Add named project for building symmetry-restricted tensors#208
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mtfishman
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…support (#203) ## Summary Adds `project`, an owned convenience over the existing `project_map` hook for building a symmetry-restricted array from a dense one. The three-argument form takes an explicit codomain/domain split and the two-argument form takes a flat list of axes (an empty domain), both forwarding to `project_map`, and `checked_project` is the verified counterpart of `checked_project_map`. This mirrors the `zeros`/`zeros_map` pairing, where the unsuffixed name is the convenience that also accepts the codomain/domain split. Also adds the `TensorMap` path in the TensorKit extension so `project` can build a `TensorMap` from a dense array: `similar_map` allocates a same-device buffer whose block storage type follows the dense prototype, `projectto!` fills the symmetry-allowed blocks through `project_symmetric!` and discards the rest, and `checked_projectto!` verifies the projection by densifying the result and reusing the dense path's elementwise `isapprox(src, dest)` check, so it keeps one `InexactError`/`kwargs` contract across backends. The named-index `project` for `AbstractITensor` is added in ITensor/ITensorBase.jl#208.
mtfishman
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Adds methods extending TensorAlgebra's `project` and `checked_project` that build a named tensor from a dense array and the indices to attach. The three-argument form takes a codomain/domain split (an operator), the two-argument form a flat list of indices (a state). The index axes select the backend, so the same call builds an `Array`, a block-sparse array, or a `TensorMap`. The named entry strips to the unnamed array plus axes, lowers to `TensorAlgebra.project`, and reattaches the names.
Route `project`/`checked_project` through a shared `project_nameddims` / `checked_project_nameddims` helper and add the empty-codomain method, so an all-domain projection (`project(a, (), (i,))`, the mirror of the flat all-codomain state) strips names correctly instead of falling through to the unnamed-axis generic. This matches the two-dispatch-entry pattern of the `similar_map` construction hooks.
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Summary
Adds methods extending
TensorAlgebra.projectandTensorAlgebra.checked_project(added in ITensor/TensorAlgebra.jl#203) that build a named tensor from a dense array and the indices to attach. The three-argument form takes a codomain/domain split (an operator), and the two-argument form takes a flat list of indices (a state, i.e. an empty domain). The index axes select the backend, so the same call builds anArrayon dense indices, a block-sparse array on graded indices, and aTensorMapon TensorKit spaces. The named entry strips to the unnamed array plus axes, lowers toTensorAlgebra.project, and reattaches the names.This is the named-index projection primitive for building symmetric operators and states from a dense basis matrix:
project(Sz, (i',), (i,))for an operator,project(v, (i,))for a state.