def read_bg(directory, file_name):
    """
    Read a bedgraph file representing potential TAD track.
    NOTE: bedgraph must be binned at a pre-defined constant window.
    Args:
       directory (str): directory of the file location (ex: '/Users/kimm/')
       file_name (str): name of the file (ex: 'SHG0008H.bedgraph')
    Returns:
       cov_dict (dict): dictionary of coverage
    """
    cov_dict = {}
    with open(directory + file_name) as f:
        in_cov = [line.strip().split("\t") for line in f]
    chrom_list = list(set([x[0] for x in in_cov]))
    for chrom in chrom_list:
        tmp_cov = [int(float(x[3])) for x in in_cov if x[0]==chrom]
        cov_dict[chrom] = tmp_cov
    return cov_dict