openfermion.utils.map_two_pdm_to_one_pdm

Contract a 2-RDM to a 1-RDM

tpdm (numpy.ndarray): The 2-RDM as a 4-index tensor. Indices follow the internal convention of tpdm[p, q, r, s] == :math:a_{p}^{\dagger}a_{q}^{\dagger}a_{r}a_{s}. particle_number (float): number of particles in the system

opdm (numpy.ndarray): The 1-RDM contracted from the tpdm.