Support conversion to/from ITensors.jl and ITensorNetworks.jl (#200)

* Init extension

* Support conversion from `ITensor` to `Tensor`

* Support conversion from `Vector{ITensor}` to `TensorNetwork`

* Fix call to `id`

* Support conversion from `ITensorNetwork` to `Quantum`, `TensorNetwork`

* Lower compat bound of KrylovKit to v0.7

Required by ITensorNetworks

* Support conversion from `Tensor`, `TensorNetwork` to `ITensor`, `Vector{ITensor}`

* Rename `Tensor`, `TensorNetwork`, `Quantum` methods to `Base.convert` methods

* Support conversion from `AbstractTensorNetwork` to `ITensorNetwork`

* Fix some typos and problems

* Implement `sites` method for recovering site from `Symbol`

* Support conversion from `AbstractQuantum` to `ITensorNetwork`

* Comment future idea

* Test `ITensors`, `ITensorNetworks` integration

* Fix `Vector{ITensor}` to `TensorNetwork` conversion

* Fix tests

* Defer ITensorNetworks instantiation to test time

* Add Pkg package to test dependencies

Project.toml

@@ -26,6 +26,8 @@ Dagger = "d58978e5-989f-55fb-8d15-ea34adc7bf54"
 FiniteDifferences = "26cc04aa-876d-5657-8c51-4c34ba976000"
 GraphMakie = "1ecd5474-83a3-4783-bb4f-06765db800d2"
 Graphs = "86223c79-3864-5bf0-83f7-82e725a168b6"
+ITensorNetworks = "2919e153-833c-4bdc-8836-1ea460a35fc7"
+ITensors = "9136182c-28ba-11e9-034c-db9fb085ebd5"
 KrylovKit = "0b1a1467-8014-51b9-945f-bf0ae24f4b77"
 Makie = "ee78f7c6-11fb-53f2-987a-cfe4a2b5a57a"
 PythonCall = "6099a3de-0909-46bc-b1f4-468b9a2dfc0d"
@@ -41,6 +43,8 @@ TenetChainRulesTestUtilsExt = ["ChainRulesCore", "ChainRulesTestUtils"]
 TenetDaggerExt = "Dagger"
 TenetFiniteDifferencesExt = "FiniteDifferences"
 TenetGraphMakieExt = ["GraphMakie", "Makie"]
+TenetITensorNetworksExt = "ITensorNetworks"
+TenetITensorsExt = "ITensors"
 TenetKrylovKitExt = ["KrylovKit"]
 TenetPythonCallExt = "PythonCall"
 TenetQuacExt = "Quac"
@@ -60,8 +64,10 @@ EinExprs = "0.5, 0.6"
 FiniteDifferences = "0.12"
 GraphMakie = "0.4,0.5"
 Graphs = "1.7"
+ITensorNetworks = "0.11"
+ITensors = "0.6"
 KeywordDispatch = "0.3"
-KrylovKit = "0.8.1"
+KrylovKit = "0.7, 0.8"
 LinearAlgebra = "1.9"
 Makie = "0.18,0.19,0.20, 0.21"
 OMEinsum = "0.7, 0.8"

ext/TenetITensorNetworksExt.jl

@@ -0,0 +1,42 @@
+module TenetITensorNetworksExt
+
+using Tenet
+using ITensorNetworks: ITensorNetworks, ITensorNetwork, ITensor, Index, siteinds, plev, vertices, rename_vertices
+const ITensors = ITensorNetworks.ITensors
+const DataGraphs = ITensorNetworks.DataGraphs
+const TenetITensorsExt = Base.get_extension(Tenet, :TenetITensorsExt)
+
+Base.convert(::Type{TensorNetwork}, tn::ITensorNetwork) = TensorNetwork([convert(Tensor, tn[v]) for v in vertices(tn)])
+
+function Base.convert(::Type{ITensorNetwork}, tn::Tenet.AbstractTensorNetwork; inds=Dict{Symbol,Index}())
+    return ITensorNetwork(convert(Vector{ITensor}, tn; inds))
+end
+
+function Base.convert(::Type{Quantum}, tn::ITensorNetwork)
+    sitedict = Dict(
+        map(pairs(DataGraphs.vertex_data(siteinds(tn)))) do (loc, index)
+            index = only(index)
+            primelevel = plev(index)
+            @assert primelevel ∈ (0, 1)
+
+            # NOTE ITensors' Index's tag only has space for 16 characters
+            tag = ITensors.id(index)
+            Site(loc; dual=Bool(primelevel)) => TenetITensorsExt.symbolize(index)
+        end,
+    )
+    return Quantum(convert(TensorNetwork, tn), sitedict)
+end
+
+function Base.convert(::Type{ITensorNetwork}, tn::Tenet.AbstractQuantum)
+    itn = @invoke convert(ITensorNetwork, tn::Tenet.AbstractTensorNetwork)
+
+    return rename_vertices(itn) do v
+        itensor = itn[v]
+        indices = map(x -> Symbol(replace(x, "\"" => "")), string.(ITensors.tags.(ITensors.inds(itensor))))
+        tensor = only(tensors(tn; contains=indices))
+        physical_index = only(inds(tn; set=:physical) ∩ inds(tensor))
+        return sites(tn; at=physical_index).id
+    end
+end
+
+end

ext/TenetITensorsExt.jl

@@ -0,0 +1,47 @@
+module TenetITensorsExt
+
+using Tenet
+using ITensors: ITensors, ITensor, Index
+
+function symbolize(index::Index)
+    tag = string(ITensors.id(index))
+
+    # NOTE ITensors' Index's tag only has space for 16 characters
+    return Symbol(length(tag) > 16 ? tag[(end - 16 + 1):end] : tag)
+end
+
+function tagize(index::Symbol)
+    tag = string(index)
+
+    # NOTE ITensors' Index's tag only has space for 16 characters
+    return length(tag) > 16 ? tag[(end - 16 + 1):end] : tag
+end
+
+# TODO customize index names
+function Base.convert(::Type{Tensor}, tensor::ITensor)
+    array = ITensors.array(tensor)
+    is = map(symbolize, ITensors.inds(tensor))
+    return Tensor(array, is)
+end
+
+function Base.convert(::Type{ITensor}, tensor::Tensor; inds=Dict{Symbol,Index}())
+    indices = map(Tenet.inds(tensor)) do i
+        haskey(inds, i) ? inds[i] : Index(size(tensor, i), tagize(i))
+    end
+    return ITensor(parent(tensor), indices)
+end
+
+Base.convert(::Type{TensorNetwork}, tn::Vector{ITensor}) = TensorNetwork(map(t -> convert(Tensor, t), tn))
+
+function Base.convert(::Type{Vector{ITensor}}, tn::Tenet.AbstractTensorNetwork; inds=Dict{Symbol,Index}())
+    indices = merge(inds, Dict(
+        map(Iterators.filter(!Base.Fix1(haskey, inds), Tenet.inds(tn))) do i
+            i => Index(size(tn, i), tagize(i))
+        end,
+    ))
+    return map(tensors(tn)) do tensor
+        ITensor(parent(tensor), map(i -> indices[i], Tenet.inds(tensor)))
+    end
+end
+
+end

src/Quantum.jl

@@ -242,6 +242,11 @@ end
     end
 end
 
+@kwmethod function sites(tn::AbstractQuantum; at::Symbol)
+    tn = Quantum(tn)
+    return findfirst(==(at), tn.sites)
+end
+
 @deprecate Base.getindex(q::Quantum, site::Site) inds(q; at=site) false
 
 function Base.replace!(tn::Quantum, old_new::Base.AbstractVecOrTuple{Pair{Symbol,Symbol}})

test/Project.toml

@@ -8,12 +8,14 @@ Dagger = "d58978e5-989f-55fb-8d15-ea34adc7bf54"
 DeltaArrays = "10b0fc19-5ccc-4427-889b-d75dd6306188"
 Distributed = "8ba89e20-285c-5b6f-9357-94700520ee1b"
 GraphMakie = "1ecd5474-83a3-4783-bb4f-06765db800d2"
+ITensors = "9136182c-28ba-11e9-034c-db9fb085ebd5"
 KrylovKit = "0b1a1467-8014-51b9-945f-bf0ae24f4b77"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 Makie = "ee78f7c6-11fb-53f2-987a-cfe4a2b5a57a"
 NetworkLayout = "46757867-2c16-5918-afeb-47bfcb05e46a"
 OMEinsum = "ebe7aa44-baf0-506c-a96f-8464559b3922"
 Permutations = "2ae35dd2-176d-5d53-8349-f30d82d94d4f"
+Pkg = "44cfe95a-1eb2-52ea-b672-e2afdf69b78f"
 Quac = "b9105292-1415-45cf-bff1-d6ccf71e6143"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"

test/integration/ITensorNetworks_test.jl

@@ -0,0 +1,29 @@
+# breaks in instantiation on Julia 1.9
+using Pkg
+Pkg.add("ITensorNetworks")
+
+@testset "ITensorNetworks" begin
+    using ITensors: ITensors, ITensor, Index, array
+    using ITensorNetworks: ITensorNetwork, vertices
+
+    i = Index(2, "i")
+    j = Index(3, "j")
+    k = Index(4, "k")
+    l = Index(5, "l")
+    m = Index(6, "m")
+
+    a = ITensor(rand(2, 3), i, j)
+    b = ITensor(rand(3, 4, 5), j, k, l)
+    c = ITensor(rand(5, 6), l, m)
+    itn = ITensorNetwork([a, b, c])
+
+    tn = convert(TensorNetwork, itn)
+    @test tn isa TensorNetwork
+    @test issetequal(arrays(tn), array.([a, b, c]))
+
+    itn = convert(ITensorNetwork, tn)
+    @test itn isa ITensorNetwork
+    @test issetequal(map(v -> array(itn[v]), vertices(itn)), array.([a, b, c]))
+
+    # TODO test Quantum
+end

test/integration/ITensors_test.jl

@@ -0,0 +1,32 @@
+@testset "ITensors" begin
+    using ITensors: ITensors, ITensor, Index, array
+
+    i = Index(2, "i")
+    j = Index(3, "j")
+    k = Index(4, "k")
+
+    itensor = ITensor(rand(2, 3, 4), i, j, k)
+
+    tensor = convert(Tensor, itensor)
+    @test tensor isa Tensor
+    @test size(tensor) == (2, 3, 4)
+    @test parent(tensor) == array(itensor)
+
+    tensor = Tensor(rand(2, 3, 4), (:i, :j, :k))
+    itensor = convert(ITensor, tensor)
+    @test itensor isa ITensor
+    @test size(itensor) == (2, 3, 4)
+    @test array(itensor) == parent(tensor)
+    @test all(
+        splat(==),
+        zip(map(x -> replace(x, "\"" => ""), string.(ITensors.tags.(ITensors.inds(itensor)))), ["i", "j", "k"]),
+    )
+
+    tn = rand(TensorNetwork, 4, 3)
+    itensors = convert(Vector{ITensor}, tn)
+    @test itensors isa Vector{ITensor}
+
+    tnr = convert(TensorNetwork, itensors)
+    @test tnr isa TensorNetwork
+    @test issetequal(arrays(tn), arrays(tnr))
+end

test/runtests.jl

@@ -23,6 +23,8 @@ if VERSION >= v"1.10"
         include("integration/Makie_test.jl")
         include("integration/KrylovKit_test.jl")
         include("integration/Quac_test.jl")
+        include("integration/ITensors_test.jl")
+        include("integration/ITensorNetworks_test.jl")
     end
 end