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Performance improvement of _DiagonalEstimator #9229

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merged 4 commits into from
Dec 5, 2022
Merged

Performance improvement of _DiagonalEstimator #9229

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2942e3a
performance improvement of _DiagonalEstimator
t-imamichi Dec 2, 2022
48621d8
optimize
t-imamichi Dec 5, 2022
3d078a4
add reno
t-imamichi Dec 5, 2022
ef58306
Merge branch 'main' into fast-diag
mergify[bot] Dec 5, 2022
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16 changes: 4 additions & 12 deletions qiskit/algorithms/minimum_eigensolvers/diagonal_estimator.py
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Original file line number Diff line number Diff line change
Expand Up @@ -182,18 +182,10 @@ def aggregate(measurements):


def _evaluate_sparsepauli(state: int, observable: SparsePauliOp) -> complex:
return sum(
coeff * _evaluate_bitstring(state, paulistring)
for paulistring, coeff in observable.label_iter()
)


def _evaluate_bitstring(state: int, paulistring: str) -> float:
"""Evaluate a bitstring on a Pauli label."""
n = len(paulistring) - 1
return np.prod(
[-1 if state & (1 << (n - i)) else 1 for i, pauli in enumerate(paulistring) if pauli == "Z"]
)
packed_uint8 = np.packbits(observable.paulis.z, axis=1, bitorder="little").astype(object)
power_uint8 = 1 << (8 * np.arange(packed_uint8.shape[1], dtype=object))
bits = (packed_uint8 @ power_uint8) & state
return sum(coeff * (-1) ** bin(bit).count("1") for coeff, bit in zip(observable.coeffs, bits))


def _check_observable_is_diagonal(observable: SparsePauliOp) -> bool:
Expand Down