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---
title: get_subsystem_density_matrix
description: API reference for qiskit.aqua.utils.get_subsystem_density_matrix
in_page_toc_min_heading_level: 1
python_api_type: function
python_api_name: qiskit.aqua.utils.get_subsystem_density_matrix
---
# qiskit.aqua.utils.get\_subsystem\_density\_matrix
<Function id="qiskit.aqua.utils.get_subsystem_density_matrix" isDedicatedPage={true} github="https://github.com/qiskit-community/qiskit-aqua/tree/stable/0.9/qiskit/aqua/utils/subsystem.py" signature="get_subsystem_density_matrix(statevector, trace_systems)">
Compute the reduced density matrix of a quantum subsystem.
**Parameters**
* **statevector** (*list|array*) The state vector of the complete system
* **trace\_systems** (*list|range*) The indices of the qubits to be traced out.
**Returns**
The reduced density matrix for the desired subsystem
**Return type**
numpy.ndarray
</Function>