def num2julian(n):
    """
    Convert a Julian days to a matplotlib date.

    Parameters
    ----------
    n : numpy.ndarray : int32
        Number of days since 0001-01-01 00:00:00 UTC *plus* *one*.

    Returns
    -------
    j : numpy.ndarray : int32
        Julian days.
    """
    return n + 1721424.5
