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CouplingModel

TenNetLib.jl degines as struct, called the CouplingModel, to store the Hamiltonian terms. In case of MPS based algorithms, CouplingModel can replace MPO without modifying rest of the code. For Tree Tensor Network (TTN) codes, only CouplingModel can be used. Different elements of CouplingModel are contracted in parallel.

TenNetLib.CouplingModel — Type
struct CouplingModel
    sites::Vector{Index}
    terms::Vector{IDTensors}
end

CouplingModel for a given OpStrings Hamiltonian terms and sites::Vector{Index}.

  • sites::Vector{Index}: Site Indexs.
  • terms::Vector{IDTensors}: Collection of Hamiltonian terms.
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TenNetLib.CouplingModel — Method
function CouplingModel(os::OpStrings,
                       sites::Vector{Index};
                       merge::Bool = true,
                       maxdim::Int = typemax(Int),
                       mindim::Int = 1,
                       cutoff::Float64 = Float64_threshold(),
                       svd_alg::String = "divide_and_conquer",
                       chunksize::Int = 12)

Constructor of the CouplingModel from os::OpStrings and sites::Vector{Index}.

Named arguments and their default values:

  • merge::Bool = true. If true, merges all the terms having same spatial support resulting in larger virtual dimension. Otherwise, all the terms have virtual dimension one.
  • 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".
  • chunksize::Int = 12.

Example:

os = OpStrings()    
for j=1:N-1
    os += 1, "Sz" => j, "Sz" => j+1
    os += 0.5, "S+" => j, "S-" => j+1
    os += 0.5, "S-" => j, "S+" => j+1
end    
H = CouplingModel(os,sites)
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TenNetLib.CouplingModel — Method
function CouplingModel(os::OpStrings,
                       mpo::MPO;
                       merge::Bool = true,
                       maxdim::Int = typemax(Int),
                       mindim::Int = 1,
                       cutoff::Float64 = Float64_threshold(),
                       svd_alg::String = "divide_and_conquer",
                       chunksize::Int = 12)

Constructor of the CouplingModel from os::OpStrings and mpo::MPO. Resultant CouplingModel is the sum of os and the mpo.

Named arguments and their default values:

  • merge::Bool = true. If true, merges all the terms having same spatial support resulting in larger virtual dimension. Otherwise, all the terms have virtual dimension one.
  • 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".
  • chunksize::Int = 12.
source
TenNetLib.CouplingModel — Method
function CouplingModel(mpos::MPO...)

Constructs CouplingModel from a collection of MPOs. Different MPO terms can be contracted in parallel during different MPS/TTN algorithms. Useful for TTN codes.

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Base.length — Method
function Base.length(model::CouplingModel)

Number of sites in the system.

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Base.copy — Method
function Base.copy(model::CouplingModel)

Shallow copy of CouplingModel.

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Base.getindex — Method
function Base.getindex(model::CouplingModel, n)

Returns Hamiltonian terms for nth site(s) in the CouplingModel.

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