(a2, diff2))
+    xz = real(dot(diff1, diff1) * dot(a2, diff2))
+    yz = real(dot(b1, diff1) * dot(diff2, diff2))
+    return sqrt(abs(xx + yy + zz + 2 * (xy + xz + yz)))
+end
+
+using LinearAlgebra: dot, promote_leaf_eltypes
+function Base.isapprox(
+        a::AbstractKroneckerArray, b::AbstractKroneckerArray;
+        atol::Real = 0,
+        rtol::Real = Base.rtoldefault(promote_leaf_eltypes(a), promote_leaf_eltypes(b), atol),
+        norm::Function = norm
+    )
+    a1, a2 = arg1(a), arg2(a)
+    b1, b2 = arg1(b), arg2(b)
+    d = if a1 == b1
+        norm(a1) * norm(a2 - b2)
+    elseif a2 == b2
+        norm(a1 - b1) * norm(b2)
+    else
+        # This could be defined as `KroneckerArrays.dist_kronecker(a, b)`, but that might have
+        # numerical precision issues so for now we just error.
+        error(
+            "`isapprox` not implemented for KroneckerArrays where both arguments differ. " *
+                "In those cases, you can use `isapprox(collect(a), collect(b); kwargs...)`."
+        )
+    end
+    return iszero(rtol) ? d <= atol : d <= max(atol, rtol * max(norm(a), norm(b)))
 end
+
 function Base.iszero(a::AbstractKroneckerArray)
     return iszero(arg1(a)) || iszero(arg2(a))
 end

test/test_basics.jl

@@ -4,20 +4,9 @@ using DerivableInterfaces: zero!
 using DiagonalArrays: diagonal
 using GPUArraysCore: @allowscalar
 using JLArrays: JLArray
-using KroneckerArrays:
-    KroneckerArrays,
-    KroneckerArray,
-    KroneckerStyle,
-    CartesianProductUnitRange,
-    CartesianProductVector,
-    ⊗,
-    ×,
-    arg1,
-    arg2,
-    cartesianproduct,
-    cartesianrange,
-    kron_nd,
-    unproduct
+using KroneckerArrays: KroneckerArrays, KroneckerArray, KroneckerStyle,
+    CartesianProductUnitRange, CartesianProductVector, ⊗, ×, arg1, arg2, cartesianproduct,
+    cartesianrange, kron_nd, unproduct
 using LinearAlgebra: Diagonal, I, det, eigen, eigvals, lq, norm, pinv, qr, svd, svdvals, tr
 using StableRNGs: StableRNG
 using Test: @test, @test_broken, @test_throws, @testset
@@ -219,10 +208,11 @@ elts = (Float32, Float64, ComplexF32, ComplexF64)
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     b = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
-    c = a.arg1 ⊗ b.arg2
+    c = arg1(a) ⊗ arg2(b)
     U, S, V = svd(a)
     @test collect(U * diagonal(S) * V') ≈ collect(a)
-    @test svdvals(a) ≈ S
+    @test arg1(svdvals(a)) ≈ arg1(S)
+    @test arg2(svdvals(a)) ≈ arg2(S)
     @test sort(collect(S); rev = true) ≈ svdvals(collect(a))
     @test collect(U'U) ≈ I
     @test collect(V * V') ≈ I
@@ -246,4 +236,10 @@ elts = (Float32, Float64, ComplexF32, ComplexF64)
             @test_throws ArgumentError $f($a)
         end
     end
+
+    # KroneckerArrays.dist
+    rng = StableRNG(123)
+    a = randn(rng, 100, 100) ⊗ randn(rng, 100, 100)
+    b = (arg1(a) + 1.0e-1 * randn(rng, size(arg1(a)))) ⊗ (arg2(a) + 1.0e-1 * randn(rng, size(arg2(a))))
+    @test KroneckerArrays.dist_kronecker(a, b) ≈ norm(collect(a) - collect(b)) rtol = 1.0e-2
 end

test/test_matrixalgebrakit.jl

@@ -1,25 +1,8 @@
-using KroneckerArrays: ⊗, arguments
+using KroneckerArrays: ⊗, arg1, arg2
 using LinearAlgebra: Hermitian, I, diag, hermitianpart, norm
-using MatrixAlgebraKit:
-    eig_full,
-    eig_trunc,
-    eig_vals,
-    eigh_full,
-    eigh_trunc,
-    eigh_vals,
-    left_null,
-    left_orth,
-    left_polar,
-    lq_compact,
-    lq_full,
-    qr_compact,
-    qr_full,
-    right_null,
-    right_orth,
-    right_polar,
-    svd_compact,
-    svd_full,
-    svd_trunc,
+using MatrixAlgebraKit: eig_full, eig_trunc, eig_vals, eigh_full, eigh_trunc,
+    eigh_vals, left_null, left_orth, left_polar, lq_compact, lq_full, qr_compact,
+    qr_full, right_null, right_orth, right_polar, svd_compact, svd_full, svd_trunc,
     svd_vals
 using Test: @test, @test_throws, @testset
 using TestExtras: @constinferred
@@ -31,18 +14,26 @@ herm(a) = parent(hermitianpart(a))
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     d, v = eig_full(a)
-    @test a * v ≈ v * d
+    av = a * v
+    vd = v * d
+    @test arg1(av) ≈ arg1(vd)
+    @test arg2(av) ≈ arg2(vd)
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     @test_throws ArgumentError eig_trunc(a)
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     d = eig_vals(a)
-    @test d ≈ diag(eig_full(a)[1])
+    d′ = diag(eig_full(a)[1])
+    @test arg1(d) ≈ arg1(d′)
+    @test arg2(d) ≈ arg2(d′)
 
     a = herm(randn(elt, 2, 2)) ⊗ herm(randn(elt, 3, 3))
     d, v = eigh_full(a)
-    @test a * v ≈ v * d
+    av = a * v
+    vd = v * d
+    @test arg1(av) ≈ arg1(vd)
+    @test arg2(av) ≈ arg2(vd)
     @test eltype(d) === real(elt)
     @test eltype(v) === elt
 
@@ -56,22 +47,30 @@ herm(a) = parent(hermitianpart(a))
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     u, c = qr_compact(a)
-    @test u * c ≈ a
+    uc = u * c
+    @test arg1(uc) ≈ arg1(a)
+    @test arg2(uc) ≈ arg2(a)
     @test collect(u'u) ≈ I
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     u, c = qr_full(a)
-    @test u * c ≈ a
+    uc = u * c
+    @test arg1(uc) ≈ arg1(a)
+    @test arg2(uc) ≈ arg2(a)
     @test collect(u'u) ≈ I
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     c, u = lq_compact(a)
-    @test c * u ≈ a
+    cu = c * u
+    @test arg1(cu) ≈ arg1(a)
+    @test arg2(cu) ≈ arg2(a)
     @test collect(u * u') ≈ I
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     c, u = lq_full(a)
-    @test c * u ≈ a
+    cu = c * u
+    @test arg1(cu) ≈ arg1(a)
+    @test arg2(cu) ≈ arg2(a)
     @test collect(u * u') ≈ I
 
     a = randn(elt, 3, 2) ⊗ randn(elt, 4, 3)
@@ -84,27 +83,37 @@ herm(a) = parent(hermitianpart(a))
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     u, c = left_orth(a)
-    @test u * c ≈ a
+    uc = u * c
+    @test arg1(uc) ≈ arg1(a)
+    @test arg2(uc) ≈ arg2(a)
     @test collect(u'u) ≈ I
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     c, u = right_orth(a)
-    @test c * u ≈ a
+    cu = c * u
+    @test arg1(cu) ≈ arg1(a)
+    @test arg2(cu) ≈ arg2(a)
     @test collect(u * u') ≈ I
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     u, c = left_polar(a)
-    @test u * c ≈ a
+    uc = u * c
+    @test arg1(uc) ≈ arg1(a)
+    @test arg2(uc) ≈ arg2(a)
     @test collect(u'u) ≈ I
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     c, u = right_polar(a)
-    @test c * u ≈ a
+    cu = c * u
+    @test arg1(cu) ≈ arg1(a)
+    @test arg2(cu) ≈ arg2(a)
     @test collect(u * u') ≈ I
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     u, s, v = svd_compact(a)
-    @test u * s * v ≈ a
+    usv = u * s * v
+    @test arg1(usv) ≈ arg1(a)
+    @test arg2(usv) ≈ arg2(a)
     @test eltype(u) === elt
     @test eltype(s) === real(elt)
     @test eltype(v) === elt
@@ -113,7 +122,9 @@ herm(a) = parent(hermitianpart(a))
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     u, s, v = svd_full(a)
-    @test u * s * v ≈ a
+    usv = u * s * v
+    @test arg1(usv) ≈ arg1(a)
+    @test arg2(usv) ≈ arg2(a)
     @test eltype(u) === elt
     @test eltype(s) === real(elt)
     @test eltype(v) === elt
@@ -125,5 +136,7 @@ herm(a) = parent(hermitianpart(a))
 
     a = randn(elt, 2, 2) ⊗ randn(elt, 3, 3)
     s = svd_vals(a)
-    @test s ≈ diag(svd_compact(a)[2])
+    s′ = diag(svd_compact(a)[2])
+    @test arg1(s) ≈ arg1(s′)
+    @test arg2(s) ≈ arg2(s′)
 end