lkdvos · Oct 12, 2026 · Oct 12, 2026 · Oct 12, 2026 · Oct 12, 2026 · Oct 12, 2026
diff --git a/benchmark/MPSKitBenchmarks/scripts/setup_heisenberg.jl b/benchmark/MPSKitBenchmarks/scripts/setup_heisenberg.jl
@@ -23,7 +23,7 @@ function initial_state(H)
     @assert allequal(physicalspace(H))
 
     pspace = physicalspace(H, 1)
-    A = rand(oneunit(pspace) ⊗ pspace^2 ← oneunit(pspace))
+    A = rand(unitspace(pspace) ⊗ pspace^2 ← unitspace(pspace))
     As = MPSKit.decompose_localmps(A)
     return FiniteMPS(repeat(As, length(H) ÷ 2))
 end

diff --git a/docs/src/changelog.md b/docs/src/changelog.md
@@ -34,6 +34,7 @@ When releasing a new version, move the "Unreleased" changes to a new version sec
 ### Fixed
 
 - `convert(TensorMap, H)` for single-site `FiniteMPOHamiltonian`s no longer contracts the site tensor with itself. ([#252](https://github.com/QuantumKitHub/MPSKit.jl/pull/252))
+- `show` methods for finite MPS/MPOs no longer check unit space condition through `oneunit`, which is not defined for multifusion spaces. ([#538](https://github.com/QuantumKitHub/MPSKit.jl/pull/538))
 
 ### Performance
 

diff --git a/docs/src/examples/quantum1d/6.hubbard/index.md b/docs/src/examples/quantum1d/6.hubbard/index.md
@@ -184,7 +184,7 @@ charges = fill(FermionParity(1) ⊠ U1Irrep(1) ⊠ SU2Irrep(0), 2);
 H_u1_su2 = MPSKit.add_physical_charge(H_u1_su2, charges);
 
 pspaces = physicalspace.(Ref(H_u1_su2), 1:2)
-vspaces = [oneunit(eltype(pspaces)), first(pspaces)]
+vspaces = [unitspace(eltype(pspaces)), first(pspaces)]
 psi = InfiniteMPS(pspaces, vspaces)
 psi = compute_groundstate(psi, H_u1_su2; expansionfactor = 1 / 3)
 E = real(expectation_value(psi, H_u1_su2)) / 2

diff --git a/docs/src/examples/quantum1d/6.hubbard/main.ipynb b/docs/src/examples/quantum1d/6.hubbard/main.ipynb
@@ -261,7 +261,7 @@
     "H_u1_su2 = MPSKit.add_physical_charge(H_u1_su2, charges);\n",
     "\n",
     "pspaces = physicalspace.(Ref(H_u1_su2), 1:2)\n",
-    "vspaces = [oneunit(eltype(pspaces)), first(pspaces)]\n",
+    "vspaces = [unitspace(eltype(pspaces)), first(pspaces)]\n",
     "psi = InfiniteMPS(pspaces, vspaces)\n",
     "psi = compute_groundstate(psi, H_u1_su2; expansionfactor = 1 / 3)\n",
     "E = real(expectation_value(psi, H_u1_su2)) / 2\n",
@@ -499,4 +499,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 3
-}
+}
diff --git a/examples/quantum1d/6.hubbard/main.jl b/examples/quantum1d/6.hubbard/main.jl
@@ -122,7 +122,7 @@ charges = fill(FermionParity(1) ⊠ U1Irrep(1) ⊠ SU2Irrep(0), 2);
 H_u1_su2 = MPSKit.add_physical_charge(H_u1_su2, charges);
 
 pspaces = physicalspace.(Ref(H_u1_su2), 1:2)
-vspaces = [oneunit(eltype(pspaces)), first(pspaces)]
+vspaces = [unitspace(eltype(pspaces)), first(pspaces)]
 psi = InfiniteMPS(pspaces, vspaces)
 psi = compute_groundstate(psi, H_u1_su2; expansionfactor = 1 / 3)
 E = real(expectation_value(psi, H_u1_su2)) / 2

diff --git a/src/algorithms/timestep/clusterexpansion.jl b/src/algorithms/timestep/clusterexpansion.jl
@@ -95,7 +95,7 @@ end
 
 function exponentiate_onsite_tensor(ham_tensor, τ, ::Type{A}) where {A}
     physical_space = physicalspace(ham_tensor)
-    levels = ⊞(oneunit(physical_space))
+    levels = ⊞(rightunitspace(physical_space))
     blocktype = tensormaptype(spacetype(physical_space), 2, 2, A)
     tensor = SparseBlockTensorMap{blocktype}(undef, levels ⊗ physical_space ← physical_space ⊗ levels)
     onsite = removeunit(removeunit(ham_tensor[1, 1, 1, end], 4), 1)

diff --git a/src/utility/show.jl b/src/utility/show.jl
@@ -36,9 +36,9 @@ function Base.show(io::IO, ::MIME"text/plain", ψ::FiniteMPS)
 
     # special handling of edge spaces => don't print if trivial
     Vright = right_virtualspace(ψ, L)
-    right_trivial = Vright == oneunit(Vright)
+    right_trivial = isunitspace(Vright)
     Vleft = left_virtualspace(ψ, 1)
-    left_trivial = Vleft == oneunit(Vleft)
+    left_trivial = isunitspace(Vleft)
 
 
     right_trivial || println(io, "│ ", Vright)
@@ -122,9 +122,9 @@ function Base.show(io::IO, ::MIME"text/plain", mpo::AbstractMPO)
     if isfinite(mpo)
         # special handling of edge spaces => don't print if trivial
         Vright = right_virtualspace(mpo, L)
-        right_trivial = Vright == oneunit(Vright)
+        right_trivial = isunitspace(Vright)
         Vleft = left_virtualspace(mpo, 1)
-        left_trivial = Vleft == oneunit(Vleft)
+        left_trivial = isunitspace(Vleft)
 
         right_trivial || println(io, "│ ", Vright)
         for i in reverse(1:L)

diff --git a/test/algorithms/changebonds.jl b/test/algorithms/changebonds.jl
@@ -113,7 +113,7 @@ end
     H = kitaev_model(ComplexF64, Trivial; t = 1.0, mu = 0, Delta = 0, L = L)
     P = physicalspace(H)[1]
     S = typeof(P)
-    Vtriv = oneunit(P)
+    Vtriv = unitspace(P)
     Vodd = S(c => dim(P, c) for c in sectors(P) if !isone(c))
     # single particle created on the last site: interior bonds carry only the even sector, so
     # the expansion content on them is exactly zero

diff --git a/test/groundstate/approximate.jl b/test/groundstate/approximate.jl
@@ -23,7 +23,7 @@ end
 function _random_mpo_mps(pspace, Dspace, L; elt = ComplexF64)
     Random.seed!(1357)
     Wspace = Dspace
-    Vspaces = [oneunit(Wspace); fill(Wspace, L - 1); oneunit(Wspace)]
+    Vspaces = [unitspace(Wspace); fill(Wspace, L - 1); unitspace(Wspace)]
     O = FiniteMPO(
         [rand(ComplexF64, Vspaces[i] ⊗ pspace ← pspace ⊗ Vspaces[i + 1]) for i in 1:L]
     )
@@ -211,7 +211,7 @@ end
         @test info.truncation_errors ≈ info_ref.truncation_errors
 
         # a destination with unrelated contents is overwritten entirely
-        dst = FiniteMPS(rand, ComplexF64, length(ψ), pspace, oneunit(Dspace) ⊕ Dspace ⊕ Dspace)
+        dst = FiniteMPS(rand, ComplexF64, length(ψ), pspace, unitspace(Dspace) ⊕ Dspace ⊕ Dspace)
         got, info = approximate!(dst, (O, ψ), alg)
         @test norm(ref - got) / norm(ref) < 1.0e-12
         @test info.truncation_errors ≈ info_ref.truncation_errors
@@ -248,8 +248,8 @@ end
     @testset "Zip-up with non-square MPO $(spacetype(pspace))" for (pspace, Dspace, _) in zipup_spacelist
         Random.seed!(1357)
         L = 4
-        pspace′ = pspace ⊕ oneunit(pspace) # output physical space, different from the input one
-        Vspaces = [oneunit(Dspace); fill(Dspace, L - 1); oneunit(Dspace)]
+        pspace′ = pspace ⊕ unitspace(pspace) # output physical space, different from the input one
+        Vspaces = [unitspace(Dspace); fill(Dspace, L - 1); unitspace(Dspace)]
         O = FiniteMPO(
             [rand(ComplexF64, Vspaces[i] ⊗ pspace′ ← pspace ⊗ Vspaces[i + 1]) for i in 1:L]
         )

diff --git a/test/hamiltonian/mixed.jl b/test/hamiltonian/mixed.jl
@@ -91,7 +91,7 @@ Ts = fast_tests ? (Float64,) : (Float64, ComplexF64)
         ((i, i + 2) => h for i in 1:(L - 2))...,
         ((i, i + 3) => h for i in 1:(L - 3))...,
     )
-    mps1 = FiniteMPS(physicalspace(H1), oneunit(V))
+    mps1 = FiniteMPS(physicalspace(H1), unitspace(V))
 
     for T in Ts
         H2 = if VERSION <= v"1.12"
@@ -106,7 +106,7 @@ Ts = fast_tests ? (Float64,) : (Float64, ComplexF64)
     end
 
     H3 = InfiniteMPOHamiltonian(fill(V, L), (1, 2) => h, (1, 3) => h, (1, 4) => h)
-    mps2 = InfiniteMPS(physicalspace(H3), [oneunit(V)])
+    mps2 = InfiniteMPS(physicalspace(H3), [unitspace(V)])
     for T in Ts
         H4 = if VERSION <= v"1.12"
             # this is type unstable for LTS for some reason

diff --git a/test/states/infinitemps.jl b/test/states/infinitemps.jl
@@ -101,7 +101,7 @@ end
     end
 
     # product state has zero entropy everywhere
-    ψ_product = InfiniteMPS([d, d], [oneunit(D), oneunit(D)])
+    ψ_product = InfiniteMPS([d, d], [unitspace(D), unitspace(D)])
     Ss_product = entropy(ψ_product)
     @test all(S -> isapprox(S, 0; atol = 1.0e-10), Ss_product)
 end