TensoredExpvalMeasMitigator gives "Unknown fitter" error

[omarshehab]

Informations

• Qiskit Ignis version: 0.6.0
• Python version: 3.9.5 (default, May 18 2021, 12:31:01) [Clang 10.0.0 ]
• Operating system: Darwin

What is the current behavior?

When I use TensoredExpvalMeasMitigator for a 15 qubit QSVM experiment, I get the following error.

---------------------------------------------------------------------------
QiskitError                               Traceback (most recent call last)
/var/folders/5p/_ydvdq5959v8p0kntv58swdc0000gn/T/ipykernel_2969/2322411278.py in <module>
----> 1 adhoc_matrix_train_q_em = adhoc_kernel.evaluate(x_vec=train_features)
      2 adhoc_matrix_test_q_em = adhoc_kernel.evaluate(x_vec=test_features,
      3                                           y_vec=train_features)

~/opt/anaconda3/envs/py39/lib/python3.9/site-packages/qiskit_machine_learning/kernels/quantum_kernel.py in evaluate(self, x_vec, y_vec)
    331                 ]
    332 
--> 333                 results = self._quantum_instance.execute(circuits)
    334 
    335                 matrix_elements = [

~/opt/anaconda3/envs/py39/lib/python3.9/site-packages/qiskit/utils/quantum_instance.py in execute(self, circuits, had_transpiled)
    486                         state_labels,
    487                         circuit_labels,
--> 488                     ) = build_measurement_error_mitigation_circuits(
    489                         qubit_index,
    490                         self._meas_error_mitigation_cls,

~/opt/anaconda3/envs/py39/lib/python3.9/site-packages/qiskit/utils/measurement_error_mitigation.py in build_measurement_error_mitigation_circuits(qubit_list, fitter_cls, backend, backend_config, compile_config, mit_pattern)
    166         )
    167     else:
--> 168         raise QiskitError(f"Unknown fitter {fitter_cls}")
    169 
    170     # the provided `qubit_list` would be used as the initial layout to

QiskitError: "Unknown fitter <class 'qiskit.ignis.mitigation.expval.tensored_mitigator.TensoredExpvalMeasMitigator'>"

Steps to reproduce the problem

Instantiate QuantumInstance in the following manner and use it in a QSVM project with 15 qubits.

adhoc_backend = QuantumInstance(backend, shots=1024,
                                seed_transpiler=seed, optimization_level = 3, measurement_error_mitigation_cls=
TensoredExpvalMeasMitigator)

What is the expected behavior?

It should work without any error.

Suggested solutions