From 32ebca76e9029b15249f65625204a4f5548e957a Mon Sep 17 00:00:00 2001
From: Joey <joeytindall94@googlemail.com>
Date: Fri, 18 Oct 2024 17:53:43 +0100
Subject: [PATCH] Post order dsf edges region

---
 src/abstractitensornetwork.jl                       | 5 +----
 src/edge_sequences.jl                               | 5 +++++
 src/treetensornetworks/abstracttreetensornetwork.jl | 9 +++------
 3 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/src/abstractitensornetwork.jl b/src/abstractitensornetwork.jl
index 653303aa..244a24d7 100644
--- a/src/abstractitensornetwork.jl
+++ b/src/abstractitensornetwork.jl
@@ -631,10 +631,7 @@ end
 # the network as a tree spanned by a spanning tree.
 # TODO: Rename `tree_orthogonalize`.
 function ITensorMPS.orthogonalize(ψ::AbstractITensorNetwork, region::Vector)
-  spanning_tree_edges = post_order_dfs_edges(bfs_tree(ψ, first(region)), first(region))
-  spanning_tree_edges = filter(
-    e -> !(src(e) ∈ region && dst(e) ∈ region), spanning_tree_edges
-  )
+  spanning_tree_edges = post_order_dfs_edges_region(bfs_tree(ψ, first(region)), region)
   return orthogonalize(ψ, spanning_tree_edges)
 end
 
diff --git a/src/edge_sequences.jl b/src/edge_sequences.jl
index 9dab9fff..9b385c68 100644
--- a/src/edge_sequences.jl
+++ b/src/edge_sequences.jl
@@ -44,3 +44,8 @@ end
 @traitfn function edge_sequence(::Algorithm"parallel", g::::(!IsDirected))
   return [[e] for e in vcat(edges(g), reverse.(edges(g)))]
 end
+
+function post_order_dfs_edges_region(g::AbstractGraph, region)
+  es = post_order_dfs_edges(g, first(region))
+  return filter(e -> !((src(e) ∈ region) && (dst(e) ∈ region)), es)
+end
diff --git a/src/treetensornetworks/abstracttreetensornetwork.jl b/src/treetensornetworks/abstracttreetensornetwork.jl
index 13d78197..f75e9de2 100644
--- a/src/treetensornetworks/abstracttreetensornetwork.jl
+++ b/src/treetensornetworks/abstracttreetensornetwork.jl
@@ -10,7 +10,6 @@ using NamedGraphs: namedgraph_a_star
 using IsApprox: IsApprox, Approx
 using ITensors: @Algorithm_str, directsum, hasinds, permute, plev
 using ITensorMPS: linkind, loginner, lognorm, orthogonalize
-using TupleTools: TupleTools
 
 abstract type AbstractTreeTensorNetwork{V} <: AbstractITensorNetwork{V} end
 
@@ -36,11 +35,9 @@ function set_ortho_region(tn::AbstractTTN, new_region)
 end
 
 function ITensorMPS.orthogonalize(ttn::AbstractTTN, region::Vector; kwargs...)
-  paths = [
-    namedgraph_a_star(underlying_graph(ttn), rp, r) for r in region for
-    rp in ortho_region(ttn)
-  ]
-  path = unique(reduce(vcat, paths))
+  new_path = post_order_dfs_edges_region(ttn, region)
+  existing_path = post_order_dfs_edges_region(ttn, ortho_region(ttn))
+  path = setdiff(new_path, existing_path)
   if !isempty(path)
     ttn = typeof(ttn)(orthogonalize(ITensorNetwork(ttn), path; kwargs...))
   end