Fix a small bug related to caching in approx_itensornetwork (#89)

src/approx_itensornetwork.jl

@@ -327,30 +327,31 @@ function _rem_vertex!(
   rem_vertex!(alg_graph.out_tree, root)
   # update es_to_pdm
   truncate_dfs_tree = dfs_tree(alg_graph.out_tree, alg_graph.root)
-  for es in keys(caches.es_to_pdm)
-    if dst(first(es)) == root
-      delete!(caches.es_to_pdm, es)
-    elseif dst(first(es)) == new_root
-      parent_edge = NamedEdge(parent_vertex(truncate_dfs_tree, new_root), new_root)
-      edge_to_remove = NamedEdge(root, new_root)
-      if intersect(es, [parent_edge]) == []
-        new_es = setdiff(es, [edge_to_remove])
-        caches.es_to_pdm[new_es] = _optcontract(
-          [caches.es_to_pdm[es], root_tensor];
-          contraction_sequence_alg,
-          contraction_sequence_kwargs,
-        )
+  for es in filter(es -> dst(first(es)) == root, keys(caches.es_to_pdm))
+    delete!(caches.es_to_pdm, es)
+  end
+  for es in filter(es -> dst(first(es)) == new_root, keys(caches.es_to_pdm))
+    parent_edge = NamedEdge(parent_vertex(truncate_dfs_tree, new_root), new_root)
+    edge_to_remove = NamedEdge(root, new_root)
+    if intersect(es, Set([parent_edge])) == Set()
+      new_es = setdiff(es, [edge_to_remove])
+      if new_es == Set()
+        new_es = Set([NamedEdge(nothing, new_root)])
       end
-      # Remove old caches since they won't be used anymore,
-      # and removing them saves later contraction costs.
-      delete!(caches.es_to_pdm, es)
+      @assert length(new_es) >= 1
+      caches.es_to_pdm[new_es] = _optcontract(
+        [caches.es_to_pdm[es], root_tensor];
+        contraction_sequence_alg,
+        contraction_sequence_kwargs,
+      )
     end
+    # Remove old caches since they won't be used anymore,
+    # and removing them saves later contraction costs.
+    delete!(caches.es_to_pdm, es)
   end
   # update e_to_dm
-  for edge in keys(caches.e_to_dm)
-    if dst(edge) in [root, new_root]
-      delete!(caches.e_to_dm, edge)
-    end
+  for edge in filter(e -> dst(e) in [root, new_root], keys(caches.e_to_dm))
+    delete!(caches.e_to_dm, edge)
   end
   return U
 end

test/test_binary_tree_partition.jl

@@ -1,10 +1,14 @@
 using ITensors, OMEinsumContractionOrders
+using Graphs, NamedGraphs
+using ITensors: contract
 using ITensorNetworks:
   _root,
   _mps_partition_inds_order,
   _mincut_partitions,
   _is_rooted_directed_binary_tree,
-  _contract_deltas_ignore_leaf_partitions
+  _contract_deltas_ignore_leaf_partitions,
+  _rem_vertex!,
+  _DensityMartrixAlgGraph
 
 @testset "test mincut functions on top of MPS" begin
   i = Index(2, "i")
@@ -83,17 +87,54 @@ end
     out2 = contract(network2...)
     @test isapprox(out1, out2)
     # test approx_itensornetwork (here we call `contract` to test the interface)
-    approx_tn, lognorm = contract(
-      tn;
-      alg="density_matrix",
-      output_structure=binary_tree_structure,
-      contraction_sequence_alg="sa_bipartite",
+    for structure in [path_graph_structure, binary_tree_structure]
+      approx_tn, lognorm = contract(
+        tn;
+        alg="density_matrix",
+        output_structure=structure,
+        contraction_sequence_alg="sa_bipartite",
+      )
+      network3 = Vector{ITensor}(approx_tn)
+      out3 = contract(network3...) * exp(lognorm)
+      i1 = noncommoninds(network...)
+      i3 = noncommoninds(network3...)
+      @test (length(i1) == length(i3))
+      @test isapprox(out1, out3)
+    end
+  end
+end
+
+@testset "test caching in approx_itensornetwork" begin
+  i = Index(2, "i")
+  j = Index(2, "j")
+  k = Index(2, "k")
+  l = Index(2, "l")
+  m = Index(2, "m")
+  T = randomITensor(i, j, k, l, m)
+  M = MPS(T, (i, j, k, l, m); cutoff=1e-5, maxdim=5)
+  tn = ITensorNetwork(M[:])
+  out_tree = path_graph_structure(tn)
+  input_partition = partition(tn, out_tree; alg="mincut_recursive_bisection")
+  underlying_tree = underlying_graph(input_partition)
+  # Change type of each partition[v] since they will be updated
+  # with potential data type chage.
+  p = DataGraph()
+  for v in vertices(input_partition)
+    add_vertex!(p, v)
+    p[v] = ITensorNetwork{Any}(input_partition[v])
+  end
+  alg_graph = _DensityMartrixAlgGraph(p, underlying_tree, _root(out_tree))
+  path = post_order_dfs_vertices(underlying_tree, _root(out_tree))
+  for v in path[1:2]
+    _rem_vertex!(
+      alg_graph,
+      v;
+      cutoff=1e-15,
+      maxdim=10000,
+      contraction_sequence_alg="optimal",
+      contraction_sequence_kwargs=(;),
     )
-    network3 = Vector{ITensor}(approx_tn)
-    out3 = contract(network3...) * exp(lognorm)
-    i1 = noncommoninds(network...)
-    i3 = noncommoninds(network3...)
-    @test (length(i1) == length(i3))
-    @test isapprox(out1, out3)
   end
+  # Check that a specific density matrix info has been cached
+  @test haskey(alg_graph.caches.es_to_pdm, Set([NamedEdge(nothing, path[3])]))
 end