def solvedbi_sm_c(ah, a, rho, axis=4):
    r"""
    Compute cached component used by :func:`solvedbi_sm`.

    Parameters
    ----------
    ah : array_like
      Linear system component :math:`\mathbf{a}^H`
    a : array_like
      Linear system component :math:`\mathbf{a}`
    rho : float
      Linear system parameter :math:`\rho`
    axis : int, optional (default 4)
      Axis along which to solve the linear system

    Returns
    -------
    c : ndarray
      Argument :math:`\mathbf{c}` used by :func:`solvedbi_sm`
    """

    return ah / (inner(ah, a, axis=axis) + rho)