[ITensors] Fix non-QN eigen with auto-fermion enabled (#1380)

ITensor · Apr 4, 2024 · ec6af32 · ec6af32
1 parent f3a9dd0
commit ec6af32
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diff --git a/src/tensor_operations/matrix_decomposition.jl b/src/tensor_operations/matrix_decomposition.jl
@@ -353,7 +353,7 @@ function eigen(
   end
 
   # <fermions>
-  if using_auto_fermion()
+  if hasqns(A) && using_auto_fermion()
     if !all(i -> dir(i) == Out, Lis)
       error("With auto_fermion enabled, left inds in eigen must have Out arrows")
     end

diff --git a/test/base/test_fermions.jl b/test/base/test_fermions.jl
@@ -768,5 +768,14 @@ import ITensors: Out, In
     end
   end # Regression Tests
 
+  @testset "Non-QN eigen Regression Test" begin
+    # Test that non-QN eigen runs properly
+    # with auto-fermion enabled.
+    i = Index(2)
+    a = randomITensor(i', i)
+    d, u = eigen(a)
+    @test norm(a * u - u' * d) ≈ 0 atol = √(eps(real(eltype(a))))
+  end
+
   ITensors.disable_auto_fermion()
 end