def spinflipandhop(slaves):
    """Calculates the interaction term of a spin flip and pair hopping"""

    Sdw = [csr_matrix(spin_gen(slaves, i, 0)) for i in range(slaves)]
    Sup = [mat.T for mat in Sdw]

    sfh = np.zeros_like(Sup[0])
    orbitals = slaves//2
    for n in range(orbitals):
        for m in range(n+1, orbitals):
            sfh += Sup[2*n  ] * Sdw[2*n + 1] * Sup[2*m + 1] * Sdw[2*m  ]
            sfh += Sup[2*n+1] * Sdw[2*n    ] * Sup[2*m    ] * Sdw[2*m+1]

            sfh += Sup[2*n] * Sup[2*n + 1] * Sdw[2*m] * Sdw[2*m+1]
            sfh += Sup[2*m] * Sup[2*m + 1] * Sdw[2*n] * Sdw[2*n+1]

    return sfh
Calculates the interaction term of a spin flip and pair hopping