Export the phase error to an hdf5 file

    Parameters
    ----------
    h5path: str or pathlib.Path
        path to hdf5 output file
    identifier: str
        unique identifier of the input phase
        (e.g. `qpimage.QPImage["identifier"]`)
    index: int
        iteration index
    phase: 2d real-valued np.ndarray
        phase image
    mphase: 2d real-valued np.ndarray
        reference phase image
    model: str
        sphere model name
    n0: float
        initial object index
    r0: float
        initial object radius [m]
    spi_params: dict
        parameter dictionary of :func:`SpherePhaseInterpolator`

def export_phase_error_hdf5(h5path, identifier, index, phase, mphase,
                            model, n0, r0, spi_params):
    """Export the phase error to an hdf5 file

    Parameters
    ----------
    h5path: str or pathlib.Path
        path to hdf5 output file
    identifier: str
        unique identifier of the input phase
        (e.g. `qpimage.QPImage["identifier"]`)
    index: int
        iteration index
    phase: 2d real-valued np.ndarray
        phase image
    mphase: 2d real-valued np.ndarray
        reference phase image
    model: str
        sphere model name
    n0: float
        initial object index
    r0: float
        initial object radius [m]
    spi_params: dict
        parameter dictionary of :func:`SpherePhaseInterpolator`
    """
    with h5py.File(h5path, mode="a") as h5:
        if identifier in h5:
            grp = h5[identifier]
        else:
            grp = h5.create_group(identifier)
        ds = grp.create_dataset("phase_error_{:05d}".format(index),
                                data=mphase-phase)
        ds.attrs["index initial"] = n0
        ds.attrs["radius initial"] = r0
        ds.attrs["sim model"] = model
        ds.attrs["sim index"] = spi_params["sphere_index"]
        ds.attrs["sim radius"] = spi_params["radius"]
        ds.attrs["sim center"] = spi_params["center"]
        ds.attrs["fit iteration"] = index
        ds.attrs["fit iteration"] = index