def METHOD_NAME(
    df: pd.DataFrame, column_name: Hashable
) -> pd.DataFrame:
    """Convert Matlab's serial date number into Python datetime format.
    Implementation is also from
    [Stack Overflow](https://stackoverflow.com/questions/13965740/converting-matlabs-datenum-format-to-python).
    This method mutates the original DataFrame.
    Examples:
        >>> import pandas as pd
        >>> import janitor
        >>> df = pd.DataFrame({"date": [737125.0, 737124.815863, 737124.4985, 737124]})
        >>> df
                    date
        0  737125.000000
        1  737124.815863
        2  737124.498500
        3  737124.000000
        >>> df.convert_matlab_date('date')
                                date
        0 2018-03-06 00:00:00.000000
        1 2018-03-05 19:34:50.563200
        2 2018-03-05 11:57:50.399999
        3 2018-03-05 00:00:00.000000
    Args:
        df: A pandas DataFrame.
        column_name: A column name.
    Returns:
        A pandas DataFrame with corrected dates.
    """  # noqa: E501
    days = pd.Series([dt.timedelta(v % 1) for v in df[column_name]])
    df[column_name] = (
        df[column_name].astype(int).apply(dt.datetime.fromordinal)
        + days
        - dt.timedelta(days=366)
    )
    return df