VQC algorithm fails with initial_layout and measurement_error_mitigation_cls

[AzizNgoueya]

Informations

• Qiskit Aqua version: 0.6.1
• Python version: 3.7.4
• Operating system: Windows

What is the current behavior?

I created a quantum instance with initial_layout and measurement_error_mitigation_cls, then i ran the VQC algo on rochester backend, a LayoutError: Integer list length must equal number of qubits in circuit is produced.

Steps to reproduce the problem

feature_map=3
vqc = VQC(optimizer, feature_map, var_form, training_input, test_input)
quantum_instance = QuantumInstance(backend, shots=shots, seed_simulator=random_seed, initial_layout=[42,43,44] , measurement_error_mitigation_cls=CompleteMeasFitter, measurement_error_mitigation_shots=4096, seed_transpiler=random_seed, skip_qobj_validation=True)
result = vqc.run(quantum_instance)

What is the expected behavior?

The algorithm shouldn't fail with this initial_layout=[42,43,44]. It only works if we specify all the qubits like: [42,43,44] +list(range(3, 42))+[0,1,2] or if the length of initial_layout list is equal to the number of register qubits of the circuits for measurement error mitigation.

Suggested solutions

The complete_meas_cal method from ignis use qubits from 0 to max(qubit_list). So specify an initial layout as above will produce a terra error because the length of layout is less than the number of qubits used for the error mitigation.
I think, updating the compile_config argument to consider the new initial_layout after the complete_meas_cal will resolve this issue.
https://github.com/Qiskit/qiskit-aqua/blob/997a378cb54c30049fe0d0b7549e86717a46133f/qiskit/aqua/utils/measurement_error_mitigation.py#L116

[woodsp-ibm]

Hi, would you be able to post the complete script that is failing? We tried on both stable (since you reported 0.6.1 above) and on the latest master and could not reproduce the error.