code: def expected_purity_ising_xx(param):
      """Returns the analytical purity for subsystems of the IsingXX"""
      return np.cos(param / 2) ** 4 + np.sin(param / 2) ** 4
  
imports: import pytest
  import pennylane
  from pennylane import numpy
label_desc: Use image node_id 1 for calling a global function with example usage: expected_purity_ising_xx(param) and returns: unknown