Adapt linsolve.

src/ITensorNetworks.jl

@@ -110,6 +110,7 @@ include(joinpath("solvers", "eigsolve.jl"))
 include(joinpath("solvers", "exponentiate.jl"))
 include(joinpath("solvers", "dmrg_x.jl"))
 include(joinpath("solvers", "contract.jl"))
+include(joinpath("solvers", "linsolve.jl"))
 include(joinpath("treetensornetworks", "abstracttreetensornetwork.jl"))
 include(joinpath("treetensornetworks", "ttn.jl"))
 include(joinpath("treetensornetworks", "opsum_to_ttn.jl"))

src/solvers/linsolve.jl

@@ -0,0 +1,22 @@
+function linsolve_updater(
+  init;
+  state!,
+  projected_operator!,
+  outputlevel,
+  which_sweep,
+  sweep_plan,
+  which_region_update,
+  region_kwargs,
+  updater_kwargs,
+)
+  default_updater_kwargs = (;
+    ishermitian=false, tol=1E-14, krylovdim=30, maxiter=100, verbosity=0, a₀, a₁
+  )
+  updater_kwargs = merge(default_updater_kwargs, updater_kwargs)
+  P = projected_operator![]
+  (; a₀, a₁) = updater_kwargs
+  updater_kwargs = Base.structdiff(updater_kwargs, (; a₀=nothing, a₁=nothing))
+  b = dag(only(proj_mps(P)))
+  x, info = KrylovKit.linsolve(P, b, init, a₀, a₁; updater_kwargs...)
+  return x, (;)
+end

src/treetensornetworks/solvers/linsolve.jl

@@ -28,39 +28,21 @@ function linsolve(
   x₀::AbstractTTN,
   a₀::Number=0,
   a₁::Number=1;
-  normalize,
-  region,
-  half_sweep,
+  updater=linsolve_updater,
+  nsweeps,  #it makes sense to require this to be defined
+  nsites=2,
+  (sweep_observer!)=observer(),
+  root_vertex=default_root_vertex(init),
+  updater_kwargs=(;),
+  kwargs...,
 )
-  function linsolve_solver(
-    P,
-    x₀;
-    ishermitian=false,
-    solver_tol=1E-14,
-    solver_krylovdim=30,
-    solver_maxiter=100,
-    solver_verbosity=0,
-  )
-    b = dag(only(proj_mps(P)))
-    x, info = KrylovKit.linsolve(
-      P,
-      b,
-      x₀,
-      a₀,
-      a₁;
-      ishermitian,
-      tol=solver_tol,
-      krylovdim=solver_krylovdim,
-      maxiter=solver_maxiter,
-      verbosity=solver_verbosity,
-    )
-    return x, NamedTuple()
-  end
-
+  updater_kwargs = (; a₀, a₁, updater_kwargs...)
   error("`linsolve` for TTN not yet implemented.")
 
+  sweep_plan = default_sweep_regions(nsites, x0)
   # TODO: Define `itensornetwork_cache`
   # TODO: Define `linsolve_cache`
+
   P = linsolve_cache(itensornetwork_cache(x₀', A, x₀), itensornetwork_cache(x₀', b))
-  return alternating_update(linsolve_solver, P, x₀; kwargs...)
+  return alternating_update(linsolve_updater, P, x₀; sweep_plan, updater_kwargs, kwargs...)
 end

test/test_treetensornetworks/test_solvers/test_linsolve.jl

@@ -41,11 +41,11 @@ using Random
     x_c =
       random_mps(s; states, internal_inds_space=4) +
       0.1im * random_mps(s; states, internal_inds_space=2)
-    b = apply(H, x_c; cutoff)
+    b = apply(H, x_c; alg="fit", nsweeps=3) #cutoff is unsupported kwarg for apply/contract
 
     x0 = random_mps(s; states, internal_inds_space=10)
     x = @test_broken linsolve(
-      H, b, x0; cutoff, maxdim, nsweeps, ishermitian=true, solver_tol=1E-6
+      H, b, x0; cutoff, maxdim, nsweeps, updater_kwargs=(; tol=1E-6, ishermitian=true)
     )
 
     # @test norm(x - x_c) < 1E-3