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Perform local updates

At the lowest-level of abstraction, TenNetLib.jl allows for updating the StateEnvs for each sites/bonds manually.

Skip this part if you want to avoid lower-level abstraction.

TenNetLib.update_position! — Method
update_position!(sysenv::StateEnvs, solver, pos::Int, nsite::Int, ortho::String; kwargs...)

Updates StateEnvs at position pos by solver.

Arguments:

  • sysenv::StateEnvs
  • solver: Solver for update. Available ones: eig_solver and exp_solver.
  • pos::Int: Position of the bond (nsite=2) or site (nsite=1).
  • nsite of the environment. Either 1 or 2 for one-site or two-site update respectively.
  • ortho::String: Direction of the sweep. Either "left" or "right".

Named arguments and their default values:

  • time_step::Union{Float64, ComplexF64, Nothing} = nothing: Time step for TDVP.
  • normalize::Bool = true: Whether to normalize after update.
  • maxdim::Int = typemax(Int): Maximum bond dimension after SVD truncation.
  • mindim::Int = 1: Minimum bond dimension after SVD truncation.
  • cutoff::Float64 = Float64_threshold(): Cutoff for SVD truncation.
  • svd_alg::String = "divide_and_conquer".
  • noise::Float64 = 0.0.
  • reverse_step::Bool = false if time_step = nothing, true otherwise.

Named arguments for solver and their default values:

See the documentation of KrylovKit.jl.

  • ishermitian::Bool = true.
  • solver_tol::Float64 = 1E-14 if eig_solver, 1E-12 if exp_solver.
  • solver_krylovdim::Int = 5 if eig_solver, 30 if exp_solver.
  • solver_maxiter::Int = 2 if eig_solver, 100 if exp_solver.
  • solver_outputlevel::Int = 0: See verbosity in KrylovKit.jl.
  • solver_eager::Bool = false if eig_solver, true if exp_solver.
  • solver_check_convergence::Bool = false if eig_solver, true if exp_solver.

Return values:

  • ::Float64: Energy.
  • ::Float64: Truncation Error.
  • ::Vector{Float64}: SVD spectrum.
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