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[ITensor] [Bug] Fix replaceinds for long inputs #1098

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[ITensor] [Bug] Fix replaceinds for long inputs #1098

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030862a
Add ReferenceTests to Project.toml
kmp5VT Mar 13, 2023
fd03770
Merge branch 'main' of github.com:kmp5VT/ITensors.jl
kmp5VT Mar 14, 2023
49a7224
Revert "Add ReferenceTests to Project.toml"
kmp5VT Mar 14, 2023
1aaad4d
Merge branch 'main' of github.com:kmp5VT/ITensors.jl
kmp5VT Mar 20, 2023
9fea70d
Convert pair to tuple after modifying indices
kmp5VT Mar 20, 2023
cbab792
Don't use tuple in replaceinds
kmp5VT Mar 20, 2023
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2 changes: 1 addition & 1 deletion src/indexset.jl
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@mtfishman mtfishman Mar 20, 2023 •
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The method:

function replaceinds(is::Indices, rep_inds::Vector{<:Pair{<:Index,<:Index}})
  return replaceinds(is, rep_inds...)
end

is also potentially problematic since splatting with ... has similar to using Tuple when it comes to performance for long lists (i.e. we should avoid splatting long lists).

I think we could just use this instead:

function replaceinds(is::Indices, rep_inds::Vector{<:Pair{<:Index,<:Index}})
  return replaceinds(is, first.(rep_inds), last.(rep_inds))
end

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Also, I would rewrite:

function replaceinds(is::Indices, rep_inds::Tuple{Vararg{Pair{<:Index,<:Index}}})
  return replaceinds(is, rep_inds...)
end

as:

function replaceinds(is::Indices, rep_inds::Tuple{Vararg{Pair{<:Index,<:Index}}})
  return replaceinds(is, first.(rep_inds), last.(rep_inds))
end

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Another simplification I would suggest is changing:

function replaceinds(is::Indices, rep_inds::Pair{<:Index,<:Index}...)
  return replaceinds(is, zip(rep_inds...)...)
end

to:

function replaceinds(is::Indices, rep_inds::Pair{<:Index,<:Index}...)
  return replaceinds(is, first.(rep_inds), last.(rep_inds))
end

(The zip version is too clever by half.)

Another thing I noticed looking back through this code is that we might have to add a missing method:

replaceinds(is::Indices, i1::Index, i2::Index) = replaceinds(is, (i1,), (i2,))

for trying to replace a single Index.

Original file line number Diff line number Diff line change
Expand Up @@ -557,7 +557,7 @@ function replaceinds(is::Indices, rep_inds::Tuple{Vararg{Pair{<:Index,<:Index}}}
end

function replaceinds(is::Indices, rep_inds::Pair)
return replaceinds(is, Tuple(first(rep_inds)) .=> Tuple(last(rep_inds)))
return replaceinds(is, first(rep_inds) .=> last(rep_inds))
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I wonder if we can just use:

  return replaceinds(is, first(rep_inds), last(rep_inds))

instead, which would then directly call the core version replaceinds(is::Indices, inds1, inds2). The logic of this code is a bit spaghetti-like, it's hard to track what is calling what and how it finally gets to the core implementation (which is my fault, this is some very early-days ITensors.jl code which has not been revisited in a while).

end

# Check that the QNs are all the same
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