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Added an 'identity' tensor splitting option #241

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Added an 'identity' tensor splitting option #241

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Added an 'identity' tensor splitting option
rballester Jun 26, 2024
ad30164
PR update
rballester Sep 11, 2024
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13 changes: 13 additions & 0 deletions quimb/tensor/decomp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -185,6 +185,19 @@
return U, None, VH


@compose
def identity(x, backend=None, **kwargs):
"""
No-op "decomposition" that leaves the input unchanged. Can be useful to quickly build a tensor network representing a given tensor "as is".
"""

with backend_like(backend):
if x.shape[0] < x.shape[1]:
return do("eye", x.shape[0]), do("ones", x.shape[0]), x

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else:
return x, do("ones", x.shape[1]), do("eye", x.shape[1])

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The middle element should probably just be left as None, otherwise it flags to calling functions above that 'singular values' have been returned. This happens with other methods only when the option absorb=None. Or one could add that option and but default to absorb=0 (which means absorbed on either side), if you imagine that it might be useful to initialize simple update gauges for example.

I also suggest here using do("eye", x.shape[0], like=x) and do("ones", x.shape[0], like=x) rather than backend_like since autoray now supports picking up the correct device and dtype for these array creation routines.



@compose
def svd_truncated(
x,
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1 change: 1 addition & 0 deletions quimb/tensor/tensor_core.py
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Expand Up @@ -325,6 +325,7 @@ def rand_uuid(base=""):

_VALID_SPLIT_GET = {None, "arrays", "tensors", "values"}
_SPLIT_FNS = {
"identity": decomp.identity,
"svd": decomp.svd_truncated,
"eig": decomp.svd_via_eig_truncated,
"lu": decomp.lu_truncated,
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