# TensoredMeasFitter

*class *`TensoredMeasFitter(results, mit_pattern, substate_labels_list=None, circlabel='')`

Bases: `object`

Measurement correction fitter for a tensored calibration.

Initialize a measurement calibration matrix from the results of running the circuits returned by measurement_calibration_circuits.

This class is not a public API. The internals are not stable and will likely change. It is used solely for the `measurement_error_mitigation_cls`

kwarg of the `QuantumInstance`

class’s constructor (as a class not an instance). Anything outside of that usage does not have the normal user-facing API stability.

**Parameters**

**results**– the results of running the measurement calibration circuits. If this is None, the user will set calibration matrices later.**mit_pattern**(`List`

[`List`

[`int`

]]) – qubits to perform the measurement correction on, divided to groups according to tensors**substate_labels_list**(`Optional`

[`List`

[`List`

[`str`

]]]) – for each calibration matrix, the labels of its rows and columns. If None, the labels are ordered lexicographically**circlabel**(`str`

) – if the qubits were labeled

**Raises**

**ValueError** – if the mit_pattern doesn’t match the substate_labels_list

## Methods

### add_data

`TensoredMeasFitter.add_data(new_results, rebuild_cal_matrix=True)`

Add measurement calibration data

**Parameters**

**new_results**(*list or**qiskit.result.Result*) – a single result or list of Result objects.**rebuild_cal_matrix**(*bool*) – rebuild the calibration matrix

### readout_fidelity

`TensoredMeasFitter.readout_fidelity(cal_index=0, label_list=None)`

Based on the results, output the readout fidelity, which is the average of the diagonal entries in the calibration matrices.

**Parameters**

**cal_index**(*integer*) – readout fidelity for this index in _cal_matrices**label_list**(*list*) – Returns the average fidelity over of the groups f states. In the form of a list of lists of states. If None, then each state used in the construction of the calibration matrices forms a group of size 1

**Returns**

The readout fidelity (assignment fidelity)

**Return type**

numpy.array

**Raises**

**QiskitError** – If the calibration matrix has not been set for the object.

#### Additional Information:

The on-diagonal elements of the calibration matrices are the probabilities of measuring state ‘x’ given preparation of state ‘x’.

### subset_fitter

`TensoredMeasFitter.subset_fitter(qubit_sublist)`

Return a fitter object that is a subset of the qubits in the original list.

This is only a partial implementation of the `subset_fitter`

method since only mitigation patterns of length 1 are supported. This corresponds to patterns of the form `[[0], [1], [2], ...]`

. Note however, that such patterns are a good first approximation to mitigate readout errors on large quantum circuits.

**Parameters**

**qubit_sublist** (*list*) – must be a subset of qubit_list

**Returns**

**A new fitter that has the calibration for a**

subset of qubits

**Return type**

**Raises**

**QiskitError**– If the calibration matrix is not initialized**QiskitError**– If the mit pattern is not a tensor of single-qubit measurement error mitigation.**QiskitError**– If a qubit in the given`qubit_sublist`

is not in the list of qubits in the mit. pattern.

## Attributes

### cal_matrices

Return cal_matrices.

### filter

Return a measurement filter using the cal matrices.

### nqubits

Return _qubit_list_sizes.

### substate_labels_list

Return _substate_labels_list.