def _syscal_write_electrode_coords(fid, spacing, N):
    """helper function that writes out electrode positions to a file descriptor

    Parameters
    ----------
    fid: file descriptor
        data is written here
    spacing: float
        spacing of electrodes
    N: int
        number of electrodes
    """
    fid.write('# X Y Z\n')
    for i in range(0, N):
        fid.write('{0} {1} {2} {3}\n'.format(i + 1, i * spacing, 0, 0))
helper function that writes out electrode positions to a file descriptor

    Parameters
    ----------
    fid: file descriptor
        data is written here
    spacing: float
        spacing of electrodes
    N: int
        number of electrodes