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Catch identities in expectation value calcs #566

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Merged
merged 3 commits into from
Sep 27, 2022
Merged

Catch identities in expectation value calcs #566

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ba3cd1a
Catch identities in expectation value calcs
95-martin-orion Sep 27, 2022
1b6938e
Add test for identity EVs
95-martin-orion Sep 27, 2022
d3c4017
order matters
95-martin-orion Sep 27, 2022
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5 changes: 4 additions & 1 deletion pybind_interface/pybind_main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -795,7 +795,10 @@ class SimulatorHelper {
for (const auto& opsum_qubit_count_pair : opsums_and_qubit_counts) {
const auto& opsum = std::get<0>(opsum_qubit_count_pair);
const auto& opsum_qubits = std::get<1>(opsum_qubit_count_pair);
if (opsum_qubits <= 6) {
if (opsum_qubits == 0) {
// This represents an identity, which always has EV=1.
results.push_back(std::complex<double>(1.0, 0.0));
} else if (opsum_qubits <= 6) {
results.push_back(ExpectationValue<IO, Fuser>(opsum, simulator, state));
} else {
Fuser::Parameter params;
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5 changes: 3 additions & 2 deletions qsimcirq_tests/qsimcirq_test.py
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Expand Up @@ -523,18 +523,19 @@ def test_expectation_values(mode: str):
]
psum1 = cirq.Z(a) + 3 * cirq.X(b)
psum2 = cirq.X(a) - 3 * cirq.Z(b)
psum3 = cirq.I(a)

if mode == "noisy":
circuit.append(NoiseTrigger().on(a))

qsim_simulator = qsimcirq.QSimSimulator()
qsim_result = qsim_simulator.simulate_expectation_values_sweep(
circuit, [psum1, psum2], params
circuit, [psum1, psum2, psum3], params
)

cirq_simulator = cirq.Simulator()
cirq_result = cirq_simulator.simulate_expectation_values_sweep(
circuit, [psum1, psum2], params
circuit, [psum1, psum2, psum3], params
)

assert cirq.approx_eq(qsim_result, cirq_result, atol=1e-6)
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