From 002662360b65994db12d3745275ec8a8254505fd Mon Sep 17 00:00:00 2001
From: Joey <joeytindall94@googlemail.com>
Date: Fri, 12 Apr 2024 11:10:18 -0400
Subject: [PATCH] Construct correct identity_network in BiLinearFormNetwork

---
 src/formnetworks/bilinearformnetwork.jl |  2 +-
 src/itensornetwork.jl                   | 12 ++++++++----
 test/test_forms.jl                      |  1 -
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/formnetworks/bilinearformnetwork.jl b/src/formnetworks/bilinearformnetwork.jl
index b7408e4c..bcb59704 100644
--- a/src/formnetworks/bilinearformnetwork.jl
+++ b/src/formnetworks/bilinearformnetwork.jl
@@ -59,7 +59,7 @@ function BilinearFormNetwork(
 )
   @assert issetequal(externalinds(bra), externalinds(ket))
   operator_inds = union_all_inds(siteinds(ket), dual_site_index_map(siteinds(ket)))
-  O = delta_network(operator_inds)
+  O = ITensorNetwork(Op("I"), operator_inds)
   return BilinearFormNetwork(O, bra, ket; dual_site_index_map, kwargs...)
 end
 
diff --git a/src/itensornetwork.jl b/src/itensornetwork.jl
index 96f4b604..a2d4af3f 100644
--- a/src/itensornetwork.jl
+++ b/src/itensornetwork.jl
@@ -164,10 +164,14 @@ function generic_state(a::AbstractArray, inds::Vector)
 end
 function generic_state(x::Op, inds::NamedTuple)
   # TODO: Figure out what to do if there is more than one site.
-  @assert length(inds.siteinds) == 2
-  i = inds.siteinds[findfirst(i -> plev(i) == 0, inds.siteinds)]
-  @assert i' ∈ inds.siteinds
-  site_tensors = [op(x.which_op, i)]
+  if !isempty(inds.siteinds)
+    @assert length(inds.siteinds) == 2
+    i = inds.siteinds[findfirst(i -> plev(i) == 0, inds.siteinds)]
+    @assert i' ∈ inds.siteinds
+    site_tensors = [op(x.which_op, i)]
+  else
+    site_tensors = []
+  end
   link_tensors = [[onehot(i => 1) for i in inds.linkinds[e]] for e in keys(inds.linkinds)]
   return contract(reduce(vcat, link_tensors; init=site_tensors))
 end
diff --git a/test/test_forms.jl b/test/test_forms.jl
index 4ff3e2d0..a9a0e453 100644
--- a/test/test_forms.jl
+++ b/test/test_forms.jl
@@ -8,7 +8,6 @@ using ITensorNetworks:
   QuadraticFormNetwork,
   bra_network,
   bra_vertex,
-  delta_network,
   dual_index_map,
   environment,
   externalinds,