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Added the function mpsmpo.mpo_to_pmps() for rank-1 MPOs #52

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Added the function mpsmpo.mpo_to_pmps() for rank-1 MPOs #52

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e86dbde
Added mpo_to_pmps()
Dec 15, 2017
d5c2342
Improved the code
Dec 15, 2017
c78ece8
Improved the code
Dec 15, 2017
4e13652
Added a first version of a test for mpsmpo.mpo_to_pmps()
May 9, 2018
751b201
Changed the decorator because there is no parameter rank in test_mpo_…
May 9, 2018
fbd05e5
Updated readme to refer to this fork
MoritzLange Sep 15, 2020
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Added mpo_to_pmps()
  • Loading branch information
Moritz Lange committed Dec 15, 2017
commit e86dbde9e09ae94f400cc91bf2a78c1009be277b
17 changes: 16 additions & 1 deletion mpnum/mpsmpo.py
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Original file line number Diff line number Diff line change
Expand Up @@ -132,9 +132,10 @@
from . import mparray as mp
from .utils import local_to_global, matdot

from scipy.linalg import eigh

__all__ = ['mps_to_mpo', 'mps_to_pmps', 'pmps_dm_to_array',
'pmps_reduction', 'pmps_to_mpo', 'pmps_to_mps',
'pmps_reduction', 'mpo_to_pmps', 'pmps_to_mpo', 'pmps_to_mps',
'reductions_mpo', 'reductions_mps_as_mpo',
'reductions_mps_as_pmps', 'reductions_pmps', 'reductions']

Expand Down Expand Up @@ -372,6 +373,20 @@ def pmps_to_mpo(pmps):
return mp.dot(pmps, pmps.adj())


def mpo_to_pmps(mpo):
"""Convert a tensor product MPO into a local purification MPS mixed state.

:param MPArray mpo: An MPA with two physical legs and rank one on all sites
:returns: An MPA with two physical legs (system and ancilla)

"""
assert_array_equal(mpo.ranks, 1)
eigs = (eigh(lten[0, ..., 0]) for lten in mpo.lt)
ltens = (i[1] * np.sqrt(i[0])[None, ...] for i in eigs)
pmps = mp.MPArray.from_kron(ltens)
return pmps / mp.norm(pmps)


def mps_to_pmps(mps):
"""Convert a pure MPS into a local purification MPS mixed state.

Expand Down