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Bug fix in vqe expectation #204

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Bug fix in vqe expectation #204

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0b5326a
Fix bug in vqe expectation
Mar 24, 2019
1b0f625
Remove unnecessary conversion from ndarray to list
Mar 24, 2019
286ec6b
Let pyquil's WavefunctionSimulator handle the summing
Mar 25, 2019
76ab132
Performance boost/bug fix of vqe expectation
Mar 27, 2019
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26 changes: 6 additions & 20 deletions grove/pyvqe/vqe.py
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Original file line number Diff line number Diff line change
Expand Up @@ -225,21 +225,7 @@ def expectation(pyquil_prog: Program,
pauli_sum = PauliSum([pauli_sum])

if samples is None:
operator_progs = []
operator_coeffs = []
for p_term in pauli_sum.terms:
op_prog = Program()
for qindex, op in p_term:
op_prog.inst(STANDARD_GATES[op](qindex))
operator_progs.append(op_prog)
operator_coeffs.append(p_term.coefficient)

result_overlaps = WavefunctionSimulator().expectation(pyquil_prog, pauli_sum.terms)
result_overlaps = list(result_overlaps)
assert len(result_overlaps) == len(operator_progs),\
"""Somehow we didn't get the correct number of results back from the QVM"""
expectation = sum(list(map(lambda x: x[0] * x[1],
zip(result_overlaps, operator_coeffs))))
expectation = WavefunctionSimulator().expectation(pyquil_prog, pauli_sum)
return expectation.real
else:
if not isinstance(samples, int):
Expand All @@ -263,11 +249,11 @@ def expectation(pyquil_prog: Program,
elif gate == 'Y':
meas_basis_change.inst(RX(np.pi / 2, index))

meas_outcome = \
expectation_from_sampling(pyquil_prog + meas_basis_change,
qubits_to_measure,
qc,
samples)
meas_outcome = \
expectation_from_sampling(pyquil_prog + meas_basis_change,
qubits_to_measure,
qc,
samples)

expectation += term.coefficient * meas_outcome

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