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Avoid state vector normalization if it worsens the round offs #6556

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Merged
pavoljuhas merged 2 commits into from
Apr 10, 2024
Merged

Avoid state vector normalization if it worsens the round offs #6556

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Avoid state vector normalization if it worsens the round offs
pavoljuhas Apr 9, 2024
754f40e
Merge branch 'main' into avoid-extra-round-offs-from-normalization
pavoljuhas Apr 10, 2024
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6 changes: 5 additions & 1 deletion cirq-core/cirq/sim/state_vector_simulator.py
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Original file line number Diff line number Diff line change
Expand Up @@ -134,7 +134,11 @@ def final_state_vector(self) -> np.ndarray:
"skipping renormalization"
)
return ret
return ret / norm
# normalize only if doing so improves the round-off on total probability
ret_norm = ret / norm
round_off_change = abs(np.vdot(ret_norm, ret_norm) - 1) - abs(np.vdot(ret, ret) - 1)
result = ret_norm if round_off_change < 0 else ret
return result

def state_vector(self, copy: bool = False) -> np.ndarray:
"""Return the state vector at the end of the computation.
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