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[ITensorMPS] Bond dimensions produced by randomCircuitMPS #870

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[ITensorMPS] Bond dimensions produced by randomCircuitMPS #870

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f3da194
Include the product of local dimensions beginning from the start of t…
Mar 17, 2022
4e436ea
Added test for randomCircuitMPS bond dimensions.
Mar 17, 2022
82a4ea4
Formating.
Mar 17, 2022
d3d81b5
Fixed randomCircuitMPS function name. Use in test for bond dimension.
Apr 5, 2022
76f507e
Merge branch 'main' into main
mtfishman Jun 29, 2022
c2a131a
Fixed test for randomCircuitMPS
Jul 13, 2022
62fa370
Merge branch 'ITensor:main' into main
markusschmitt Jul 13, 2022
62bd58e
Merge branch 'main' of https://github.com/markusschmitt/ITensors.jl
Jul 13, 2022
238e4dc
Tests passing.
Jul 13, 2022
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21 changes: 17 additions & 4 deletions src/mps/mps.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -127,7 +127,7 @@ function randomizeMPS!(M::MPS, sites::Vector{<:Index}, linkdim=1)
end
end

function randomCircuitMPS(
function myRandomCircuitMPS(
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::Type{ElT}, sites::Vector{<:Index}, linkdim::Int; kwargs...
) where {ElT<:Number}
_rmatrix(::Type{Float64}, n, m) = NDTensors.random_orthog(n, m)
Expand All @@ -144,15 +144,28 @@ function randomCircuitMPS(

l = Vector{Index}(undef, N)

# Compute the bond dimension for each link.
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Would be nice to have this as a separate function, so we could use it other places in the code and simplify the code here.

Maybe linkdims_upper_bound? It doesn't have to be exported, just internal use for now.

# It should be the the minimum of the product of local
# Hilbert space dimensions taken from either end of the chain
# or the `linkdim`.
maxdims = Vector{Int}(undef, N - 1)
maxdims[1] = min(dim(sites[1]), linkdim)
for i in 2:(N - 1)
maxdims[i] = min(maxdims[i - 1] * dim(sites[i]), linkdim)
end
maxdims[N - 1] = min(dim(sites[N]), maxdims[N - 1])
for i in (N - 2):-1:1
maxdims[i] = min(dim(sites[i + 1]) * maxdims[i + 1], maxdims[i])
end

d = dim(sites[N])
chi = min(linkdim, d)
chi = maxdims[N - 1]
l[N - 1] = Index(chi, "Link,l=$(N-1)")
O = _rmatrix(ElT, chi, d)
M[N] = itensor(O, l[N - 1], sites[N])

for j in (N - 1):-1:2
chi *= dim(sites[j])
chi = min(linkdim, chi)
chi = maxdims[j - 1]
l[j - 1] = Index(chi, "Link,l=$(j-1)")
O = _rmatrix(ElT, chi, dim(sites[j]) * dim(l[j]))
T = reshape(O, (chi, dim(sites[j]), dim(l[j])))
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10 changes: 10 additions & 0 deletions test/mps.jl
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Expand Up @@ -197,6 +197,16 @@ include("util.jl")
@test norm(phic[4]) ≈ 1.0
end

@testset "randomCircuitMPS bond dimensions" begin
phi = randomCircuitMPS(ComplexF64, sites, 32)
expected_dims = [2, 4, 8, 16, 32, 16, 8, 4, 2]

for i in 1:9
l = getfirst(x -> hastags(x, "Link,l=$(i)"), inds(mps[i]))
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@test dim(l) == expected_dims[i]
end
end

@testset "inner different MPS" begin
phi = randomMPS(sites)
psi = randomMPS(sites)
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