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Implement an MPS method initializing the tensors to identity (copy-tensors) #218

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merged 17 commits into from
Oct 14, 2024
Merged

Implement an MPS method initializing the tensors to identity (copy-tensors) #218

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0ac258f
Format code
Todorbsc Oct 9, 2024
b348911
Implement MPS identity initialization
Todorbsc Oct 9, 2024
c3800a8
Add tests for all dispatches of MPS identity init
Todorbsc Oct 9, 2024
d18f894
Format julia code
Todorbsc Oct 9, 2024
347b7bf
Rename function header & add docstring
Todorbsc Oct 9, 2024
a5b07de
Fix test set for identity MPS
Todorbsc Oct 9, 2024
36a43f4
Format code
Todorbsc Oct 9, 2024
0112833
Rewrite MPS identity init function to nsites instead of arrays' dimen…
Todorbsc Oct 10, 2024
36ad5c2
Format julia code
Todorbsc Oct 10, 2024
50d5b3c
Update docstring of identity
Todorbsc Oct 10, 2024
b7917c9
Clean code in test (suggested by Jofre)
Todorbsc Oct 11, 2024
984ba14
Format julia code
Todorbsc Oct 11, 2024
b582cca
Refactor virtualdims in identity (suggested by Sergio)
Todorbsc Oct 14, 2024
e4e719c
Update src/Ansatz/MPS.jl
mofeing Oct 14, 2024
3d32a5c
Restrict to default order in identity MPS
Todorbsc Oct 14, 2024
31f5482
Update src/Ansatz/MPS.jl
mofeing Oct 14, 2024
5e2ac42
Remove order parameter in identity
Todorbsc Oct 14, 2024
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24 changes: 24 additions & 0 deletions src/Ansatz/MPS.jl
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Expand Up @@ -62,6 +62,30 @@ function MPS(arrays::Vector{<:AbstractArray}; order=defaultorder(MPS))
return MPS(ansatz, NonCanonical())
end

MPS(arraysdims::NTuple{N,<:Vector{Int}}; order=defaultorder(MPS)) where {N} = MPS(collect(arraysdims); order=order)
MPS(arraysdims::Vector{<:Tuple{Vararg{Int}}}; order=defaultorder(MPS)) = MPS(collect.(arraysdims); order=order)
function MPS(arraysdims::NTuple{N,Tuple{Vararg{Int}}}; order=defaultorder(MPS)) where {N}
return MPS(collect(collect.(arraysdims)); order=order)
end
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I would currently just delete these methods for now...

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MPS(arraysdims::NTuple{N,<:Vector{Int}}; order=defaultorder(MPS)) where {N} = MPS(collect(arraysdims); order=order)
MPS(arraysdims::Vector{<:Tuple{Vararg{Int}}}; order=defaultorder(MPS)) = MPS(collect.(arraysdims); order=order)
function MPS(arraysdims::NTuple{N,Tuple{Vararg{Int}}}; order=defaultorder(MPS)) where {N}
return MPS(collect(collect.(arraysdims)); order=order)
end

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I removed them

function MPS(arraysdims::Vector{<:Vector{Int}}; order=defaultorder(MPS))
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I would use Base.identity, not a constructor since you're not passing arrays.

Suggested change
function MPS(arraysdims::Vector{<:Vector{Int}}; order=defaultorder(MPS))
function Base.identity(::Type{MPS}, arraysdims; order=defaultorder(MPS))

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This was one possibility along with the one @jofrevalles suggested below of using ones. I replaced the constructor by identity as I think it fits better than ones.

@assert length(arraysdims[1]) == 2 "First array must have 2 dimensions"
@assert all(==(3) ∘ length, arraysdims[2:(end - 1)]) "All arrays must have 3 dimensions"
@assert length(arraysdims[end]) == 2 "Last array must have 2 dimensions"
issetequal(order, defaultorder(MPS)) ||
throw(ArgumentError("order must be a permutation of $(String.(defaultorder(MPS)))"))

return MPS(
map(arraysdims) do arrdims
mindim = minimum(arrdims)
arr = zeros(ComplexF64, arrdims...)
deltas = ntuple(x -> ntuple(_ -> x, length(arrdims)), mindim)
broadcast(delta -> arr[delta...] = 1.0, deltas)
arr
end;
order=order,
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)
end

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I would not create another constructor for MPS, since that may be misleading to the user who wants to directly create an MPS with some specific arrays. Instead, you could extend the function ones or one similiar, to make that when we call ones(MPS, arraydims ... ) we get this kind of MPS. Something similar to the things we do with rand.

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As I said above, I agree it is better to not implement another constructor. The option that fits the best for me is Base.identity, check it out :)

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@mofeing mofeing Oct 9, 2024 •
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Yeah, in general I agree with @jofrevalles but I think ones might be misleading since it could mean you're initializing the MPS to a $\ket{11\dots 1}$ state.

I think identity is better because contracting against another "identity" MPS gives you 1, all the tensors are just COPY-tensors and "identity initialization" is how is known in some packages (it's also known as eye-initialization but eye is how the identity is known on those languages).

function Base.convert(::Type{MPS}, tn::Product)
@assert socket(tn) == State()

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3 changes: 1 addition & 2 deletions test/Ansatz_test.jl
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@@ -1,2 +1 @@
@testset "Ansatz" begin
end
@testset "Ansatz" begin end
22 changes: 22 additions & 0 deletions test/MPS_test.jl
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Expand Up @@ -26,6 +26,28 @@
@test inds(ψ; at=site"3", dir=:left) == inds(ψ; at=site"2", dir=:right) !== nothing
@test all(i -> size(ψ, inds(ψ; at=Site(i))) == 2, 1:nsites(ψ))

dispatch_arraysdims = [
([2, 4], [5, 4, 3], [2, 3]),
[(2, 4), (5, 4, 3), (2, 3)],
((2, 4), (5, 4, 3), (2, 3)),
[[2, 4], [5, 4, 3], [2, 3]],
]
for arraysdims in dispatch_arraysdims
ψ = MPS(arraysdims) # Default order (:o, :l, :r)
@test size(tensors(ψ; at=site"1")) == (2, 4)
@test size(tensors(ψ; at=site"2")) == (5, 4, 3)
@test size(tensors(ψ; at=site"3")) == (2, 3)
t1 = tensors(ψ; at=site"1")
@test t1[1, 1] == t1[2, 2] == 1
@test sum(t1) == 2
t2 = tensors(ψ; at=site"2")
@test t2[1, 1, 1] == t2[2, 2, 2] == t2[3, 3, 3] == 1
@test sum(t2) == 3
t3 = tensors(ψ; at=site"3")
@test t3[1, 1] == t3[2, 2] == 1
@test sum(t3) == 2
end

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Wrap this into a @testset

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Done

@testset "Site" begin
ψ = MPS([rand(2, 2), rand(2, 2, 2), rand(2, 2)])

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