jaunatisblue
eed42dcfa9
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56 lines
1.6 KiB
Python
56 lines
1.6 KiB
Python
# This code is part of qtealeaves.
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#
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# This code is licensed under the Apache License, Version 2.0. You may
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# obtain a copy of this license in the LICENSE.txt file in the root directory
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# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
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#
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# Any modifications or derivative works of this code must retain this
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# copyright notice, and modified files need to carry a notice indicating
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# that they have been altered from the originals.
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"""
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Common permutations often used in tensor network methods.
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"""
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from functools import lru_cache
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__all__ = []
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@lru_cache(maxsize=None)
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def _transpose_idx1(num_legs, contracted_idx):
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"""Move second last index instead of last in `_transpose_idx`."""
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return _transpose_idx(num_legs - 1, contracted_idx) + (num_legs - 1,)
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@lru_cache(maxsize=None)
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def _transpose_idx2(num_legs, contracted_idx):
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"""Move third last index instead of last in `_transpose_idx`."""
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return _transpose_idx(num_legs - 2, contracted_idx) + (
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num_legs - 2,
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num_legs - 1,
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)
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@lru_cache(maxsize=None)
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def _transpose_idx(num_legs, contracted_idx):
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"""
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Transpose in the original order the indexes
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of a n-legs tensor contracted over the
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index `contracted_idx`
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Parameters
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----------
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contracted_idx : int
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Index over which there has been a contraction
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Returns
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-------
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tuple
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Indexes for the transposition
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"""
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if contracted_idx > num_legs - 1:
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raise ValueError(
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f"Cannot contract leg {contracted_idx} of tensor with {num_legs} legs"
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)
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return (*range(contracted_idx), num_legs - 1, *range(contracted_idx, num_legs - 1))
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