def ccmod_setcoef(k):
    """Set the coefficient maps for the ccmod stage. The only parameter is
    the slice index `k` and there are no return values; all inputs and
    outputs are from and to global variables.
    """

    # Set working coefficient maps for ccmod step and compute DFT of
    # coefficient maps Z and Z^T S
    mp_Zf[k] = sl.rfftn(mp_Z_Y[k], mp_cri.Nv, mp_cri.axisN)
    mp_ZSf[k] = np.conj(mp_Zf[k]) * mp_Sf[k]
Set the coefficient maps for the ccmod stage. The only parameter is
    the slice index `k` and there are no return values; all inputs and
    outputs are from and to global variables.