From 1b180e9abc335d5df2bdadfdd8698adc407223cc Mon Sep 17 00:00:00 2001
From: maartenvd <maartenvd1994@gmail.com>
Date: Tue, 21 Apr 2026 13:55:39 +0200
Subject: [PATCH 1/8] windowhamiltonian poc

---
 src/MPSKit.jl                          |  3 ++-
 src/algorithms/propagator/corvector.jl |  6 ++---
 src/environments/finite_envs.jl        |  8 +++---
 src/operators/windowhamiltonian.jl     | 36 ++++++++++++++++++++++++++
 test/states/windowmps.jl               |  7 ++---
 5 files changed, 49 insertions(+), 11 deletions(-)
 create mode 100644 src/operators/windowhamiltonian.jl

diff --git a/src/MPSKit.jl b/src/MPSKit.jl
index c1b47dc40..0137080a4 100644
--- a/src/MPSKit.jl
+++ b/src/MPSKit.jl
@@ -19,7 +19,7 @@ export QP, LeftGaugedQP, RightGaugedQP
 export AbstractMPO
 export MPO, FiniteMPO, InfiniteMPO
 export JordanMPOTensor, JordanMPOTensorMap
-export MPOHamiltonian, FiniteMPOHamiltonian, InfiniteMPOHamiltonian
+export MPOHamiltonian, FiniteMPOHamiltonian, InfiniteMPOHamiltonian, WindowMPOHamiltonian
 export MultilineMPO
 export UntimedOperator, TimedOperator, MultipliedOperator, LazySum
 
@@ -122,6 +122,7 @@ include("operators/abstractmpo.jl")
 include("operators/mpo.jl")
 include("operators/jordanmpotensor.jl")
 include("operators/mpohamiltonian.jl") # the mpohamiltonian objects
+include("operators/windowhamiltonian.jl")
 include("operators/ortho.jl")
 include("operators/multilinempo.jl")
 include("operators/projection.jl")
diff --git a/src/algorithms/propagator/corvector.jl b/src/algorithms/propagator/corvector.jl
index f4936c002..f33961433 100644
--- a/src/algorithms/propagator/corvector.jl
+++ b/src/algorithms/propagator/corvector.jl
@@ -59,7 +59,7 @@ See also [`Jeckelmann`](@ref) for the original approach.
 struct NaiveInvert <: DDMRG_Flavour end
 
 function propagator(
-        A::AbstractFiniteMPS, z::Number, H::FiniteMPOHamiltonian,
+        A::AbstractFiniteMPS, z::Number, H,
         alg::DynamicalDMRG{NaiveInvert}; init = copy(A)
     )
     h_envs = environments(init, H) # environments for h
@@ -119,7 +119,7 @@ See also [`NaiveInvert`](@ref) for a less costly but less accurate alternative.
 struct Jeckelmann <: DDMRG_Flavour end
 
 function propagator(
-        A::AbstractFiniteMPS, z, H::FiniteMPOHamiltonian,
+        A::AbstractFiniteMPS, z, H,
         alg::DynamicalDMRG{Jeckelmann}; init = copy(A)
     )
     ω = real(z)
@@ -176,7 +176,7 @@ function propagator(
 end
 
 function squaredenvs(
-        state::AbstractFiniteMPS, H::FiniteMPOHamiltonian, envs = environments(state, H)
+        state::AbstractFiniteMPS, H, envs = environments(state, H)
     )
     H² = conj(H) * H
     L = length(state)
diff --git a/src/environments/finite_envs.jl b/src/environments/finite_envs.jl
index 6372f65ab..9194e5cb5 100644
--- a/src/environments/finite_envs.jl
+++ b/src/environments/finite_envs.jl
@@ -53,14 +53,14 @@ function environments(
     return environments(below, O, above, leftstart, rightstart)
 end
 function environments(
-        below::WindowMPS, O::Union{InfiniteMPOHamiltonian, InfiniteMPO}, above = nothing;
-        lenvs = environments(below.left_gs, O),
-        renvs = environments(below.right_gs, O)
+        below::WindowMPS, O::WindowMPOHamiltonian, above = nothing;
+        lenvs = environments(below.left_gs, O.left_ham),
+        renvs = environments(below.right_gs, O.right_ham)
     )
     leftstart = copy(lenvs.GLs[1])
     rightstart = copy(renvs.GRs[end])
 
-    return environments(below, O, above, leftstart, rightstart)
+    return environments(below, O.finite_ham, above, leftstart, rightstart)
 end
 
 function environments(below::S, above::S) where {S <: Union{FiniteMPS, WindowMPS}}
diff --git a/src/operators/windowhamiltonian.jl b/src/operators/windowhamiltonian.jl
new file mode 100644
index 000000000..7eed2c458
--- /dev/null
+++ b/src/operators/windowhamiltonian.jl
@@ -0,0 +1,36 @@
+"""
+A WindowMPS is a finite MPS embedded between an infinite mps to the left, and an inifite mps to the right. 
+The associated hamiltonian has also an infinite part to the left, a finite hamiltonian in the middle, and an infinite part to the right.
+
+Acts simalar as just a finite hamiltonian, but we 'remember' the boundary hamiltonians.
+"""
+
+# todo - what is the required interface for abstractmpo?
+# support densempo windows?
+struct WindowMPOHamiltonian{O} <: AbstractMPO{O}
+    left_ham :: InfiniteMPOHamiltonian{O}
+    finite_ham :: FiniteMPOHamiltonian{O}
+    right_ham :: InfiniteMPOHamiltonian{O}
+end
+
+#utility constructor
+function WindowMPOHamiltonian(ham::InfiniteMPOHamiltonian, interval::UnitRange)
+    
+    # to make sure the interval corresponds with finite_ham, it is important that the unitcell of the left/right hamiltonians is circshifted correctly
+    left_edge = (interval.start-1) % length(ham)
+    left_ham = InfiniteMPOHamiltonian([ham[i] for i in (left_edge-length(ham)+1):left_edge])
+    right_edge = (interval.stop+1)%length(ham)
+    right_ham = InfiniteMPOHamiltonian([ham[i] for i in right_edge:(right_edge+length(ham)-1)])
+
+    finite_ham = FiniteMPOHamiltonian([ham[i] for i in  interval])
+    WindowMPOHamiltonian(left_ham, finite_ham, right_ham)
+end
+#
+Base.parent(h::WindowMPOHamiltonian) = h.finite_ham
+
+Base.copy(h::WindowMPOHamiltonian) = WindowMPOHamiltonian(copy(h.left_ham), copy(h.finite_ham), copy(h.right_ham))
+
+# some basic linalg
+for fun in (:(Base.:+), :(Base.:-), :(Base.:*))
+    @eval $fun(a::WindowMPOHamiltonian,b::WindowMPOHamiltonian) = WindowMPOHamiltonian($fun(a.left_ham,b.left_ham),$fun(a.finite_ham,b.finite_ham),$fun(a.right_ham,b.right_ham))
+end
diff --git a/test/states/windowmps.jl b/test/states/windowmps.jl
index 3cbddf09d..2106dab0e 100644
--- a/test/states/windowmps.jl
+++ b/test/states/windowmps.jl
@@ -63,14 +63,15 @@ using TensorKit: ℙ
 
     e1 = expectation_value(window, (2, 3) => O)
 
-    window, envs, _ = find_groundstate(window, ham, DMRG(; verbosity = 0))
+    w_ham = WindowMPOHamiltonian(ham,1:length(window))
+    window, envs, _ = find_groundstate(window, w_ham, DMRG(; verbosity = 0))
 
     e2 = expectation_value(window, (2, 3) => O)
 
     @test real(e2) ≤ real(e1)
 
-    window, envs = timestep(window, ham, 0.1, 0.0, TDVP2(; trscheme = truncrank(20)), envs)
-    window, envs = timestep(window, ham, 0.1, 0.0, TDVP(), envs)
+    window, envs = timestep(window, w_ham, 0.1, 0.0, TDVP2(; trscheme = truncrank(20)), envs)
+    window, envs = timestep(window, w_ham, 0.1, 0.0, TDVP(), envs)
 
     e3 = expectation_value(window, (2, 3) => O)
 

From 4413074111778ce375855d3f3f8f61c76ea8ea58 Mon Sep 17 00:00:00 2001
From: maartenvd <maartenvd1994@gmail.com>
Date: Tue, 28 Apr 2026 20:29:27 +0200
Subject: [PATCH 2/8] test

---
 src/algorithms/expval.jl           |  7 +++++++
 src/operators/windowhamiltonian.jl |  5 +++++
 test/algorithms/dynamical_dmrg.jl  | 31 +++++++++++++++++++++++++++++-
 3 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/src/algorithms/expval.jl b/src/algorithms/expval.jl
index b5db28f12..aff3e375f 100644
--- a/src/algorithms/expval.jl
+++ b/src/algorithms/expval.jl
@@ -128,6 +128,13 @@ function expectation_value(
     return dot(ψ, H, ψ, envs) / dot(ψ, ψ)
 end
 
+function expectation_value(
+        ψ::WindowMPS, H::WindowMPOHamiltonian,
+        envs::AbstractMPSEnvironments = environments(ψ, H)
+    )
+    return dot(ψ, H, ψ, envs) / dot(ψ, ψ)
+end
+
 function expectation_value(
         ψ::InfiniteMPS, H::InfiniteMPOHamiltonian,
         envs::AbstractMPSEnvironments = environments(ψ, H)
diff --git a/src/operators/windowhamiltonian.jl b/src/operators/windowhamiltonian.jl
index 7eed2c458..e9ee8c629 100644
--- a/src/operators/windowhamiltonian.jl
+++ b/src/operators/windowhamiltonian.jl
@@ -34,3 +34,8 @@ Base.copy(h::WindowMPOHamiltonian) = WindowMPOHamiltonian(copy(h.left_ham), copy
 for fun in (:(Base.:+), :(Base.:-), :(Base.:*))
     @eval $fun(a::WindowMPOHamiltonian,b::WindowMPOHamiltonian) = WindowMPOHamiltonian($fun(a.left_ham,b.left_ham),$fun(a.finite_ham,b.finite_ham),$fun(a.right_ham,b.right_ham))
 end
+
+TensorKit.dot(
+        bra::WindowMPS, H::WindowMPOHamiltonian, ket::WindowMPS = bra,
+        envs = environments(bra, H, ket)
+        ) = dot(bra.window, H.finite_ham, ket.window,envs)
diff --git a/test/algorithms/dynamical_dmrg.jl b/test/algorithms/dynamical_dmrg.jl
index 2b7a821b7..8fb1d712c 100644
--- a/test/algorithms/dynamical_dmrg.jl
+++ b/test/algorithms/dynamical_dmrg.jl
@@ -12,7 +12,7 @@ using TensorKit: ℙ
 
 verbosity_conv = 1
 
-@testset "Dynamical DMRG" verbose = true begin
+@testset "Dynamical DMRG FiniteMPS" verbose = true begin
     L = 10
     H = force_planar(-transverse_field_ising(; L, g = -4))
     gs, = find_groundstate(FiniteMPS(L, ℙ^2, ℙ^10), H; verbosity = verbosity_conv)
@@ -32,3 +32,32 @@ verbosity_conv = 1
         @test data ≈ predicted atol = 1.0e-8
     end
 end
+
+
+@testset "Dynamical DMRG WindowMPS" verbose = true begin
+    N = 20
+
+    H = transverse_field_ising(g = -4)
+    Ω = InfiniteMPS(ComplexSpace(2),ComplexSpace(20))
+
+    (Ω,_) = find_groundstate(Ω, H, VUMPS(verbosity = verbosity_conv))
+    XΩ = WindowMPS(Ω,N)
+    H_w = WindowMPOHamiltonian(H,1:N)
+    
+
+    gs_en =  expectation_value(XΩ, H_w)
+    vals = range(gs_en - 1.0,gs_en+1.0, length=5)
+    eta = 0.3im
+    predicted = [1 / (v + eta - gs_en) for v in vals]
+
+
+    @testset "Flavour $f" for f in (Jeckelmann(), NaiveInvert())
+        alg = DynamicalDMRG(; flavour = f, verbosity = 0, tol = 1.0e-8)
+        data = map(vals) do v
+            result, = propagator(XΩ, v + eta, H_w, alg)
+            return result
+        end
+        @test data ≈ predicted atol = 1.0e-8
+    end
+end
+

From 870a577da221136a5630355517745066caa63568 Mon Sep 17 00:00:00 2001
From: maartenvd <maartenvd1994@gmail.com>
Date: Wed, 29 Apr 2026 10:07:07 +0200
Subject: [PATCH 3/8] remove parent

---
 src/operators/windowhamiltonian.jl | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/operators/windowhamiltonian.jl b/src/operators/windowhamiltonian.jl
index e9ee8c629..030d6c59a 100644
--- a/src/operators/windowhamiltonian.jl
+++ b/src/operators/windowhamiltonian.jl
@@ -25,8 +25,7 @@ function WindowMPOHamiltonian(ham::InfiniteMPOHamiltonian, interval::UnitRange)
     finite_ham = FiniteMPOHamiltonian([ham[i] for i in  interval])
     WindowMPOHamiltonian(left_ham, finite_ham, right_ham)
 end
-#
-Base.parent(h::WindowMPOHamiltonian) = h.finite_ham
+
 
 Base.copy(h::WindowMPOHamiltonian) = WindowMPOHamiltonian(copy(h.left_ham), copy(h.finite_ham), copy(h.right_ham))
 

From 7ecdd3cffb26bb043fddaebedb9a5628aff44d7d Mon Sep 17 00:00:00 2001
From: maartenvd <maartenvd1994@gmail.com>
Date: Wed, 29 Apr 2026 10:07:55 +0200
Subject: [PATCH 4/8] format

---
 src/operators/windowhamiltonian.jl | 28 ++++++++++++++--------------
 test/algorithms/dynamical_dmrg.jl  | 14 +++++++-------
 test/states/windowmps.jl           |  2 +-
 3 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/src/operators/windowhamiltonian.jl b/src/operators/windowhamiltonian.jl
index 030d6c59a..98f72390f 100644
--- a/src/operators/windowhamiltonian.jl
+++ b/src/operators/windowhamiltonian.jl
@@ -8,22 +8,22 @@ Acts simalar as just a finite hamiltonian, but we 'remember' the boundary hamilt
 # todo - what is the required interface for abstractmpo?
 # support densempo windows?
 struct WindowMPOHamiltonian{O} <: AbstractMPO{O}
-    left_ham :: InfiniteMPOHamiltonian{O}
-    finite_ham :: FiniteMPOHamiltonian{O}
-    right_ham :: InfiniteMPOHamiltonian{O}
+    left_ham::InfiniteMPOHamiltonian{O}
+    finite_ham::FiniteMPOHamiltonian{O}
+    right_ham::InfiniteMPOHamiltonian{O}
 end
 
 #utility constructor
 function WindowMPOHamiltonian(ham::InfiniteMPOHamiltonian, interval::UnitRange)
-    
+
     # to make sure the interval corresponds with finite_ham, it is important that the unitcell of the left/right hamiltonians is circshifted correctly
-    left_edge = (interval.start-1) % length(ham)
-    left_ham = InfiniteMPOHamiltonian([ham[i] for i in (left_edge-length(ham)+1):left_edge])
-    right_edge = (interval.stop+1)%length(ham)
-    right_ham = InfiniteMPOHamiltonian([ham[i] for i in right_edge:(right_edge+length(ham)-1)])
+    left_edge = (interval.start - 1) % length(ham)
+    left_ham = InfiniteMPOHamiltonian([ham[i] for i in (left_edge - length(ham) + 1):left_edge])
+    right_edge = (interval.stop + 1) % length(ham)
+    right_ham = InfiniteMPOHamiltonian([ham[i] for i in right_edge:(right_edge + length(ham) - 1)])
 
-    finite_ham = FiniteMPOHamiltonian([ham[i] for i in  interval])
-    WindowMPOHamiltonian(left_ham, finite_ham, right_ham)
+    finite_ham = FiniteMPOHamiltonian([ham[i] for i in interval])
+    return WindowMPOHamiltonian(left_ham, finite_ham, right_ham)
 end
 
 
@@ -31,10 +31,10 @@ Base.copy(h::WindowMPOHamiltonian) = WindowMPOHamiltonian(copy(h.left_ham), copy
 
 # some basic linalg
 for fun in (:(Base.:+), :(Base.:-), :(Base.:*))
-    @eval $fun(a::WindowMPOHamiltonian,b::WindowMPOHamiltonian) = WindowMPOHamiltonian($fun(a.left_ham,b.left_ham),$fun(a.finite_ham,b.finite_ham),$fun(a.right_ham,b.right_ham))
+    @eval $fun(a::WindowMPOHamiltonian, b::WindowMPOHamiltonian) = WindowMPOHamiltonian($fun(a.left_ham, b.left_ham), $fun(a.finite_ham, b.finite_ham), $fun(a.right_ham, b.right_ham))
 end
 
 TensorKit.dot(
-        bra::WindowMPS, H::WindowMPOHamiltonian, ket::WindowMPS = bra,
-        envs = environments(bra, H, ket)
-        ) = dot(bra.window, H.finite_ham, ket.window,envs)
+    bra::WindowMPS, H::WindowMPOHamiltonian, ket::WindowMPS = bra,
+    envs = environments(bra, H, ket)
+) = dot(bra.window, H.finite_ham, ket.window, envs)
diff --git a/test/algorithms/dynamical_dmrg.jl b/test/algorithms/dynamical_dmrg.jl
index 8fb1d712c..146c43af3 100644
--- a/test/algorithms/dynamical_dmrg.jl
+++ b/test/algorithms/dynamical_dmrg.jl
@@ -38,15 +38,15 @@ end
     N = 20
 
     H = transverse_field_ising(g = -4)
-    Ω = InfiniteMPS(ComplexSpace(2),ComplexSpace(20))
+    Ω = InfiniteMPS(ComplexSpace(2), ComplexSpace(20))
 
-    (Ω,_) = find_groundstate(Ω, H, VUMPS(verbosity = verbosity_conv))
-    XΩ = WindowMPS(Ω,N)
-    H_w = WindowMPOHamiltonian(H,1:N)
-    
+    (Ω, _) = find_groundstate(Ω, H, VUMPS(verbosity = verbosity_conv))
+    XΩ = WindowMPS(Ω, N)
+    H_w = WindowMPOHamiltonian(H, 1:N)
 
-    gs_en =  expectation_value(XΩ, H_w)
-    vals = range(gs_en - 1.0,gs_en+1.0, length=5)
+
+    gs_en = expectation_value(XΩ, H_w)
+    vals = range(gs_en - 1.0, gs_en + 1.0, length = 5)
     eta = 0.3im
     predicted = [1 / (v + eta - gs_en) for v in vals]
 
diff --git a/test/states/windowmps.jl b/test/states/windowmps.jl
index 2106dab0e..ab37bbab8 100644
--- a/test/states/windowmps.jl
+++ b/test/states/windowmps.jl
@@ -63,7 +63,7 @@ using TensorKit: ℙ
 
     e1 = expectation_value(window, (2, 3) => O)
 
-    w_ham = WindowMPOHamiltonian(ham,1:length(window))
+    w_ham = WindowMPOHamiltonian(ham, 1:length(window))
     window, envs, _ = find_groundstate(window, w_ham, DMRG(; verbosity = 0))
 
     e2 = expectation_value(window, (2, 3) => O)

From 4e2007a2e7b588802b1dd94aa9101515df4b8aaf Mon Sep 17 00:00:00 2001
From: maartenvd <maartenvd1994@gmail.com>
Date: Fri, 1 May 2026 09:35:06 +0200
Subject: [PATCH 5/8] ::Number

---
 src/algorithms/propagator/corvector.jl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/algorithms/propagator/corvector.jl b/src/algorithms/propagator/corvector.jl
index f33961433..dcb8282e2 100644
--- a/src/algorithms/propagator/corvector.jl
+++ b/src/algorithms/propagator/corvector.jl
@@ -119,7 +119,7 @@ See also [`NaiveInvert`](@ref) for a less costly but less accurate alternative.
 struct Jeckelmann <: DDMRG_Flavour end
 
 function propagator(
-        A::AbstractFiniteMPS, z, H,
+        A::AbstractFiniteMPS, z::Number, H,
         alg::DynamicalDMRG{Jeckelmann}; init = copy(A)
     )
     ω = real(z)

From 0b9e49d748dd6b26d6025d6ddc53283291942b4e Mon Sep 17 00:00:00 2001
From: maartenvd <maartenvd1994@gmail.com>
Date: Fri, 1 May 2026 09:52:33 +0200
Subject: [PATCH 6/8] constructor in line with windowhamiltonian

---
 src/states/windowmps.jl | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/src/states/windowmps.jl b/src/states/windowmps.jl
index 5c0bab9d0..fa23acdf1 100644
--- a/src/states/windowmps.jl
+++ b/src/states/windowmps.jl
@@ -106,18 +106,27 @@ function WindowMPS(N::Int, V::VectorSpace, args...; kwargs...)
     return WindowMPS(fill(V, N), args...; kwargs...)
 end
 
-function WindowMPS(ψ::InfiniteMPS{A, B}, L::Int) where {A, B}
+
+WindowMPS(ψ::InfiniteMPS, L::Int) = WindowMPS(ψ, 1:L)
+
+function WindowMPS(ψ::InfiniteMPS{A, B}, interval::UnitRange) where {A,B}
+
+    # to make sure the interval corresponds with finite_ham, it is important that the unitcell of the left/right hamiltonians is circshifted correctly
+    left_edge = (interval.start - 1) % length(ψ)
+    right_edge = (interval.stop + 1) % length(ψ)
+
+    L = length(interval)
     CLs = Vector{Union{Missing, B}}(missing, L + 1)
     ALs = Vector{Union{Missing, A}}(missing, L)
     ARs = Vector{Union{Missing, A}}(missing, L)
     ACs = Vector{Union{Missing, A}}(missing, L)
 
-    ALs .= ψ.AL[1:L]
-    ARs .= ψ.AR[1:L]
-    ACs .= ψ.AC[1:L]
-    CLs .= ψ.C[0:L]
+    ALs .= ψ.AL[interval]
+    ARs .= ψ.AR[interval]
+    ACs .= ψ.AC[interval]
+    CLs .= ψ.C[interval.start-1:interval.stop]
 
-    return WindowMPS(ψ, FiniteMPS(ALs, ARs, ACs, CLs), ψ)
+    return WindowMPS(circshift(ψ, -left_edge), FiniteMPS(ALs, ARs, ACs, CLs), circshift(ψ,-right_edge + 1))
 end
 
 #===========================================================================================

From 42c0ba1551d784abc198362e895532bce6c9c131 Mon Sep 17 00:00:00 2001
From: maartenvd <maartenvd1994@gmail.com>
Date: Fri, 1 May 2026 09:56:54 +0200
Subject: [PATCH 7/8] circshift

---
 src/operators/mpohamiltonian.jl    | 2 +-
 src/operators/windowhamiltonian.jl | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/operators/mpohamiltonian.jl b/src/operators/mpohamiltonian.jl
index daf7eb6a5..f2008f755 100644
--- a/src/operators/mpohamiltonian.jl
+++ b/src/operators/mpohamiltonian.jl
@@ -706,7 +706,7 @@ end
 function Base.similar(H::MPOHamiltonian, ::Type{T}) where {T <: Number}
     return MPOHamiltonian(similar.(parent(H), T))
 end
-
+Base.circshift(H::InfiniteMPOHamiltonian, shift::Integer) = InfiniteMPOHamiltonian(circshift(parent(copy(H)), shift))
 # Linear Algebra
 # --------------
 function Base.:+(
diff --git a/src/operators/windowhamiltonian.jl b/src/operators/windowhamiltonian.jl
index 98f72390f..071e0eca3 100644
--- a/src/operators/windowhamiltonian.jl
+++ b/src/operators/windowhamiltonian.jl
@@ -18,15 +18,15 @@ function WindowMPOHamiltonian(ham::InfiniteMPOHamiltonian, interval::UnitRange)
 
     # to make sure the interval corresponds with finite_ham, it is important that the unitcell of the left/right hamiltonians is circshifted correctly
     left_edge = (interval.start - 1) % length(ham)
-    left_ham = InfiniteMPOHamiltonian([ham[i] for i in (left_edge - length(ham) + 1):left_edge])
+    left_ham = circshift(ham, -left_edge)
     right_edge = (interval.stop + 1) % length(ham)
-    right_ham = InfiniteMPOHamiltonian([ham[i] for i in right_edge:(right_edge + length(ham) - 1)])
+    right_ham = circshift(ham, -right_edge + 1)
 
     finite_ham = FiniteMPOHamiltonian([ham[i] for i in interval])
     return WindowMPOHamiltonian(left_ham, finite_ham, right_ham)
 end
 
-
+Base.parent(h::WindowMPOHamiltonian) = h.finite_ham
 Base.copy(h::WindowMPOHamiltonian) = WindowMPOHamiltonian(copy(h.left_ham), copy(h.finite_ham), copy(h.right_ham))
 
 # some basic linalg

From b481f64befc3645a350b951da0b6a63f7f0cac30 Mon Sep 17 00:00:00 2001
From: maartenvd <maartenvd1994@gmail.com>
Date: Fri, 1 May 2026 09:57:15 +0200
Subject: [PATCH 8/8] format

---
 src/states/windowmps.jl | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/states/windowmps.jl b/src/states/windowmps.jl
index fa23acdf1..7c5d48327 100644
--- a/src/states/windowmps.jl
+++ b/src/states/windowmps.jl
@@ -109,7 +109,7 @@ end
 
 WindowMPS(ψ::InfiniteMPS, L::Int) = WindowMPS(ψ, 1:L)
 
-function WindowMPS(ψ::InfiniteMPS{A, B}, interval::UnitRange) where {A,B}
+function WindowMPS(ψ::InfiniteMPS{A, B}, interval::UnitRange) where {A, B}
 
     # to make sure the interval corresponds with finite_ham, it is important that the unitcell of the left/right hamiltonians is circshifted correctly
     left_edge = (interval.start - 1) % length(ψ)
@@ -124,9 +124,9 @@ function WindowMPS(ψ::InfiniteMPS{A, B}, interval::UnitRange) where {A,B}
     ALs .= ψ.AL[interval]
     ARs .= ψ.AR[interval]
     ACs .= ψ.AC[interval]
-    CLs .= ψ.C[interval.start-1:interval.stop]
+    CLs .= ψ.C[(interval.start - 1):interval.stop]
 
-    return WindowMPS(circshift(ψ, -left_edge), FiniteMPS(ALs, ARs, ACs, CLs), circshift(ψ,-right_edge + 1))
+    return WindowMPS(circshift(ψ, -left_edge), FiniteMPS(ALs, ARs, ACs, CLs), circshift(ψ, -right_edge + 1))
 end
 
 #===========================================================================================