def test_max_weight_observable():
q0, q1 = cirq.LineQubit.range(2)
observables = [cirq.X(q0), cirq.X(q1)]
assert _max_weight_observable(observables) == cirq.X(q0) * cirq.X(q1)
observables = [cirq.X(q0), cirq.X(q1), cirq.Z(q1)]
assert _max_weight_observable(observables) is None
def _validate_setting(self, setting: InitObsSetting, what: str):
mws = _max_weight_state([self.max_setting.init_state, setting.init_state])
mwo = _max_weight_observable([self.max_setting.observable, setting.observable])
if mws is None or mwo is None:
raise ValueError(
f"You requested the {what} for a setting that is not compatible "
f"with this BitstringAccumulator's meas_spec."
)
def group_settings_greedy(
settings: Iterable[InitObsSetting],
) -> Dict[InitObsSetting, List[InitObsSetting]]:
"""Greedily group settings which can be simultaneously measured.
We construct a dictionary keyed by `max_setting` (see docstrings
for `_max_weight_state` and `_max_weight_observable`) where the value
is a list of settings compatible with `max_setting`. For each new setting,
we try to find an existing group to add it and update `max_setting` for
that group if necessary. Otherwise, we make a new group.
In practice, this greedy algorithm performs comparably to something
more complicated by solving the clique cover problem on a graph
of simultaneously-measurable settings.
Args:
settings: The settings to group.
Returns:
A dictionary keyed by `max_setting` which need not exist in the
input list of settings. Each dictionary value is a list of
settings compatible with `max_setting`.
"""
grouped_settings: Dict[InitObsSetting, List[InitObsSetting]] = {}
for setting in settings:
for max_setting, simul_settings in grouped_settings.items():
trial_grouped_settings = simul_settings + [setting]
new_max_weight_state = _max_weight_state(
stg.init_state for stg in trial_grouped_settings)
new_max_weight_obs = _max_weight_observable(
stg.observable for stg in trial_grouped_settings)
compatible_init_state = new_max_weight_state is not None
compatible_observable = new_max_weight_obs is not None
can_be_inserted = compatible_init_state and compatible_observable
if can_be_inserted:
new_max_weight_state = cast(value.ProductState,
new_max_weight_state)
new_max_weight_obs = cast(ops.PauliString, new_max_weight_obs)
del grouped_settings[max_setting]
new_max_setting = InitObsSetting(new_max_weight_state,
new_max_weight_obs)
grouped_settings[new_max_setting] = trial_grouped_settings
break
else:
# made it through entire dict without finding a compatible group,
# thus a new group needs to be created
# Strip coefficients before using as key
new_max_weight_obs = setting.observable.with_coefficient(1.0)
new_max_setting = InitObsSetting(setting.init_state,
new_max_weight_obs)
grouped_settings[new_max_setting] = [setting]
return grouped_settings
