Fix regression when constructing an ITensorNetwork using a TreeTensorNetwork resulting in empty tensors.

Author: jack-dunham

src/treetensornetworks/abstracttreetensornetwork.jl

@@ -94,7 +94,7 @@ end
 
 # For ambiguity error
 function Base.truncate(tn::AbstractTTN, edge::AbstractEdge; kwargs...)
-    return typeof(tn)(truncate(itensornetwork(tn), edge; kwargs...))
+    return typeof(tn)(truncate(ITensorNetwork(tn), edge; kwargs...))
 end
 
 #
@@ -108,7 +108,7 @@ function NDTensors.contract(
     tn = copy(tn)
     # reverse post order vertices
     traversal_order = reverse(post_order_dfs_vertices(tn, root_vertex))
-    return contract(itensornetwork(tn); sequence = traversal_order, kwargs...)
+    return contract(ITensorNetwork(tn); sequence = traversal_order, kwargs...)
     # # forward post order edges
     # tn = copy(tn)
     # for e in post_order_dfs_edges(tn, root_vertex)

src/treetensornetworks/treetensornetwork.jl

@@ -83,14 +83,14 @@ end
 
 # Field access
 """
-    itensornetwork(tn::TreeTensorNetwork) -> ITensorNetwork
+    ITensorNetwork(tn::TreeTensorNetwork) -> ITensorNetwork
 
 Convert a `TreeTensorNetwork` to a plain `ITensorNetwork`, discarding orthogonality
 metadata. The returned network shares the same underlying tensor data.
 
 See also: [`TreeTensorNetwork`](@ref), [`ttn`](@ref).
 """
-itensornetwork(tn::TTN) = getfield(tn, :tensornetwork)
+ITensorNetwork(tn::TTN) = copy(tn.tensornetwork)
 
 """
     ortho_region(tn::TreeTensorNetwork) -> Indices
@@ -99,10 +99,10 @@ Return the set of vertices that currently form the orthogonality center of `tn`.
 
 See also: [`orthogonalize`](@ref).
 """
-ortho_region(tn::TTN) = getfield(tn, :ortho_region)
+ortho_region(tn::TTN) = tn.ortho_region
 
 # Required for `AbstractITensorNetwork` interface
-data_graph(tn::TTN) = data_graph(itensornetwork(tn))
+data_graph(tn::TTN) = data_graph(tn.tensornetwork)
 
 function data_graph_type(G::Type{<:TTN})
     return data_graph_type(fieldtype(G, :tensornetwork))

test/test_ttns.jl

@@ -1,6 +1,7 @@
 using DataGraphs: vertex_data
 using Graphs: vertices
-using ITensorNetworks: contract, ortho_region, siteinds, ttn
+using ITensorNetworks:
+    ITensorNetwork, TreeTensorNetwork, contract, ortho_region, orthogonalize, siteinds, ttn
 using ITensors: @disable_warn_order, random_itensor
 using LinearAlgebra: norm
 using NamedGraphs.NamedGraphGenerators: named_comb_tree
@@ -32,7 +33,30 @@ using Test: @test, @testset
         @test norm(S - S1) < 1.0e2 * cutoff
     end
 
+    @testset "Convert ITN <-> TTN" begin
+        g = named_comb_tree((3, 2))
+        sites = siteinds("S=1/2", g)
+
+        psi = ttn(sites)  # zero-initialised
+        psi = ttn(v -> "Up", sites)  # product state
+
+        itn = ITensorNetwork(psi)  # TTN → ITensorNetwork
+        new_psi = TreeTensorNetwork(itn)  # ITensorNetwork → TTN
+
+        @test !(new_psi === itn) # test we make a copy
+    end
+
     @testset "Ortho" begin
-        # TODO
+        g = named_comb_tree((3, 2))
+        sites = siteinds("S=1/2", g)
+
+        psi = ttn(sites)  # zero-initialised
+        psi = ttn(v -> "Up", sites)  # product state
+
+        v1 = collect(vertices(psi))[1]
+        v2 = collect(vertices(psi))[2]
+
+        @test collect(ortho_region(orthogonalize(psi, v1))) == [v1]
+        @test collect(ortho_region(orthogonalize(psi, [v1, v2]))) == [v1, v2]
     end
 end