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---
title: mutual_information (v0.29)
description: API reference for qiskit.quantum_info.mutual_information in qiskit v0.29
in_page_toc_min_heading_level: 1
python_api_type: function
python_api_name: qiskit.quantum_info.mutual_information
---
<span id="qiskit-quantum-info-mutual-information" />
# qiskit.quantum\_info.mutual\_information
<Function id="qiskit.quantum_info.mutual_information" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.18/qiskit/quantum_info/states/measures.py" signature="mutual_information(state, base=2)">
Calculate the mutual information of a bipartite state.
The mutual information $I$ is given by:
$$
I(\rho_{AB}) = S(\rho_A) + S(\rho_B) - S(\rho_{AB})
$$
where $\rho_A=Tr_B[\rho_{AB}], \rho_B=Tr_A[\rho_{AB}]$, are the reduced density matrices of the bipartite state $\rho_{AB}$.
**Parameters**
* **state** ([*Statevector*](qiskit.quantum_info.Statevector "qiskit.quantum_info.Statevector") *or*[*DensityMatrix*](qiskit.quantum_info.DensityMatrix "qiskit.quantum_info.DensityMatrix")) a bipartite state.
* **base** (*int*) the base of the logarithm \[Default: 2].
**Returns**
The mutual information $I(\rho_{AB})$.
**Return type**
float
**Raises**
* **QiskitError** if the input state is not a valid QuantumState.
* **QiskitError** if input is not a bipartite QuantumState.
</Function>