fixedpoint improvements (#337)

* Add `check_input` method for `fixedpoint`

* Add `contraction_metrics` tuple to returned `info`

* Add tests for real C4v optimization and QR-CTMRG optimizations

* Fix `truncation_error` in sequential mode and catch `:fixed` mode error for real tensors in tests

* Use type parameters in `check_input` and use old seed again

* Use `:linsolver` by default for C4v CTMRG

* Update changelog

* Rerender Heisenberg example

* Alter seed to make QR-CTMRG not hickup

* Update src/algorithms/optimization/peps_optimization.jl

Co-authored-by: Lukas Devos <ldevos98@gmail.com>

* Add symmetrization to `_check_algorithm_combination`

---------

Co-authored-by: Lander Burgelman <39218680+leburgel@users.noreply.github.com>
Co-authored-by: Lukas Devos <ldevos98@gmail.com>

Author: 3 people

docs/src/changelog.md

@@ -25,6 +25,7 @@ When releasing a new version, move the "Unreleased" changes to a new version sec
 ### Changed
 
 - Bump OptimKit.jl compatibility to v0.4
+- Move `info.truncation_error` and `info.condition_number` into the `info.contraction_metrics` named tuple for `leading_boundary` and `fixedpoint`
 
 ### Deprecated
 

docs/src/examples/heisenberg/index.md

@@ -204,17 +204,19 @@
    "cell_type": "markdown",
    "source": [
     "Besides the converged environment, `leading_boundary` also returns a `NamedTuple` of\n",
-    "informational quantities such as the last maximal truncation error - that is, the SVD\n",
-    "approximation error incurred in the last CTMRG iteration, maximized over all spatial\n",
-    "directions and unit cell entries:"
+    "informational quantities which contains, among other things, a `contraction_metric` tuple.\n",
+    "This may contain different quantities depending on the method of contraction, and for this\n",
+    "CTMRG variant we return the last maximal truncation error (the SVD approximation\n",
+    "error maximized over all spatial directions and unit cell entries) as well as the condition\n",
+    "number of the decomposition (the ratio of largest to smallest singular value):"
    ],
    "metadata": {}
   },
   {
    "outputs": [],
    "cell_type": "code",
    "source": [
-    "@show info_ctmrg.truncation_error;"
+    "@show info_ctmrg.contraction_metrics;"
    ],
    "metadata": {},
    "execution_count": null
@@ -382,11 +384,11 @@
    "file_extension": ".jl",
    "mimetype": "application/julia",
    "name": "julia",
-   "version": "1.11.7"
+   "version": "1.12.5"
   },
   "kernelspec": {
-   "name": "julia-1.11",
-   "display_name": "Julia 1.11.7",
+   "name": "julia-1.12",
+   "display_name": "Julia 1.12.5",
    "language": "julia"
   }
  },

docs/src/examples/heisenberg/main.ipynb

@@ -7,4 +7,4 @@ heisenberg_su = "3eb8556d949c0e47e39c679e9e438bc04d3e2a3ffe73e0a682963b37b05f9e9
 xxz = "0231f0c1af2013e8edd9e5c192b108e1ab19a7dca22251c3bde525e3eee2a6aa"
 fermi_hubbard = "4997680c826e555557c661e605e1d7d363e0cee15522d0895fa0cfd53b1de001"
 j1j2_su = "c00fd13c0be323ab5825af59f3e7b31c3e51d3f65211d3836657b64274504c1c"
-heisenberg = "d610c92223d41e296348f9858fab52eacbfe2a578f64f4f8ac4c70d486fb4da2"
+heisenberg = "80bb9cc57ed85297b1b789a6c5f09494dac81b23631f48c6600ede9424c5d248"

examples/Cache.toml

@@ -102,12 +102,14 @@ env₀, info_ctmrg = leading_boundary(env_random, peps₀; boundary_alg...);
 
 md"""
 Besides the converged environment, `leading_boundary` also returns a `NamedTuple` of
-informational quantities such as the last maximal truncation error - that is, the SVD
-approximation error incurred in the last CTMRG iteration, maximized over all spatial
-directions and unit cell entries:
+informational quantities which contains, among other things, a `contraction_metric` tuple.
+This may contain different quantities depending on the method of contraction, and for this
+CTMRG variant we return the last maximal truncation error (the SVD approximation
+error maximized over all spatial directions and unit cell entries) as well as the condition
+number of the decomposition (the ratio of largest to smallest singular value):
 """
 
-@show info_ctmrg.truncation_error;
+@show info_ctmrg.contraction_metrics;
 
 md"""
 ## Ground state search

examples/heisenberg/main.jl

@@ -86,8 +86,7 @@ $(TYPEDFIELDS)
 
     C4vQRProjector(; kwargs...)
 
-Construct the C₄ᵥ `qr`-based projector algorithm
-based on the following keyword arguments:
+Construct the C₄ᵥ `qr`-based projector algorithm based on the following keyword arguments:
 
 * `decomposition_alg=QRAdjoint()` : `left_orth` algorithm including the reverse rule. See [`QRAdjoint`](@ref).
 """
@@ -104,7 +103,7 @@ PROJECTOR_SYMBOLS[:c4v_qr] = C4vQRProjector
 _set_truncation(alg::C4vQRProjector, ::TruncationStrategy) = alg
 
 function check_input(
-        network::InfiniteSquareNetwork, env::CTMRGEnv, alg::C4vCTMRG; atol = 1.0e-10
+        ::typeof(leading_boundary), network::InfiniteSquareNetwork, env::CTMRGEnv, alg::C4vCTMRG; atol = 1.0e-10
     )
     # check unit cell size
     length(network) == 1 || throw(ArgumentError("C4v CTMRG is only compatible with single-site unit cells."))
@@ -144,6 +143,10 @@ function ctmrg_iteration(
     enlarged_corner = c4v_enlarge(network, env, alg.projector_alg)
     corner′, projector, info = c4v_projector!(enlarged_corner, alg.projector_alg)
     edge′ = c4v_renormalize_edge(network, env, projector)
+    info = (;
+        contraction_metrics = (; info.truncation_error, info.condition_number),
+        info.D, info.V, info.D_full, info.V_full, info.truncation_indices,
+    )
     return CTMRGEnv(corner′, edge′), info
 end
 function ctmrg_iteration(
@@ -155,6 +158,7 @@ function ctmrg_iteration(
     projector, info = c4v_projector!(enlarged_corner, alg.projector_alg)
     edge′ = c4v_renormalize_edge(network, env, projector)
     corner′ = c4v_qr_renormalize_corner(edge′, projector, info.R)
+    info = (; contraction_metrics = (;), info.Q, info.R)
     return CTMRGEnv(corner′, edge′), info
 end
 

src/algorithms/ctmrg/c4v.jl

@@ -44,14 +44,6 @@ Perform a single CTMRG iteration in which all directions are being grown and ren
 """
 function ctmrg_iteration(network, env, alg::CTMRGAlgorithm) end
 
-"""
-    check_input(network, env, alg::CTMRGAlgorithm)
-
-Check compatibility of a given network and environment with a specified CTMRG algorithm.
-"""
-function check_input(network, env, alg::CTMRGAlgorithm) end
-@non_differentiable check_input(args...)
-
 """
     leading_boundary(env₀, network; kwargs...) -> env, info
     # expert version:
@@ -91,30 +83,15 @@ supplied via the keyword arguments or directly as an [`CTMRGAlgorithm`](@ref) st
 * `projector_alg::Symbol=:$(Defaults.projector_alg)` : Variant of the projector algorithm. See also [`ProjectorAlgorithm`](@ref).
     - `:halfinfinite` : Projection via SVDs of half-infinite (two enlarged corners) CTMRG environments.
     - `:fullinfinite` : Projection via SVDs of full-infinite (all four enlarged corners) CTMRG environments.
-    - `:c4v_eigh` : Projection via `eigh` of the Hermitian enlarged corner.
+    - `:c4v_eigh` : Projection via `eigh` of the Hermitian enlarged corner, works only for [`C4vCTMRG`](@ref).
+    - `:c4v_qr` : Projection via QR decomposition of the lower-rank column-enlarged corner, works only for [`C4vCTMRG`](@ref).
 
 ## Return values
 
-The CTMRG routine returns the final CTMRG environment as well as an information `NamedTuple`
-containing the following fields:
-
-* `truncation_error` : Last (maximal) SVD truncation error of the CTMRG projectors.
-* `condition_number` : Last (maximal) condition number of the enlarged CTMRG environment.
-
-In case the `alg` is a `SimultaneousCTMRG`, the last SVD will also be returned:
-
-* `U` : Last unit cell of left singular vectors.
-* `S` : Last unit cell of singular values.
-* `V` : Last unit cell of right singular vectors.
-
-If, in addition, the specified SVD algorithm computes the full, untruncated SVD, the full
-set of vectors and values will be returned as well:
-
-* `U_full` : Last unit cell of all left singular vectors.
-* `S_full` : Last unit cell of all singular values.
-* `V_full` : Last unit cell of all right singular vectors.
-
-For `C4vCTMRG` instead the last eigendecomposition `V` and `D` (and `V_full`, `D_full`) will be returned.
+The `leading_boundary` routine returns the final environment as well as an information `NamedTuple`
+that generally contains a `contraction_metrics` `NamedTuple` storing different contents depending
+on the chosen `alg`. Depending on the contraction method, the information tuple may also contain
+the final tensor decomposition (used in the projectors) including its truncation indices.
 """
 function leading_boundary(env₀::CTMRGEnv, network::InfiniteSquareNetwork; kwargs...)
     alg = select_algorithm(leading_boundary, env₀; kwargs...)
@@ -123,7 +100,7 @@ end
 function leading_boundary(
         env₀::CTMRGEnv, network::InfiniteSquareNetwork, alg::CTMRGAlgorithm
     )
-    check_input(network, env₀, alg)
+    check_input(leading_boundary, network, env₀, alg)
     log = ignore_derivatives(() -> MPSKit.IterLog("CTMRG"))
     return LoggingExtras.withlevel(; alg.verbosity) do
         env = deepcopy(env₀)
@@ -154,6 +131,14 @@ function leading_boundary(env₀::CTMRGEnv, state, args...; kwargs...)
     return leading_boundary(env₀, InfiniteSquareNetwork(state), args...; kwargs...)
 end
 
+"""
+    check_input(::typeof(leading_boundary), network, env, alg::CTMRGAlgorithm)
+
+Check compatibility of a given network and environment with a specified CTMRG algorithm.
+"""
+function check_input(::typeof(leading_boundary), network, env, alg::CTMRGAlgorithm) end
+@non_differentiable check_input(args...)
+
 # custom CTMRG logging
 function ctmrg_loginit!(log, η, network, env)
     return @infov 2 loginit!(log, η, network_value(network, env))

src/algorithms/ctmrg/ctmrg.jl

@@ -69,7 +69,7 @@ function ctmrg_iteration(network, env::CTMRGEnv, alg::SequentialCTMRG)
         network = rotate_north(network, EAST)
         env = rotate_north(env, EAST)
     end
-    return env, (; truncation_error, condition_number)
+    return env, (; contraction_metrics = (; truncation_error, condition_number))
 end
 
 """

src/algorithms/ctmrg/sequential.jl

@@ -48,6 +48,10 @@ function ctmrg_iteration(network, env::CTMRGEnv, alg::SimultaneousCTMRG)
     end  # expand environment
     projectors, info = simultaneous_projectors(enlarged_corners, env, alg.projector_alg)  # compute projectors on all coordinates
     env′ = renormalize_simultaneously(enlarged_corners, projectors, network, env)  # renormalize enlarged corners
+    info = (;
+        contraction_metrics = (; info.truncation_error, info.condition_number),
+        info.U, info.S, info.V, info.U_full, info.S_full, info.V_full, info.truncation_indices,
+    )
     return env′, info
 end
 

src/algorithms/ctmrg/simultaneous.jl

@@ -201,13 +201,19 @@ EigSolver(; kwargs...) = GradMode(; alg = :eigsolver, kwargs...)
 GRADIENT_MODE_SYMBOLS[:eigsolver] = EigSolver
 
 """
-    _check_algorithm_combination(boundary_alg, gradient_alg)
+    _check_algorithm_combination(boundary_alg, gradient_alg_or_symmetrization)
+    _check_algorithm_combination(boundary_alg, gradient_alg, symmetrization)
 
 Check for allowed combinations of gradient algorithm and boundary algorithm to be used for
 computing the gradient of a `leading_boundary` call. Throws an error containing a
 recommended fix if the combination is not allowed or broken.
 """
-function _check_algorithm_combination(boundary_alg, gradient_alg) end
+function _check_algorithm_combination(boundary_alg, gradient_alg_or_symmetrization) end
+function _check_algorithm_combination(boundary_alg, gradient_alg, symmetrization)
+    _check_algorithm_combination(boundary_alg, gradient_alg)
+    _check_algorithm_combination(boundary_alg, symmetrization)
+    return nothing
+end
 function _check_algorithm_combination(::SequentialCTMRG, ::GradMode{:fixed})
     msg = "`:fixed` mode is not compatible with `SequentialCTMRG` since the sequential \
           application of SVDs does not allow to differentiate through a fixed set of \
@@ -216,10 +222,18 @@ function _check_algorithm_combination(::SequentialCTMRG, ::GradMode{:fixed})
 end
 function _check_algorithm_combination(::C4vCTMRG{<:C4vEighProjector}, ::GradMode{:diffgauge})
     msg = "`:diffgauge` mode is currently not compatible with eigh-based C4v CTMRG; \
-          either switch to a different projector algorithm (e.g. `c4v_qr`), or use :fixed \
-          mode for differentiation instead."
+        either switch to a different projector algorithm (e.g. `c4v_qr`), or use :fixed \
+        mode for differentiation instead."
     throw(ArgumentError(msg))
 end
+function _check_algorithm_combination(::C4vCTMRG, symm::Union{Nothing, <:SymmetrizationStyle})
+    if !(symm isa RotateReflect)
+        msg = "C4vCTMRG optimization is compatible only with RotateReflect symmetrization. \
+            Make sure to set `symmetrization = RotateReflect()`."
+        throw(ArgumentError(msg))
+    end
+    return nothing
+end
 
 #=
 Evaluating the gradient of the cost function for CTMRG: