Change some internal names from tdvp to alternating_update, sweep_upd…

…ate, region_update

examples/05_utils.jl

@@ -1,5 +1,5 @@
 using ITensors: MPS, maxlinkdim
-using ITensorTDVP: TDVPOrder, process_sweeps, tdvp_solver, tdvp_step, process_sweeps
+using ITensorTDVP: ITensorTDVP
 using Observers: observer, update!
 using Printf: @printf
 
@@ -20,12 +20,14 @@ function tdvp_nonuniform_timesteps(
   kwargs...,
 )
   nsweeps = length(time_steps)
-  maxdim, mindim, cutoff, noise = process_sweeps(; nsweeps, maxdim, mindim, cutoff, noise)
-  tdvp_order = TDVPOrder(order, Base.Forward)
+  maxdim, mindim, cutoff, noise = ITensorTDVP.process_sweeps(;
+    nsweeps, maxdim, mindim, cutoff, noise
+  )
+  tdvp_order = ITensorTDVP.TDVPOrder(order, Base.Forward)
   current_time = time_start
   for sw in 1:nsweeps
     sw_time = @elapsed begin
-      psi, PH, info = tdvp_step(
+      psi, PH, info = ITensorTDVP.sweep_update(
         tdvp_order,
         solver,
         PH,
@@ -42,9 +44,7 @@ function tdvp_nonuniform_timesteps(
       )
     end
     current_time += time_steps[sw]
-
     update!(step_observer!; psi, sweep=sw, outputlevel, current_time)
-
     if outputlevel ≥ 1
       print("After sweep ", sw, ":")
       print(" maxlinkdim=", maxlinkdim(psi))
@@ -70,7 +70,7 @@ function tdvp_nonuniform_timesteps(
   kwargs...,
 )
   return tdvp_nonuniform_timesteps(
-    tdvp_solver(
+    ITensorTDVP.tdvp_solver(
       exponentiate;
       ishermitian,
       issymmetric,

src/ITensorTDVP.jl

@@ -6,8 +6,8 @@ include("update_observer.jl")
 include("solver_utils.jl")
 include("tdvporder.jl")
 include("tdvpinfo.jl")
-include("tdvp_step.jl")
-include("tdvp_generic.jl")
+include("sweep_update.jl")
+include("alternating_update.jl")
 include("tdvp.jl")
 include("dmrg.jl")
 include("dmrg_x.jl")

src/tdvp_generic.jl → src/alternating_update.jl

@@ -1,20 +1,10 @@
-using ITensors:
-  AbstractObserver,
-  MPO,
-  MPS,
-  ProjMPOSum,
-  check_hascommoninds,
-  checkdone!,
-  disk,
-  linkind,
-  maxlinkdim,
-  permute
+using ITensors: AbstractObserver, MPS, checkdone!, disk, maxlinkdim
 
-function _tdvp_compute_nsweeps(t; time_step=default_time_step(t), nsweeps=default_nsweeps())
+function _compute_nsweeps(t; time_step=default_time_step(t), nsweeps=default_nsweeps())
   if isinf(t) && isnothing(nsweeps)
     nsweeps = 1
   elseif !isnothing(nsweeps) && time_step != t
-    error("Cannot specify both time_step and nsweeps in tdvp")
+    error("Cannot specify both time_step and nsweeps in alternating_update")
   elseif isfinite(time_step) && abs(time_step) > 0 && isnothing(nsweeps)
     nsweeps = convert(Int, ceil(abs(t / time_step)))
     if !(nsweeps * time_step ≈ t)
@@ -44,7 +34,7 @@ function process_sweeps(; nsweeps, maxdim, mindim, cutoff, noise)
   return (; maxdim, mindim, cutoff, noise)
 end
 
-function tdvp(
+function alternating_update(
   solver,
   PH,
   t::Number,
@@ -66,9 +56,9 @@ function tdvp(
   cutoff=default_cutoff(Float64),
   noise=default_noise(),
 )
-  nsweeps = _tdvp_compute_nsweeps(t; time_step, nsweeps)
+  nsweeps = _compute_nsweeps(t; time_step, nsweeps)
   maxdim, mindim, cutoff, noise = process_sweeps(; nsweeps, maxdim, mindim, cutoff, noise)
-  tdvp_order = TDVPOrder(order, Base.Forward)
+  forward_order = TDVPOrder(order, Base.Forward)
   psi = copy(psi0)
   # Keep track of the start of the current time step.
   # Helpful for tracking the total time, for example
@@ -87,8 +77,8 @@ function tdvp(
       PH = disk(PH)
     end
     sweep_time = @elapsed begin
-      psi, PH, info = tdvp_step(
-        tdvp_order,
+      psi, PH, info = sweep_update(
+        forward_order,
         solver,
         PH,
         time_step,
@@ -118,7 +108,7 @@ function tdvp(
     end
     isdone = false
     if !isnothing(checkdone)
-      isdone = checkdone(; psi, sweep, outputlevel) #, kwargs...)
+      isdone = checkdone(; psi, sweep, outputlevel)
     elseif observer! isa AbstractObserver
       isdone = checkdone!(observer!; psi, sweep, outputlevel)
     end
@@ -127,66 +117,29 @@ function tdvp(
   return psi
 end
 
-"""
-    tdvp(H::MPO,psi0::MPS,t::Number; kwargs...)
-    tdvp(H::MPO,psi0::MPS,t::Number; kwargs...)
-
-Use the time dependent variational principle (TDVP) algorithm
-to compute `exp(t*H)*psi0` using an efficient algorithm based
-on alternating optimization of the MPS tensors and local Krylov
-exponentiation of H.
-                    
-Returns:
-* `psi::MPS` - time-evolved MPS
+# Convenience wrapper to not have to specify time step.
+# Use a time step of `Inf` as a convention, since TDVP
+# with an infinite time step corresponds to DMRG.
+function alternating_update(solver, H, psi0::MPS; kwargs...)
+  return alternating_update(solver, H, ITensors.scalartype(psi0)(Inf), psi0; kwargs...)
+end
 
-Optional keyword arguments:
-* `outputlevel::Int = 1` - larger outputlevel values resulting in printing more information and 0 means no output
-* `observer` - object implementing the [Observer](@ref observer) interface which can perform measurements and stop early
-* `write_when_maxdim_exceeds::Int` - when the allowed maxdim exceeds this value, begin saving tensors to disk to free memory in large calculations
-"""
-function tdvp(solver, H::MPO, t::Number, psi0::MPS; kwargs...)
+function alternating_update(solver, H::MPO, t::Number, psi0::MPS; kwargs...)
   check_hascommoninds(siteinds, H, psi0)
   check_hascommoninds(siteinds, H, psi0')
   # Permute the indices to have a better memory layout
   # and minimize permutations
   H = permute(H, (linkind, siteinds, linkind))
   PH = ProjMPO(H)
-  return tdvp(solver, PH, t, psi0; kwargs...)
-end
-
-function tdvp(solver, t::Number, H, psi0::MPS; kwargs...)
-  return tdvp(solver, H, t, psi0; kwargs...)
+  return alternating_update(solver, PH, t, psi0; kwargs...)
 end
 
-function tdvp(solver, H, psi0::MPS, t::Number; kwargs...)
-  return tdvp(solver, H, t, psi0; kwargs...)
-end
-
-"""
-    tdvp(Hs::Vector{MPO},psi0::MPS,t::Number; kwargs...)
-    tdvp(Hs::Vector{MPO},psi0::MPS,t::Number, sweeps::Sweeps; kwargs...)
-
-Use the time dependent variational principle (TDVP) algorithm
-to compute `exp(t*H)*psi0` using an efficient algorithm based
-on alternating optimization of the MPS tensors and local Krylov
-exponentiation of H.
-                    
-This version of `tdvp` accepts a representation of H as a
-Vector of MPOs, Hs = [H1,H2,H3,...] such that H is defined
-as H = H1+H2+H3+...
-Note that this sum of MPOs is not actually computed; rather
-the set of MPOs [H1,H2,H3,..] is efficiently looped over at 
-each step of the algorithm when optimizing the MPS.
-
-Returns:
-* `psi::MPS` - time-evolved MPS
-"""
-function tdvp(solver, Hs::Vector{MPO}, t::Number, psi0::MPS; kwargs...)
+function alternating_update(solver, Hs::Vector{MPO}, t::Number, psi0::MPS; kwargs...)
   for H in Hs
     check_hascommoninds(siteinds, H, psi0)
     check_hascommoninds(siteinds, H, psi0')
   end
   Hs .= ITensors.permute.(Hs, Ref((linkind, siteinds, linkind)))
   PHs = ProjMPOSum(Hs)
-  return tdvp(solver, PHs, t, psi0; kwargs...)
+  return alternating_update(solver, PHs, t, psi0; kwargs...)
 end

src/contract_mpo_mps.jl

@@ -32,13 +32,10 @@ function ITensors.contract(
   if n == 1
     return MPS([A[1] * psi0[1]])
   end
-
   any(i -> isempty(i), siteinds(commoninds, A, psi0)) &&
     error("In `contract(A::MPO, x::MPS)`, `A` and `x` must share a set of site indices")
-
   # In case A and psi0 have the same link indices
   A = sim(linkinds, A)
-
   # Fix site and link inds of init_mps
   init_mps = deepcopy(init_mps)
   init_mps = sim(linkinds, init_mps)
@@ -53,13 +50,10 @@ function ITensors.contract(
     end
   end
   replace_siteinds!(init_mps, ti)
-
-  t = Inf
   reverse_step = false
   PH = ProjMPOApply(psi0, A)
-  psi = tdvp(
-    contractmpo_solver(; kwargs...), PH, t, init_mps; nsweeps, reverse_step, kwargs...
+  psi = alternating_update(
+    contractmpo_solver(; kwargs...), PH, init_mps; nsweeps, reverse_step, kwargs...
   )
-
   return psi
 end

src/dmrg.jl

@@ -38,9 +38,8 @@ function dmrg(
   solver_verbosity=default_solver_verbosity(),
   kwargs...,
 )
-  t = Inf # DMRG is TDVP with an infinite timestep and no reverse step
   reverse_step = false
-  psi = tdvp(
+  psi = alternating_update(
     dmrg_solver(
       eigsolve;
       solver_which_eigenvalue,
@@ -51,7 +50,6 @@ function dmrg(
       solver_verbosity,
     ),
     H,
-    t,
     psi0;
     reverse_step,
     kwargs...,

src/dmrg_x.jl

@@ -11,7 +11,6 @@ function dmrg_x_solver(PH, t, psi0; current_time, outputlevel)
 end
 
 function dmrg_x(PH, psi0::MPS; reverse_step=false, kwargs...)
-  t = ITensors.scalartype(psi0)(Inf)
-  psi = tdvp(dmrg_x_solver, PH, t, psi0; reverse_step, kwargs...)
+  psi = alternating_update(dmrg_x_solver, PH, psi0; reverse_step, kwargs...)
   return psi
 end

src/linsolve.jl

@@ -37,8 +37,6 @@ function KrylovKit.linsolve(
     x, info = linsolve(P, b, x₀, a₀, a₁; solver_kwargs...)
     return x, nothing
   end
-
-  t = Inf
   P = ProjMPO_MPS2(A, b)
-  return tdvp(linsolve_solver, P, t, x₀; reverse_step=false, tdvp_kwargs...)
+  return alternating_update(linsolve_solver, P, x₀; reverse_step=false, tdvp_kwargs...)
 end

src/tdvp_step.jl → src/sweep_update.jl

@@ -4,15 +4,15 @@ using LinearAlgebra: norm, normalize!, svd
 using Observers: update!
 using Printf: @printf
 
-function tdvp_step(
+function sweep_update(
   order::TDVPOrder, solver, PH, time_step::Number, psi::MPS; current_time=0, kwargs...
 )
   order_orderings = orderings(order)
   order_sub_time_steps = eltype(time_step).(sub_time_steps(order))
   order_sub_time_steps *= time_step
   info = nothing
   for substep in 1:length(order_sub_time_steps)
-    psi, PH, info = tdvp_sweep(
+    psi, PH, info = sub_sweep_update(
       order_orderings[substep],
       solver,
       PH,
@@ -47,7 +47,7 @@ function is_half_sweep_done(direction, b, n; ncenter)
          is_reverse_done(direction, b, n; ncenter)
 end
 
-function tdvp_sweep(
+function sub_sweep_update(
   direction::Base.Ordering,
   solver,
   PH,
@@ -71,7 +71,7 @@ function tdvp_sweep(
   psi = copy(psi)
   if length(psi) == 1
     error(
-      "`tdvp` currently does not support system sizes of 1. You can diagonalize the MPO tensor directly with tools like `LinearAlgebra.eigen`, `KrylovKit.exponentiate`, etc.",
+      "`tdvp`, `dmrg`, `linsolve`, etc. currently does not support system sizes of 1. You can diagonalize the MPO tensor directly with tools like `LinearAlgebra.eigen`, `KrylovKit.exponentiate`, etc.",
     )
   end
   N = length(psi)
@@ -92,7 +92,7 @@ function tdvp_sweep(
   maxtruncerr = 0.0
   info = nothing
   for b in sweep_bonds(direction, N; ncenter=nsite)
-    current_time, maxtruncerr, spec, info = tdvp_site_update!(
+    current_time, maxtruncerr, spec, info = region_update!(
       solver,
       PH,
       psi,
@@ -149,7 +149,7 @@ function tdvp_sweep(
   return psi, PH, TDVPInfo(maxtruncerr)
 end
 
-function tdvp_site_update!(
+function region_update!(
   solver,
   PH,
   psi,
@@ -169,7 +169,7 @@ function tdvp_site_update!(
   mindim,
   maxtruncerr,
 )
-  return tdvp_site_update!(
+  return region_update!(
     Val(nsite),
     Val(reverse_step),
     solver,
@@ -191,7 +191,7 @@ function tdvp_site_update!(
   )
 end
 
-function tdvp_site_update!(
+function region_update!(
   nsite_val::Val{1},
   reverse_step_val::Val{false},
   solver,
@@ -230,7 +230,7 @@ function tdvp_site_update!(
   return current_time, maxtruncerr, spec, info
 end
 
-function tdvp_site_update!(
+function region_update!(
   nsite_val::Val{1},
   reverse_step_val::Val{true},
   solver,
@@ -290,7 +290,7 @@ function tdvp_site_update!(
   return current_time, maxtruncerr, spec, info
 end
 
-function tdvp_site_update!(
+function region_update!(
   nsite_val::Val{2},
   reverse_step_val::Val{false},
   solver,
@@ -342,7 +342,7 @@ function tdvp_site_update!(
   return current_time, maxtruncerr, spec, info
 end
 
-function tdvp_site_update!(
+function region_update!(
   nsite_val::Val{2},
   reverse_step_val::Val{true},
   solver,
@@ -407,7 +407,7 @@ function tdvp_site_update!(
   return current_time, maxtruncerr, spec, info
 end
 
-function tdvp_site_update!(
+function region_update!(
   ::Val{nsite},
   ::Val{reverse_step},
   solver,
@@ -428,6 +428,6 @@ function tdvp_site_update!(
   maxtruncerr,
 ) where {nsite,reverse_step}
   return error(
-    "`tdvp` with `nsite=$nsite` and `reverse_step=$reverse_step` not implemented."
+    "`tdvp`, `dmrg`, `linsolve`, etc. with `nsite=$nsite` and `reverse_step=$reverse_step` not implemented.",
   )
 end