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handle edges correctly in approximate(..., ::IDMRG2) #430

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Merged
lkdvos merged 1 commit into from
May 21, 2026
Merged

handle edges correctly in approximate(..., ::IDMRG2) #430

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44 changes: 42 additions & 2 deletions src/algorithms/approximate/idmrg.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -76,7 +76,7 @@ function approximate!(
C_current = ψ.C[:, 0]

# sweep from left to right
for site in 1:size(ψ, 2)
for site in 1:(size(ψ, 2) - 1)
for row in 1:size(ψ, 1)
AC2′ = AC2_projection(
CartesianIndex(row, site), ψ, toapprox, envs;
Expand All @@ -95,10 +95,31 @@ function approximate!(
transfer_rightenv!(envs, ψ, toapprox, site)
end

# update the edge
ψ.AL[1, end] = ψ.AC[1, end] / ψ.C[1, end]
ψ.AC[1, 1] = _mul_tail(ψ.AL[1, 1], ψ.C[1, 1])
for row in 1:size(ψ, 1)
AC2′ = AC2_projection(CartesianIndex(row, size(ψ, 2)), ψ, toapprox, envs; kind = :ALAC)
al, c, ar = svd_trunc!(AC2′; trunc = alg.trscheme, alg = alg.alg_svd)
normalize!(c)

ψ.AL[row + 1, end] = al
ψ.C[row + 1, end] = complex(c)
ψ.AR[row + 1, 1] = _transpose_front(ar)

ψ.AC[row + 1, end] = _mul_tail(al, c)
ψ.AC[row + 1, 1] = _transpose_front(c * ar)
ψ.AL[row + 1, 1] = ψ.AC[row + 1, 1] / ψ.C[row + 1, 1]

end
# update environments
transfer_leftenv!(envs, ψ, toapprox, 1)
transfer_rightenv!(envs, ψ, toapprox, 0)

normalize!(envs, ψ, toapprox)

# sweep from right to left
for site in reverse(0:(size(ψ, 2) - 1))
for site in reverse(1:(size(ψ, 2) - 1))
for row in 1:size(ψ, 1)
AC2′ = AC2_projection(
CartesianIndex(row, site), ψ, toapprox, envs;
Expand All @@ -116,6 +137,25 @@ function approximate!(
transfer_rightenv!(envs, ψ, toapprox, site)
end

# update the edge
ψ.AC[1, end] = _mul_front(ψ.C[1, end - 1], ψ.AR[1, end])
ψ.AR[1, 1] = _transpose_front(ψ.C[1, end] \ _transpose_tail(ψ.AC[1, 1]))
for row in 1:size(ψ, 1)
AC2′ = AC2_projection(CartesianIndex(row, 0), ψ, toapprox, envs; kind = :ACAR)
al, c, ar = svd_trunc!(AC2′; trunc = alg.trscheme, alg = alg.alg_svd)
normalize!(c)

ψ.AL[row, end] = al
ψ.C[row, end] = complex(c)
ψ.AR[row, 1] = _transpose_front(ar)

ψ.AR[row, end] = _transpose_front(ψ.C[row, end - 1] \ _transpose_tail(al * c))
ψ.AC[row, 1] = _transpose_front(c * ar)
end
transfer_leftenv!(envs, ψ, toapprox, 1)
transfer_rightenv!(envs, ψ, toapprox, 0)


normalize!(envs, ψ, toapprox)

# update error
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