From b3a0726491d46702808b74ae9f12e861d34e5a85 Mon Sep 17 00:00:00 2001
From: Paul Brehmer <paul.brehmer@univie.ac.at>
Date: Tue, 9 Jul 2024 16:04:46 +0200
Subject: [PATCH] Fix missing cnext in ctmrg, update README example

---
 README.md               | 13 +++----------
 docs/src/index.md       | 13 +++----------
 src/algorithms/ctmrg.jl |  1 +
 3 files changed, 7 insertions(+), 20 deletions(-)

diff --git a/README.md b/README.md
index a45818d6..e069d7a2 100644
--- a/README.md
+++ b/README.md
@@ -36,19 +36,12 @@ For example, in order to obtain the groundstate of the 2D Heisenberg model, we c
 using TensorKit, PEPSKit, KrylovKit, OptimKit
 
 # constructing the Hamiltonian:
-Jx, Jy, Jz = (-1, 1, -1) # sublattice rotation to obtain single-site unit cell
-physical_space = ComplexSpace(2)
-T = ComplexF64
-σx = TensorMap(T[0 1; 1 0], physical_space, physical_space)
-σy = TensorMap(T[0 im; -im 0], physical_space, physical_space)
-σz = TensorMap(T[1 0; 0 -1], physical_space, physical_space)
-H = (Jx * σx ⊗ σx) + (Jy * σy ⊗ σy) + (Jz * σz ⊗ σz)
-Heisenberg_hamiltonian = NLocalOperator{NearestNeighbor}(H / 4)
+H = square_lattice_heisenberg(; Jx=-1, Jy=1, Jz=-1) # sublattice rotation to obtain single-site unit cell
 
 # configuring the parameters
 D = 2
 chi = 20
-ctm_alg = CTMRG(; trscheme = truncdim(chi), tol=1e-20, miniter=4, maxiter=100, verbosity=1)
+ctm_alg = CTMRG(; tol=1e-10, miniter=4, maxiter=100, verbosity=1, trscheme=truncdim(chi))
 opt_alg = PEPSOptimize(;
     boundary_alg=ctm_alg,
     optimizer=LBFGS(4; maxiter=100, gradtol=1e-4, verbosity=2),
@@ -60,7 +53,7 @@ opt_alg = PEPSOptimize(;
 # ground state search
 state = InfinitePEPS(2, D)
 ctm = leading_boundary(CTMRGEnv(state; Venv=ComplexSpace(chi)), state, ctm_alg)
-result = fixedpoint(state, Heisenberg_hamiltonian, opt_alg, ctm)
+result = fixedpoint(state, H, opt_alg, ctm)
 
 @show result.E # -0.6625...
 ```
diff --git a/docs/src/index.md b/docs/src/index.md
index 305f6d84..ea76186c 100644
--- a/docs/src/index.md
+++ b/docs/src/index.md
@@ -21,19 +21,12 @@ For example, in order to obtain the groundstate of the 2D Heisenberg model, we c
 using TensorKit, PEPSKit, KrylovKit, OptimKit
 
 # constructing the Hamiltonian:
-Jx, Jy, Jz = (-1, 1, -1) # sublattice rotation to obtain single-site unit cell
-physical_space = ComplexSpace(2)
-T = ComplexF64
-σx = TensorMap(T[0 1; 1 0], physical_space, physical_space)
-σy = TensorMap(T[0 im; -im 0], physical_space, physical_space)
-σz = TensorMap(T[1 0; 0 -1], physical_space, physical_space)
-H = (Jx * σx ⊗ σx) + (Jy * σy ⊗ σy) + (Jz * σz ⊗ σz)
-Heisenberg_hamiltonian = NLocalOperator{NearestNeighbor}(H / 4)
+H = square_lattice_heisenberg(; Jx=-1, Jy=1, Jz=-1) # sublattice rotation to obtain single-site unit cell
 
 # configuring the parameters
 D = 2
 chi = 20
-ctm_alg = CTMRG(; trscheme = truncdim(chi), tol=1e-20, miniter=4, maxiter=100, verbosity=1)
+ctm_alg = CTMRG(; tol=1e-10, miniter=4, maxiter=100, verbosity=1, trscheme=truncdim(chi))
 opt_alg = PEPSOptimize(;
     boundary_alg=ctm_alg,
     optimizer=LBFGS(4; maxiter=100, gradtol=1e-4, verbosity=2),
@@ -45,7 +38,7 @@ opt_alg = PEPSOptimize(;
 # ground state search
 state = InfinitePEPS(2, D)
 ctm = leading_boundary(CTMRGEnv(state; Venv=ComplexSpace(chi)), state, ctm_alg)
-result = fixedpoint(state, Heisenberg_hamiltonian, opt_alg, ctm)
+result = fixedpoint(state, H, opt_alg, ctm)
 
 @show result.E # -0.6625...
 ```
diff --git a/src/algorithms/ctmrg.jl b/src/algorithms/ctmrg.jl
index d0073465..69d4a465 100644
--- a/src/algorithms/ctmrg.jl
+++ b/src/algorithms/ctmrg.jl
@@ -346,6 +346,7 @@ function left_move(state, env::CTMRGEnv{C,T}, alg::ProjectorAlg) where {C,T}
 
     for col in 1:size(state, 2)
         cprev = _prev(col, size(state, 2))
+        cnext = _next(col, size(state, 2))
 
         # Compute projectors
         for row in 1:size(state, 1)