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expectation value of a one-site operator for MPS using mixedcanonical form #384

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expectation value of a one-site operator for MPS using mixedcanonical form #384

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restore evolve() since we export it
Aug 6, 2025
0d8bd37
add basic expectation value on MPS for one-site operators
Aug 6, 2025
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starsfordummies Aug 6, 2025
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experimenting with expectation values
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20 changes: 19 additions & 1 deletion src/Components/MPS.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -209,5 +209,23 @@ end
maxbondsize(psi::MPS) = maximum(bondsizes(psi; sorted=false))

function Base.show(io::IO, psi::MPS)
print(io, "MPS (#tensors=$(ntensors(psi)), #inds=$(ninds(psi)) #maxbondsize=$(maxbondsize(psi)))")
print(io, "MPS (#tensors=$(ntensors(psi)), #inds=$(ninds(psi)), maxbondsize=$(maxbondsize(psi)))")
end

""" Expectation value for a one-site operator `op` on site `op_site` of mps `psi`, brings `psi` to canonical form. """
function expect_1site!(psi::MPS, op::AbstractArray, op_site::Int)
canonize!(psi, MixedCanonical(site"$(op_site)"))
plug_ind = ind_at(psi, plug"$(op_site)")
temp_ind = Index(:_temp_bra)
ev = binary_einsum(psi[op_site], Tensor(op, [temp_ind, plug_ind]))
ev = binary_einsum(ev, conj(replace(psi[op_site], plug_ind => temp_ind)))

return ev
end

""" Expectation value for a one-site operator `op` on site `op_site` of mps `psi`.
This makes a copy of the MPS """
function expect_1site(psi::MPS, op::AbstractArray, op_site::Int)
psi = copy(psi)
expect_1site!(psi, op, op_site)
end
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mind moving them to a Operations/expect.jl file please?

5 changes: 5 additions & 0 deletions src/Operations/evolve.jl
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Expand Up @@ -11,6 +11,11 @@ struct ZipUpAlgorithm <: EvolveAlgorithm end

function evolve! end

function evolve(tn, op; kwargs...)
tn = copy(tn)
evolve!(tn, op; kwargs...)
end

evolve!(tn, op; kwargs...) = evolve!(tn, op, DelegatorTrait(Evolvable(), tn); kwargs...)
evolve!(tn, op, ::DelegateToField; kwargs...) = evolve!(delegator(Evolvable(), tn), op; kwargs...)
evolve!(tn, op, ::DontDelegate; algorithm=UnknownAlgorithm(), kwargs...) = evolve!(algorithm, tn, op; kwargs...)
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